Tag Archives: Pattern Formation and Solitons

i-SPin 2: An integrator for general spin-s Gross-Pitaevskii systems [CL]

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http://arxiv.org/abs/2305.01675


We provide an algorithm for evolving general spin-$s$ Gross-Pitaevskii / non-linear Schr\”odinger systems carrying a variety of interactions, where the $2s+1$ components of the `spinor’ field represent the different spin-multiplicity states. We consider many nonrelativistic interactions up to quartic order in the Schr\”odinger field (both short and long-range, and spin-dependent and spin-independent interactions), including explicit spin-orbit couplings. The algorithm allows for spatially varying external and/or self-generated vector potentials that couple to the spin density of the field. Our work can be used for scenarios ranging from laboratory systems such as spinor Bose-Einstein condensates (BECs), to cosmological/astrophysical systems such as self-interacting bosonic dark matter. As examples, we provide results for two different setups of spin-$1$ BECs that employ a varying magnetic field and spin-orbit coupling, respectively, and also collisions of spin-$1$ solitons in dark matter. Our symplectic algorithm is second-order accurate in time, and is extensible to the known higher-order accurate methods.

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M. Jain, M. Amin and H. Pu
Thu, 4 May 23
23/60

Comments: 13 pages, 3 figures, 2 appendices

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

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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)

Kinetic relaxation and Bose-star formation in multicomponent dark matter- I [CEA]

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http://arxiv.org/abs/2304.01985


Using wave kinetics, we estimate the emergence time-scale of gravitating Bose-Einstein condensates/Bose stars in the kinetic regime for a general multicomponent Schr\”{o}dinger-Poisson (SP) system. We identify some effects of the diffusion and friction pieces in the wave-kinetic Boltzmann equation (at leading order in perturbation theory) and provide estimates for the kinetic nucleation rate of condensates. We test our analysis using full $3+1$ dimensional simulations of multicomponent SP system. With an eye towards applications to multicomponent dark matter, we investigate two general cases in detail. First is a massive spin-$s$ field with $N=2s+1$ components (scalar $s=0$, vector $s=1$ and tensor $s=2$). We find that for a democratic population of different components, the condensation time-scale is $\tau_{(s)}\approx \tau_0\times N$, where $\tau_0$ is the condensation time scale for the scalar case. Second is the case of two scalars with different boson masses. In this case, we map-out how the condensation time depends on the ratios of their average mass densities and boson masses, revealing competition and assistance between components, and a guide towards which component condenses first. For instance, with $m_1 < m_2$ and not too disparate mass densities, we verify that the time scale of condensation of the first species quickly becomes independent of $m_2/m_1$, whereas for equal average number densities, the emergence time scale decreases with increasing $m_2/m_1$.

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M. Jain, M. Amin, J. Thomas, et. al.
Wed, 5 Apr 23
13/62

Comments: 8 pages + 3 appendices, 5 figures. Videos from simulations are available at this https URL

Nonperturbative structure in coupled axion sectors and implications for direct detection [CL]

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http://arxiv.org/abs/2208.05501


Pairs of misalignment-produced axions with nearby masses can experience a nonlinear resonance that leads to enhanced direct and astrophysical signatures of axion dark matter. In much of the relevant parameter space, self-interactions cause axion fluctuations to become nonperturbative and to collapse in the early Universe. We investigate the observational consequences of such nonperturbative structure in this “friendly axion” scenario with $3+1$ dimensional simulations. Critically, we find that nonlinear dynamics work to equilibrate the abundance of the two axions, making it easier than previously expected to experimentally confirm the existence of a resonant pair. We also compute the gravitational wave emission from friendly axion dark matter; while the resulting stochastic background is likely undetectable for axion masses above $10^{-22} \, \text{eV}$, the polarization of the cosmic microwave background does constrain possible hyperlight, friendly subcomponents. Finally, we demonstrate that dense, self-interaction–bound oscillons formed during the period of strong nonlinearity are driven by the homogeneous axion background, enhancing their lifetime beyond the in-vacuum expectation.

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D. Cyncynates, O. Simon, J. Thompson, et. al.
Mon, 15 Aug 22
42/54

Comments: 19 pages, 8 figures

Multi-Scale Decomposition of Astronomical Maps — Constrained Diffusion Method [IMA]

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http://arxiv.org/abs/2201.05484


We propose a new, efficient multi-scale method to decompose a map (or signal in general) into components maps that contain structures of different sizes. In the widely-used wave transform, artifacts containing negative values arise around regions with sharp transitions due to the application of band-limited filters. In our approach, the decomposition is achieved by solving a modified, non-linear version of the diffusion equation. This is inspired by the anisotropic diffusion methods, which establish the link between image filtering and partial differential equations. In our case, the artifact issue is addressed where the positivity of the decomposed images is guaranteed. Our new method is particularly suitable for signals which contain localized, non-linear features, as typical of astronomical observations. It can be used to study the multi-scale structures of astronomical maps quantitatively and should be useful in observation-related tasks such as background removal. We thus propose a new measure called the ”scale spectrum”, which describes how the image values distribute among different components in the scale space, to describe maps. The method allows for input arrays of an arbitrary number of dimensions, and a python3 implementation of the algorithms is included in the Appendix and available at https://gxli.github.io/Constrained-Diffusion-Decomposition/.

