Tag Archives: Quantum Gases

Exploring $^3P_0$ Superfluid in Dilute Spin-Polarized Neutron Matter [CL]

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http://arxiv.org/abs/2305.08690


We study the theoretical possibility of $^3P_0$ neutron superfluid in dilute spin-polarized neutron matter, which may be relevant to the crust region of a magnetized neutron star. In such a dilute regime where the neutron Fermi energy is less than 1 MeV, the $^1S_0$ neutron superfluid can be exhausted by a strong magnetic field of the compact star. At low-energy limit relevant for dilute neutron matter, the $^3P_0$ interaction is stronger than the $^3P_2$ one, which is believed to induce the triplet superfluid in the core. We present the ground-state phase diagram of dilute neutron matter with respect to the magnetic field and numerically estimate the critical temperature of $^3P_0$ neutron superfluid, which exceeds $10^7$~K.

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H. Tajima, H. Funaki, Y. Sekino, et. al.
Tue, 16 May 23
61/83

Comments: 6 pages, 3 figures

Stability of interlinked neutron vortex and proton flux-tube arrays in a neutron star — III. Proton feedback [HEAP]

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http://arxiv.org/abs/2305.04482


The coupled, time-dependent Gross-Pitaevskii and Ginzburg-Landau equations are solved simultaneously in three dimensions to investigate the equilibrium state and far-from-equilibrium, spin-down dynamics of an interpenetrating neutron superfluid and proton type-II superconductor, as an idealized description of the outer core of a neutron star. The simulations generalize previous calculations without the time-dependent Ginzburg-Landau equation, where proton feedback is absent. If the angle $\theta$ between the rotation and magnetic axes does not equal zero, the equilibrium state consists of geometrically complicated neutron vortex and proton flux-tube tangles, as the topological defects pin to one another locally but align with different axes globally. During spin-down, new types of motion are observed. For $\theta = 0$, entire vortices pair rectilinearly with flux tubes and move together while pinned. For $\theta \neq 0$, vortex segments pair with segments from one or more flux tubes, and the paired segments move together while pinned. The degree to which proton feedback impedes the deceleration of the crust is evaluated as a function of $\theta$ and the pinning strength, $\eta$. Key geometric properties of vortex-flux-tube tangles, such as filament length, mean curvature, and polarity are analysed. It is found that proton feedback smooths the deceleration of the crust, reduces the rotational glitch sizes, and stabilizes the vortex tangle dynamics. The dimensionless control parameters in the simulations are mutually ordered to match what is expected in a real neutron star, but their central values and dynamics ranges differ from reality by many orders of magnitude due to computational limitations.

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K. Thong, A. Melatos and L. Drummond
Tue, 9 May 23
60/88

Comments: N/A

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)

Polaronic Proton and Diproton Clustering in Neutron-Rich Matter [CL]

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http://arxiv.org/abs/2304.00535


We show that strong spin-triplet neutron-proton interaction causes polaronic protons to occur in neutron matter at subnuclear densities and nonzero temperature. As the neutron density increases, proton spectra exhibit a smooth crossover from a bare impurity to a repulsive polaron branch; this branch coexists with an attractive polaron branch. With the neutron density increased further, the attractive polarons become stable with respect to deuteron formation. For two adjacent protons, we find that the polaron effects and the neutron-mediated attraction are sufficient to induce a bound diproton, which leads possibly to diproton formation in the surface region of neutron-rich nuclei in laboratories as well as in neutron stars.

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H. Tajima, H. Moriya, W. Horiuchi, et. al.
Tue, 4 Apr 23
20/111

Comments: 6 pages, 4 figures (8 pages, 6 figures in the supplement)

On particle scattering in Gross-Pitaevskii theory and implications for dark matter halos [GA]

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http://arxiv.org/abs/2212.05812


Bose-Einstein-condensed dark matter (BEC-DM), also called scalar field dark matter (SFDM), has become a popular alternative to the standard, collisionless cold dark matter (CDM) model, due to its long-held potential to resolve the small-scale crisis of CDM. Halos made of BEC-DM have been modelled using the Gross-Pitaevskii (GP) equation coupled to the Poisson equation; the so-called GPP equations of motion. These equations are based on fundamental microphysical conditions that need to be fulfilled in order for the equations to be valid in the first place, related to the diluteness of the DM gas and the nature of the scattering model. We use these conditions in order to derive the implications for the BEC-DM particle parameters, notably the self-interaction coupling strength $g$. We compare the bounds with the constraint that results from the assumption of virial equilibrium of the central cores of halos, deriving a relationship that connects the BEC-DM parameters $g$ and particle mass $m$. We find that the GPP conditions are greatly fulfilled, for BEC-DM particle masses of interest, if such models also obey the virial condition that turns out to be the strongest constraint. We also derive the implications for the elastic scattering cross section (per particle mass) in BEC-DM halos, based on the scattering model of GPP, and find a huge range of possible values, depending on the strength of self-interaction. We put our results into context to recent literature which predicts sub-kpc core size.

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T. Rindler-Daller
Tue, 13 Dec 22
43/105

Comments: 22 pages; 3 figures; subm. to Front. Astron. Space Sci

Density-Induced Hadron-Quark Crossover via the Formation of Cooper Triples [CL]

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http://arxiv.org/abs/2211.14194


We discuss the hadron-quark crossover accompanied by the formation of Cooper triples (three-body counterpart of Cooper pairs), by analogy with the Bose-Einstein condensate to Bardeen-Cooper-Schrieffer crossover in two-component fermionic systems. Such a crossover is different from a phase transition, which often involves symmetry breaking. We calculate the in-medium three-body energy from the three-body $T$-matrix with a phenomenological three-body force characterizing a bound hadronic state in vacuum. With increasing density, the hadronic bound-state pole smoothly undergoes a crossover toward the Cooper triple phase where the in-medium three-body clusters coexist with the quark Fermi sea.

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H. Tajima, S. Tsutsui, T. Doi, et. al.
Mon, 28 Nov 22
48/93

Comments: 7 pages, 3 figures

Bose-Einstein Condensate Dark Matter That Involves Composites [GA]

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http://arxiv.org/abs/2211.11614


By improving the Bose-Einstein condensate model of dark matter through the repulsive three-particle interaction to better reproduce observables such as rotation curves, both different thermodynamic phases and few-particle correlations are revealed. Using the numerically found solutions of the Gross-Pitaevskii equation for averaging the products of local densities and for calculating thermodynamic functions at zero temperature, it is shown that the few-particle correlations imply a first-order phase transition and are reduced to the product of single-particle averages with a simultaneous increase in pressure, density, and quantum fluctuations. Under given conditions, dark matter exhibits rather the properties of an ideal gas with an effective temperature determined by quantum fluctuations. Characteristics of oscillations between bound and unbound states of three particles are estimated within a simple random walk approach to qualitatively models the instability of particle complexes. On the other hand, the density-dependent conditions for the formation of composites are analyzed using chemical kinetics without specifying the bonds formed. The obtain results can be extended to the models of multicomponent dark matter consisting of composites formed by particles with a large scattering length.

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A. Gavrilik and A. Nazarenko
Tue, 22 Nov 22
9/83

Comments: 18 pages, 5 figures

i-SPin: An integrator for multicomponent Schrödinger-Poisson systems with self-interactions [CEA]

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http://arxiv.org/abs/2211.08433


We provide an algorithm and a publicly available code to numerically evolve multicomponent Schr\”{o}dinger-Poisson (SP) systems, including attractive or repulsive self-interactions in addition to gravity. Focusing on the case where the SP system represents the non-relativistic limit of a massive vector field, non-gravitational self-interactions (in particular, spin-spin type interactions) introduce new challenges related to mass and spin conservation which are not present in purely gravitational systems. We address these challenges with an analytical solution for the non-trivial `kick’ step in the algorithm. Equipped with this analytical solution, the full field evolution is second order accurate, preserves spin and mass to machine precision, and is reversible. Our algorithm allows for: general $n$-component fields with SO$(n)$ symmetry, an expanding universe relevant for cosmology, and the inclusion of external potentials relevant for laboratory settings.

