Self-similar growth of Bose stars [CEA]

http://arxiv.org/abs/2305.01005


We analytically solve the problem of Bose star growth in the bath of gravitationally interacting particles. We find that after nucleation of this object, the bath is described by a self-similar solution of the kinetic equation, which is an attractor. Together with the conservation laws, this fixes mass evolution of the Bose star. Our results explain slowdown of the star growth at a certain “core-halo” mass, but also predict formation of the heavier and lighter objects in magistral dark matter models.

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A. Dmitriev, D. Levkov, A. Panin, et. al.
Wed, 3 May 23
46/67

Comments: 4 pages, 2 figures

Universality of Bose-Einstein Condensation and Quenched Formation Dynamics [CL]

http://arxiv.org/abs/2304.09541


The emergence of macroscopic coherence in a many-body quantum system is a ubiquitous phenomenon across different physical systems and scales. This Chapter reviews key concepts characterizing such systems (correlation functions, condensation, quasi-condensation) and applies them to the study of emerging non-equilibrium features in the dynamical path towards such a highly-coherent state: particular emphasis is placed on emerging universal features in the dynamics of conservative and open quantum systems, their equilibrium or non-equilibrium nature, and the extent that these can be observed in current experiments with quantum gases. Characteristic examples include symmetry-breaking in the Kibble-Zurek mechanism, coarsening and phase-ordering kinetics, and universal spatiotemporal scalings around non-thermal fixed points and in the context of the Kardar- Parisi-Zhang equation; the Chapter concludes with a brief review of the potential relevance of some of these concepts in modelling the large-scale distribution of dark matter in the universe.

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N. Proukakis
Thu, 20 Apr 23
11/57

Comments: Invited contribution to the Encyclopedia of Condensed Matter Physics (Elsevier, 2nd Edition)

Relative efficiency of three mechanisms of vector fields growth in a random media [CL]

http://arxiv.org/abs/2303.14388


We consider a model of a random media with fixed and finite memory time with abrupt losses of memory (renovation model). Within the memory intervals we can observe either amplification or oscillation of the vector field in a given particle. The cumulative effect of amplifications in many subsequent intervals leads to amplification of the mean field and mean energy. Similarly, the cumulative effect of intermittent amplifications or oscillations also leads to amplification of the mean field and mean energy, however, at a lower rate. Finally, the random oscillations alone can resonate and yield the growth of the mean field and energy. These are the three mechanisms that we investigate and compute analytically and numerically the growth rates based on the Jacobi equation with the random curvature parameter.

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E. Illarionov and D. Sokoloff
Tue, 28 Mar 23
14/81

Comments: N/A

Gravitational polarization of test-mass potential in equilibrium polytropic sheets with non-negative polytropic indexes [GA]

http://arxiv.org/abs/2303.14876


Gravitational polarization is examined for equilibrium self-gravitating polytropic sheets perturbed by gravitational field due to test mass sheet. We find equilibrium solutions to the corresponding perturbed Lane-Emden equations for non-negative polytropic indexes. It is shown that gravitational polarization may be observed even in a finite extent of self-gravitating systems in addition to previously discussed infinite systems. In the polytropic sheets, the maximum gravitational amplification gets greater with a higher polytropic index while the height at which the maximum amplification occurs gets lower. The ratio of height change to the original height increases with polytropic index. The last result constrains the linear approximation method used for the present perturbation method.

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Y. Ito
Tue, 28 Mar 23
78/81

Comments: N/A

Scale Invariance in X-ray Flares of Gamma-ray Bursts [HEAP]

http://arxiv.org/abs/2212.08813


X-ray flares are generally believed to be produced by the reactivation of the central engine, and may have the same energy dissipation mechanism as the prompt emission of gamma-ray bursts (GRBs). X-ray flares can therefore provide important clues to understanding the nature of the central engines of GRBs. In this work, we study for the first time the physical connection between differential size and return distributions of X-ray flares of GRBs with known redshifts. We find that the differential distributions of duration, energy, and waiting time can be well fitted by a power-law function. In particular, the distributions for the differences of durations, energies, and waiting times at different times (i.e., the return distributions) well follow a $q$-Gaussian form. The $q$ values in the $q$-Gaussian distributions keep nearly steady for different temporal interval scales, implying a scale-invariant structure of GRB X-ray flares. Moreover, we verify that the $q$ parameters are related to the power-law indices $\alpha$ of the differential size distributions, characterized as $q=(\alpha+2)/\alpha$. These statistical features can be well explained within the physical framework of a self-organizing criticality system.

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J. Wei
Tue, 20 Dec 22
13/97

Comments: 6 pages, 3 figures, 2 tables. Accepted for publication in Phys. Rev. Research

Quantum field corrections to the equation of state of freely streaming matter in the Friedman-Robertson-Walker space-time [CL]

http://arxiv.org/abs/2212.05518


We calculate the expectation value of the energy density and pressure of a scalar field after its decoupling from a thermal bath in the spatially flat Friedman-Robertson-Walker space-time, within the framework of quantum statistical mechanics. By using the density operator determined by the condition of local thermodynamic equilibrium, we determine the mean value of the stress-energy tensor of a real scalar field by subtracting the vacuum expectation value at the time of the decoupling. The obtained expressions of energy density and pressure involve corrections with respect to the classical free-streaming solution of the relativistic Boltzmann equation, which may become relevant even at long times.

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F. Becattini and D. Roselli
Tue, 13 Dec 22
80/105

Comments: 16 pages, 1 figure

Computing First-Passage Times with the Functional Renormalisation Group [CEA]

http://arxiv.org/abs/2211.09649


We use Functional Renormalisation Group (FRG) techniques to analyse the behaviour of a spectator field, $\sigma$, during inflation that obeys an overdamped Langevin equation. We briefly review how a derivative expansion of the FRG can be used to obtain Effective Equations of Motion (EEOM) for the one- and two-point function and derive the EEOM for the three-point function. We show how to compute quantities like the amplitude of the power spectrum and the spectral tilt from the FRG. We do this explicitly for a potential with multiple barriers and show that in general many different potentials will give identical predictions for the spectral tilt suggesting that observations are agnostic to localised features in the potential. Finally we use the EEOM to compute first-passage time (FPT) quantities for the spectator field. The EEOM for the one- and two-point function are enough to accurately predict the average time taken $\left\langle \mathcal{N}\right\rangle$ to travel between two field values with a barrier in between and the variation in that time $\delta \mathcal{N}^2$. It can also accurately resolve the full PDF for time taken $\rho (\mathcal{N})$, predicting the correct exponential tail. This suggests that an extension of this analysis to the inflaton can correctly capture the exponential tail that is expected in models producing Primordial Black Holes.

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G. Rigopoulos and A. Wilkins
Fri, 18 Nov 22
25/70

Comments: 24 pages, 8 figures, 2 tables

Derivation of an equation of pair correlation function from BBGKY hierarchy in a weakly coupled self gravitating system [CL]

http://arxiv.org/abs/2210.15442


An equation of pair correlation function has been derived from the first two members of BBGKY hierarchy in a weakly coupled inhomogeneous self gravitating system in quasi thermal equilibrium. This work may be useful to study the thermodynamic properties of the central region of a star cluster which is older than a few or more central relaxation time.

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A. Bose
Mon, 14 Nov 22
61/69

Comments: N/A

A Comprehensive Perturbative Formalism for Phase-Mixing in Perturbed Disks. I. Phase spirals in an Infinite, Isothermal Slab [GA]

http://arxiv.org/abs/2208.05038


Galactic disks are highly responsive systems that often undergo external perturbations and subsequent collisionless equilibration, predominantly via phase-mixing. We use linear perturbation theory to study the response of infinite isothermal slab analogues of disks to perturbations with diverse spatio-temporal characteristics. Without self-gravity of the response, the dominant Fourier modes that get excited in a disk are the bending and breathing modes, which, due to vertical phase-mixing, trigger local phase-space spirals that are one- and two-armed, respectively. We demonstrate how the lateral streaming motion of slab stars causes phase spirals to damp out over time. The ratio of the perturbation timescale ($\tau_{\mathrm{P}}$) to the local, vertical oscillation time ($\tau_z$) ultimately decides which of the two modes is excited. Faster, more impulsive ($\tau_{\mathrm{P}} < \tau_z$) and slower, more adiabatic ($\tau_{\mathrm{P}} > \tau_z$) perturbations excite stronger breathing and bending modes, respectively, although the response to very slow perturbations is exponentially suppressed. For encounters with satellite galaxies, this translates to more distant and more perpendicular encounters triggering stronger bending modes. We compute the direct response of the Milky Way disk to several of its satellite galaxies, and find that recent encounters with all of them excite bending modes in the Solar neighborhood. The encounter with Sagittarius triggers a response that is at least $1-2$ orders of magnitude larger than that due to any other satellite, including the Large Magellanic Cloud. We briefly discuss how ignoring the presence of a dark matter halo and the self-gravity of the response might impact our conclusions.

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U. Banik, M. Weinberg and F. Bosch
Thu, 11 Aug 22
49/68

Comments: Accepted for publication in ApJ; 7 figures, 1 table

The Disordered Heterogeneous Universe: Galaxy Distribution and Clustering Across Length Scales [CEA]

http://arxiv.org/abs/2207.00519


Studies of disordered heterogeneous media and galaxy cosmology share a common goal: analyzing the distribution of particles at microscales' to predict physical properties atmacroscales’, whether for a liquid, composite material, or entire Universe. The former theory provides an array of techniques to characterize a wide class of microstructures; in this work, we apply them to the distributions of galaxies. We focus on the lower-order correlation functions, void' andparticle’ nearest-neighbor functions, pair-connectedness functions, percolation properties, and a scalar order metric. Compared to homogeneous Poisson and typical disordered systems, the cosmological simulations exhibit enhanced large-scale clustering and longer tails in the nearest-neighbor functions, due to the presence of quasi-long-range correlations. On large scales, the system appears hyperuniform', due to primordial density fluctuations, whilst on the smallest scales, the system becomes almostantihyperuniform’, and, via the order metric, is shown to be a highly correlated disordered system. Via a finite scaling analysis, we show that the percolation threshold of the galaxy catalogs is significantly lower than for Poisson realizations; this is consistent with the observation that the galaxy distribution contains larger voids. However, the two sets of simulations share a fractal dimension, implying that they lie in the same universality class. Finally, we consider the ability of large-scale clustering statistics to constrain cosmological parameters using simulation-based inference. Both the nearest-neighbor distribution and pair-connectedness function considerably tighten bounds on the amplitude of cosmological fluctuations at a level equivalent to observing twenty-five times more galaxies. These are a useful alternative to the three-particle correlation, and are computable in much reduced time. (Abridged)

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O. Philcox and S. Torquato
Mon, 4 Jul 22
30/62

Comments: 27 pages, submitted to Phys. Rev. X

Regularized phase-space volume for the three-body problem [CL]

http://arxiv.org/abs/2205.04294


The micro-canonical phase-space volume for the three-body problem is an elementary quantity of intrinsic interest, and within the flux-based statistical theory, it sets the scale of the disintegration time. While the bare phase-volume diverges, we show that a regularized version can be defined by subtracting a reference phase-volume, which is associated with hierarchical configurations. The reference quantity, also known as a counter-term, can be chosen from a 1-parameter class. The regularized phase-volume of a given (negative) total energy, $\bar\sigma(E)$, is evaluated. First, it is reduced to a function of the masses only, which is sensitive to the choice of a regularization scheme only through an additive constant. Then, analytic integration is used to reduce the integration to a sphere, known as shape sphere. Finally, the remaining integral is evaluated numerically, and presented by a contour plot in parameter space. Regularized phase-volumes are presented for both the planar three-body system and the full 3d system. In the test mass limit, the regularized phase-volume is found to become negative, thereby signalling the breakdown of the non-hierarchical statistical theory. This work opens the road to the evaluation of $\bar\sigma(E,L)$, where $L$ is the total angular momentum, and it turn, to comparison with simulation determined disintegration times.

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Y. Dandekar, B. Kol, L. Lederer, et. al.
Tue, 10 May 22
38/70

Comments: 27 pages, 6 figures

An intuition for physicists: information gain from experiments [CL]

http://arxiv.org/abs/2205.00009


How much one has learned from an experiment is quantifiable by the information gain, also known as the Kullback-Leibler divergence. The narrowing of the posterior parameter distribution $P(\theta|D)$ compared with the prior parameter distribution $\pi(\theta)$, is quantified in units of bits, as: $ D_{\mathrm{KL}}(P|\pi)=\int\log_{2}\left(\frac{P(\theta|D)}{\pi(\theta)}\right)\,P(\theta|D)\,d\theta $. This research note gives an intuition what one bit of information gain means. It corresponds to a Gaussian shrinking its standard deviation by a factor of three.

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J. Buchner
Tue, 3 May 22
34/82

Comments: Accepted to RNAAS

Long-term relaxation of ${1D}$ self-gravitating systems [CL]

http://arxiv.org/abs/2204.02834


We investigate the long-term relaxation of one-dimensional (${1D}$) self-gravitating systems, using both kinetic theory and $N$-body simulations. We consider thermal and Plummer equilibria, with and without collective effects. All combinations are found to be in clear agreement with respect to the Balescu-Lenard and Landau predictions for the diffusion coefficients. Interestingly, collective effects reduce the diffusion by a factor ${\sim 10}$. The predicted flux for Plummer equilibrium matches the measured one, which is a remarkable validation of kinetic theory. We also report on a situation of quasi kinetic blocking for the same equilibrium.