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G. Li
Mon, 17 Jan 22
8/59

Comments: Accepted by ApJS. The Code is available at this https URL

Multi-Scale Decomposition of Astronomical Maps — Constrained Diffusion Method [IMA]

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http://arxiv.org/abs/2201.05484


We propose a new, efficient multi-scale method to decompose a map (or signal in general) into components maps that contain structures of different sizes. In the widely-used wave transform, artifacts containing negative values arise around regions with sharp transitions due to the application of band-limited filters. In our approach, the decomposition is achieved by solving a modified, non-linear version of the diffusion equation. This is inspired by the anisotropic diffusion methods, which establish the link between image filtering and partial differential equations. In our case, the artifact issue is addressed where the positivity of the decomposed images is guaranteed. Our new method is particularly suitable for signals which contain localized, non-linear features, as typical of astronomical observations. It can be used to study the multi-scale structures of astronomical maps quantitatively and should be useful in observation-related tasks such as background removal. We thus propose a new measure called the ”scale spectrum”, which describes how the image values distribute among different components in the scale space, to describe maps. The method allows for input arrays of an arbitrary number of dimensions, and a python3 implementation of the algorithms is included in the Appendix and available at https://gxli.github.io/Constrained-Diffusion-Decomposition/.

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G. Li
Mon, 17 Jan 22
21/59

Comments: Accepted by ApJS. The Code is available at this https URL

Long-term Trends of Regolith Movement on the Surface of Small Bodies [EPA]

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http://arxiv.org/abs/2112.12460


This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of “trigger-slide” motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.

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C. Huang, Y. Yu, B. Cheng, et. al.
Fri, 24 Dec 21
55/58

Comments: N/A

Long-term Trends of Regolith Movement on the Surface of Small Bodies [EPA]

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http://arxiv.org/abs/2112.12460


This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of “trigger-slide” motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.

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C. Huang, Y. Yu, B. Cheng, et. al.
Fri, 24 Dec 21
48/58

Comments: N/A

Friendship in the Axiverse: Late-time direct and astrophysical signatures of early-time nonlinear axion dynamics [CL]

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http://arxiv.org/abs/2109.09755


A generic low-energy prediction of string theory is the existence of a large collection of axions, commonly known as a string axiverse. Axions also have a natural cosmological production mechanism, vacuum misalignment, making them well-motivated dark matter (DM) candidates. Much work on axion production has considered the case of a single free axion, but in a realistic axiverse, string axions are expected to be distributed densely over many orders of magnitude in mass, and to interact with one another through their joint potential. In this paper, we show that non-linearities in this potential lead to a new type of resonant energy transfer between axions with nearby masses. This resonance generically transfers energy from axions with larger decay constants to those with smaller decay constants, and leads to a multitude of signatures. These include enhanced direct detection prospects for a resonant pair comprising even a small subcomponent of dark matter, and boosted small-scale structure if the pair is the majority of DM. Near-future iterations of experiments such as ADMX and DM Radio will be sensitive to this scenario, as will astrophysical probes of DM substructure.

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D. Cyncynates, T. Giurgica-Tiron, O. Simon, et. al.
Wed, 22 Sep 21
6/57

Comments: 36 pages, 18 figures

Polarized solitons in higher-spin wave dark matter [CL]

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http://arxiv.org/abs/2109.04892


We first show that the effective non-relativistic theory of gravitationally interacting, massive integer-spin fields (spin-$0$, $1$, and $2$ in particular) is described by a $2s+1$ component Schr\”{o}dinger-Poisson action, where $s$ is the spin of the field. We then construct $s+1$ distinct, gravitationally supported solitons in this non-relativistic theory from identically polarized plane waves. Such solitons are extremally polarized, with macroscopically large spin, but no orbital angular momentum. These $s+1$ solitons form a basis set, out of which partially polarized solitons can be constructed. All such solitons are ground states, have a spherically symmetric energy density but not field configurations. We discuss how solitons in higher-spin fields can be distinguished from scalar solitons, and potential gravitational and non-gravitational probes of them.

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M. Jain and M. Amin
Mon, 13 Sep 21
8/52

Comments: 14 + 2 pages, 5 figures

Cosmological Formation of (2+1)-Dimensional Soliton Structures in Models Possessing Potentials with Local Peaks [CL]

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http://arxiv.org/abs/2109.03271


Production of domain walls and string-like solitons in the model with two real scalar fields and potential with at least one saddle point and a local maximum is considered. The model is regarded as 2-dimensional spatial slices of 3-dimensional entire structures. It is shown that, in the early Universe, both types of solitons may appear. In addition, the qualitative estimate of the domain walls and strings formation probabilities is presented. It is found that the probability of the formation of string-like solitons is suppressed compared to that of domain walls.