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M. Jain and M. Amin
Thu, 17 Nov 22
34/63

Comments: 18 pages, 3 figures, 4 appendices. A python code based on our algorithm in provided at, this https URL . Animations of the numerical simulation results can be found at, this https URL

Finite temperature effects on magnetized Bose-Einstein condensate stars [HEAP]

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http://arxiv.org/abs/2209.00136


We study the role of temperature and magnetic field on the equation of state and macroscopic properties of Bose-Einstein condensate stars. These compact objects are composed of a condensed gas of interacting neutral vector bosons coupled to a uniform and constant magnetic field. We found that the main consequence of a finite temperature in the magnetized equations of state is to increase the inner pressure of the star. As a consequence, magnetized hot Bose-Einstein condensate stars are larger and heavier than their zero-temperature counterparts. However, the maximum masses obtained by the model remain almost unchanged, and the magnetic deformation of the star increases with the temperature. Besides, augmenting the temperature reduces the number of stable stars, an effect that the magnetic field enhances. The implications of our results for the star’s evolution, compactness, redshift, and mass quadupolar moment are also analyzed.

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G. Angulo, L. González, A. Martínez, et. al.
Fri, 2 Sep 22
27/62

Comments: N/A

Studying radiation of a white dwarf star falling on a black hole [HEAP]

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http://arxiv.org/abs/2208.11525


We investigate electromagnetic and gravitational radiation generated during a process of the tidal stripping of a white dwarf star circulating a black hole. We model a white dwarf star by a Bose-Fermi droplet at zero temperature and use the quantum hydrodynamic equations to simulate evolution of a black hole-white dwarf binary system. While going through the periastron, the white dwarf loses a small fraction of its mass. The mass falling onto a black hole is a source of powerful electromagnetic and gravitational radiation. Bursts of ultraluminous radiation are flared at each periastron passage by a white dwarf. This resembles the recurrent flaring of X-ray sources discovered recently by Irwin et al. Gravitational energy bursts occur mainly through emission at very low frequencies. The accretion disc, formed due to the stripping of a white dwarf, starts at some point to contribute continuously to radiation of both electromagnetic and gravitational type.

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T. Karpiuk, M. Nikołajuk and M. Brewczyk
Thu, 25 Aug 22
8/43

Comments: 9 pages, 5 figures. arXiv admin note: text overlap with arXiv:1907.12419

Vortex Pinning in Neutron Stars, Slip-stick Dynamics, and the Origin of Spin Glitches [HEAP]

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http://arxiv.org/abs/2208.11494


We study pinning and unpinning of superfluid vortices in the inner crust of a neutron star using 3-dimensional dynamical simulations. Strong pinning occurs for certain lattice orientations of an idealized, body-centered cubic lattice, and occurs generally in an amorphous or impure nuclear lattice. The pinning force per unit length is $\sim 10^{16}$ dyn cm$^{-1}$ for a vortex-nucleus interaction that is repulsive, and $\sim 10^{17}$ dyn cm$^{-1}$ for an attractive interaction. The pinning force is strong enough to account for observed spin jumps (glitches). Vortices forced through the lattice move with a slip-stick character; for a range of superfluid velocities, the vortex can be in either a cold, pinned state or a hot unpinned state, with strong excitation of Kelvin waves on the vortex. This two-state nature of vortex motion sets the stage for large-scale vortex movement that creates an observable spin glitch. We argue that the vortex array is likely to become tangled as a result of repeated unpinnings and repinnings. We conjecture that during a glitch, the Kelvin-wave excitation spreads rapidly along the direction of the mean superfluid vorticity and slower in the direction perpendicular to it, akin to an anisotropic deflagration.

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B. Link and Y. Levin
Thu, 25 Aug 22
23/43

Comments: 12 pages, 7 figures (two animations)

Effects of pairing gap and band gap on superfluid density in the inner crust of neutron stars [CL]

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http://arxiv.org/abs/2205.10742


Calculations of the superfluid density in the inner crust of neutron stars by different approaches are in strong disagreement, which causes a debate on the accountability of pulsar glitches based on superfluidity. Taking a simple unified model, we study the dependence on approximation of the superfluid density in a periodic potential. In comparison with the Hartree-Fock-Bogoliubov (HF-Bogoliubov) theory which treats the effects of the band gap and the pairing gap on equal footing, we examine the HF-BCS-type approximation in which the former is incorporated in priority, and another approximation in which the latter is incorporated in priority. We find that, when the pairing gap and the band gap are comparable as in the inner crust of neutron stars, they need to be treated on equal footing, and the HF-BCS approximation can considerably underestimate the superfluid density even if the pairing gap is much smaller than the Fermi energy. Our result suggests that the validity of the HF-BCS approximation for evaluating the superfluid density in neutron star crusts is questionable.

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Y. Minami and G. Watanabe
Tue, 24 May 22
83/92

Comments: 8 pages, 4 figures

Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase [CL]

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http://arxiv.org/abs/2112.14350


Background: In the solid crust of neutron stars, a variety of crystalline structure may exist. Recently the band theory of solids has been applied to the inner crust of neutron stars and significance of the entrainment between dripped neutrons and the solid crust was advocated. Since it influences interpretations of various phenomena of neutron stars, it has been desired to develop deeper understanding of the microphysics behind.
Purpose: The purpose of the present article is to propose a fully self-consistent microscopic framework for describing time-dependent dynamics of neutron star matter, which allows us to explore diverse properties of nuclear matter, including the entrainment effect.
Results: As the first application of the time-dependent self-consistent band theory for nuclear systems, we investigate the slab phase of nuclear matter with various proton fractions. From a dynamic response of the system to an external force, we extract the collective mass of a slab, associated with entrained neutrons as well as bound nucleons. We find that the extracted collective mass is smaller than a naive estimation based on a potential profile and single-particle energies. We show that the reduction is mainly caused by “counterflow” of dripped neutrons towards the direction opposite to the motion of the slabs. We interpret it as an “anti-entrainment” effect. As a result, the number of effectively bound neutrons is reduced, indicating an enhancement of the number density of conduction neutrons. We demonstrate that those findings are consistent with a static treatment in the band theory of solids.
*shortened due to the arXiv’s word limit.

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K. Sekizawa, S. Kobayashi and M. Matsuo
Thu, 30 Dec 21
59/71

Comments: 19 pages, 9 figures, 3 tables

Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase [CL]

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http://arxiv.org/abs/2112.14350


Background: In the solid crust of neutron stars, a variety of crystalline structure may exist. Recently the band theory of solids has been applied to the inner crust of neutron stars and significance of the entrainment between dripped neutrons and the solid crust was advocated. Since it influences interpretations of various phenomena of neutron stars, it has been desired to develop deeper understanding of the microphysics behind.
Purpose: The purpose of the present article is to propose a fully self-consistent microscopic framework for describing time-dependent dynamics of neutron star matter, which allows us to explore diverse properties of nuclear matter, including the entrainment effect.
Results: As the first application of the time-dependent self-consistent band theory for nuclear systems, we investigate the slab phase of nuclear matter with various proton fractions. From a dynamic response of the system to an external force, we extract the collective mass of a slab, associated with entrained neutrons as well as bound nucleons. We find that the extracted collective mass is smaller than a naive estimation based on a potential profile and single-particle energies. We show that the reduction is mainly caused by “counterflow” of dripped neutrons towards the direction opposite to the motion of the slabs. We interpret it as an “anti-entrainment” effect. As a result, the number of effectively bound neutrons is reduced, indicating an enhancement of the number density of conduction neutrons. We demonstrate that those findings are consistent with a static treatment in the band theory of solids.
*shortened due to the arXiv’s word limit.