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M. Roule, J. Fouvry, C. Pichon, et. al.
Thu, 7 Apr 22
14/45

Comments: 12 pages, 11 figures, submitted to APS

Adiabatic lapse rate of real gases [CL]

http://arxiv.org/abs/2203.12040


We derive a formula for the dry adiabatic lapse rate of atmospheres composed of real gases. We restrict our study to those described by a family of two-parameter cubic equations of state and the recent Guevara non-cubic equation. Since our formula depends on the adiabatic curves, we compute them all at once considering molecules that can move, rotate, and vibrate, for any equation of state. To illustrate our results, we estimate the lapse rate of the troposphere of Titan, obtaining a better approximation to the observed data in some instances, when compared to the estimation provided by the virial expansion up to third order.

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B. Díaz, M. Ariza and J. Ramírez
Thu, 24 Mar 22
7/56

Comments: N/A

The Fractality and Size Distributions of Astrophysical Self-Organized Criticality Systems [SSA]

http://arxiv.org/abs/2203.12484


The statistics of nonlinear processes in avalanching systems, based on the {\sl self-organized criticality (SOC)} concept of Bak et al.~(1987), predicts power law-like size (or occurrence frequency) distribution functions. Following up on previous work we define a {\sl standard SOC model} in terms of six assumptions: (i) multi-fractality; (ii) the length-area-volume relationship of Mandelbrot (1977); (iii) the flux-volume relationship, (iv) classical diffusion, (v) the Euclidean volume limit at the event peak time, and (vi) the spatio-temporal fluence or energy of an avalanche event. We gather data of the fractal dimension and power law slopes from 162 publications and assemble them in 28 groups (e.g., solar and stellar flare energies), from which we find that 75\% of the groups are consistent with the standard SOC model. Alternative SOC models (Levy-flight, flat-world, non-fractal) are slightly less correlated with the data. The remaining discrepancies are attributed to outliers caused by small-number statistics, background subtraction problems, inadequate fitting ranges, and deviations from ideal power laws.

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M. Aschwanden
Thu, 24 Mar 22
12/56

Comments: 51 pages, 6 Figures, 16 Tables

Photon frequency diffusion process [CL]

http://arxiv.org/abs/2202.08660


We introduce a stochastic multi-photon dynamics on reciprocal space. Assuming isotropy, we derive the diffusion limit for a tagged photon to be a nonlinear Markov process on frequency. The nonlinearity stems from the stimulated emission. In the case of Compton scattering with thermal electrons, the limiting process describes the dynamical fluctuations around the Kompaneets equation. More generally, we construct a photon frequency diffusion process which enables to include nonequilibrium effects. Modifications of the Planck Law may thus be explored, where we focus on the low-frequency regime.

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G. Oliveira, C. Maes and K. Meerts
Fri, 18 Feb 22
12/63

Comments: 28 pages, 6 figures

Self-Organization In Stellar Evolution: Size-Complexity Rule [SSA]

http://arxiv.org/abs/2202.02318


Complexity Theory is highly interdisciplinary, therefore any regularities must hold on all levels of organization, independent on the nature of the system. An open question in science is how complex systems self-organize to produce emergent structures and properties, a branch of non-equilibrium thermodynamics. It has long been known that there is a quantity-quality transition in natural systems. This is to say that the properties of a system depend on its size. More recently, this has been termed the size-complexity rule, which means that to increase their size, systems must increase their complexity, and that to increase their complexity they must grow in size. This rule goes under different names in different disciplines and systems of different nature, such as the area-speciation rule, economies of scale, scaling relations (allometric) in biology and for cities, and many others. We apply the size-complexity rule to stars to compare them with other complex systems in order to find universal patterns of self-organization independent of the substrate. Here, as a measure of complexity of a star, we are using the degree of grouping of nucleons into atoms, which reduces nucleon entropy, increases the variety of elements, and changes the structure of the star. As seen in our previous work, complexity, using action efficiency, is in power law proportionality of all other characteristics of a complex system, including its size. Here we find that, as for the other systems studied, the complexity of stars is in a power law proportionality with their size – the bigger a system is, the higher its level of complexity is – despite differing explosion energies and initial metallicities from simulations and data, which confirms the size-complexity rule and our model.

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T. Butler and G. Georgiev
Mon, 7 Feb 22
25/46

Comments: 20 pages, 3 figures, 11 tables, 9 equations, Conference on Complex Systems CCS2017, Cancun, Mexico, Sattelite meeting “Efficiency in complex systems”

Equilibrium solution for cold dynamical systems and self-similarity. (II) [CL]

http://arxiv.org/abs/2201.12282


Numerical simulations demonstrate a link between dynamically cold initial solutions and self-similarity. However the nature of this link is not fully understood. Cold initial conditions alone without further symmetry do not lead to self-similarity. Here we show that when the system approaches equilibrium a new symmetry appears. The combination of this equilibrium symmetry with the cold symmetry in the initial conditions leads to full self-similarity. As a consequence for any initially cold system even if the initial spatial distribution is not self-similar we will observe an evolution towards self-similarity near equilibrium. The case of one dimensional systems or spherically symmetric systems in 3D are discussed in detail. Systems depending on the energy and other integrals are also considered. The problem of the degeneracy of the self-similar solutions at equilibrium is tackled. It is shown that very small perturbations at the center of the system have the ability to break this degeneracy and lead to the convergence towards a specific auto-similar solution.

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C. Alard
Mon, 31 Jan 22
44/55

Comments: 9 pages, 3 figures

Statistical properties of the gravitational force in a random homogeneous medium [CL]

http://arxiv.org/abs/2201.08478


We discuss the statistical distribution of the gravitational (Newtonian) force exerted on a test particle in a infinite random and homogeneous gas of non-correlated particles. The exact solution is known as the Holtsmark distribution at the limit of infinite system corresponding to the number of particle N within the volume and the volume going to infinity. The statistical behaviour of the gravitational force for scale comparable to the inter-distance particle can be analyzed through the combination of the n-th nearest neighbor particle contribution to the total gravitational force, which can be derived from the joint probability density of location for a set of N particles. We investigate two independent approaches to derive the joint probability density of location for a set of N neighbors using integral forms and order statistics to give a general expression of such probability distribution with generalised dimension of space. We found that the non-finite dispersion of the Holtsmark distribution is due to the single contribution of the first nearest neighbor in the total gravitational force.

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C. Payerne
Mon, 24 Jan 22
22/59

Comments: 11 pages, 5 figures

Non-Gaussian Effects of the Saha's Ionization in the Early Universe [CEA]

http://arxiv.org/abs/2201.07922


Tsallis’ thermostatistical has received increasing attention due to its success in describing phenomena that manifest unusual thermodynamic properties. In this context, the generalized Saha equation must follow a condition of generalized thermal equilibrium of matter and radiation. The present work aims to explore the non-Gaussian effects on Saha’s ionization via Tsallis statistics. To accomplish this, we generalized the number density taking into account a non-Gaussian Fermi-Dirac distribution, and then set out the Saha equation for the cosmological recombination. As a result, we highlight two new non-Gaussian effects: $i$) two generalized chemical equilibrium conditions, one for the relativistic regime and the other for the non-relativistic one; and $ii$) the hydrogen binding $q$-energy. We demonstrated that to yields smooth shifts in the binding energy, the $a$-parameter must be very small. We also showed that binding $q$-energy exhibits symmetrical behavior around the value of the standard binding energy. Besides, we used the $q$-energy in order to access other hydrogen energy levels, and we ascertained the values of the $a$-parameter that access those levels and their relationship to temperature. Finally, we employed these results to examine the non-Gaussian effects of the deuterium bottleneck, recombination and the particle anti-particle excess.

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L. Sales, F. Carvalho, E. Bento, et. al.
Fri, 21 Jan 22
46/60

Comments: 9 pages, 2 figures

Collisionless relaxation of a Lynden-Bell plasma [CL]

http://arxiv.org/abs/2201.03376


A plasma whose Coulomb-collision rate is very small may relax on a shorter time scale to non-Maxwellian quasi-equilibria, which, nevertheless, have a universal form, with dependence on initial conditions retained only via an infinite set of Casimir invariants enforcing phase-volume conservation. These are distributions derived by Lynden-Bell (1967) via a statistical-mechanical entropy-maximisation procedure, assuming perfect mixing of phase-space elements. To show that these equilibria are reached dynamically, one must derive an effective `collisionless collision integral’ for which they are fixed points — unique and inevitable provided the integral has an appropriate H-theorem. We describe how such collision integrals are derived and what assumptions are required for them to have a closed form, how to prove the H-theorems for them, and why, for a system carrying sufficiently large electric-fluctuation energy, collisionless relaxation should be fast. It is suggested that collisionless dynamics may favour maximising entropy locally in phase space before converging to global maximum-entropy states.

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R. Ewart, A. Brown, T. Adkins, et. al.
Tue, 11 Jan 22
19/95

Comments: 35 pages, submitted to JPP

Thermodynamically consistent entropic inflation including subdominant contribution [CL]

http://arxiv.org/abs/2201.03385


Entropic-force cosmology provides, in contrast with dark energy descriptions, a concrete physical understanding of the accelerated expansion of the universe. The acceleration appears to be a consequence of the entropy associated with the information storage in the universe. We study the effects of including a subdominant power-law term within a thermodynamically admissible entropic-force model. The temperature of the universe horizon is obtained by requiring that the Legendre structure of thermodynamics is preserved. The correction term is introduced to explain different periods of acceleration and deceleration in the late-time universe. We analyze the various types of behaviors, and we satisfactorily compare them with the observational red-shift dependencies of the Hubble parameter $H$ and of the luminosity distance data available from supernovae.

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D. Zamora and C. Tsallis
Tue, 11 Jan 22
54/95

Comments: arXiv admin note: substantial text overlap with arXiv:2201.01835

Thermodynamically consistent entropic-force cosmology [CL]

http://arxiv.org/abs/2201.01835


We analyze the thermodynamical consistency of entropic-force cosmological models. Our analysis is based on a generalized entropy scaling with an arbitrary power of the Hubble radius. The Bekenstein-Hawking entropy, proportional to the area, and the nonadditive $S_{\delta=3/2}$-entropy, proportional to the volume, are particular cases. One of the points to be solved by entropic-force cosmology for being taken as a serious alternative to mainstream cosmology is to provide a physical principle that points out what entropy and temperature have to be used. We determine the temperature of the universe horizon by requiring that the Legendre structure of thermodynamics is preserved. We compare the performance of thermodynamically consistent entropic-force models with regard to the available supernovae data by providing appropriate constraints for optimizing alternative entropies and temperatures of the Hubble screen. Our results point out that the temperature differs from the Hawking one.

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D. Zamora and C. Tsallis
Fri, 7 Jan 22
17/34

Comments: N/A

Symplectic coarse graining approach to the dynamics of spherical self-gravitating models [GA]

http://arxiv.org/abs/2112.10709


We investigate the evolution of the phase-space distribution function around slightly perturbed stationary states and the process of violent relaxation in the context of the dissipationless collapse of an isolated spherical self-gravitating system. By means of the recently introduced symplectic coarse graining technique, we obtain an effective evolution equation that allows us to compute the scaling of the frequencies around a stationary state, as well as the damping times of Fourier modes of the distribution function, with the magnitude of the Fourier $k-$vectors themselves. We compare our analytical results with $N$-body simulations.

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L. Barbieri, P. Cintio, G. Giachetti, et. al.
Tue, 21 Dec 21
33/86

Comments: 17 pages 7 figures. Submitted to MNRAS, comments welcome

On the stability of satellites at unstable libration points of sun-planet-moon systems [EPA]

http://arxiv.org/abs/2109.12612


The five libration points of a sun-planet system are stable or unstable fixed positions at which satellites or asteroids can remain fixed relative to the two orbiting bodies. A moon orbiting around the planet causes a time-dependent perturbation on the system. Here, we address the sense in which invariant structure remains. We employ a transition state theory developed previously for periodically driven systems with a rank-1 saddle in the context of chemical reactions. We find that a satellite can be parked on a so-called time-periodic transition state trajectory — which is an orbit restricted to the vicinity of the libration point L2 for infinitely long time — and investigate the stability properties of that orbit.

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J. Reiff, J. Zatsch, J. Main, et. al.
Tue, 28 Sep 21
19/89

Comments: Main article has 15 pages, 6 figures. arXiv admin note: text overlap with arXiv:2011.04029

Non-ideal self-gravity and cosmology: the importance of correlations in the dynamics of the large-scale structures of the Universe [GA]

http://arxiv.org/abs/2109.09087


Inspired by the statistical mechanics of an ensemble of interacting particles (BBGKY hierarchy), we propose to account for small-scale inhomogeneities in self-gravitating astrophysical fluids by deriving a non-ideal Virial theorem and non-ideal Navier-Stokes equations using a decomposition of the gravitational force into a near- and far-field component. These equations involve the pair radial distribution function (similar to the two-point correlation function), similarly to the interaction energy and equation of state in liquids. Small-scale correlations lead to a non-ideal amplification of the gravitational interaction energy, whose omission leads to a missing mass problem, e.g., in galaxies and galaxy clusters. We also propose an extension of the Friedmann equations in the non-ideal regime. We estimate the non-ideal amplification factor of the gravitational interaction energy of the baryons to lie between 5 and 20, potentially explaining the observed value of the Hubble parameter. Within this framework, the acceleration of the expansion emerges naturally because of the increasing number of sub-structures induced by gravitational collapse, which increases their contribution to the total gravitational energy. A simple estimate predicts a non-ideal deceleration parameter qni~-1;this is potentially the first determination of the observed value based on an intuitively physical argument. We show that correlations and gravitational interactions can produce a transition to a viscous regime that can lead to flat rotation curves. This transition can also explain the dichotomy between (Keplerian) LSB elliptical galaxy and (non-Keplerian) spiral galaxy rotation profiles. Overall, our results demonstrate that non-ideal effects induced by inhomogeneities must be taken into account in order to properly determine the gravitational dynamics of galaxies and the larger scale universe.