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A. Kirillov, B. Murygin and V. Nikulin
Thu, 9 Sep 21
69/78

Comments: N/A

Jammed Keplerian gas leads to the formation and disappearance of spiral arms in a coupled map lattice for astronomical objects [CL]

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http://arxiv.org/abs/2109.00458


The formation and disappearance of spiral arms are studied by focusing on jammed Keplerian gas in a coupled map lattice (CML) with a minimal set of procedures for simulating diverse patterns in astronomical objects. The CML shows that a spiral arm is a type of traffic jam, and its motion is governed by both a gas inflow into and outflow from the jam. In particular, a new mechanism for the disappearance of spiral arms is found. It is caused not by conventional differential rotation, but by the gas flow rate difference between the light inflow and heavy outflow, here called “light-in and heavy-out”, leading to the disappearance of traffic jams. Furthermore, we propose a general approximate formula for the lifetime of spiral arms, which is simply derived from the mechanism of the “light-in and heavy-out”. The proposed formula is successfully applied to the CML simulations, and moreover, to the observational data of the spiral galaxy M51.

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E. Nozawa
Thu, 2 Sep 21
43/59

Comments: 8 pages, 4 figures

Symmetric multi-field oscillons [CL]

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http://arxiv.org/abs/2010.07789


Oscillons are spatially localized structures that appear in scalar field theories and exhibit extremely long life-times. We go beyond single-field analyses and study oscillons comprised of multiple interacting fields, each having an identical potential with quadratic, quartic and sextic terms. We consider quartic interaction terms of either attractive or repulsive nature. In the two-field case, we construct semi-analytical oscillon profiles for different values of the potential parameters and coupling strength using the two-timing small-amplitude formalism. We show that the interaction sign, attractive or repulsive, leads to different oscillon solutions, albeit with similar characteristics, like the emergence of “flat-top” shapes. In the case of attractive interactions, the oscillons can reach higher values of the energy density and smaller values of the width. For repulsive interactions we identify a threshold for the coupling strength, above which oscillons do not exist within the two-timing small-amplitude framework. We extend the Vakhitov-Kolokolov (V-K) stability criterion, which has been used to study single-field oscillons, and show that the symmetry of the potential leads to similar equations as in the single-field case, albeit with modified terms. We explore the basin of attraction of stable oscillon solutions numerically to test the validity of the V-K criterion and show that, depending on the initial perturbation size, unstable oscillons can either completely disperse or relax to the closest stable configuration. Similarly to the V-K criterion, the decay rate and lifetime of two-field oscillons are found to be qualitatively and quantitatively similar to their single-field counterparts. Finally, we generalize our analysis to multi-field oscillons and show that the governing equations for their shape and stability can be mapped to the ones arising in the two-field case.

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F. Dissel and E. Sfakianakis
Thu, 28 Jan 21
5/64

Comments: 30 pages, 8 figures

Pattern dark matter and galaxy scaling relations [GA]

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http://arxiv.org/abs/2101.08372


We argue that a natural explanation for a variety of robust galaxy scaling relations comes from the perspective of pattern formation and self-organization as a result of symmetry breaking. We propose a simple Lagrangian model that combines a conventional model for normal matter in a galaxy with a conventional model for stripe pattern formation in systems that break continuous translation invariance. We show that the energy stored in the pattern field acts as an effective dark matter. Our theory reproduces the gross features of elliptic galaxies as well as disk galaxies (HSB and LSB) including their detailed rotation curves, the radial acceleration relation (RAR), and the Freeman law. We investigate the stability of disk galaxies in the context of our model and obtain scaling relations for the central dispersion for elliptical galaxies. A natural interpretation of our results is that (1) `dark matter’ is potentially a collective, emergent phenomenon and not necessarily an as yet undiscovered particle, and (2) MOND is an effective theory for the description of a self-organized complex system rather than a fundamental description of nature that modifies Newton’s second law.

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S. Venkataramani and A. Newell
Fri, 22 Jan 21
35/69

Comments: 41 Pages, 12 figures, 2 Appendices. Comments are very welcome

Gravitational effects on oscillon lifetimes [CL]

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http://arxiv.org/abs/2011.11720


Many scalar field theories with attractive self-interactions support exceptionally long-lived, spatially localized and time-periodic field configurations called oscillons. A detailed study of their longevity is important for understanding their applications in cosmology. In this paper, we study gravitational effects on the decay rate and lifetime of dense oscillons, where self-interactions are more or at least equally important compared with gravitational interactions. As examples, we consider the $\alpha$-attractor T-model of inflation and the axion monodromy model, where the potentials become flatter than quadratic at large field values beyond some characteristic field distance $F$ from the minimum. For oscillons with field amplitudes of $\mathcal{O}(F)$ and for $F\ll 0.1 M_\mathrm{pl}$, we find that their evolution is almost identical to cases where gravity is ignored. For $F\sim 0.1 M_\mathrm{pl}$, however, including gravitational interactions reduces the lifetime slightly.

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H. Zhang
Wed, 25 Nov 2020
50/65

Comments: 14 pages, 5 figures

Characterizing the spatial pattern of solar supergranulation using the bispectrum [SSA]

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http://arxiv.org/abs/2002.08262