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K. Sekizawa, S. Kobayashi and M. Matsuo
Thu, 30 Dec 21
2/71

Comments: 19 pages, 9 figures, 3 tables

Skyrme-based extrapolation for the static response of neutron matter [CL]

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http://arxiv.org/abs/2111.08056


The study of inhomogeneous neutron matter can provide insights into the structure of neutron stars as well as their dynamics in neutron-star mergers. In this work we tackle pure neutron matter in the presence of a periodic external field by considering a finite (but potentially large) number of particles placed in periodic boundary conditions. We start with the simpler setting of a noninteracting gas and then switch to a Skyrme-Hartree-Fock approach, showing static-response results for five distinct Skyrme parametrizations. We explain both the technical details of our computational approach, as well as the significance of these results as a general finite-size extrapolation scheme that may be used by ab initi} practitioners to approach the static-response problem of neutron matter in the thermodynamic limit.

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M. Buraczynski, S. Martinello and A. Gezerlis
Wed, 17 Nov 21
27/64

Comments: 18 pages, 20 figures

Living on the Fermi Edge: On Baryon Transport and Fermi Condensation [CEA]

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http://arxiv.org/abs/2105.02900


The transfer function of the baryon power spectrum from redshift $z\approx 1100$ to today has recently been, for the first time, determined from data by Pardo and Spergel. We observe a remarkable coincidence between this function and the transport function of a cold ideal Fermi gas at different redshifts. Guided by this, we unveil an infinite set of critical temperatures of the relativistic ideal Fermi gas which depend on a very finely quantized long-distance cutoff. The sound horizon scale of Baryon Acoustic Oscillations (BAO) seems set such a cutoff, which dials a critical temperature that is subsequently reached during redshift. At the critical point the Fermi gas becomes scale invariant and may condense to subsequently undergo gravitational collapse, seeding small scale structure. We mention some profound implications including the apparent quantization of Fermi momentum conjugate to the cutoff and the corresponding “gapping” of temperature.

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A. Trautner
Mon, 10 May 21
56/60

Comments: 9 pages, 8 figures

Simulating cosmological supercooling with a cold atom system II [CL]

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http://arxiv.org/abs/2104.07428


We perform an analysis of the supercooled state in an analogue of an early universe phase transition based on a one dimensional, two-component Bose gas with time-dependent interactions. We demonstrate that the system behaves in the same way as a thermal, relativistic Bose gas undergoing a first order phase transition. We propose a way to prepare the state of the system in the metastable phase as an analogue to supercooling in the early universe. While we show that parametric resonances in the system can be suppressed by thermal damping, we find that the theoretically estimated thermal damping in our model is too weak to suppress the resonances for realistic experimental parameters. However, we propose that experiments to investigate the effective damping rate in experiments would be worthwhile.

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T. Billam, K. Brown, A. Groszek, et. al.
Fri, 16 Apr 2021
42/58

Comments: 21 pages, 5 figures

Angular Momentum and the Absence of Vortices in the Cores of Fuzzy Dark Matter Haloes [GA]

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http://arxiv.org/abs/2101.04958


Scalar Field Dark Matter (SFDM), comprised of ultralight ($\gtrsim 10^{-22}$ eV) bosons, is distinguished from massive ($\gtrsim$ GeV), collisionless Cold Dark Matter (CDM) by its novel structure-formation dynamics as Bose-Einstein condensate (BEC) and quantum superfluid with wave-like properties, described by the Gross-Pitaevski and Poisson (GPP) equations. In the free-field (fuzzy) limit of SFDM (FDM), structure is inhibited below the de Broglie wavelength $\lambda_{\text{deB}}$, but resembles CDM on larger scales. Virialized haloes have solitonic cores of radius $\sim \lambda_{\text{deB}}$ that follow the ground-state attractor solution of GPP, surrounded by CDM-like envelopes. As a superfluid, SFDM is irrotational but can be unstable to vortex formation; outside of vortices it remains vorticity-free. We previously showed that halo cores can form vortices, from angular momentum expected during structure formation, if a strong enough repulsive self-interaction (SI) is present, which inhibits structure below a second length scale $\lambda_{\text{SI}}$, with $\lambda_{\text{SI}} > \lambda_{\text{deB}}$, suggesting FDM cores could not. FDM simulations later found vortices, but only outside halo cores, consistent with our suggestion. Extending our analysis now to FDM, we show explicitly that vortices should not arise in solitonic cores from angular momentum, modelling them as either Gaussian spheres or compressible, ($n = 2$)-polytropic, irrotational Riemann-S ellipsoids. For typical halo spin parameters, angular momentum per particle is below $\hbar$, the minimum required for one singly-quantized vortex in the center. Even for larger angular momentum, vortex formation is not energetically favoured.

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S. Schobesberger, T. Rindler-Daller and P. Shapiro
Thu, 14 Jan 21
48/79

Comments: submitted to MNRAS, 27 pages, 7 figures

Detection of Gravitational Waves using Parametric Resonance in Bose-Einstein Condensates [CL]

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http://arxiv.org/abs/2101.03691


An interesting proposal for detecting gravitational waves involves quantum metrology of Bose-Einstein condensates (BECs). We consider a forced modulation of the BEC trap, whose frequency matches that of an incoming continuous gravitational wave. The trap modulation induces parametric resonance in the BEC, which in turn enhances sensitivity of the BEC to gravitational waves. We find that such a BEC detector could potentially be used to detect gravitational waves across several orders of magnitude in frequency, with the sensitivity depending on the speed of sound, size of the condensate, and frequency of the phonons. We outline a possible BEC experiment and discuss the current technological limitations. We also comment on the potential noise sources as well as what is necessary for such a detector to become feasible.

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M. Robbins, N. Afshordi, A. Jamison, et. al.
Tue, 12 Jan 21
83/90

Comments: 20 pages, 9 figures

Superfluid dynamics in neutron star crusts: the Iordanskii force and chemical gauge covariance [HEAP]

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http://arxiv.org/abs/2012.10288


We present a geometrical derivation of the relativistic dynamics of the superfluid inner crust of a neutron star. The resulting model is analogous to the Hall-Vinen-Bekarevich-Khalatnikov hydrodynamics for a single-component superfluid at finite temperature, but particular attention should be paid to the fact that some fraction of the neutrons are locked to the motion of the protons in nuclei. This gives rise to an ambiguity in the definition of the two currents (the normal and the superfluid one) on which the model is built, a problem that manifests itself as a chemical gauge freedom of the theory. To ensure chemical gauge covariance of the hydrodynamic model, the phenomenological equation of motion for a quantized vortex should contain an extra transverse force, that is the relativistic version of the Iordanskii force discussed in the context of superfluid Helium. Hence, we extend the mutual friction model of Langlois et al. (1998) to account for the possible presence of this Iordanskii-like force. Furthermore, we propose that a better understanding of the (still not completely settled) controversy around the presence of the Iordanskii force in superfluid Helium, as well as in neutron stars, may be achieved by considering that the different incompatible results present in the literature pertain to two, opposite, dynamical regimes of the fluid system.

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L. Gavassino, M. Antonelli and B. Haskell
Mon, 21 Dec 20
39/75

Comments: 35 pages, 1 figure

Magnetized vector boson gas at any temperature [CL]

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http://arxiv.org/abs/2012.01537


We study the thermodynamic properties of a relativistic magnetized neutral vector boson gas at any temperature. By comparing the results with the low temperature and the non relativistic descriptions of this gas, we found that the fully relativistic case can be separated in two regimes according to temperature. For low temperatures, magnetic field effects dominate and the system shows a spontaneous magnetization, its pressure splits in two components and, eventually, a transversal magnetic collapse might occur. In the high temperature region, the gas behavior is led by pair production. The presence of antiparticles preserves the isotropy in the pressure, and increases the magnetization and the total pressure of the system by several orders. Astrophysical implications of those behaviors are discussed.