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P. Tremblin, G. Chabrier, T. Padioleau, et. al.
Tue, 21 Sep 21
52/85

Comments: submitted to A&A

The Universe as a driven quantum system: Unbounded heating in cyclic cosmologies [CL]

http://arxiv.org/abs/2109.01660


The Hamiltonian of an evolving Universe is shown to be formally equivalent to that of a driven quantum system, whose driving follows from the temporal dependence of the spacetime metric. This analogy allows insights from the field of driven quantum systems to be applied to cosmological settings. In particular, it is shown that periodic cyclic cosmologies are generically prohibited (except under certain limiting constraints) due to their correspondence with periodically-driven quantum systems (which are typically expected to experience unbounded heating in the infinite future). This result highlights how future work on non-periodically-driven quantum systems is required to fully describe the dynamics of more general cyclic cosmologies (for which a qualitative picture is briefly discussed).

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J. Vieira
Tue, 7 Sep 21
46/89

Comments: N/A

Inflation in a Gaussian RandomLandscape [CL]

http://arxiv.org/abs/2107.09870


Random, multifield functions can set generic expectations for landscape-style cosmologies. We consider the inflationary implications of a landscape defined by a Gaussian random function, which is perhaps the simplest such scenario. Many key properties of this landscape, including the distribution of saddles as a function of height in the potential, depend only on its dimensionality, N, and a single parameter, {\gamma}, which is set by the power spectrum of the random function. We show that for saddles with a single downhill direction the negative mass term grows smaller, relative to the average mass, as N increases, a result with potential implications for the {\eta}-problem in landscape scenarios. For some power spectra Planck-scale saddles have {\eta} ~ 1 and eternal, topological inflation would be common in these scenarios. Lower-lying saddles typically have large {\eta}, but the fraction of these saddles which would support inflation is computable, allowing us to identify which scenarios can deliver a universe that resembles ours. Finally, by drawing inferences about the relative viability of different multiverse proposals we also illustrate ways in which quantitative analyses of multiverse scenarios are feasible.

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L. Low, R. Easther and S. Hotchkiss
Thu, 22 Jul 21
57/59

Comments: 21 pages, 13 figures

Relativistic Langevin Equation derived from a particle-bath Lagrangian [CL]

http://arxiv.org/abs/2107.07205


We show how a relativistic Langevin equation can be derived from a Lorentz-covariant version of the Caldeira-Leggett particle-bath Lagrangian. In one of its limits, we identify the obtained equation with the Langevin equation used in contemporary extensions of statistical mechanics to the near-light-speed motion of a Brownian particle in non-relativistic dissipative fluids. The proposed framework provides a more rigorous and first-principles form of the Langevin equation often quoted or postulated as ansatz in previous works. We then refine the aforementioned results by considering more terms in the particle-bath coupling, which improves the precision of the approximation for fully relativistic settings where not only the tagged particle but also the thermal bath motion is relativistic. We discuss the implications of the apparent breaking of space-time translation and parity invariance, showing that these effects are not necessarily in contradiction with the assumptions of statistical mechanics. The intrinsically non-Markovian character of the fully relativistic generalized Langevin equation derived here, and of the associated fluctuation-dissipation theorem, is also discussed.

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A. Petrosyan and A. Zaccone
Fri, 16 Jul 21
25/61

Comments: N/A

Proving the Lorentz invariance of the entropy and the covariance of thermodynamics [CL]

http://arxiv.org/abs/2105.09294


The standard argument for the Lorentz invariance of the thermodynamic entropy in equilibrium is based on the assumption that it is possible to perform an adiabatic transformation whose only outcome is to accelerate a macroscopic body, keeping its rest mass unchanged. The validity of this assumption constitutes the very foundation of relativistic thermodynamics and needs to be tested in greater detail. We show that, indeed, such a transformation is always possible, at least in principle. The only two assumptions invoked in the proof are that there is at least one inertial reference frame in which the second law of thermodynamics is valid and that the microscopic theory describing the internal dynamics of the body is a field theory, with Lorentz invariant Lagrangian density. The proof makes no reference to the connection between entropy and probabilities and is valid both within classical and quantum physics. To avoid any risk of circular reasoning, we do not postulate that the laws of thermodynamics are the same in every reference frame, but we obtain this fact as a direct consequence of the Lorentz invariance of the entropy.

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L. Gavassino
Thu, 20 May 21
22/56

Comments: 8 pages

Zipf's law for cosmic structures: how large are the greatest structures in the universe? [CEA]

http://arxiv.org/abs/2105.06110


The statistical characterization of the distribution of visible matter in the universe is a central problem in modern cosmology. In this respect, a crucial question still lacking a definitive answer concerns how large are the greatest structures in the universe. This point is closely related to whether or not such a distribution can be approximated as being homogeneous on large enough scales. Here we assess this problem by considering the size distribution of superclusters of galaxies and by leveraging on the properties of Zipf-Mandelbrot law, providing a novel approach which complements standard analysis based on the correlation functions. We find that galaxy superclusters are well described by a pure Zipf’s law with no deviations and this implies that all the catalogs currently available are not sufficiently large to spot a truncation in the power-law behavior. This finding provides evidence that structures larger than the greatest superclusters already observed are expected to be found when deeper redshift surveys will be completed. As a consequence the scale beyond which galaxy distribution crossovers toward homogeneity, if any, should increase accordingly

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i. Marzo, F. Labini and L. Pietronero
Fri, 14 May 21
18/67

Comments: 9 pages, 3 figures, accepted for publication in Astronomy and Astrophysics

Cratering of Soil by Impinging Jets of Gas, with Application to Landing Rockets on Planetary Surfaces [EPA]

http://arxiv.org/abs/2104.05195


Several physical mechanisms are involved in excavating granular materials beneath a vertical jet of gas. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. A series of experiments and simulations have been performed to provide a detailed view of the complex gas/soil interactions. Measurements have also been taken from the Apollo lunar landing videos and from photographs of the resulting terrain, and these help to demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the on-going design of higher-fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from landing spacecraft must be accurately predicted and controlled lest it erosively damage the surrounding hardware.

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P. Metzger, B. Vu, D. Taylor, et. al.
Tue, 13 Apr 2021
54/93

Comments: 6 pages, 5 figures

The number of populated electronic configurations in a hot dense plasma [CL]

http://arxiv.org/abs/2103.07663


In hot dense plasmas of intermediate or high-Z elements in the state of local thermodynamic equilibrium, the number of electronic configurations contributing to key macroscopic quantities such as the spectral opacity and equation of state, can be enormous. In this work we present systematic methods for the analysis of the number of relativistic electronic configurations in a plasma. While the combinatoric number of configurations can be huge even for mid-Z elements, the number of configurations which have non negligible population is much lower and depends strongly and non-trivially on temperature and density. We discuss two useful methods for the estimation of the number of populated configurations: (i) using an exact calculation of the total combinatoric number of configurations within superconfigurations in a converged super-transition-array (STA) calculation, and (ii) by using an estimate for the multidimensional width of the probability distribution for electronic population over bound shells, which is binomial if electron exchange and correlation effects are neglected. These methods are analyzed, and the mechanism which leads to the huge number of populated configurations is discussed in detail. Comprehensive average atom finite temperature density functional theory (DFT) calculations are performed in a wide range of temperature and density for several low, mid and high Z plasmas. The effects of temperature and density on the number of populated configurations are discussed and explained.

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M. Krief
Tue, 16 Mar 21
59/92

Comments: N/A

Real scalar phase transitions: a nonperturbative analysis [CL]

http://arxiv.org/abs/2101.05528


We study the thermal phase transitions of a generic real scalar field, without a $Z_2$-symmetry, referred to variously as an inert, sterile or singlet scalar, or $\phi^3+\phi^4$ theory. Such a scalar field arises in a wide range of models, including as the inflaton, or as a portal to the dark sector. At high temperatures, we perform dimensional reduction, matching to an effective theory in three dimensions, which we then study both perturbatively and on the lattice. For strong first-order transitions, with large tree-level cubic couplings, our lattice Monte-Carlo simulations agree with perturbation theory within error. However, as the size of the cubic coupling decreases, relative to the quartic coupling, perturbation theory becomes less and less reliable, breaking down completely in the approach to the $Z_2$-symmetric limit, in which the transition is of second order. Notwithstanding, the renormalisation group is shown to significantly extend the validity of perturbation theory. Throughout, our calculations are made as explicit as possible so that this article may serve as a guide for similar calculations in other theories.

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O. Gould
Fri, 15 Jan 21
48/60

Comments: 41 pages, 14 figures

Phase transition in Modified Newtonian Dynamics (MONDian) self-gravitating systems [CL]

http://arxiv.org/abs/2012.06622


We study the statistical mechanics of binary systems under gravitational interaction of the Modified Newtonian Dynamics (MOND) in three-dimensional space. Considering the binary systems, in the microcanonical and canonical ensembles, we show that in the microcanonical systems, unlike the Newtonian gravity, there is a sharp phase transition, with a high-temperature homogeneous phase and a low temperature clumped binary one. Defining an order parameter in the canonical systems, we find a smoother phase transition and identify the corresponding critical temperature in terms of physical parameters of the binary system. Our results for the binary system provide a hint to understand the phase transitions in the N-body system by considering it as a constituent of binary subsystems.

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M. Haghighi, S. Rahvar and M. Tabar
Wed, 16 Dec 20
19/93

Comments: 15 pages, 6 figures

New probability distributions in astrophysics: IV. The relativistic Maxwell-Boltzmann distribution [CL]

http://arxiv.org/abs/2012.05797


Two relativistic distributions which generalizes the Maxwell Boltzman (MB) distribution are analyzed: the relativistic MB and the Maxwell-J{\”u}ttner (MJ) distribution. For the two distributions we derived in terms of special functions the constant of normalization, the average value, the second moment about the origin, the variance, the mode, the asymptotic behavior, approximate expressions for the average value as function of the temperature and the connected inverted expressions for the temperature as function of the average value. Two astrophysical applications to the synchrotron emission in presence of the magnetic field and the relativistic electrons are presented.

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L. Zaninetti
Fri, 11 Dec 20
11/75

Comments: 15 pages and 17 figures

A first comparison of Kinetic Field Theory with Eulerian Standard Perturbation Theory [CEA]

http://arxiv.org/abs/2012.05812


We present a detailed comparison of the newly developed particle-based Kinetic Field Theory framework for cosmic large-scale structure formation with the established formalism of Eulerian Standard Perturbation Theory. We highlight the qualitative differences of both approaches by a comparative analysis of the respective equations of motion and implementation of initial conditions. A natural starting point for a first quantitative comparison is given by the non-interacting regime of free-streaming kinematics. Our results suggest that Kinetic Field Theory contains a complete resummation of Standard Perturbation Theory in this regime. We further show that the exact free-streaming solution of Kinetic Field Theory can not be recovered in any finite order of Standard Perturbation Theory. Kinetic Field Theory should therefore provide a better starting point for perturbative treatments of non-linear structure formation.

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E. Kozlikin, R. Lilow, F. Fabis, et. al.
Fri, 11 Dec 20
37/75

Comments: N/A

Non-Maxwellian rate coefficients for electron and ion collisions in Rydberg plasmas: implications for excitation and ionization [CL]

http://arxiv.org/abs/2012.04069


Scattering phenomena between charged particles and highly excited Rydberg atoms are of critical importance in many processes in plasma physics and astrophysics. While a Maxwell-Boltzmann (MB) energy distribution for the charged particles is often assumed for calculations of collisional rate coefficients, in this contribution we relax this assumption and use two different energy distributions, a bimodal MB distribution and a $\kappa$-distribution. Both variants share a high-energy tails occurring with higher probability than the corresponding MB distribution. The high energy tail may significantly affect rate coefficients for various processes. We focus the analysis to specific situations by showing the dependence of the rate coefficients on the principal quantum number of hydrogen atoms in n-changing collisions with electrons in the excitation and ionization channels and in a temperature range relevant to the divertor region of a tokamak device. We finally discuss the implications for diagnostics of laboratory plasmas.

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D. Vrinceanu, R. Onofrio and H. Sadeghpour
Wed, 9 Dec 20
64/80

Comments: 14 pages, 4 figures, Journal of Plasma Physics collection on ‘Laboratory and Astrophysical Plasmas: New Perspectives’

Variable energy flux in turbulence [CL]

http://arxiv.org/abs/2011.07291


In three-dimensional hydrodynamic turbulence forced at large length scales, a constant energy flux $ \Pi_u $ flows from large scales to intermediate scales, and then to small scales. It is well known that for multiscale energy injection and dissipation, the energy flux $\Pi_u$ varies with scales. In this review we describe this principle and show how this general framework is useful for describing a variety of turbulent phenomena. Compared to Kolmogorov’s spectrum, the energy spectrum steepens in turbulence involving quasi-static magnetofluid, Ekman friction, stable stratification, magnetohydrodynamics, and solution with dilute polymer. However, in turbulent thermal convection, in unstably stratified turbulence such as Rayleigh-Taylor turbulence, and in shear turbulence, the energy spectrum has an opposite behaviour due to an increase of energy flux with wavenumber. In addition, we briefly describe the role of variable energy flux in quantum turbulence, in binary-fluid turbulence including time-dependent Landau-Ginzburg and Cahn-Hillianrd equations, and in Euler turbulence.