Context. The spatial power spectrum of supergranulation does not fully characterize the underlying physics of turbulent convection. For example, it does not describe the non-Gaussianity in the horizontal flow divergence.
Aims. Our aim is to statistically characterize the spatial pattern of solar supergranulation beyond the power spectrum. The next-order statistic is the bispectrum. It measures correlations of three Fourier components and is related to the nonlinearities in the underlying physics.
Methods. We estimated the bispectrum of supergranular horizontal surface divergence maps that were obtained using local correlation tracking (LCT) and time-distance helioseismology (TD) from one year of data from the Helioseismic and Magnetic Imager on-board the Solar Dynamics Observatory starting in May 2010.
Results. We find significantly nonzero and consistent estimates for the bispectrum. The strongest nonlinearity is present when the three coupling wave vectors are at the supergranular scale. These are the same wave vectors that are present in regular hexagons, which were used in analytical studies of solar convection. At these Fourier components, the bispectrum is positive, consistent with the positive skewness in the data and with supergranules preferentially consisting of outflows surrounded by a network of inflows. We use the bispectrum to generate synthetic divergence maps that are very similar to the data by a model that consists of a Gaussian term and a weaker quadratic nonlinear component. Thereby, we estimate the fraction of the variance in the divergence maps from the nonlinear component to be of the order of 4-6%.
Conclusions. We propose that bispectral analysis is useful for understanding solar turbulent convection, for example for comparing observations and numerical models of supergranular flows. This analysis may also be useful to generate synthetic flow fields.

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V. Böning, A. Birch, L. Gizon, et. al.
Thu, 20 Feb 20
51/61

Comments: 16 pages, 12 figures, accepted for publication by A&A

Spiral galaxies and the fingerprints of dark matter [GA]

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http://arxiv.org/abs/1910.14649


Motivated by and generalizing the Cross-Newell energy functional for pattern forming systems, we propose a modification of the Einstein-Hilbert action on galactic scales. We introduce additional terms that reflect the presence of phase hyper surfaces connected with patterns related to the clumping instability of baryonic matter. The resulting pattern structures carry an additional energy density which, remarkably, accounts for many of the phenomena that are generally attributed to dark matter.

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S. Venkataramani and A. Newell
Fri, 1 Nov 19
43/54

Comments: 7 pages, 6 figures

Solitons in Einstein's Universe [CEA]

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http://arxiv.org/abs/1910.10216


We show that equations of Newtonian hydrodynamics and gravity with Einstein’s cosmological constant included admit gravitostatic wave solutions propagating in the background of Einstein’s static Universe. In the zero pressure limit these waves exist at an average matter density exceeding that of Einstein’s Universe. They have the form of a lattice of integrable density singularities localized at the maxima of the gravitational potential. These singularities are steady-state counterparts of the so-called Zeldovich pancakes (ZP), interim wall-like structures appearing at nonlinear stages of development of gravitational instability. As the average matter density decreases, the period of the ZP lattice increases diverging at the density of Einstein’s Universe. Solitary wave solutions are found at exactly the density of Einstein’s Universe, and at a slightly larger density the wave may be viewed as a lattice of well-separated ZP solitons.

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E. Kolomeisky and E. Sarabamoun
Thu, 24 Oct 19
51/68

Comments: 7 pages, 3 figures

Dispersion Properties, Nonlinear Waves and Birefringence in Classical Nonlinear Electrodynamics [CL]

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http://arxiv.org/abs/1910.08586


Using the very basic physics principles, we have studied the implications of quantum corrections to classical electrodynamics and the propagation of electromagnetic waves and pulses.
The initial nonlinear wave equation for the electromagnetic vector potential is solved perturbatively about the known exact plane wave solution in both the free vacuum case, as well as when a constant magnetic field is applied. A nonlinear wave equation with nonzero convective part for the (relatively) slowly varying amplitude of the first-order perturbation has been derived. This equation governs the propagation of electromagnetic waves with a reduced speed of light, where the reduction is roughly proportional to the intensity of the initial pumping plane wave. A system of coupled nonlinear wave equations for the two slowly varying amplitudes of the first-order perturbation, which describe the two polarization states, has been obtained for the case of constant magnetic field background.
Further, the slowly varying wave amplitude behavior is shown to be similar to that of a cnoidal wave, known to describe surface gravity waves in shallow water. It has been demonstrated that the two wave modes describing the two polarization states are independent, and they propagate at different wave frequencies. This effect is usually called nonlinear birefringence.

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S. Tzenov, K. Spohr and K. Tanaka
Tue, 22 Oct 19
56/91

Comments: 11 pages, 3 figures

Steady flows, nonlinear gravitostatic waves and Zeldovich pancakes in a Newtonian gas [GA]

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http://arxiv.org/abs/1903.11992


We show that equations of Newtonian hydrodynamics and gravity describing one-dimensional steady gas flow possess nonlinear periodic solutions. In the case of a zero-pressure gas the solution exhibits hydrodynamic similarity and is universal: it is a lattice of integrable density singularities coinciding with maxima of the gravitational potential. With finite pressure effects included, there exists critical matter density that separates two regimes of behavior. If the average density is below the critical, the solution is a density wave which is in phase with the wave of the gravitational potential. If the average density is above the critical, the waves of the density and potential are out of phase. Traveling nonlinear gravitostatic waves are also predicted and their properties elucidated. Specifically, subsonic wave is made out of two out of phase oscillations of matter density and gravitational potential. If the wave is supersonic, the density-potential oscillations are in phase.