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G. Angulo, L. González, A. Martínez, et. al.
Fri, 4 Dec 20
4/77

Comments: 26 pages, 7 figures

Structure Factors of Neutron Matter at Finite Temperature [CL]

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http://arxiv.org/abs/2008.02824


We compute continuum and infinite volume limit extrapolations of the structure factors of neutron matter at finite temperature and density. Using a lattice formulation of leading-order pionless effective field theory, we compute the momentum dependence of the structure factors at finite temperature and at densities beyond the reach of the virial expansion. The Tan contact parameter is computed and the result agrees with the high momentum tail of the vector structure factor. All errors, statistical and systematic, are controlled for. This calculation is a first step towards a model-independent understanding of the linear response of neutron matter at finite temperature, a realm until now little explored.

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A. Alexandru, P. Bedaque, E. Berkowitz, et. al.
Mon, 10 Aug 20
-787/53

Comments: 5 pages, 3 figures, data included in submission

Simulating cosmological supercooling with a cold atom system [CL]

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http://arxiv.org/abs/2006.09820


We perform an analysis of the supercooled state in an analogue to an early universe phase transition based on a one dimensional, two-component Bose gas. We demonstrate that the thermal fluctuations in the relative phase between the components are characteristic of a relativistic thermal system. Furthermore, we demonstrate the equivalence of two different approaches to the decay of the metastable state: specifically a non-perturbative thermal instanton calculation and a stochastic Gross–Pitaevskii simulation.

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T. Billam, K. Brown and I. Moss
Thu, 18 Jun 20
42/84

Comments: 6 pages, 4 figures

Rotating self-gravitating Bose-Einstein condensates with a crust: a minimal model for pulsar glitches [HEAP]

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http://arxiv.org/abs/2005.13310


We develop a minimal model for \textit{pulsar glitches} by introducing a solid-crust potential in the three-dimensional (3D) Gross-Pitaevskii-Poisson equation (GPPE), which we have used earlier to study gravitationally bound Bose-Einstein Condensates (BECs), i.e., bosonic stars. In the absence of the crust potential, we show that, if we rotate such a bosonic star, it is threaded by vortices. We then show, via extensive direct numerical simulations (DNSs), that the interaction of these vortices with the crust potential yields (a) stick-slip dynamics and (b) dynamical glitches. We demonstrate that, if enough momentum is transferred to the crust from the bosonic star, then the vortices are expelled from the star and the crust’s angular momentum $J_c$ exhibits features that can be interpreted naturally as glitches. From the time series of $J_c$, we compute the cumulative probability distribution functions (CPDFs) of event sizes, event durations, and waiting times. We show that these CPDFs have signatures of self-organized criticality (SOC), which have been seen in observations on pulsar glitches.

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A. Verma, R. Pandit and M. Brachet
Thu, 28 May 20
14/55

Comments: N/A

Effects of oscillating spacetime metric background on a complex scalar field and formation of topological vortices [CL]

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http://arxiv.org/abs/1911.13216


We study time evolution of complex scalar field in the symmetry broken phase in presence of oscillating spacetime metric background. In our (2+1)-dimensional simulations, we show that the spacetime oscillations excite the initial ‘small’ fluctuations of the field configuration. This field excitations occur for a wide range of frequencies of spacetime metric. For smaller frequencies mostly the transverse excitations(Goldstone modes) dominate, while for larger frequencies longitudinal excitations(radial modes) of the field also get generated. For a given system size, there is a lower cut-off of the frequency of spacetime oscillations below which we do not see large enhancement in the fluctuations of the field. At a particular stage of field evolution, spacetime oscillation generates a periodic variation of phase of field in the physical space. This periodic spatial variation of phase of field oscillates in some time duration about its initial configuration with the frequency of spacetime oscillation, which shows that these excitations arise due to the phenomena of parametric resonance. We find that these field excitations at later stage lead to the formation of vortex-antivortex pairs. At sufficient large time of field evolution, field configuration achieves a disorder state. For some parameters of the theory, we see the formation of vortex-antivortex lattice structure in the system. This study suggests that spacetime oscillations may play an important role in the time evolution of the superfluid phase inside neutron stars during the binary neutron star (BNS) merger.

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S. Dave and S. Digal
Wed, 4 Dec 19
2/58

Comments: 12 pages, 10 figures

Helicities tighten up the turbulent gases [CL]

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http://arxiv.org/abs/1910.04638


The helicity-effect problem for a single compressible flow is transformed to the pure-background-field-effect one, reducing to the pure (compressible-version) Taylor-Proudman effect (TPE) and/or its magnetic analogue. A chiral base flow/field (CBF) is used to mostly clearly and simply materialize the screw-and-knot scenario for the `tightening-up’ notion, raised from the statistical result of helicity-reducing-turbulence-compressibility effect found earlier for the neutral-gas case. In the CBF, the existence of helicity nontrivially indicates a kind of mean rotation, naturally invoking the compressible version of the TPE, with horizontal-compressibility reduction but without direct constraint on the vertical velocity, which serves as the genuine mechanism, \textit{i.e.}, the underlying element of the statistical effect. The statistical fluctuations in the compressibility reduction effect may be due to that of the variation of the vertical derivative of the vertical velocity. A minimal working model with disorders in the CBFs bridges the single-flow and statistical arguments, completing the story. I further argue \textit{a posteriori} that recent data, of the superfluid and Bose-Einstein condensate model, also agree the result from my previous \textit{a priori} analysis. Statistical mechanical analyses, of compressible magnetohydrodynamics (MHD) and extended MHD for the ionized gas flows, show that helicities may reduce compressive and density modes relevant to the compressibility, i.e., tightening up the ionized-gas turbulence, implying the \textit{universality} of the notion. And, a \textit{unified} view is offered, with substantial extensions of the CBF and the analogue of the compressible TPE for a strong background magnetic field encapsulating the geometry of the Alfv\’en theorem for the (magnetised) plasma.

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J. Zhu
Fri, 11 Oct 19
54/76

Comments: 2 figures

Notes on the Squashed Sphere Lowest Landau Level [CL]

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http://arxiv.org/abs/1909.08042


In a recent article, we were motivated by the question of whether any of the remarkable condensed matter phenomena, such as the quantum Hall effect (QHE), the Integer quantum Hall effect (IQHE) etc., could potentially be observed in the extreme astrophysical environments of neutron stars. As a prequel to that work, and with the aim of understanding better the role of the geometry of the conducting surface on the structure of Landau levels, in this article we study the quantum dynamics of a quantum particle on a squashed sphere. More specifically, we study the dynamics of a single particle on an oblate squashed Haldane sphere i.e. a 2-sphere enclosing a single magnetic monopole at its center. While several features of the conventional Haldane sphere persist, by numerically solving the Schrodinger equation in this background, we find that the particle becomes increasingly localised in a band between the equator and the poles, with a corresponding increase of the eccentricity of the spheroid.

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J. Murugan, J. Shock and R. Slayen
Thu, 19 Sep 19
68/71

Comments: 23 pages and 10 figures

Structure Factors of The Unitary Gas Under Supernova Conditions [CL]

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http://arxiv.org/abs/1907.03914


We compute with lattice field theory the vector and axial static structure factors of the unitary gas for arbitrary temperature above the superfluid transition and for fugacities 0.1 < z < 1.0. Using the lattice formulation, we calculate beyond the validity of the virial expansion, a commonly used technique in many-body physics. We find qualitative differences in the behavior of the structure factors at high fugacity compared to the predictions of the virial expansion. Due to the large scattering length of neutrons, we expect the unitary gas structure factors to approximate the structure factors of hot neutron gases, and we therefore expect our calculations to be useful in supernova simulations, where neutron gas structure factors are needed to compute in-medium neutrino-neutron scattering rates.