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M. Verma
Wed, 18 Nov 20
66/79

Comments: 69 pages

The role of energy in ballistic agglomeration [CL]

http://arxiv.org/abs/2010.01106


We study a ballistic agglomeration process in the reaction-controlled limit. Cluster densities obey an infinite set of Smoluchowski rate equations, with rates dependent on the average particle energy. The latter is the same for all cluster species in the reaction-controlled limit and obeys an equation depending on densities. We express the average energy through the total cluster density that allows us to reduce the governing equations to the standard Smoluchowski equations. We derive basic asymptotic behaviors and verify them numerically. We also apply our formalism to the agglomeration of dark matter.

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N. Brilliantov, A. Osinsky and P. Krapivsky
Mon, 5 Oct 20
37/61

Comments: N/A

Properties of self gravitating quasi-stationary states [CEA]

http://arxiv.org/abs/2009.11624


Initially far out-of-equilibrium self-gravitating systems form, through a collisionless relaxation dynamics, quasi-stationary states (QSS). These may arise from a bottom-up aggregation of structures or in a top-down frame; their quasi-equilibrium properties are well described by the Jeans equation and are not universal, i.e. they depend on initial conditions. To understand the origin of such dependence, we present results of numerical experiments of initially cold and spherical systems characterized by various choices of the spectrum of initial density fluctuations. The amplitude of such fluctuations determines whether the system relaxes in a top-down or a bottom-up manner. We find that statistical properties of the resulting QSS mainly depend upon the amount of energy exchanged during the formation process. In particular, in the violent top-down collapses the energy exchange is large and the QSS show an inner core with an almost flat density profile and a quasi Maxwell-Boltzmann (isotropic) velocity distribution, while their outer regions display a density profile $\rho(r) \propto r^{-\alpha}$ ($\alpha >0$) with radially elongated orbits. We analytically show that $\alpha=4$ in agreement with numerical experiments. In the less violent bottom-up dynamics, the energy exchange is much smaller, the orbits are less elongated and $0< \alpha(r) \le 4$, with a a density profile well fitted by the Navarro-Frenk-White behavior. Such a dynamical evolution is shown by both non-uniform spherical isolated systems and by halos extracted from cosmological simulations. We consider the relation of these results with the core-cusp problem concluding that this is naturally solved if galaxies form through a monolithic collapse.

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F. Labini and R. Capuzzo-Dolcetta
Fri, 25 Sep 20
-1843/62

Comments: 15 pages, 24 figures, Accepteb for publication in Astronomy and Astrophysics

Formation of disks with long-lived spiral arms from violent gravitational dynamics [GA]

http://arxiv.org/abs/2008.02605


By means of simple dynamical experiments we study the combined effect of gravitational and gas dynamics in the evolution of an initially out-of-equilibrium, uniform and rotating massive over-density thought as in isolation. The rapid variation of the system mean field potential makes the point-like particles (PP), that interact only via Newtonian gravity, to form a quasi-stationary thick disk dominated by rotational motions surrounded by far out-of-equilibrium spiral arms. On the other side, the gas component is subjected to compression shocks and radiative cooling so to develop a much flatter disk, where rotational motions are coherent and the velocity dispersion is smaller than that of PP. Around such gaseous disk long-lived, but non-stationary, spiral arms form: these are made of gaseous particles that move coherently because have acquired a specific phase-space correlation during the gravitational collapse phase. Such a phase-space correlation represents a signature of the violent origin of the arms and implies both the motion of matter and the transfer of energy. On larger scales, where the radial velocity component is significantly larger than the rotational one, the gas follows the same out-of-equilibrium spiral arms traced by PP We finally outline the astrophysical and cosmological implications of our results.

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F. Labini, L. Pinto and R. Capuzzo-Dolcetta
Fri, 7 Aug 20
-750/46

Comments: 23 pages, 26 figures. To be published in Physical Review E. Movies of the simulations are available at this https URL

Resummed Kinetic Field Theory: a model of coupled baryonic and dark matter [CEA]

http://arxiv.org/abs/2007.09484


We present a new analytical description of cosmic structure formation in a mixture of dark and baryonic matter, using the framework of Kinetic Field Theory (KFT) — a statistical field theory for classical particle dynamics. So far, KFT has only been able to describe a single type of particles, sufficient to consider structure growth due to the gravitational interactions between dark matter. However, the influence of baryonic gas dynamics becomes increasingly relevant when describing smaller scales. In this paper, we thus demonstrate how to extend the KFT formalism as well as a previously presented resummation scheme towards describing such mixtures of two particle species. Thereby, the gas dynamics of baryons are accounted for using the recently developed model of Mesoscopic Particle Hydrodynamics. Assuming a flat $\Lambda$CDM Universe and a simplified model for the thermal gas evolution, we demonstrate the validity of this approach by computing the linear evolution of the individual and total matter power spectra between the epoch of recombination and today. Our results correctly reproduce the expected behaviour, showing a suppression of both baryonic and dark matter structure growth on scales smaller than the baryonic Jeans length, in good agreement with results from the numerical Boltzmann solver CLASS. Nonlinear corrections within this approach will be investigated in upcoming works.

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D. Geiss, I. Kostyuk, R. Lilow, et. al.
Tue, 21 Jul 20
-391/75

Comments: 23 pages, 9 figures

The zeroth law of thermodynamics in special relativity [CL]

http://arxiv.org/abs/2005.06396


We critically revisit the definition of thermal equilibrium, in its operational formulation, provided by standard thermodynamics. We show that it refers to experimental conditions which break the covariance of the theory at a fundamental level and that, therefore, it cannot be applied to the case of moving bodies. We propose an extension of this definition which is manifestly covariant and can be applied to the study of isolated systems in special relativity. The zeroth law of thermodynamics is, then, proven to establish an equivalence relation among bodies which have not only the same temperature, but also the same center of mass four-velocity.

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L. Gavassino
Thu, 14 May 20
12/56

Comments: 15 pages, 0 figures

Simulations of Multi-Component Relativistic Thermalization [CL]

http://arxiv.org/abs/2004.13186


We report on the development and application of a multi dimensional relativistic Monte-Carlo code to explore the thermalization process in a relativistic multi-component environment. As an illustration we simulate the fully relativistic three dimensional Brownian-motion-like solution to the thermalization of a high mass particle in a bath of relativistic low-mass particles. We follow the thermalization and ultimate equilibrium distribution of the Brownian-like particle as can happen in the cosmic plasma during Big bang nucleosynthesis.

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A. Kedia, N. Sasankan, G. Mathews, et. al.
Thu, 30 Apr 20
29/71

Comments: N/A

Euler Turbulence and thermodynamic equilibrium [CL]

http://arxiv.org/abs/2004.09053


We perform a unique direct numerical simulation of Euler turbulence using delta-correlated velocity field as an initial condition, and report a full range of $k^2$ and $k$ energy spectra for 3D and 2D flows respectively, zero energy flux, and Maxwell-Boltzmann distribution for the velocity field. These are direct verification of the predictions of the absolute equilibrium theory of turbulence. For a coherent vortex as an initial condition, Euler turbulence transitions from a mixture of nonequilibrium-equilibrium state to a equilibrium state through a process called thermalization. In this letter, we present a model for thermalization in Euler turbulence.

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M. Verma, S. Bhattacharya and S. Chatterjee
Tue, 21 Apr 20
23/90

Comments: 5 pages

The Distribution of Vacua in Random Landscape Potentials [CL]

http://arxiv.org/abs/2004.04429


Landscape cosmology posits the existence of a convoluted, multidimensional, scalar potential — the “landscape” — with vast numbers of metastable minima. Random matrices and random functions in many dimensions provide toy models of the landscape, allowing the exploration of conceptual issues associated with these scenarios. We compute the relative number and slopes of minima as a function of the vacuum energy $\Lambda$ in an $N$-dimensional Gaussian random potential, quantifying the associated probability density, $p(\Lambda)$. After normalisations $p(\Lambda)$ depends only on the dimensionality $N$ and a single free parameter $\gamma$, which is related to the power spectrum of the random function. For a Gaussian landscape with a Gaussian power spectrum, the fraction of positive minima shrinks super-exponentially with $N$; at $N=100$, $p(\Lambda>0) \approx 10^{-780}$. Likewise, typical eigenvalues of the Hessian matrices reveal that the flattest approaches to typical minima grow flatter with $N$, while the ratio of the slopes of the two flattest directions grows with $N$. We discuss the implications of these results for both swampland and conventional anthropic constraints on landscape cosmologies. In particular, for parameter values when positive minima are extremely rare, the flattest approaches to minima where $\Lambda \approx 0$ are much flatter than for typical minima, increasingly the viability of quintessence solutions.

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L. Low, S. Hotchkiss and R. Easther
Fri, 10 Apr 20
34/56

Comments: 22 pages, 11 figures

Second law of black hole thermodynamics [CL]

http://arxiv.org/abs/2001.02897


If simple entropy in the Bekenstein-Hawking area law for a black hole is replaced with ‘negative’ quantum conditional entropy, which quantifies quantum entanglement, of positive-energy particles of the black hole relative to its outside, a paradox with the original pair-creation picture of Hawking radiation, the first law for black hole mechanics and quantum mechanics is resolved. However, there was no way to judge experimentally which area law is indeed adopted by black holes. Here, with the no-hair conjecture, we derive the perfect picture of a second law of black hole thermodynamics from the modified area law, rather than Bekenstein’s generalized one from the original area law. The second law is testable with an event horizon telescope, in contrast to Bekenstein’s. If this is confirmed, the modified area law is exalted to the first example of fundamental equations in physics which cannot be described without the concept of quantum information.

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K. Azuma and G. Kato
Fri, 10 Jan 20
40/65

Comments: 7 pages, 1 figure

Beyond Boltzmann: The Potential Energy Distribution of Objects in the Atmosphere [CL]

http://arxiv.org/abs/2001.02081


Estimates of the number and potential energy of molecules, aerosols, cloud droplets, insects, birds, planes and satellites in the atmosphere yield a distribution which is for potential energies below 10^2 kBT described by the Boltzmann distribution, but for the range from 10^2 kBT to 10^33 kBT by a power law with an exponent of approximately -1. An explanation for this surprising behavior is not found.

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H. Hess
Wed, 8 Jan 20
64/64

Comments: 2 pages, 1 figure

Model for Asteroid Regolith to Guide Simulant Development [EPA]

http://arxiv.org/abs/1912.10618


When creating asteroid regolith simulant, it is necessary to have a model of asteroid regolith to guide and to evaluate the simulant. We created a model through evaluation and synthesis of the available data sets including (1) the returned sample from Itokawa by the Hayabusa spacecraft, (2) imagery from the Hayabusa and NEAR spacecraft visiting Itokawa and Eros, respectively, (3) thermal infrared observations from asteroids, (4) the texture of meteorite regolith breccias, and (5) observations and modeling of the ejecta clouds from disrupted asteroids. Comparison of the Hayabusa returned sample with other data sets suggest the surficial material in the smooth regions of asteroids is dissimilar to the bulk regolith, probably due to removal of fines by photoionization and solar wind interaction or by preferential migration of mid-sized particles into the smooth terrain. We found deep challenges interpreting and applying the thermal infrared data so we were unable to use those observations in the model. Texture of regolith breccias do not agree with other data sets, suggesting the source regolith on Vesta was coarser than typical asteroid regolith. The observations of disrupted asteroids present a coherent picture of asteroid bulk regolith in collisional equilibrium, unlike lunar regolith, HED textures, and the Itokawa returned sample. The model we adopt consists of power laws for the bulk regolith in unspecified terrain (differential power index -3.5, representing equilibrium), and the surficial regolith in smooth terrain (differential power index -2.5, representing disequilibrium). Available data do not provide adequate constraints on maximum and minimum particle sizes for these power laws, so the model treats them as user-selectable parameters for the simulant.

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P. Metzger and D. Britt
Tue, 24 Dec 19
6/79

Comments: 15 pages, 4 figures

Measuring the Fidelity of Asteroid Regolith and Cobble Simulants [EPA]

http://arxiv.org/abs/1912.10622


NASA has developed a “Figure of Merit” method to grade the fidelity of lunar simulants for scientific and engineering purposes. Here we extend the method to grade asteroid simulants, both regolith and cobble variety, and we apply the method to the newly developed asteroid regolith and cobble simulant UCF/DSI-CI-2. The reference material that is used to evaluate this simulant for most asteroid properties is the Orgueil meteorite. Those properties are the mineralogical and elemental composition, grain density, bulk density of cobbles, magnetic susceptibility, mechanical strength of cobbles, and volatile release patterns. To evaluate the regolith simulant’s particle sizing we use a reference model that was based upon the sample returned from Itokawa by Hayabusa, the boulder count on Hayabusa, and four cases of disrupted asteroids that indicate particle sizing of the subsurface material. Compared to these references, the simulant has high figures of merit, indicating it is a good choice for a wide range of scientific and engineering applications. We recommend this methodology to the wider asteroid community and in the near future will apply it to additional asteroid simulants currently under development.