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E. Kolomeisky
Fri, 29 Mar 19
40/78

Comments: 4 pages, 1 figure

Gravitational perturbations from oscillons and transients after inflation [CEA]

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http://arxiv.org/abs/1902.06736


We study the scalar and tensor perturbations generated by the fragmentation of the inflaton condensate into oscillons or transients after inflation, using nonlinear classical lattice simulations. Without including the backreaction of metric perturbations, we find that the magnitude of scalar metric perturbations never exceeds a few $\times 10^{-3}$, whereas the maximal strength of the gravitational wave signal today is $\mathcal{O}(10^{-9})$ for standard post-inflationary expansion histories. We provide parameter scalings for the $\alpha$-attractor models of inflation, which can be easily applied to other models. We also discuss the likelihood of primordial black hole formation, as well as conditions under which the gravitational wave signal can be at observationally interesting frequencies and amplitudes.
Finally, we provide an upper bound on the frequency of the peak of the gravitational wave signal, which applies to all preheating scenarios.

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K. Lozanov and M. Amin
Tue, 19 Feb 19
45/57

Comments: 18 pages, 8 figures

Evading Derrick's theorem in curved space: Static metastable spherical domain wall [CL]

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http://arxiv.org/abs/1901.06659


A recent analysis by one of the authors\cite{Perivolaropoulos:2018cgr} has pointed out that Derrick’s theorem can be evaded in curved space. Here we extend that analysis by demonstrating the existence of a static metastable solution in a wide class of metrics that include a Schwarzschild-Rindler-AntideSitter spacetime (Grumiller metric) defined as $ds^2= f(r) dt^2 – f(r)^{-1} dr^2 – r^2 (d\theta^2 +\sin^2\theta d\phi^2)$ with $f(r)=1-\frac{2Gm}{r}+2br-\frac{\Lambda}{3} r^2$ ($\Lambda<0\; b<0$). This metric emerges generically as a spherically symmetric vacuum solution in a class of scalar-tensor theories\cite{Grumiller:2010bz} as well as in Weyl conformal gravity\cite{Mannheim:1988dj}. It also emerges in General Relativity (GR) in the presence of a cosmological constant and a proper spherically symmetric perfect fluid. We demonstrate that this metric supports a static spherically symmetric metastable soliton scalar field solution that corresponds to a spherical domain wall. We derive the static solution numerically and identify a range of parameters $m, b, \Lambda$ of the metric for which the spherical wall is metastable. Our result is supported by both a minimization of the scalar field energy functional with proper boundary conditions and by a numerical simulation of the scalar field evolution. The metastable solution is very well approximated as $\phi(r) = Tanh\left[q (r-r_0)\right]$ where $r_0$ is the radius of the metastable wall that depends on the parameters of the metric and $q$ determines the width of the wall. We also find the gravitational effects of the thin spherical wall solution and its backreaction on the background metric that allows its formation. We show that this backreaction does not hinder the metastability of the solution even though it can change the range of parameters that correspond to metastability.

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G. Alestas and L. Perivolaropoulos
Wed, 23 Jan 19
81/111

Comments: 11 pages, 8 Figures. The Mathematica files that lead to the production of the Figures are publicly available at this http URL

Conditional recovery of time-reversal symmetry in many nucleus systems [CL]

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http://arxiv.org/abs/1809.10461


Propagation of non-topological soliton in many-nucleus systems is studied based on time-dependent density functional calculations with focusing on mass and energy dependence. The dispersive property and the nonlinearity of the system, which are inherently included in the nuclear density functional, are essential factors to form a non-topological soliton. On the other hand the soliton propagation is prevented by the charge equilibration dynamics, and the competition possibly appears. In this article, based on the energy-dependence of the two competitive factors, the concept of conditional recovery of time-reversal symmetry is proposed in many nucleus systems. It clarifies a possibility of preserving nuclear medium inside natural or artificial nuclear reactors, under a suitable temperature. From an astrophysical point of view, the existence of the low-temperature solitonic core of compact stars is suggested.

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Y. Iwata and P. Stevenson
Fri, 28 Sep 18
48/52

Comments: Submitted

How Nanoflares Produce Kinetic Waves, Nano-Type III Radio Bursts, and Non-Thermal Electrons in the Solar Wind [SSA]

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http://arxiv.org/abs/1807.10942


Observations of the solar corona and the solar wind discover that the solar wind is unsteady and originates from the impulsive events near the surface of the Sun’s atmosphere. How solar coronal activities affect the properties of the solar wind is a fundamental issue in heliophysics. We report a simulation and theoretical investigation of how nanoflare accelerated electron beams affect the kinetic-scale properties of the solar wind and generate coherent radio emission. We show that nanoflare-accelerated electron beams can trigger a nonlinear electron two stream instability, which generates kinetic Alfv\’en and whistler waves, as well as a non-Maxwellian electron velocity distribution function, consistent with observations of the solar wind. The plasma coherent emission produced in our model agrees well with the observations of Type III, J and V solar radio bursts. Open questions in the kinetic solar wind model are also discussed.