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A. Alexandru, P. Bedaque and N. Warrington
Wed, 10 Jul 19
7/53

Comments: 10 pages, 6 figures, 1 table

Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter [CL]

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http://arxiv.org/abs/1906.02098


We investigate superfluid phase transitions of asymmetric nuclear matter at finite temperature ($T$) and density ($\rho$) with a low proton fraction ($Y_{\rm p} \le 0.2$) which is relevant to the inner crust and outer core of neutron stars. A strong-coupling theory developed for two-component atomic Fermi gases is generalized to the four-component case and is applied to the system of spin-$1/2$ neutrons and protons. The empirical phase shifts of neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) interactions up to $k = 2$ ${\rm fm}^{-1}$ are described by multi-rank separable potentials. We show that (i) the critical temperature of the neutron superfluidity $T_{\rm c}^{\rm nn}$ at $Y_{\rm p}=0$ agrees well with Monte Carlo data at low densities and takes a maximum value $T_{\rm c}^{\rm nn}=1.68$ MeV at $\rho/\rho_0 = 0.14$ with $\rho_0=0.17$ fm$^{-3}$, (ii) the critical temperature of the proton superconductivity $T_{\rm c}^{\rm pp}$ for $Y_{\rm p} \le 0.2$ is substantially suppressed at low densities due to np-pairing fluctuations and starts to dominate over $T_{\rm c}^{\rm nn}$ only above $\rho/\rho_0 = 0.70$ $(0.77)$ for $Y_p =0.1$ $(0.2)$, and (iii) the deuteron condensation temperature $T_{\rm c}^{\rm d}$ is suppressed at $Y_{\rm p}\le 0.2$ due to the large mismatch of the two Fermi surfaces.

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H. Tajima, T. Hatsuda, P. Wyk, et. al.
Thu, 6 Jun 19
26/67

Comments: 23 pages, 12 figures

Neutron matter at the interface(s): from interactions to ab initio and from there to phenomenology [CL]

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http://arxiv.org/abs/1906.01674


Neutron matter is interesting both as an extension of terrestrial nuclear physics and due to its significance for the study of neutron stars. In this work, after some introductory comments on nuclear forces, nuclear ab initio theory, and nuclear phenomenology, we employ two techniques, Quantum Monte Carlo (QMC) and Density Functional Theory, to practically handle an extended system composed of strongly interacting neutrons. We start by summarizing work on the static response of neutron matter, which considers the impact of external influences on the time-independent system. We then proceed to discuss new results of the energy of quasiparticle excitations in neutron matter, including QMC calculations with chiral or phenomenological nucleon-nucleon interactions. As part of this study, we carefully study the approach of our finite-number computations toward the infinite-system limit.

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M. Buraczynski, N. Ismail and A. Gezerlis
Thu, 6 Jun 19
29/67

Comments: 13 pages, 8 figures

Quantum simulation of dark energy candidates [CL]

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http://arxiv.org/abs/1811.06927


Additional scalar fields from scalar-tensor, modified gravity or higher dimensional theories beyond general relativity may account for dark energy and the accelerating expansion of the Universe. These theories have lead to proposed models of screening mechanisms, such as chameleon and symmetron fields, to account for the tight experimental bounds on fifth-force searches. Cold atom systems have been very successfully used to constrain the parameters of these screening models, and may in future eliminate the interesting parameter space of some models entirely. In this paper, we show how to manipulate a Bose-Einstein condensate to simulate the effect of any screened scalar field model coupled conformally to the metric. We give explicit expressions for the simulation of various common models. This result may be useful for investigating the computationally challenging evolution of particles on a screened scalar field background, as well as for testing the metrology scheme of an upcoming detector proposal.

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D. Hartley, C. Käding, R. Howl, et. al.
Tue, 14 May 19
55/91

Comments: 26 pages, 3 figures

Nonlinear Dynamics of the Cold Atom Analog False Vacuum [CL]

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http://arxiv.org/abs/1904.07873


We investigate the nonlinear dynamics of cold atom systems that can in principle serve as quantum simulators of false vacuum decay. The analog false vacuum manifests as a metastable vacuum state for the relative phase in a two-species Bose-Einstein condensate (BEC), induced by a driven periodic coupling between the two species. In the appropriate low energy limit, the evolution of the relative phase is approximately governed by a relativistic wave equation exhibiting true and false vacuum configurations. In previous work, a linear stability analysis identified exponentially growing short-wavelength modes driven by the time-dependent coupling. These modes threaten to destabilize the analog false vacuum. Here, we employ numerical simulations of the coupled Gross-Pitaevski equations (GPEs) to determine the non-linear evolution of these linearly unstable modes. We find that unless a physical mechanism modifies the GPE on short length scales, the analog false vacuum is indeed destabilized. We briefly discuss various physically expected corrections to the GPEs that may act to remove the exponentially unstable modes. To investigate the resulting dynamics in cases where such a removal mechanism exists, we implement a hard UV cutoff that excludes the unstable modes as a simple model for these corrections. We use this to study the range of phenomena arising from such a system. In particular, we show that by modulating the strength of the time-dependent coupling, it is possible to observe the crossover between a second and first order phase transition out of the false vacuum.

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J. Braden, M. Johnson, H. Peiris, et. al.
Thu, 18 Apr 19
37/75

Comments: 21 pages+appendices, 15 figures, to be submitted

Non-perturbative Extraction of the Effective Mass in Neutron Matter [CL]

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http://arxiv.org/abs/1901.00870


We carry out non-perturbative calculations of the single-particle excitation spectrum in strongly interacting neutron matter. These are microscopic quantum Monte Carlo computations of many-neutron energies at different densities as well as several excited states of the single particle. As input, we employ both phenomenological and chiral two- and three-nucleon interactions. We use the single-particle spectrum to extract the effective mass in neutron matter. With a view to systematizing the error involved in this extraction, we carefully assess finite-size effects on the quasiparticle dispersion relation. We find an effective-mass ratio that drops from 1 as the density is increased. We conclude by connecting our results with the physics of ultracold gases as well as with energy-density functional theories of nuclei and neutron-star matter.

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N. Ismail, M. Buraczynski and A. Gezerlis
Mon, 7 Jan 19
27/52

Comments: 5+ pages, 3 figures

Emergent long-range interactions in Bose-Einstein Condensates [CL]

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http://arxiv.org/abs/1812.09332


We consider a massive complex scalar field with contact interactions with a source and show that, upon Bose-Einstein condensation, there is an emergent long-range interaction between sources. This interaction becomes long-range in the limit of vanishing self-interaction between Bose-Einstein constituents. More generally, the range is given by $\ell^{-1}\propto \sqrt{\lambda n/m}$, with $\lambda$ being the 2-body self-interaction coupling constant, $n$ the particle number density in the condensate, and $m$ the mass of the condensed particles. Naively this may sound surprising since in $\lambda\rightarrow 0$ limit gapless excitations of the condensate have dispersion relation $\omega_k=k^2/2m$, yet for the mediated force we have $F\propto 1/r^2$. The reason behind this seemingly counterintuitive result lies in the fact that the force is being mediated by the phonon, which happens to acquire a nontrivial derivative interaction with the source. We discuss the potential ramifications of this observation for dark matter models. In particular, we show that this force can compete with gravity on galactic scales for a wide range of dark matter mass, provided that the interaction with baryons allows the presence of an extended dark matter condensate core. The effect could be of particular interest in ultra-light dark matter models, such as Fuzzy Dark Matter.

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L. Berezhiani and J. Khoury
Thu, 27 Dec 18
21/80

Comments: 11 pages

Emergent long-range interactions in Bose-Einstein Condensates [CL]

Posted on by

http://arxiv.org/abs/1812.09332


We consider a massive complex scalar field with contact interactions with a source and show that, upon Bose-Einstein condensation, there is an emergent long-range interaction between sources. This interaction becomes long-range in the limit of vanishing self-interaction between Bose-Einstein constituents. More generally, the range is given by $\ell^{-1}\propto \sqrt{\lambda n/m}$, with $\lambda$ being the 2-body self-interaction coupling constant, $n$ the particle number density in the condensate, and $m$ the mass of the condensed particles. Naively this may sound surprising since in $\lambda\rightarrow 0$ limit gapless excitations of the condensate have dispersion relation $\omega_k=k^2/2m$, yet for the mediated force we have $F\propto 1/r^2$. The reason behind this seemingly counterintuitive result lies in the fact that the force is being mediated by the phonon, which happens to acquire a nontrivial derivative interaction with the source. We discuss the potential ramifications of this observation for dark matter models. In particular, we show that this force can compete with gravity on galactic scales for a wide range of dark matter mass, provided that the interaction with baryons allows the presence of an extended dark matter condensate core. The effect could be of particular interest in ultra-light dark matter models, such as Fuzzy Dark Matter.