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P. Metzger, D. Britt, S. Covey, et. al.
Tue, 24 Dec 19
30/79

Comments: 42 pages, 11 figures

Explaining the cuspy dark matter halo by Landau-Ginzburg theory [CEA]

http://arxiv.org/abs/1912.09374


Twenty three years ago, cosmological N-body simulations revealed quasi-universal NFW dark matter halos, whose physical origin is still unclear. This work tries to solve this issue by Landau-Ginzburg (LG) theory in equilibrium statistical mechanics. We replace the order parameter in LG theory by density and consider the dark matter halos as fluctuations from the equilibrium state of the background, which can be the main halos for the subhalos, or the homogeneous and isotropic Universe for the galaxy cluster halos. With the assumption that the fluctuations of Helmholtz free energy depend mainly on the density and its gradient, which is shown to be consistent with the behavior of the power spectrum near the cluster scale, we can easily obtain the universal $r^{-1}$ cusp of the equilibrium dark matte halo without other requirements. This work strongly suggests that more studies should be done for the self-gravitating systems by statistical mechanics.

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D. Dong-Biao and K. Kang
Fri, 20 Dec 19
3/63

Comments: 5 pages, 2 figures. Comments are welcome

Emergence of modified Newtonian gravity from thermodynamics [CL]

http://arxiv.org/abs/1912.00252


Being inspired by Verlinde’s proposal that general relativistic gravity has a thermodynamic origin as an entropic force, Newtonian gravity is reexamined in view of nonequilibrium thermodynamics. Here, firstly, an unspecified scalar field potential is introduced and treated as a thermodynamic variable on an equal footing with the fluid variables. Then, the effects of irreversibility on the field are explored through the analysis of the entropy production rate in the linear regime. Remarkably, the second law of thermodynamics imposes a stringent constraint on the allowable field, which turns out to be of gravity. The resulting field equation for the gravitational potential contains a dissipative term originating from irreversibility. It is found that the system relaxes to the conventional theory of Newtonian gravity up to a certain spatial scale (typically the solar scale), whereas on the larger scale (such as the galaxy scale) a potential needed in Modified Newtonian Dynamics (MOND) naturally appears. A comment is made on an implication of the result to the astrophysical phenomenon regarding dark matter.

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P. Ván and S. Abe
Tue, 3 Dec 19
25/90

Comments: 18 pages, 1 figure

Brownian motion approach to anomalous rotation of galaxies [CL]

http://arxiv.org/abs/1912.00737


It has been shown that the weak-interacting limit of the metric-skew-tensor-gravity (MSTG) can explain the anomalous rotation of galaxies without non-baryonic dark matter. We show that MSTG is related to the equilibrium-state of ordinary Brownian motion. We also explore if other stochastic processes can model anomalous rotation. Furthermore, we analyze phase-diagrams that elucidate the condensation of a gravitating cloud towards a Kepler-Newton system and illustrate regions of existence of rotating objects.

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A. Jurisch
Tue, 3 Dec 19
81/90

Comments: 8 pages, 4 figures

Similarities between Insect Swarms and Isothermal Globular Clusters [CL]

http://arxiv.org/abs/1912.00395


Previous work has suggested that disordered swarms of flying insects can be well modeled as self-gravitating systems, as long as the “gravitational” interaction is adaptive. Motivated by this work we compare the predictions of the classic, mean-field King model for isothermal globular clusters to observations of insect swarms. Detailed numerical simulations of regular and adaptive gravity allow us to expose the features of the swarms’ density profiles that are captured by the King model phenomenology, and those that are due to adaptivity and short-range repulsion. Our results provide further support for adaptive gravity as a model for swarms.

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D. Gorbonos, K. Vaart, M. Sinhuber, et. al.
Tue, 3 Dec 19
83/90

Comments: N/A

Statistical Mechanics of Gravitational Systems with Regular Orbits: Rigid Body Model of Vector Resonant Relaxation [GA]

http://arxiv.org/abs/1910.05735


I consider a self-gravitating, N-body system assuming that the N constituents follow regular orbits about the center of mass of the cluster, where a central massive object may be present. I calculate the average over a characteristic timescale of the full, N-body Hamiltonian including all kinetic and potential energy terms. The resulting effective system allows for the identification of the orbital planes with N rigid, disk-shaped tops, that can rotate about their fixed common centre and are subject to mutual gravitational torques. The time-averaging imposes boundaries on the canonical generalized momenta of the resulting canonical phase space. I investigate the statistical mechanics induced by the effective Hamiltonian on this bounded phase space and calculate the thermal equilibrium states. These are a result of the relaxation of spins’ directions, identified with orbital planes’ orientations, which is called vector resonant relaxation. I calculate the dependence of spins’ angular velocity dispersion on temperature and calculate the velocity distribution functions. I argue that the range of validity of the gravitational phase transitions, identified in the special case of zero kinetic term by Roupas, Kocsis & Tremaine, is expanded to non-zero values of the ratio of masses between the cluster of N-bodies and the central massive object. The relevance with astrophysics is discussed focusing on star clusters. The same analysis performed on an unbounded phase space accounts for continuous rigid tops.

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Z. Roupas
Tue, 15 Oct 19
21/90

Comments: N/A

Coarse-grained collisionless dynamics with long-range interactions [CL]

http://arxiv.org/abs/1910.01436


We derive an effective evolution equation for a coarse-grained distribution function in the case of long-range-interacting systems by performing a coarse graining that preserves the symplectic structure of the collisionless Boltzmann, or Vlasov, equation obeyed by the fine-grained distribution function. We first derive a general form of such an equation based on symmetry considerations and very general assumptions only. We then restrict ourselves to the case of one-dimensional systems, performing the coarse-graining and obtaining an explicit version of the equation. Finally, we use such an equation to predict the dependence of the damping times on the coarse-graining scale and check them against numerical results for the Hamiltonian Mean Field (HMF) model.

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G. Giachetti, A. Santini and L. Casetti
Fri, 4 Oct 19
39/61

Comments: 5 pages main paper + 9 pages of supplemental material, 1 figure in the main paper + 3 figures in the supplemental material

A Note on the Entropy Force in Kinetic Theory and Black Holes [CL]

http://arxiv.org/abs/1908.09665


The entropy force is the collective effect of inhomogeneity in disorder in a statistical many particle system. We demonstrate its presumable effect on one particular astrophysical object, the black hole. We then derive the kinetic equations of a large system of particles including the entropy force. It adds a collective therefore integral term to the Klimontovich equation for the evolution of the one-particle distribution function. Its integral character transforms the basic one particle kinetic equation into an integro-differential equation already on the elementary level, showing that not only the microscopic forces but the hole system reacts to its evolution of its probability distribution in a holistic way. It also causes a collisionless dissipative term which however is small in the inverse particle number and thus negligible. However it contributes an entropic collisional dissipation term. The latter is defined via the particle correlations but lacks any singularities and thus is large scale. It allows also for the derivation of a kinetic equation for the entropy density in phase space. This turns out to be of same structure as the equation for the phase space density. The entropy density determines itself holistically via the integral entropy force thus providing a self-controlled evolution of entropy in phase space.

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R. Treumann and W. Baumjohann
Tue, 24 Sep 19
8/70

Comments: 22 pp., no figures

Developing a self-consistent AGB wind model: II. Non-classical, non-equilibrium polymer nucleation in a chemical mixture [SSA]

http://arxiv.org/abs/1908.09633


Unravelling the composition and characteristics of gas and dust lost by asymptotic giant branch (AGB) stars is important as these stars play a vital role in the chemical life cycle of galaxies. The general hypothesis of their mass loss mechanism is a combination of stellar pulsations and radiative pressure on dust grains. However, current models simplify dust formation, which starts as a microscopic phase transition called nucleation. Various nucleation theories exist, yet all assume chemical equilibrium, growth restricted by monomers, and commonly use macroscopic properties for a microscopic process. Such simplifications for initial dust formation can have large repercussions on the type, amount, and formation time of dust. By abandoning equilibrium assumptions, discarding growth restrictions, and using quantum mechanical properties, we have constructed and investigated an improved nucleation theory in AGB wind conditions for four dust candidates, TiO$_2$, MgO, SiO and Al$_2$O$_3$. This paper reports the viability of these candidates as first dust precursors and reveals implications of simplified nucleation theories. Monomer restricted growth underpredicts large clusters at low temperatures and overpredicts formation times. Assuming the candidates are present, Al$_2$O$_3$ is the favoured precursor due to its rapid growth at the highest considered temperatures. However, when considering an initially atomic chemical mixture, only TiO$_2$-clusters form. Still, we believe Al$_2$O$_3$ to be the prime candidate due to substantial physical evidence in presolar grains, observations of dust around AGB stars at high temperatures, and its ability to form at high temperatures and expect the missing link to be insufficient quantitative data of Al-reactions.

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J. Boulangier, D. Gobrecht, L. Decin, et. al.
Tue, 27 Aug 19
78/85

Comments: Accepted for publication in MNRAS. 19 pages (68 incl. appendix)

On a possible nonequilibrium imprint in the cosmic background at low frequencies [CEA]

http://arxiv.org/abs/1908.08876


The cosmic background radiation has been observed to deviate from the Planck law expected from a blackbody at $\sim$2.7 K at frequencies below $\sim$3 GHz. We discuss the abundance of the low-energy photons from the perspective of nonequilibrium statistical mechanics by specifying an evolution to a frequency distribution fitting the observed discrepancies. We mention possible physical mechanisms that enter the derivation of that dynamics, where a low-frequency localization is combined with photon cooling as result of e.g. induced Compton scattering. In that sense, the so called ‘space roar’ we observe today is interpreted as a nonequilibrium echo of the early universe.

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M. Baiesi, C. Burigana, L. Conti, et. al.
Mon, 26 Aug 19
6/55

Comments: 27 pages, 2 figures, 1 table

Bose-Einstein condensation in relativistic plasma [CL]

http://arxiv.org/abs/1908.04402


The phenomenon of Bose-Einstein condensation is traditionally associated with and experimentally verified for low temperatures: either of nano-Kelvin scale for alkali atoms [1-3] or room temperatures for quasi-particles [4,5] or photons in two dimensions [6]. Here we demonstrate out of first principles that for certain initial conditions non-equilibrium plasma at relativistic temperatures of billions of Kelvin undergoes condensation, predicted by Zeldovich and Levich in their seminal work [7]. We determine the necessary conditions for the onset of condensation and discuss the possibilities to observe such a phenomenon in laboratory and astrophysical conditions.

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M. Prakapenia and G. Vereshchagin
Wed, 14 Aug 19
47/60

Comments: N/A

Boundary Crossing in Stochastic Inflation with Critical Number of Fields [CL]

http://arxiv.org/abs/1907.13149


We study boundary crossing probability in the context of stochastic inflation. We prove that for a generic multi-field inflationary potential, the probability that the inflaton reaches infinitely far regions in the field space is critically dependent on the number of fields, being nonzero for more than two fields, and zero otherwise. We also provide several examples where the boundary crossing probability can be calculated exactly, most notably, for a particular landscape of a two-field model with a multi-well potential.

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M. Noorbala and H. Firouzjahi
Thu, 1 Aug 19
60/66

Comments: 22 pages, 7 figures

A 1D kinetic model for CMB Comptonization [CL]

http://arxiv.org/abs/1907.07294


This work presents a novel derivation of the expressions that describe the distortions of the CMB curve due to the interactions between photons and the electrons present in dilute ionized systems. In this approach, a simplified a one-dimensional evolution equation for the photon number occupation is applied in order to describe the aforemationed interaction. This methodology allows to emphasize the physical features of the Sunyaev-Zeldovich effect and suggests the existence of links between basic statistical physics and complex applications involving radiative processes.

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A. Sandoval-Villalbazo
Thu, 18 Jul 19
53/64

Comments: 7 pages, 2 figures

Granular Gas Instabilities in a Gravitational Field [CL]

http://arxiv.org/abs/1907.00602


A kinetic and hydrodynamic descriptions are developed in order to analyze the instabilities of a granular gas in the presence of a gravitational field. In the kinetic description the Boltzmann equation is coupled with the Poisson equation, while in the hydrodynamic description the Poisson equation is coupled with the balance equations of mass density, hydrodynamic velocity and temperature for an Eulerian fluid. In the background solution for both descriptions the fluid is at rest with constant mass density and gravitational potential while the temperature depends on time through Haff’s law. In the kinetic description the perturbed distribution function and gravitational potential in the Fourier space are related to time dependent small amplitudes. In the hydrodynamic description the perturbed mass density, hydrodynamic velocity and temperature in the Fourier space are functions of time dependent small amplitudes. From the analysis of the system of coupled differential equations for the amplitudes for the two descriptions the time evolution of the density contrast — a parameter that indicate where there are local enhancements in the matter density — is determined. The solutions depend on two parameters, one is the mean free path of the gas particles and another Jeans’ wavelength, which is a function of the gravitational constant, mass density and speed of sound of the gas. It is shown that instabilities due to the inelastic collisions occur when the Jeans and the perturbation wavelengths are larger than the mean free path, while Jeans’ instabilities due to the gravitational field happen when the mean free path and the perturbation wavelength are larger than Jeans’ wavelength.