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H. Che
Tue, 31 Jul 18
38/69

Comments: Submitted to the Proceedings of 17th Annual International Astrophysics Conference, Santa Fe, 2018

Thermal convection in rotating spherical shells: temperature-dependent internal heat generation using the example of triple-$α$ burning [HEAP]

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http://arxiv.org/abs/1807.05120


We present an exhaustive study of Boussinesq thermal convection including a temperature-dependent internal heating source, based on numerical three-dimensional simulations. The temperature dependence mimics triple alpha nuclear reactions and the fluid geometry is a rotating spherical shell. These are key ingredients for the study of convective accreting neutron star oceans. A new dimensionless parameter Ran , measuring the relevance of nuclear heating, is defined. We explore how flow characteristics change with increasing Ran and give an astrophysical motivation. The onset of convection is investigated with respect to the new parameter and periodic, quasiperiodic, chaotic flows with coherent structures, and fully turbulent flows are exhibited as Ran is varied. Several regime transitions are identified and compared with previous results on differentially heated convection. Finally, we explore (tentatively) the potential applicability of our results to the evolution of thermonuclear bursts in accreting neutron star oceans.

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F. Garcia, F. Chambers and A. Watts
Mon, 16 Jul 18
28/55

Comments: 9 Figures, 6 Tables. Submitted to Physical Review Fluids

Turbulent superstructures in Rayleigh-Bénard convection [CL]

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http://arxiv.org/abs/1801.04478


Turbulent Rayleigh-B\’enard convection displays a large-scale order in the form of rolls and cells on lengths larger than the layer height once the fluctuations of temperature and velocity are removed. These turbulent superstructures are reminiscent of the patterns close to the onset of convection. They are analyzed by numerical simulations of turbulent convection in fluids at different Prandtl number ranging from 0.005 to 70 and for Rayleigh numbers up to $10^7$. For each case, we identify characteristic scales and times that separate the fast, small-scale turbulent fluctuations from the gradually changing large-scale superstructures. The characteristic scales of the large-scale patterns, which change with Prandtl and Rayleigh number, are also found to be correlated with the boundary layer dynamics, and in particular the clustering of thermal plumes at the top and bottom plates. Our analysis suggests a scale separation and thus the existence of a simplified description of the turbulent superstructures in geo- and astrophysical settings.

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A. Pandey, J. Scheel and J. Schumacher
Tue, 16 Jan 18
43/79

Comments: 16 pages (incl. Supplementary Material), 12 figures (all with downsized figure size)

Spatial solitons in thermo-optical media from the nonlinear Schrodinger-Poisson equation and dark matter analogues [CL]

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http://arxiv.org/abs/1703.09095


We analyze theoretically the Schrodinger-Poisson equation in two transverse dimensions in the presence of a Kerr term. The model describes the nonlinear propagation of optical beams in thermooptical media and can be regarded as an analogue system for a self-gravitating self-interacting wave. We compute numerically the family of radially symmetric ground state bright stationary solutions for focusing and defocusing local nonlinearity, keeping in both cases a focusing nonlocal nonlinearity. We also analyze excited states and oscillations induced by fixing the temperature at the borders of the material. We provide simulations of soliton interactions, drawing analogies with the dynamics of galactic cores in the scalar field dark matter scenario.

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A. Navarrete, A. Paredes, J. Salgueiro, et. al.
Tue, 28 Mar 17
37/68

Comments: 13 pages, 11 figures

Two-Scale Oscillons [CL]

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http://arxiv.org/abs/1612.07228


Oscillons are spatially stationary, quasi-periodic solutions of nonlinear field theories seen in settings ranging from granular systems, low temperature condensates and early universe cosmology. We describe a new class of oscillon in which the spatial envelope can have “off centre” maxima and pulsate on timescales much longer than the fundamental frequency. These are exact solutions of the 1-D sine-Gordon equation and we demonstrate numerically that similar solutions exist in up to three dimensions for a range of potentials. The dynamics of these solutions match key properties of oscillons that may form after cosmological inflation in string-motivated monodromy scenarios.

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C. Liu and R. Easther
Thu, 22 Dec 16
30/65

Comments: 4 pages, figues; animations and further background at this http URL

Non-linear Ion-Wake Excitation by the Time-Asymmetric Electron Wakefields of Intense Energy Sources with applications to the Crunch-in regime [CL]

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http://arxiv.org/abs/1612.03520


A model for the excitation of a non-linear ion-wake mode by a train of plasma electron oscillations in the non-linear time-asymmetric regime is developed using analytical theory and particle-in-cell based computational solutions. The ion-wake is shown to be a driven non-linear ion-acoustic wave in the form of a cylindrical ion-soliton. The near-void and radially-outwards propagating ion-wake channel of a few plasma skin-depth radius, is explored for application to “Crunch-in” regime of positron acceleration. The coupling from the electron wakefield mode to the ion-mode dictates the long-term evolution of the plasma and the time for its relaxation back to an equilibrium, limiting the repetition-rate of a plasma accelerator. Using an analytical model it is shown that it is the time asymmetric phases of the oscillating radial electric fields of the nearly-stationary electron bubble that excite time-averaged inertial ion motion radially. The electron compression in the back of the bubble sucks-in the ions whereas the space-charge within the bubble cavity expels them, driving a cylindrical ion-soliton structure with on-axis and bubble-edge density-spikes. Once formed, the channel-edge density-spike is sustained over the length of the plasma and driven radially outwards by the thermal pressure of the wake energy in electrons. Its channel-like structure is independent of the energy-source, electromagnetic wave or particle beam, driving the bubble electron wake. Particle-In-Cell simulations are used to study the ion-wake soliton structure, its driven propagation and its use for positron acceleration in the “Crunch-in” regime.