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L. Berezhiani and J. Khoury
Thu, 27 Dec 18
51/80

Comments: 11 pages

Simulating seeded vacuum decay in a cold atom system [CL]

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http://arxiv.org/abs/1811.09169


We propose to test the concept of seeded vacuum decay in cosmology using an analogue gravity Bose-Einstein condensate system. The role of the nucleation seed is played by a vortex within the condensate. We present two complementary theoretical analyses that demonstrate seeded decay is the dominant decay mechanism of the false vacuum. First, we adapt the standard instanton methods to the Gross-Pitaevskii equation. Second, we use the truncated Wigner method to study vacuum decay.

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T. Billam, R. Gregory, F. Michel, et. al.
Mon, 26 Nov 18
12/100

Comments: 5 Pages, 4 figues

Neutrino Spectral Split in the Exact Many Body Formalism [HEAP]

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http://arxiv.org/abs/1805.11767


We consider the many-body system of neutrinos interacting with each other through neutral current weak force. Emerging many-body effects in such a system could play important roles in some astrophysical sites such as the core collapse supernovae. In the literature this many-body system is usually treated within the mean field approximation which is an effective one-body description based on omitting entangled neutrino states. In this paper, we consider the original many-body system in an effective two flavor mixing scenario under the single angle approximation and present a solution without using the mean field approximation. Our solution is formulated around a special class of many-body eigenstates which do not undergo any level crossings as the neutrino self interaction rate decreases while the neutrinos radiate from the supernova. In particular, an initial state which consists of electron neutrinos and antineutrinos of an orthogonal flavor can be entirely decomposed in terms of those eigenstates. Assuming that the conditions are perfectly adiabatic so that the evolution of these eigenstates follow their variation with the interaction rate, we show that this initial state develops a spectral split at exactly the same energy predicted by the mean field formulation.

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S. Birol, Y. Pehlivan, A. Balantekin, et. al.
Thu, 31 May 18
26/45

Comments: 29 pages, 11 figures

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

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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

Screening and anti-screening of the pairing interaction in low-density neutron matter [CL]

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http://arxiv.org/abs/1804.04332


We study pairing in low-density neutron matter including the screening interaction due to the exchange of particle-hole and RPA excitations. As bare force we employ the effective low-momentum interaction $V_{low\,k}$, while the Fermi-liquid parameters are taken from a phenomenological energy density functional (SLy4) which correctly reproduces the equation of state of neutron matter. At low density, we find screening, i.e., pairing is reduced, while at higher densities, we find anti-screening, i.e., pairing is enhanced. This enhancement is mostly due to the strongly attractive Landau parameter $f_0$. We discuss in detail the critical temperature $T_c$ in the limit of low densities and show that the suppression of $T_c$ predicted by Gor’kov and Melik-Barkhudarov can only be reproduced if the cutoff of the $V_{low\,k}$ interaction is scaled with the Fermi momentum. We also discuss the effect of non-condensed pairs on the density dependence of $T_c$ in the framework of the Nozi`eres-Schmitt-Rink theory.

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S. Ramanan and M. Urban
Fri, 13 Apr 18
33/47

Comments: 15 pages, 16 figures

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

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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

Superfluidity in nuclear systems and neutron stars [CL]

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http://arxiv.org/abs/1802.00017


Nuclear matter and finite nuclei exhibit the property of superfluidity by forming Cooper pairs due to the attractive component of the nuclear interaction. We review the microscopic theories and methods that are being employed to understand the basic properties of superfluid nuclear systems, with emphasis on the spacially extended ensembles encountered in neutron stars and in nuclear collisions. Our survey includes techniques which are based on Green functions, correlated basis functions, and Monte Carlo sampling of quantum states. Novel phases arise in nuclear and related systems (such as ultra-cold atomic gases) under imbalance in the populations of the fermions that form Cooper pairs. Such phases include current-carrying superfluid states, heterogeneous phase-separated states, and phases involving deformation of Fermi surfaces. The phase diagram of imbalanced superfluids is reviewed, focusing especially on the crossover from Bardeen-Cooper-Schrieffer (BCS) pairing to a Bose-Einstein condensate (BEC) of tightly bound dimers under increase of the coupling strength of the theory. The neutron, proton, and hyperonic condensates that may exist under conditions prevailing in neutron stars are discussed, and calculations of weak-interaction rates within the Green functions formalism are examined in detail. We close with a discussion of quantum vortex states in nuclear systems and their dynamics in neutron-star crusts.

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A. Sedrakian and J. Clark
Fri, 2 Feb 18
26/48

Comments: 50 pages, 27 figures; review article, comments are welcome

Stability of interlinked neutron vortex and proton flux tube arrays in a neutron star. II. Far-from-equilibrium dynamics [HEAP]

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http://arxiv.org/abs/1712.02938


The equilibrium configurations of neutron superfluid vortices interacting with proton superconductor flux tubes in a rotating, harmonic trap are non-trivial in general, when the magnetorotational symmetry is broken. A non-zero angle $\theta$ between the magnetic and rotation axes leads to tangled vorticity due to competition between vortex-vortex repulsion and vortex-flux-tube pinning. Here we investigate the far-from-equilibrium behaviour of the vortices, as the trap decelerates, by solving the time-dependent, stochastic, Gross-Pitaevskii equation numerically in three dimensions. The numerical simulations reveal new vortex behaviours. Key geometrical attributes of the evolving vortex tangle are characterised, as is the degree to which pinning impedes the deceleration of the neutron condensate as a function of $\eta$, the pinning strength, and $\theta$. The simulated system is a partial analogue of the outer core of a decelerating neutron star, albeit in a very different parameter regime.

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L. Drummond and A. Melatos
Mon, 11 Dec 17
16/62

Comments: 12 pages, 10 figures, accepted for publication in MNRAS

Towards the cold atom analog false vacuum [CL]

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http://arxiv.org/abs/1712.02356


Analog condensed matter systems present an exciting opportunity to simulate early Universe models in table-top experiments. We consider a recent proposal for an analog condensed matter experiment to simulate the relativistic quantum decay of the false vacuum. In the proposed experiment, two ultra-cold condensates are coupled via a time-varying radio-frequency field. The relative phase of the two condensates in this system is approximately described by a relativistic scalar field with a potential possessing a series of false and true vacuum local minima. If the system is set up in a false vacuum, it would then decay to a true vacuum via quantum mechanical tunnelling. Should such an experiment be realized, it would be possible to answer a number of open questions regarding non-perturbative phenomena in quantum field theory and early Universe cosmology. In this paper, we illustrate a possible obstruction: the time-varying coupling that is invoked to create a false vacuum for the long-wavelength modes of the condensate leads to a destabilization of shorter wavelength modes within the system via parametric resonance. We focus on an idealized setup in which the two condensates have identical properties and identical background densities. Describing the system by the coupled Gross-Pitaevskii equations (GPE), we use the machinery of Floquet theory to perform a linear stability analysis, calculating the wavenumber associated with the first instability band for a variety of experimental parameters. However, we demonstrate that, by tuning the frequency of the time-varying coupling, it may be possible to push the first instability band outside the validity of the GPE, where dissipative effects are expected to damp any instabilities. This provides a viable range of experimental parameters to perform analog experiments of false vacuum decay.