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G. Kremer
Tue, 2 Jul 19
67/79

Comments: 13 pages, 2 figures

Formulating the Kramers problem in field theory [CL]

http://arxiv.org/abs/1906.08684


The escape problem is defined in the context of quantum field theory. The escape rate is explicitly derived for a scalar field governed by fluctuation-dissipation dynamics, through generalizing the standard Kramers problem. In the presence of thermal fluctuations, there is a non-vanishing probability for a classical background field, initially located at a minimum of its potential in a homogeneous configuration, to escape from the well. The simple and well-known related problem of the escape of a classical point particle due to random forces is first reviewed. We then discuss the difficulties associated with a well-defined formulation of an escape rate for a scalar field and how these can be overcome. A definition of the Kramers problem for a scalar field and a method to obtain the rate are provided. Finally, we discuss some of the potential applications of our results, which can range from condensed matter systems, i.e., nonrelativistic fields, to applications in high energy physics, like for cosmological phase transitions.

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A. Berera, J. Mabillard, B. Mintz, et. al.
Fri, 21 Jun 19
27/56

Comments: 21 pages, 3 figures, 1 appendix

Exact enumeration approach to first-passage time distribution of non-Markov random walks [CL]

http://arxiv.org/abs/1906.02081


We propose an analytical approach to study non-Markov random walks by employing an exact enumeration method. Using the method, we derive an exact expansion for the first-passage time (FPT) distribution for any continuous, differentiable non-Markov random walk with Gaussian or non-Gaussian multivariate distribution. As an example, we study the FPT distribution of a fractional Brownian motion with a Hurst exponent $H\in(1/2,1)$ that describes numerous non-Markov stochastic phenomena in physics, biology and geology, and for which the limit $H=1/2$ represents a Markov process.

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S. Baghram, F. Nikakhtar, M. Tabar, et. al.
Fri, 7 Jun 19
46/49

Comments: 23 pages, 4 figures, 1 table and 5 appendices. Published version

A solution to the initial condition problems of inflation : NATON [CEA]

http://arxiv.org/abs/1904.12703


The recent astonishing realization of the negative absolute temperature (NAT) for motional degrees of freedom \cite{Braun_ea13} inspires its possible application to the early universe. The existence of the upper bound on the energy of the system is the sufficient requirement for a NAT and this might correspond to the Planck scale at the Big Bang model. It has been argued that standard inflation requires an initial patch that is smooth over distance scales a bit larger than the causal horizon at the onset of inflation. We show that this initial condition problem can be solved if the NAT fermion, dubbed “NATON”, occupies the Universe before the standard inflation is ignited by providing mini inflation prior to the standard one. As long as NATON dominated era lasts until at least ten times older than the Planck time, it makes the Universe homogeneous enough to derive the successful standard inflation.

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S. Lee
Tue, 30 Apr 19
76/92

Comments: 11pages, 7figures

Global Stability Properties of the Climate: Melancholia States, Invariant Measures, and Phase Transitions [CL]

http://arxiv.org/abs/1903.08348


For a wide range of values of the incoming solar radiation, the Earth features at least two attracting states, which correspond to competing climates. The warm climate is analogous to the present one; the snowball climate features global glaciation and conditions that can hardly support life forms. Paleoclimatic evidences suggest that in past our planet flipped between these two states. The main physical mechanism responsible for such instability is the ice-albedo feedback. In a previous work, we defined the Melancholia states that sit between the two climates. Such states are embedded in the boundaries between the two basins of attraction and feature extensive glaciation down to relatively low latitudes. Here, we explore the global stability properties of the system by introducing random perturbations as modulations to the intensity of the incoming solar radiation. We observe noise-induced transitions between the competing basins of attractions. In the weak noise limit, large deviation laws define the invariant measure and the statistics of escape times. By empirically constructing the instantons, we show that the Melancholia states are the gateways for the noise-induced transitions. In the region of multistability, in the zero-noise limit, the measure is supported only on one of the competing attractors. For low (high) values of the solar irradiance, the limit measure is the snowball (warm) climate. The changeover between the two regimes corresponds to a first order phase transition in the system. The framework we propose seems of general relevance for the study of complex multistable systems. At this regard, we relate our results to the debate around the prominence of contigency vs. convergence in biological evolution. Finally, we propose a new method for constructing Melancholia states from direct numerical simulations, thus bypassing the need to use the edge-tracking algorithm.

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V. Lucarini and T. Bodai
Thu, 21 Mar 19
36/66

Comments: 37 Pages, 10 Figures

Dynamics to the universal structure of one-dimensional self-gravitating systems in the quasi-equilibrium state [CL]

http://arxiv.org/abs/1903.03307


We investigate the quasi-equilibrium state of one-dimensional self-gravitating systems. If the null virial condition is satisfied at initial time, it is found that the number density around the center of the system at the quasi-equilibrium state has the universality similar to two- and three-dimensional self-gravitating systems reported in \cite{Tashiro16,Tashiro10}. The reason why the null virial condition is sufficient for the universality is unveiled by the envelope equation. We present a phenomenological model to describe the universal structure by using a special Langevin equation with a distinctive random noise to self-gravitating systems. Additionally, we unveil a mechanism which decides the radius of the system.

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T. Tashiro
Mon, 11 Mar 19
39/78

Comments: N/A

Long-lived transient structure in collisionless self-gravitating systems [GA]

http://arxiv.org/abs/1901.04456


The evolution of self-gravitating systems, and long-range interacting systems more generally, from initial configurations far from dynamical equilibrium is often described as a simple two phase process: a first phase of violent relaxation bringing it to a quasi-stationary state in a few dynamical times, followed by a slow adiabatic evolution driven by collisional processes. In this context the complex spatial structure evident, e.g., in spiral galaxies is understood either in terms of instabilities of quasi-stationary states, or a result of dissipative non-gravitational interactions. We illustrate here, using numerical simulations, that purely self-gravitating systems evolving from quite simple initial configurations can in fact give rise easily to structures of this kind of which the lifetime can be large compared to the dynamical characteristic time, but short compared to the collisional relaxation time scale. More specifically, for a broad range of non-spherical and non-uniform rotating initial conditions, gravitational relaxation gives rise quite generically to long-lived non-stationary structures of a rich variety, characterized by spiral-like arms, bars and even ring-like structures in special cases. These structures are a feature of the intrinsically out-of-equilibrium nature of the system’s collapse, associated with a part of the system’s mass while the bulk is well virialized. They are characterized by predominantly radial motions in their outermost parts, but also incorporate an extended flattened region which rotates coherently about a well virialized core of triaxial shape with an approximately isotropic velocity dispersion. We discuss the possible relevance of these simple toy models to the observed structure of real galaxies emphasizing the difference between dissipative and dissipationless disc formation.

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D. Benhaiem, F. Labini and M. Joyce
Tue, 15 Jan 19
15/83

Comments: 18 pages, 11 figures, Physical Review E in print (2019)

Vector Resonant Relaxation of Stars around a Massive Black Hole [GA]

http://arxiv.org/abs/1812.07053


In the vicinity of a massive black hole, stars move on precessing Keplerian orbits. The mutual stochastic gravitational torques between the stellar orbits drive a rapid reorientation of their orbital planes, through a process called vector resonant relaxation. We derive, from first principles, the correlation of the potential fluctuations in such a system, and the statistical properties of random walks undergone by the stellar orbital orientations. We compare this new analytical approach with effective $N$-body simulations. We also provide a simple scheme to generate the random walk of a test star’s orbital orientation using a stochastic equation of motion. We finally present quantitative estimations of this process for a nuclear stellar cluster such as the one of the Milky Way.

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J. Fouvry, B. Bar-Or and P. Chavanis
Wed, 19 Dec 18
77/84

Comments: 23 pages, 10 figures, submitted to AAS journals

Galaxies as fluctuations in cosmic stellar liquid [GA]

http://arxiv.org/abs/1811.02894


Large self-gravitating stellar systems share with correlated liquids in condensed matter physics a pattern of hierarchical density variations. While it takes the microscopic time resolution to discern the correlated dynamics of the critical opalescence, characteristic astronomical times hide fluctuational dynamics of stellar liquids, where, governed by interstellar correlations, denser clusters of stars assemble and disperse. For a semi-isolated galaxy, these dynamical fluctuations are dense globular clusters. For a galaxy cluster, these dynamical fluctuations are the member galaxies, elliptical ones in the interior. Bright over-density fluctuations, galaxies, are exhibits of only a small fraction of stars found in a cosmic stellar liquid, the dark matter. Here I report a fluctuational gravitational collapse as a property of a self-gravitating system in the virial equilibrium.

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A. Kashuba
Thu, 8 Nov 18
63/72

Comments: 17 pages, 1 figure

Ginzburg-Landau Theory of Dark Energy: A Framework to Study Both Temporal and Spatial Cosmological Tensions Simultaneously [CEA]

http://arxiv.org/abs/1810.11007


A dark energy model (DE) is proposed based on Ginzburg-Landau theory of phase transition (GLT). This model, GLTofDE, surprisingly provides a framework to study not only temporal tensions in cosmology e.g. $H_0$ tension but also spatial anomalies of CMB e.g. the hemispherical asymmetry, quadrupole-octopole alignment and its orthogonality to dipole simultaneously. In the mean field approximation of GLTofDE, the potential is broken spontaneously. We modeled this transition and showed that GLTofDE can resolve both the $H_0$ tension and Lyman-$\alpha$ anomaly in a non-trivial way. According to $\chi^2$-analysis the transition happens at $z_t=0.746^{+0.028}{-0.039}$ while $H_0=73.5\pm1.1$ km/s/Mpc and $\Omega{k}=-0.196^{+0.049}_{-0.033}$ which are consistent with the latest $H(z)$ reconstructions. In addition, the GLTofDE proposes a framework to address the CMB anomalies when it is considered beyond the mean field approximation. In this regime existence of a long wavelength mode is a typical consequence which is named the Goldstone mode in the case of continuous symmetries. This mode, which is an automatic byproduct in GLTofDE, makes different directions of the sky see different cosmological constants. This means one side of the sky should be colder than the other side which can describe observed dipole in CMB. In addition between initial stochastic pattern and the final state with one long wavelength mode, we can observe smaller patches or protrusions of the biggest remaining patch in the simulation. Our simulations show these protrusions are few in numbers and will be evolved according to Alan-Cahn mechanism. These protrusions can give an additional effect on CMB which is the existence of aligned quadrupole-octopole mode and its direction should be orthogonal to the dipole direction. We conclude that GLTofDE is a very rich framework both theoretically and phenomenologically.

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A. Banihashemi, N. Khosravi and A. Shirazi
Fri, 26 Oct 18
15/64

Comments: 6 pages with 1 table and 4 figures. 8 figures and 2 tables in Appendix. Comments are welcome

Resummed Kinetic Field Theory: General formalism and linear structure growth from Newtonian particle dynamics [CEA]

http://arxiv.org/abs/1809.06942


In earlier work, we have developed a nonequilibrium statistical field theory description of cosmic structure formation, dubbed Kinetic Field Theory (KFT), which is based on the Hamiltonian phase-space dynamics of classical particles and thus remains valid beyond shell-crossing. Here, we present an exact reformulation of the KFT framework that allows to resum an infinite subset of terms appearing in the original perturbative expansion of KFT. We develop the general formalism of this resummed KFT, including a diagrammatic language for the resummed perturbation theory, and compute the lowest-order results for the power spectra of the dark matter density contrast and momentum density. This allows us to derive analytically how the linear growth of the largest structures emerges from Newtonian particle dynamics alone, which, to our knowledge, is the first time this has been achieved.

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R. Lilow, F. Fabis, E. Kozlikin, et. al.
Thu, 20 Sep 18
5/55

Comments: 30 pages, 3 figures

Relativistic Gravitational Phase Transitions and Instabilities of the Fermi Gas [CL]

http://arxiv.org/abs/1809.07169


We describe microcanonical phase transitions and instabilities of the ideal Fermi gas in general relativity at nonzero temperature confined in the interior of a spherical shell. The thermodynamic behaviour is governed by the compactness of rest mass, namely of the total rest mass over radius of the system. For a fixed value of rest mass compactness, we study the caloric curves as a function of the size of the spherical box. At low compactness values, low energies and for sufficiently big systems the system is subject to a gravothermal catastrophe, which cannot be halted by quantum degeneracy pressure, and the system collapses towards the formation of a black hole. For small systems, there appears no instability at low energies. For intermediate sizes, between two marginal values, gravothermal catastrophe is halted and a microcanonical phase transition occurs from a gaseous phase to a condensed phase with a nearly degenerate core. The system is subject to a relativistic instability at low energy, when the core gets sufficiently condensed above the Oppenheimer-Volkoff limit. For sufficiently high values of rest mass compactness the microcanonical phase transitions are suppressed. They are replaced either by an Antonov type gravothermal catastrophe for sufficiently big systems or by stable equilibria for small systems. At high energies the system is subject to the `relativistic gravothermal instability’, identified by Roupas in [1], for all values of compactness and any size.

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Z. Roupas and P. Chavanis
Thu, 20 Sep 18
36/55

Comments: N/A

Relativistic Gravothermal Instability: the Weight of Heat [CL]

http://arxiv.org/abs/1809.04408


Thermal energy points towards a disordered, completely uniform state acting counter to gravity’s tendency to generate order and structure through gravitational collapse. It is therefore expected to contribute to the stabilization of a self-gravitating, classical ideal gas over collapse. However, I identified in Ref. [1] an instability that always sets in at sufficiently high energies, the high-energy gravothermal instability'. I argue here that this instability presents an analogous core-halo structure as its Newtonian counterpart, the Antonov instability. The main difference is that in the former case the core is dominated by the gravitation of thermal energy and not rest mass energy. A relativistic generalization of Antonov's instability, thelow-energy gravothermal instability’, does also occur. The two turning points approach each other as relativistic effects become more intense and eventually merge at a single point. Thus, they may be realized as two aspects of a single phenomenon. I also investigate the implicit thermodynamic sector of General Relativity and show that the relativistic equation of hydrostatic equilibrium, the Tolman and Klein relations, and the redshift factor, all do follow from the second law of thermodynamics for any equation of state. The concentration of heat at lower gravitational potential and the local temperature gradient are dictated by the maximization of entropy. Finally, I argue that the core formed during a core-collapse supernova is subject to the relativistic gravothermal instability, if it becomes sufficiently hot and compactified at the time of the bounce. In this case it will continue to collapse towards the formation of a black hole.