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A. Sahai
Tue, 13 Dec 16
67/77

Comments: Crunch-in regime strongly contradicts the established conclusions of ZERO focusing fields in a hollow-channel (claimed and presented in several PRL, PoP, PRE and Nature papers). Since this entirely opposes and goes against established conclusions of over 20 years old work, severely damaging to the reputations of the senior physicists, it is not being allowed through the peer-review process

How the nonlinear coupled oscillators modelization explains the Blazhko effect, the synchronisation of layers, the mode selection, the limit cycle, and the red limit of the instability strip [SSA]

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http://arxiv.org/abs/1610.03323


Context. The Blazhko effect, in RR Lyrae type stars, is a century old mystery. Dozens of theory exists, but none have been able to entirely reproduce the observational facts associated to this modulation phenomenon. Existing theory all rely on the usual continuous modelization of the star. Aims. We present a new paradigm which will not only explain the Blazhko effect, but at the same time, will give us alternative explanations to the red limit of the instability strip, the synchronization of layers, the mode selection and the existence of a limit cycle for radially pulsating stars. Methods. We describe the RR Lyrae type pulsating stars as a system of coupled nonlinear oscillators. Considering a spatial discretisation of the star, supposing a spherical symmetry, we develop the equation of motion and energy up to the third order in the radial and adiabatic case. Then, we include the influence of the ionization region as a relaxation oscillator by including elements from synchronisation theory. Results. This discrete approach allows us to exploit existing results in the coupled nonlinear oscillator field. For instance, the study of synchronicity leads to an explanation of the mode selection, the layers synchronisation, the limit cycle and the red limit of the instability strip. But, most of all, the analogy with the Fermi-Pasta-Ulam (FPU) experiment enables us to understand the Blazhko effect. The transfer of energy between different modes, as induced by solitons, not only gives a plausible theory for lightcurve modulation, but also explains the asymmetry of sidelobes.

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C. Zalian
Wed, 12 Oct 16
61/64

Comments: N/A

Interference of Dark Matter Solitons and Galactic Offsets [CEA]

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http://arxiv.org/abs/1512.05121


By performing numerical simulations, we discuss the collisional dynamics of stable solitary waves in the Schrodinger-Poisson equation. In the framework of a model in which part or all of dark matter is a Bose-Einstein condensate of ultralight axions, we show that these dynamics can naturally account for the relative displacement between dark and ordinary matter in a galactic cluster, whose recent observation is the first empirical evidence of dark matter interactions beyond gravity. We argue that future observations might bear out or falsify this coherent wave interpretation of dark matter offsets.

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A. Paredes and H. Michinel
Thu, 17 Dec 15
19/55

Comments: 8 pages + appendix, 8 figures

Proca Stars: gravitating Bose-Einstein condensates of massive spin 1 particles [CL]

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http://arxiv.org/abs/1508.05395


We establish that massive complex Abelian vector fields (mass $\mu$) can form gravitating solitons, when minimally coupled to Einstein’s gravity. Such Proca stars (PSs) have a stationary, everywhere regular and asymptotically flat geometry. The Proca field, however, possesses a harmonic time dependence (frequency $w$), realizing Wheeler’s concept of geons for an Abelian spin 1 field. We obtain PSs with both a spherically symmetric (static) and an axially symmetric (stationary) line element. The latter form a countable number of families labelled by an integer $m\in \mathbb{Z}^+$. PSs, like (scalar) boson stars, carry a conserved Noether charge, and are akin to the latter in many ways. In particular, both types of stars exist for a limited range of frequencies and there is a maximal ADM mass, $M_{max}$, attained for an intermediate frequency. For spherically symmetric PSs (rotating PSs with $m=1,2,3$), $M_{max}\simeq 1.058 M_{Pl}^2/\mu$ ($M_{max}\simeq 1.568,\, 2.337, \, 3.247 \, M_{Pl}^2/\mu$), slightly larger values than those for (mini-)boson stars. We establish perturbative stability for a subset of solutions in the spherical case and anticipate a similar conclusion for fundamental modes in the rotating case. The discovery of PSs opens many avenues of research, reconsidering five decades of work on (scalar) boson stars, in particular as possible dark matter candidates.

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R. Brito, V. Cardoso, C. Herdeiro, et. al.
Tue, 25 Aug 15
7/69

Comments: 5 pages, 4 figures

Soliton Formation in Neutral Ion Gases: Exact Analysis [CL]

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http://arxiv.org/abs/1209.3077


It is shown here that in neutral ion gases the thermal energy transport can occur in the form of new types of thermal soliton waves. The solitons can form under a vanishing net heating function, and for a quadratic net heating. It is predicted that these solitons play an important role in a diversity of terrestrial and astrophysical phenomena. We claim that the reported soliton waves can be observed under ordinary laboratory conditions.

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B. Mirza
Fri, 29 May 15
34/68

Comments: Figure added, typos corrected

Phase ordering percolation and domain-wall survival in segregating binary Bose-Einstein condensates [CL]

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http://arxiv.org/abs/1505.02276


Percolation theory is applied to the phase transition dynamics of domain pattern formation in segregating quasi-two-dimensional binary Bose–Einstein condensates. Our numerical experiments revealed that the percolation threshold is close to 0.5. A long-range open domain wall appears with a fractal dimension between two percolating domains. Such a wall can survive for a long time as a relic of the phase transition according to the dynamic finite-size-scaling hypothesis, which seems to be in contrast to the current understanding in cosmology that an infinite defect violates a scale invariance.