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J. Braden, M. Johnson, H. Peiris, et. al.
Fri, 8 Dec 17
31/70

Comments: 30 pages + appendices, 9 figures, to be submitted to JHEP

Toward electrodynamics of unconventional phases of dilute nuclear matter [CL]

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http://arxiv.org/abs/1711.06984


The phase diagram of isospin-asymmetrical nuclear matter may feature a number of unconventional phases, which include the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase, and the heterogeneous phase-separated phase. Because the Cooper pairs of the condensate carry a single unit of charge, these phases are charged superconductors and respond to electromagnetic gauge fields by either forming domains (type-I superconductivity) or quantum vortices (type-II superconductivity). We evaluate the Ginzburg-Landau (GL) parameter across the phase diagram and find that the unconventional phases of isospin-asymmetrical nuclear matter are good type-II superconductors and should form Abrikosov vortices with twice the quantum of magnetic flux. We also find that the LOFF phase at the boundary of the transition to the type-I state, with the GL parameter being close to the critical value $1/\sqrt{2}$.

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A. Sedrakian and J. Clark
Tue, 21 Nov 17
75/79

Comments: Invited contribution presented by A. S. at the 19th International Conference on Recent Progress in Many-Body Theories, June 25-30, 2017, APCTP, Pohang, Korea, v1: 8 pages, 2 figs

White-dwarfs equation of state and structure: The effect of temperature [SSA]

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http://arxiv.org/abs/1709.06064


We study the effect of having a finite temperature on the equation of state and structure of a white dwarf. In order to keep the treatment as general as possible we carry on our discussion for ideal quantum gases obeying to both the Fermi-Dirac and the Bose-Einstein statistics even if we will only use the results for the free electron gas inside a white dwarf. We discuss the effect of temperature on the stability of the star and on the Fermi hole.

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R. Fantoni
Tue, 19 Sep 17
45/57

Comments: 19 pages, 3 figures

Stability of interlinked neutron vortex and proton flux tube arrays in a neutron star: equilibrium configurations [HEAP]

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http://arxiv.org/abs/1709.02254


Three-dimensional, Gross-Pitaevskii equation (GPE) simulations are presented of the interaction between neutron superfluid vortices and proton superconductor flux tubes in a rotating, harmonic trap, representing an idealised model of the outer core of a neutron star. Low-energy states of the neutron condensate are calculated by evolving the GPE in imaginary time in the presence of a prescribed, static, rectilinear flux tube array. The calculations are carried out as a function of the angle between the global magnetic and rotation axes, and the amplitude and sign of the current-current and density couplings between the neutron and proton condensates. It is found that the system is frustrated by the competition between vortex-vortex repulsion and vortex-flux-tube attraction (pinning), leading to the formation of vortex tangles and “glassy” behaviour characterized by multiple metastable states spaced closely in energy. The dimensionless parameters in the simulations are ordered as one expects in a neutron star, but the dynamic range is many orders of magnitude smaller than in reality, so caution must be exercised when assessing the astrophysical implications. Nevertheless the results suggest that tangled vorticity may be endemic in neutron star outer cores.

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L. Drummond and A. Melatos
Fri, 8 Sep 17
37/65

Comments: 21 pages, 20 figures, accepted for publication in MNRAS

Neutrino scattering in supernovae and spin correlations of a unitary gas [HEAP]

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http://arxiv.org/abs/1708.01788


Core collapse supernova simulations can be sensitive to neutrino interactions near the neutrinosphere. This is the surface of last scattering. We model the neutrinosphere region as a warm unitary gas of neutrons. A unitary gas is a low density system of particles with large scattering lengths. We calculate modifications to neutrino scattering cross sections because of spin and density correlations in the unitary gas. These correlations can be studied in laboratory cold atom experiments. We find significant reductions in cross sections, compared to free space interactions, even at relatively low densities. These reductions could reduce the delay time from core bounce to successful explosion in multidimensional supernova simulations.

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Z. Lin and C. Horowitz
Tue, 8 Aug 17
25/65

Comments: 5 pages, 2 figures

Entrainment in Superfluid Neutron Star Crusts: Hydrodynamic Description and Microscopic Origin [HEAP]

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http://arxiv.org/abs/1707.07854


In spite of the absence of viscous drag, the neutron superfluid permeating the inner crust of a neutron star cannot flow freely, and is entrained by the nuclear lattice similarly to laboratory superfluid atomic gases in optical lattices. The role of entrainment on the neutron superfluid dynamics is reviewed. For this purpose, a minimal hydrodynamical model of superfluidity in neutron-star crusts is presented. This model relies on a fully four-dimensionally covariant action principle. The equivalence of this formulation with the more traditional approach is demonstrated. In addition, the different treatments of entrainment in terms of dynamical effective masses or superfluid density are clarified. The nuclear energy density functional theory employed for the calculations of all the necessary microscopic inputs is also reviewed, focusing on superfluid properties. In particular, the microscopic origin of entrainment and the different methods to estimate its importance are discussed.

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N. Chamel
Wed, 26 Jul 17
55/68

Comments: 30 pages, 4 figures

Is there a hidden connection between massive neutron stars and dark matter in cosmology? [HEAP]

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http://arxiv.org/abs/1705.06608


Astronomical observations reveal a gap in the mass spectrum of relativistic objects: neither black holes nor neutron stars with 2 – 5 solar masses have ever been observed.
In this article I proceed in presenting the scenario which discloses a possible hidden connection between massive neutron stars (MANSs), dark matter and dark energy in cosmology. Accordingly, when the curved spacetime embedding MANSs compresses the nuclear matter to beyond a critical supranuclear density $n_{cr},$ mesons, generally transmitting the residual nuclear forces between neutrons, could gain energy by frequently interacting with a scalar field $\phi$ at the background. When the effective energy of mesons becomes comparable to the bag energy enclosing the quarks, the neutrons merge together and form a super-baryon (SB), whose interior is made of incompressible gluon-quark superfluid. It turns out that the process has a runaway-character: it enables the super-baryon to grow in mass and volume from inside-to-outside to finally metamorphose the entire object into a completely invisible dark gluon-quark object, practically indistinguishable from isolated stellar black holes. The inability of these objects to merge with other objects whilst agglomerating in clusters makes them excellent candidates both for black holes and for dark matter halos in cosmology.

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A. Hujeirat
Fri, 19 May 17
61/62

Comments: 9 pages, 12 figures

Composition of nuclear matter with light clusters and Bose-Einstein condensation of $α$ particles [CL]

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http://arxiv.org/abs/1705.02525


The Bose-Einstein condensation of $\alpha$ partciles in the multicomponent environment of dilute, warm nuclear matter is studied. We consider the cases of matter composed of light clusters with mass numbers $A\leq 4$ and matter that in addition these clusters contains $\isotope[56]{Fe}$ nuclei. We apply the quasiparticle gas model which treats clusters as bound states with infinite life-time and binding energies independent of temperature and density. We show that the $\alpha$ particles can form a condensate at low temperature $T\le 2$ MeV in such matter in the first case. When the $\isotope[56]{Fe}$ nucleus is added to the composition the cluster abundances are strongly modified at low temperatures, with an important implication that the $\alpha$ condensation at these temperatures is suppressed.

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X. Wu, S. Wang, A. Sedrakian, et. al.
Tue, 9 May 17
75/82

Comments: 15 pages, 8 figures

Superfluid Density of Neutrons in the Inner Crust of Neutron Stars: New Life for Pulsar Glitch Models [CL]

Posted on by

http://arxiv.org/abs/1704.08859


Calculations of the effects of band structure on the neutron superfluid density in the crust of neutron stars made under the assumption that the effects of pairing are small [Chamel, Phys. Rev. C 85, 035801 (2012)] lead to moments of inertia of superfluid neutrons so small that the crust alone is insufficient to account for the magnitude of neutron star glitches. Inspired by earlier work on ultracold atomic gases in an optical lattice, we investigate fermions with attractive interactions in a periodic lattice in the mean-field approximation. The effects of band structure are suppressed when the pairing gap is of order or greater than the strength of the lattice potential. By applying the results to the inner crust of neutron stars, we conclude that the reduction of the neutron superfluid density is considerably less than previously estimated and, consequently, it is premature to rule out models of glitches based on neutron superfluidity in the crust.