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Z. Roupas
Thu, 13 Sep 18
60/68

Comments: N/A

Quantum Out-of-Equilibrium Cosmology [CL]

http://arxiv.org/abs/1809.02732


In this work, our prime focus is to study the one to one correspondence between the conduction phenomena in electrical wires with impurity and the scattering events responsible for particle production during stochastic inflation and reheating implemented under a closed quantum mechanical system in early universe cosmology. In this connection, we also present a derivation of fourth order corrected version of the Fokker Planck equation and its analytical solution for studying the dynamical features of the particle creation events in the stochastic inflation and reheating stage of the universe. It is explicitly shown from our computation that quantum corrected Fokker Planck equation describe the particle creation phenomena better for Dirac delta type of scatterer. In this connection, we additionally discuss It$\hat{o}$, Stratonovich prescription and the explicit role of finite temperature effective potential for solving the probability distribution profile. Furthermore, we extend our discussion to describe the quantum description of randomness involved in the dynamics. We also present a computation to derive the expression for the measure of the stochastic non-linearity arising in the stochastic inflation and reheating epoch of the universe, often described by Lyapunov Exponent. Apart from that, we quantify the quantum chaos arising in a closed system by a more strong measure, commonly known as Spectral Form Factor using the principles of Random Matrix Theory (RMT). Additionally, we discuss the role of out of time order correlation (OTOC) function to describe quantum chaos in the present non-equilibrium field theoretic setup. Finally, for completeness, we also provide a bound on the measure of quantum chaos arising due to the presence of stochastic non-linear dynamical interactions into the closed quantum system of the early universe in a completely model-independent way.

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S. Choudhury, A. Mukherjee, P. Chauhan, et. al.
Tue, 11 Sep 18
40/62

Comments: 172 pages, 58 figures, 4 tables

Entropy Production and Luminosity-Effective Temperature Relation for Main-Sequence Stars [SSA]

http://arxiv.org/abs/1809.02026


Based on the maximum entropy production principle, a relation between luminosity and effective temperature for main-sequence stars is obtained. Simplicity of the derivation and absence of any empirical parameters in the result is a fundamental difference of the present method from the classic ones where equations of stellar structure are analyzed. Using available photometric data (Webda, GCG) for more than 7.5 thousand stars, it is shown that the obtained luminosity-temperature relation is better than previously used ones.

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L. Martyushev and S. Zubarev
Fri, 7 Sep 18
33/65

Comments: 9 pages, 4 figures

Joint Instability and Abrupt Nonlinear Transitions in a Differentially Rotating Plasma [CL]

http://arxiv.org/abs/1809.00921


Global magnetohydrodynamic (MHD) instabilities are investigated in a computationally tractable two-dimensional model of the solar tachocline. The model’s differential rotation yields stability in the absence of a magnetic field, but if a sufficiently strong magnetic field is present, a joint instability is observed. We analyze the nonlinear development of the instability via fully nonlinear direct numerical simulation, the generalized quasilinear approximation (GQL), and direct statistical simulation (DSS) based upon low-order expansion in equal-time cumulants. As the magnetic diffusivity is decreased, the nonlinear development of the instability becomes more complicated until eventually a set of parameters are identified that produce a previously unidentified long-term cycle in which energy is transformed from kinetic energy to magnetic energy and back. We find that the periodic transitions, which mimic some aspects of solar variability — for example, the quasiperiodic seasonal exchange of energy between toroidal field and waves or eddies — are unable to be reproduced when eddy-scattering processes are excluded from the model.

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A. Plummer, J. Marston and S. Tobias
Wed, 5 Sep 18
84/133

Comments: 19 pages with 16 figures

Transitions across Melancholia States in a Climate Model: Reconciling the Deterministic and Stochastic Points of View [CL]

http://arxiv.org/abs/1808.05098


The Earth is well-known to be, in the current astronomical configuration, in a regime where two asymptotic states can be realised. The warm state we live in is in competition with the ice-covered snowball state. The bistability exists as a result of the positive ice-albedo feedback. In a previous investigation performed on a intermediate complexity climate model we have identified the edge states (Melancholia states) separating the co-existing climates, and studied their dynamic and geometrical properties. The Melancholia states are ice-covered up to the mid-latitudes, are unstable, but attract trajectories initialised on the basins boundary. In this paper, we study the effect of the natural variability of a solar irradiance on the stability of the climate by stochastically perturbing the parameter controlling the intensity of the incoming solar radiation. We detect transitions between the warm and the snowball state and analyse in detail the properties of the noise-induced escapes from the corresponding basins of attraction. We construct the most probable paths for the transitions and find evidence that the Melancholia states act as gateways, similarly to saddle points in an energy landscape.

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V. Lucarini and T. Bodai
Thu, 16 Aug 18
7/46

Comments: 5 pages, 4 figures

Effective field theory of time-translational symmetry breaking in nonequilibrium open system [CL]

http://arxiv.org/abs/1805.06240


We develop the effective field theoretical (EFT) approach to time-translational symmetry breaking of nonequilibrium open systems based on the Schwinger-Keldysh formalism. In the Schwinger-Keldysh formalism, all the symmetries of the microscopic Lagrangian are doubled essentially because the dynamical fields are doubled to describe the time-evolution along the closed-time-path. The effective Lagrangian for open systems are then obtained by coarse-graining the microscopic Schwinger-Keldysh Lagrangian. As a consequence of coarse-graining procedure, there appear the noise and dissipation effects, which explicitly break the doubled time-translational symmetries into a diagonal one. We therefore need to incorporate this symmetry structure to construct the EFT for Nambu-Goldstone bosons in symmetry broken phases of open systems. Based on this observation together with the consistency of the Schwinger-Keldysh action, we construct and study the general EFT for time-translational symmetry breaking in particular, having in mind applications to synchronization, time crystal, and cosmic inflation.

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M. Hongo, S. Kim, T. Noumi, et. al.
Thu, 17 May 18
65/70

Comments: 38 pages, 3 figures

Bose Condensation by Gravitational Interactions [CEA]

http://arxiv.org/abs/1804.05857


We study Bose condensation and formation of Bose stars in the virialized dark matter halos/miniclusters by universal gravitational interactions. We prove that this phenomenon does occur and it is described by kinetic equation. We give expression for the condensation time. Our results suggest that Bose stars may form in the mainstream dark matter models such as invisible QCD axions and Fuzzy Dark Matter.

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D. Levkov, A. Panin and I. Tkachev
Wed, 18 Apr 18
47/74

Comments: 4 pages, 2 figures

Non-extensive statistical mechanics of a self-gravitating gas [CL]

http://arxiv.org/abs/1803.08126


The statistical mechanics of a cloud of particles interacting via their gravitational potentials is an old problem which encounters some issues when the traditional Boltzmann-Gibbs statistics is applied. In this article, we consider the generalized statistics of Tsallis and analyze the statistical and thermodynamical implications for a self-gravitating gas, obtaining analytical and convergent expressions for the equation of state and specific heat in the canonical as well as microcanonical ensembles. Although our results are comparable in both ensembles, it turns out that only in the canonical case the thermodynamic quantities depend explicitly on the non-extensivity parameter, indicating that the question of ensemble equivalence for Tsallis statistics must be further reviewed.

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L. Escamilla-Herrera, C. Gruber, V. Pineda-Reyes, et. al.
Fri, 23 Mar 18
4/53

Comments: 12 pages

Black hole disks in galactic nuclei [GA]

http://arxiv.org/abs/1803.07090


Gravitational torques among objects orbiting a supermassive black hole drive the rapid reorientation of orbital planes in nuclear star clusters (NSCs), a process known as vector resonant relaxation. In this letter, we determine the statistical equilibrium of systems with a distribution of masses, semi-major axes, and eccentricities. We average the interaction over the apsidal precession time and construct a Monte Carlo Markov Chain method to sample the microcanonical ensemble of the NSC. We examine the case of NSCs formed by episodes of star formation or globular cluster infall. We find that the massive stars and stellar mass black holes form a warped disk, while low mass stars resemble a spherical distribution with a possible net rotation. This explains the origin of the clockwise disk in the Galactic center and predicts a population of black holes (BHs) embedded within this structure. The rate of mergers among massive stars, tidal disruption events among BHs and massive stars, and BH-BH mergers are highly increased in such disks. The first two may explain the origin of the observed G1 and G2 clouds, the latter may be important for gravitational wave detections with LIGO and VIRGO. More generally, black holes are expected to settle in disks in all spherical dense stellar systems including globular clusters.

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A. Szolgyen and B. Kocsis
Wed, 21 Mar 2018
45/61

Comments: 5 pages, 3 figures, submitted to Physical Review Letters

Cored density profiles in the DARKexp model [CEA]

http://arxiv.org/abs/1801.06598


The DARKexp model represents a novel and promising attempt to solve a long standing problem of statistical mechanics, that of explaining from first principles the quasi–stationary states at the end of the collisionless gravitational collapse. The model, which yields good fits to observation and simulation data on several scales, was originally conceived to provide a theoretical basis for the $1/r$ cusp of the Navarro–Frenk–White profile. In this note we show that it also allows for cored density profiles that, when viewed in three dimensions, in the $r\to0$ limit have the conical shape characteristic of the Burkert profile. It remains to be established whether both cusps and cores, or only one of the two types, are allowed beyond the asymptotic analysis of this work

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C. Destri
Tue, 23 Jan 18
35/85

Comments: 15 pages

Relaxation in self-gravitating systems [GA]

http://arxiv.org/abs/1712.05862


The long timescale evolution of a self-gravitating system is generically driven by two-body encounters. In many cases, the motion of the particles is primarily governed by the mean field potential. When this potential is integrable, particles move on nearly fixed orbits, which can be described in terms of angle-action variables. The mean field potential drives fast orbital motions (angles) whose associated orbits (actions) are adiabatically conserved on short dynamical timescales. The long-term stochastic evolution of the actions is driven by the potential fluctuations around the mean field and in particular by “resonant two-body encounters”, for which the angular frequencies of two particles are in resonance. We show that the stochastic gravitational fluctuations acting on the particles can generically be described by a correlated Gaussian noise. Using this approach, the so-called $\eta$-formalism, we derive a diffusion equation for the actions in the test particle limit. We show that in the appropriate limits, this diffusion equation is equivalent to the inhomogeneous Balescu-Lenard and Landau equations. This approach provides a new view of the resonant diffusion processes associated with long-term orbital distortions. Finally, by investigating the example of the Hamiltonian Mean Field Model, we show how the present method generically allows for alternative calculations of the long-term diffusion coefficients in inhomogeneous systems.

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J. Fouvry and B. Bar-Or
Tue, 19 Dec 17
21/88

Comments: 28 pages, 3 figures, submitted to MNRAS

Isotropic-Nematic Phase Transitions in Gravitational Systems II: Higher Order Multipoles [GA]

http://arxiv.org/abs/1712.04449


The gravitational interaction among bodies orbiting in a spherical potential leads to the rapid relaxation of the orbital planes’ distribution, a process called vector resonant relaxation. We examine the statistical equilibrium of this process for a system of bodies with similar semimajor axes and eccentricities. We extend the previous model of Roupas, Kocsis, and Tremaine (2017), by accounting for the multipole moments beyond the quadrupole, which dominate the interaction for radially overlapping orbits. Nevertheless, we find no qualitative differences between the behavior of the system with respect to the model restricted to the quadrupole interaction. The equilibrium distribution resembles a counterrotating disk at low temperature and a spherical structure at high temperature. The system exhibits a first order phase transition between the disk and the spherical phase in the canonical ensemble if the total angular momentum is below a critical value. We find that the phase transition erases the high order multipoles, i.e. small-scale structure most efficiently. The small residual anisotropies are dominated by the quadrupole in the disordered phase. The system admits a maximum entropy and a maximum energy, which lead to the existence of negative temperature equilibria.

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A. Takacs and B. Kocsis
Thu, 14 Dec 17
57/74

Comments: 7 pages, 5 figures, submitted to ApJL

Bose-Einstein Condensation in a uniformly accelerated frame [CL]

http://arxiv.org/abs/1711.02306


In this article we have investigated the possibility of Bose-Einstein Condensation (BEC) in a frame undergoing uniform acceleration or in other wards, in Rindler space associated with the uniformly accelerated frame. We have followed a very simple conventional technique generally used in text book level studies. It has been observed that the critical temperature for BEC increases with the increase in magnitude of acceleration of the frame. Typically the critical temperature in an accelerated frame is of the order of the Unruh temperature. Hence we have concluded that the increase in the magnitude of acceleration of the frame facilitates the formation of condensed phase.