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H. Takeuchi, Y. Mizuno and K. Dehara
Tue, 12 May 15
3/77

Comments: 5 pages, 3 figures

Non-linear Ion-wake Excitation by Ultra-relativistic Electron Wakefields [CL]

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http://arxiv.org/abs/1504.03735


The excitation of a non-linear ion-wake by a train of ultra-relativistic plasmons is modeled and its use for a novel regime of positron acceleration is explored. Its channel-like structure is independent of the energy-source driving the bubble-shaped slowly-propagating high phase-velocity electron density waves. The back of the bubble electron compression sucks-in the ions and the space-charge within the bubble expels them, forming a near-void channel with on-axis and bubble-edge density-spikes. The channel-edge density-spike is driven radially outwards as a non-linear ion acoustic-wave by the wake electron thermal pressure. OSIRIS PIC simulations are used to study the ion-wake structure, its evolution and its use for positron acceleration.

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A. Sahai and T. Katsouleas
Thu, 16 Apr 15
47/48

Comments: submitted to Physical Review, Apr 2015

Relativistic superfluidity and vorticity from the nonlinear Klein-Gordon equation [CL]

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http://arxiv.org/abs/1408.0779


We investigate superfluidity, and the mechanism for creation of quantized vortices, in the relativistic regime. The general framework is a nonlinear Klein-Gordon equation in curved spacetime for a complex scalar field, whose phase dynamics gives rise to superfluidity. The mechanisms discussed are local inertial forces (Coriolis and centrifugal), and current-current interaction with an external source. The primary application is to cosmology, but we also discuss the reduction to the non-relativistic nonlinear Schr\”{o}dinger equation, which is widely used in describing superfluidity and vorticity in liquid helium and cold-trapped atomic gases.

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C. Xiong, M. Good, Y. Guo, et. al.
Fri, 12 Dec 14
20/57

Comments: 7 pages, 5 figures. Revised version. To appear in Phys. Rev. D

Ultra-relativistic oscillon collisions [CL]

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http://arxiv.org/abs/1410.1822


In this short note we investigate the ultra-relativistic collisions of small amplitude oscillons in 1+1 dimensions. Using the amplitude of the oscillons and the inverse relativistic boost factor $\gamma^{-1}$ as the perturbation variables, we analytically calculate the leading order spatial and temporal phase shifts, and the change in the amplitude of the oscillons after the collisions. At leading order, we find that only the temporal phase shift receives a nonzero contribution, and that the collision is elastic. This work is also the first application of the general kinematic framework for understanding ultra-relativistic collisions (arXiv:1308.0606) to intrinsically time-dependent solitons.

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M. Amin, I. Banik, C. Nagreanu, et. al.
Wed, 8 Oct 14
15/68

Comments: 12 pages, 3 figures

The end of inflation, oscillons and matter-antimatter asymmetry [CL]

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http://arxiv.org/abs/1408.1811


The dynamics at the end of inflation can generate an asymmetry between particles and anti-particles of the inflaton field. This asymmetry can be transferred to baryons via decays, generating a baryon asymmetry in our universe. We explore this idea in detail for a complex inflaton governed by an observationally consistent -“flatter than quadratic”- potential with a weakly broken global U(1) symmetry. We find that most of the inflaton asymmetry is locked in non-topological soliton like configurations (oscillons) produced copiously at the end of inflation. These solitons eventually decay into baryons and generate the observed matter-antimatter asymmetry for a range of model parameters. Through a combination of three dimensional lattice simulations and a detailed linearized analysis, we show how the inflaton asymmetry depends on the fragmentation, the magnitude of the symmetry breaking term and initial conditions at the end of inflation. We discuss the final decay into baryons, but leave a detailed analysis of the inhomogeneous annihilation, reheating and thermalization to future work.
As part of our work, we also provide a formalism for generating multifield initial conditions for field fluctuations (including metric perturbations) at the end of inflation, which might be useful for studying reheating in a much larger class of multifield models.

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K. Lozanov and M. Amin
Mon, 11 Aug 14
16/55

Comments: 19 pages, 9 figures

Improving cosmic string network simulations [CL]

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http://arxiv.org/abs/1406.1688


In real-time lattice simulations of cosmic strings in the Abelian Higgs model, the broken translational invariance introduces lattice artefacts; relativistic strings therefore decelerate and radiate. We introduce two different methods to construct a moving string on the lattice, and study in detail the lattice effects on moving strings. We find that there are two types of lattice artefact: there is an effective maximum speed with which a moving string can be placed on the lattice, and a moving string also slows down, with the deceleration approximately proportional to the exponential of the velocity. To mitigate this, we introduce and study an improved discretisation, based on the tree-level L\”{u}scher-Weisz action, which is found to reduce the deceleration by an order of magnitude, and to increase the string speed limit by an amount equivalent to halving the lattice spacing. The improved algorithm is expected to be very useful for 3D simulations of cosmic strings in the early universe, where one wishes to simulate as large a volume as possible.

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M. Hindmarsh, K. Rummukainen, T. Tenkanen, et. al.
Mon, 9 Jun 14
11/40

Comments: 13 pages, 10 figures