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S. Das and S. Chakraborty
Fri, 10 Nov 17
7/55

Comments: 7 pages Latex file( no figure)

Kinetic Field Theory: Exact free evolution of Gaussian phase-space correlations [CL]

http://arxiv.org/abs/1710.01611


In recent work we developed a description of cosmic large scale structure formation in terms of non-equilibrium ensembles of classical particles, with time evolution obtained in the framework of a statistical field theory. In these works, the initial Gaussian correlations between particles have so far been treated perturbatively or restricted to pure momentum correlations. Here we treat the correlations between all phase-space coordinates exactly by adopting a diagrammatic language for the different forms of correlations, directly inspired by the Mayer cluster expansion. We will demonstrate that explicit expressions for phase-space density cumulants of arbitrary $n$-point order, which fully capture the non-linear coupling of free streaming kinematics due to initial correlations, can be obtained from a simple set of Feynman rules. These cumulants will be the foundation for further investigations of interacting perturbation theory.

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F. Fabis, E. Kozlikin, R. Lilow, et. al.
Mon, 9 Oct 17
7/68

Comments: 32 pages

Classical orbital paramagnetism in non-equilibrium steady state [CL]

http://arxiv.org/abs/1206.3440


We report the results of our numerical simulation of classical-dissipative dynamics of a charged particle subjected to a non-markovian stochastic forcing. We find that the system develops a steady-state orbital magnetic moment in the presence of a static magnetic field. Very significantly, the sign of the orbital magnetic moment turns out to be {\it paramagnetic} for our choice of parameters, varied over a wide range. This is shown specifically for the case of classical dynamics driven by a Kubo-Anderson type non-markovian noise. Natural spatial boundary condition was imposed through (1) a soft (harmonic) confining potential, and (2) a hard potential, approximating a reflecting wall. There was no noticeable qualitative difference. What appears to be crucial to the orbital magnetic effect noticed here is the non-markovian property of the driving noise chosen. Experimental realization of this effect on the laboratory scale, and its possible implications are briefly discussed. We would like to emphasize that the above steady-state classical orbital paramagnetic moment complements, rather than contradicts the Bohr-van Leeuwen (BvL) theorem on the absence of classical orbital diamagnetism in thermodynamic equilibrium.

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A. Deshpande and N. Kumar
Mon, 25 Sep 17
58/60

Comments: 6 pages, 4 figures, Has appeared in Journal of Astrophysics and Astronomy special issue on ‘Physics of Neutron Stars and Related Objects’, celebrating the 75th birth-year of G. Srinivasan

The use of $μ$-Bose gas model for effective modeling of dark matter [CL]

http://arxiv.org/abs/1709.05931


For the recently introduced $\mu$-deformed analog of Bose gas model ($\mu$-Bose gas model), its thermodynamical aspects e.g. total number of particles and the partition function are certain functions of the parameter $\mu$. This basic $\mu$-dependence of thermodynamics of the $\mu$-Bose gas arises through the so-called $\mu$-calculus, an alternative to the known $q$-calculus (Jackson derivative, etc.), so we include main elements of $\mu$-calculus. Likewise, virial expansion of EOS and virial coefficients, the internal energy, specific heat and the entropy of $\mu$-Bose gas show $\mu$-dependence. Herein, we study thermodynamical geometry of $\mu$-Bose gas model and find the singular behavior of (scalar) curvature, signaling for Bose-like condensation. The critical temperature of condensation $T^{(\mu)}_c$ depending on $\mu$ is given and compared with the usual $T_c$, and with known $T_c^{(p,q)}$ of $p,q$-Bose gas model. Using the results on $\mu$-thermodynamics we argue that the condensate of $\mu$-Bose gas, like the earlier proposed infinite statistics system of particles, can serve for effective modeling of dark matter.

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A. Gavrilik, I. Kachurik, M. Khelashvili, et. al.
Thu, 21 Sep 17
38/50

Comments: 7 pages, two-column style, 2 figures

Dimensional Reduction of Direct Statistical Simulation [CL]

http://arxiv.org/abs/1708.07805


Direct Statistical Simulation (DSS) solves the equations of motion for the statistics of turbulent flows in place of the traditional route of accumulating statistics by Direct Numerical Simulation (DNS). DSS however is usually more expensive computationally than DNS because even low order statistics typically have higher dimension than the underlying fields (depending on the symmetry of the problem and the choice of averaging operation). That low-order statistics usually evolve slowly compared with instantaneous dynamics is one important advantage of DSS. Here we show that it is possible to go much further by using Proper Orthogonal Decomposition (POD) to address the “curse of dimensionality.” We apply POD directly to DSS in the form of expansions in the equal-time cumulants to second order (CE2). We explore two averaging operations (zonal and ensemble) and test the approach on two idealized barotropic models on a rotating sphere (a jet that relaxes deterministically towards an unstable profile, and a stochastically-driven flow that spontaneously organizes into jets). Order-of-magnitude savings in computational cost are obtained in the reduced basis, enabling access to parameter regimes beyond the reach of DNS.

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A. Allawala, S. Tobias and J. Marston
Mon, 28 Aug 17
36/46

Comments: 6 pages and 9 figures

A calculation of the Deuterium Hugoniot using the classical-map hypernetted-chain (CHNC) approach [CL]

http://arxiv.org/abs/1707.08880


The Hugoniot for Deuterium is calculated using the classical-map hyper-netted-chain (CHNC) approach using several models of the effective temperature that may be assigned to the electron-ion interaction. This effective temperature embodies the exchange-correlation and kinetic energy functional that is assigned to the electron-ion interaction. Deuterium pair distribution functions (calculated using the neutral-pseudo atom method) showing the formation of molecular pre-peaks are displayed to clarify the soft-turning over of the hugoniot in the pressure range of 0.2-0.6 Megabars. This contribution updates a previous CHNC calculation of the deuterium hugoniot given in Phys. Rev. B, 66, 014110 (2002).

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M. Dharma-wardana
Fri, 28 Jul 17
18/48

Comments: This paper contains some of the material submitted to the DOE/NNSA EOS workshop, May-31, Rochester, USA, 2017

Kinetic Field Theory: Cosmic Structure Formation and Fluctuation-Dissipation Relations [CEA]

http://arxiv.org/abs/1707.01053


Building upon the recently developed formalism of Kinetic Field Theory (KFT) for cosmic structure formation by Bartelmann et al., we investigate the effects of particle diffusion on the formation of structure in the Universe in the context of fluctuation-dissipation relations (FDRs). In our earlier analysis we observed that diffusion damps the growth of structures on small scales in the free theory. However, artificially removing some part of diffusion leads to remarkably good agreement with N-body simulations. The goal of this work is to achieve a better understanding of diffusion in KFT and the success of the approximative removal of diffusion. In the first part of this work we examine the time derivative of density correlations in the free theory and observe that structure formation on this level is a detailed balance between particle diffusion on the one side and the accumulation of structure due to initial momentum correlations on the other side. In the second part, we show that the response of the system to two-particle interactions is directly related to the evolution of particle diffusion in the form of FDRs. This demonstrates how interactions decrease diffusion and motivates the artificial removal of diffusion. Furthermore, we show that the FDRs are connected to a time-reversal symmetry of the underlying generating functional as is typical for statistical field theories.

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J. Dombrowski, F. Fabis and M. Bartelmann
Wed, 5 Jul 17
32/60

Comments: 28 pages, 6 figures, submitted to New Journal of Physics

Dressed diffusion and friction coefficients in inhomogeneous multicomponent self-gravitating systems [GA]

http://arxiv.org/abs/1706.06009


General self-consistent expressions for the coefficients of diffusion and dynamical friction in a stable, bound, multicomponent self-gravitating and inhomogeneous system are derived. They account for the detailed dynamics of the colliding particles and their self-consistent dressing by collective gravitational interactions. The associated Fokker-Planck equation is shown to be fully consistent with the corresponding inhomogeneous Balescu-Lenard equation and, in the weak self-gravitating limit, to the inhomogeneous Landau equation. Hence it provides an alternative derivation to both and demonstrates their equivalence. The corresponding stochastic Langevin equations are presented: they can be a practical alternative to numerically solving the inhomogeneous Fokker-Planck and Balescu-Lenard equations. The present formalism allows for a self-consistent description of the secular evolution of different populations covering a spectrum of masses, with a proper accounting of the induced secular mass segregation, which should be of interest to various astrophysical contexts, from galactic centers to protostellar discs.

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J. Heyvaerts, J. Fouvry, P. Chavanis, et. al.
Tue, 20 Jun 17
3/72

Comments: 27 pages, 1 figure

Entropy and the beginning of gravitational collapse [CEA]

http://arxiv.org/abs/1706.03487


Making a simple model of gravitational collapse in cosmology and astrophysics, this paper examines the creation and destruction of kinetic theory entropy after a small perturbation is introduced into a homogeneous distribution of self-gravitating particles. To keep the problem tractable, gravity is Newtonian and the focus is on a coarse-grained slice of entropy constructed from the one- and two-particle distribution functions. The slice chosen is asymptotically-dominant, in the sense that it will eventually dominate over all other entropy associated with a given scale within the system. Its entropy is destroyed within a central sphere near the initial location of the perturbation – the core – and created in a surrounding shell – the halo. The core-halo transition radii are not fixed, but are proportional to the coarse-graining length used. At leading order, creation and destruction are in balance. At next-to-leading order, destruction predominates, the rate of destruction being proportional to an exponent of the time elapsed after the perturbation was introduced, and further proportional to the square of the perturbation size, divided by the square of the coarse-graining volume. For late times, destruction of asymptotic coarse-grained entropy is at least offset by entropy creation ever further from the central perturbation. We can interpret this as gravitational collapse leading to local large-scale structure formation – that is, destruction of coarse-grained entropy – at least offset by ever more distant creation of disorder. Making a plausible assumption about the application of the second law of thermodynamics to coarse-grained entropy, that distant disorder would itself be large scale.

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A. Wren
Tue, 13 Jun 17
60/92

Comments: 47 pages, 10 figures. Mathematica notebooks available from Github at this https URL . Comments welcome

Dynamical origin of non-thermal states in galactic filaments [GA]

http://arxiv.org/abs/1706.01955


Observations strongly suggest that filaments in galactic molecular clouds are in a non-thermal state. As a simple model of a filament we study a two-dimensional system of self-gravitating point particles by means of numerical simulations of the dynamics, with various methods: direct $N$-body integration of the equations of motion, particle-in-cell simulations and a recently developed numerical scheme that includes multiparticle collisions in a particle-in-cell approach. Studying the collapse of Gaussian overdensities we find that after the damping of virial oscillations the system settles in a non-thermal steady state whose radial density profile is similar to the observed ones, thus suggesting a dynamical origin of the non-thermal states observed in real filaments. Moreover, for sufficiently cold collapses the density profiles are anticorrelated with the kinetic temperature, i.e., exhibit temperature inversion, again a feature that has been found in some observations of filaments. The same happens in the state reached after a strong perturbation of an initially isothermal cylinder. Finally, we discuss our results in the light of recent findings in other contexts (including non-astrophysical ones) and argue that the same kind of non-thermal states may be observed in any physical system with long-range interactions.

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P. Cintio, S. Gupta and L. Casetti
Thu, 8 Jun 17
41/69

Comments: 10 pages, 7 figures, MNRAS LaTeX

Quark matter revisited with non extensive MIT bag model [CL]

http://arxiv.org/abs/1706.02183


In this work we revisit the MIT bag model to describe quark matter within both the usual Fermi-Dirac and the Tsallis statistics. We verify the effects of the non-additivity of the latter by analysing two different pictures: the first order phase transition of the QCD phase diagram and stellar matter properties. While, the QCD phase diagram is visually affected by the Tsallis statistics, the resulting effects on quark star macroscopic properties are barely noticed.

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P. Cardoso, T. Silva, A. Deppman, et. al.
Thu, 8 Jun 17
68/69

Comments: 10 pagens, 5 figures

Escape dynamics through a continuously growing leak [EPA]

http://arxiv.org/abs/1706.01759


We formulate a model that describes the escape dynamics in a leaky chaotic system in which the size of the leak depends on the number of the in-falling particles. The basic motivation of this work is the astrophysical process which describes the planetary accretion. In order to study the dynamics generally, the standard map is investigated in two cases when the dynamics is fully hyperbolic and in the presence of KAM islands. In addition to the numerical calculations, an analytic solution to the temporal behavior of the model is also derived. We show that in the early phase of the leak expansion, as long as there are enough particles in the system, the number of survivors deviates from the well-known exponential decay. Furthermore, the analytic solution returns the classical result in the limiting case when the number of particles does not affect the leak size.

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T. Kovacs and J. Vanyo
Wed, 7 Jun 17
16/52

Comments: 11 pages, 11 figures

Ultrarelativistic generalized Lorentzians and the cosmic ray energy flux [HEAP]

http://arxiv.org/abs/1703.02327


We show that the rather tentative application of the ultrarelativistic generalized Lorentzian energy distribution to the spectrum of cosmic ray fluxes may provide evidence for either high TeV chemical potentials generated in the acceleration source region of the observed cosmic rays, or the presence of hypothetical particles of TeV rest mass. Such particles are not known in our accessible Universe at any accessible energies. If true they should have been produced in cosmic ray sources prior to acceleration. Conclusions of this kind depend on the validity of the generalized Lorentzian in application to cosmic rays, a hypothetical statistical mechanical equilibrium distribution occasionally encountered in observations.

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R. Treumann and W. Baumjohann
Wed, 8 Mar 17
46/60

Comments: 5 pages, 1 figure, draft prepared for submission to a meeting on cosmic rays and power law tails