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G. Watanabe and C. Pethick
Mon, 1 May 17
1/46

Comments: 5 pages, 3 figures

Massive Fermi Gas in the Expanding Universe [CEA]

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http://arxiv.org/abs/1612.07249


The behavior of a decoupled ideal Fermi gas in a homogeneously expanding three-dimensional volume is investigated, starting from an equilibrium spectrum. In case the gas is massless and/or completely degenerate, the spectrum of the gas can be described by an effective temperature and/or an effective chemical potential, both of which scale down with the volume expansion. In contrast, the spectrum of a decoupled massive and non-degenerate gas can only be described by an effective temperature if there are strong enough self-interactions such as to maintain an equilibrium distribution. Assuming perpetual equilibration, we study a decoupled gas which is relativistic at decoupling and then is red-shifted until it becomes non-relativistic. We find expressions for the effective temperature and effective chemical potential which allow us to calculate the final spectrum for arbitrary initial conditions. This calculation is enabled by a new expansion of the Fermi-Dirac integral, which is for our purpose superior to the well-known Sommerfeld expansion. We also compute the behavior of the phase space density under expansion and compare it to the case of real temperature and real chemical potential. Using our results for the degenerate case, we also obtain the mean relic velocity of the recently proposed non-thermal cosmic neutrino background.

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A. Trautner
Thu, 22 Dec 16
21/65

Comments: 19 pages, 16 figures

Microscopic Study of ${}^1{S_0}$ Superfluidity in Dilute Neutron Matter [CL]

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http://arxiv.org/abs/1612.02188


Singlet $S$-wave superfluidity of dilute neutron matter is studied within the correlated BCS method, which takes into account both pairing and short-range correlations. First, the equation of state (EOS) of normal neutron matter is calculated within the Correlated Basis Function (CBF) method in lowest cluster order using the ${}^1{S_0}$ and ${}^3P$ components of the Argonne $V_{18}$ potential, assuming trial Jastrow-type correlation functions. The ${}^1{S_0}$ superfluid gap is then calculated with the corresponding component of the Argonne $V_{18}$ potential and the optimally determined correlation functions. The dependence of our results on the chosen forms for the correlation functions is studied, and the role of the $P$-wave channel is investigated. Where comparison is meaningful, the values obtained for the ${}^1{S_0}$ gap within this simplified scheme are consistent with the results of similar and more elaborate microscopic methods.

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G. Pavlou, E. Mavrommatis, C. Moustakidis, et. al.
Thu, 8 Dec 16
35/69

Comments: 9 pages, 6 figures

Unitary Gas Constraints on Nuclear Symmetry Energy [CL]

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http://arxiv.org/abs/1611.07133


We show the existence of a lower bound on the volume symmetry energy parameter $S_0$ from unitary gas considerations. We further demonstrate that values of $S_0$ above this minimum imply upper and lower bounds on the symmetry energy parameter $L$ describing its lowest-order density dependence. The bounds are found to be consistent with both recent calculations of the energies of pure neutron matter and constraints from nuclear experiments. These results are significant because many equations of state in active use for simulations of nuclear structure, heavy ion collisions, supernovae, neutron star mergers, and neutron star structure violate these constraints.

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E. Kolomeitsev, J. Lattimer, A. Ohnishi, et. al.
Wed, 23 Nov 16
35/68

Comments: 4 pages, 4 figures

Condensate of excitations in moving superfluids [CL]

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http://arxiv.org/abs/1611.05093


A possibility of the condensation of excitations with a non-zero momentum in rectilinearly moving and rotating superfluid bosonic and fermionic (with Cooper pairing) media is considered in terms of a phenomenological order-parameter functional at zero and non-zero temperature. The results might be applicable to the description of bosonic systems like superfluid $^4$He, ultracold atomic Bose gases, charged pion and kaon condensates in rotating neutron stars, and various superconducting fermionic systems with pairing, like proton and color-superconducting components in compact stars, metallic superconductors, and neutral fermionic systems with pairing, like the neutron component in compact stars and ultracold atomic Fermi gases. Order parameters of the “mother” condensate in the superfluid and the new condensate of excitations, corresponding energy gains, critical temperatures and critical velocities are found.

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E. Kolomeitsev and D. Voskresensky
Mon, 21 Nov 16
29/63

Comments: 15 pages, 1 figure reworked and extended version of arXiv:1501.00731 submitted to Prog. Theor Exp. Phys

Microscopic Calculations of Vortex-Nucleus Interaction in the Neutron Star Crust [CL]

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http://arxiv.org/abs/1609.03865


We investigate the dynamics of a quantized vortex and a nuclear impurity immersed in a neutron superfluid within a fully microscopic time-dependent three-dimensional approach. The magnitude and even the sign of the force between the quantized vortex and the nuclear impurity have been a matter of debate for over four decades. We determine that the vortex and the impurity repel at neutron densities, 0.014 fm$^{-3}$ and 0.031 fm$^{-3}$, which are relevant to the neutron star crust and the origin of glitches, while previous calculations have concluded that the force changes its sign between these two densities and predicted contradictory signs. The magnitude of the force increases with the density of neutron superfluid, while the magnitude of the pairing gap decreases in this density range.

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K. Sekizawa, G. Wlazlowski, P. Magierski, et. al.
Wed, 14 Sep 16
58/75

Comments: 4 pages, 2 figures, Talk given at the 14th International Symposium on “Nuclei in the Cosmos” (NIC-XIV), June 19-24, 2016, Toki Messe, Niigata, Japan

Ab initio and phenomenological studies of the static response of neutron matter [CL]

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http://arxiv.org/abs/1608.03598


We investigate the problem of periodically modulated strongly interacting neutron matter. We carry out ab initio non-perturbative auxiliary-field diffusion Monte Carlo calculations using an external sinusoidal potential in addition to phenomenological two- and three-nucleon interactions. Several choices for the wave function ansatz are explored and special care is taken to extrapolate finite-sized results to the thermodynamic limit. We perform calculations at various densities as well as at different strengths and periodicities of the one-body potential. Our microscopic results are then used to constrain the isovector term from energy-density functional theories of nuclei at many different densities, while making sure to separate isovector contributions from bulk properties. Lastly, we use our results to extract the static density-density linear response function of neutron matter at different densities. Our findings provide insights into inhomogeneous neutron matter and are related to the physics of neutron-star crusts and neutron-rich nuclei.

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M. Buraczynski and A. Gezerlis
Mon, 15 Aug 16
3/43

Comments: 11 pages, 14 figures

Inflationary quasiparticle creation and thermalization dynamics in coupled Bose-Einstein condensates [CL]

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http://arxiv.org/abs/1603.04898


A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, non-equilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanche-like QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our set-up occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

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A. Posazhennikova, M. Trujillo-Martinez and J. Kroha
Tue, 7 Jun 16
28/80

Comments: 5 pages, 4 Figures, final version accepted for publication in Phys. Rev. Lett

Spectral splits of neutrinos as a BCS-BEC crossover type phenomenon [HEAP]

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http://arxiv.org/abs/1603.06360


We show that the phenomenon of neutrino spectral split, which might be observed in the next galactic supernova neutrino signal, is analogous to the BCS-BEC crossover already observed in ultra cold atomic gas experiments. Although these two phenomena belong to two very different domains of physics, the propagation of neutrinos from highly interacting inner regions to the vacuum is reminiscent of the evolution of Cooper pairs between weak and strong interaction regimes. The Hamiltonians and the corresponding ground states undergo very similar transformations if one replaces the pair quasispin of the latter with the neutrino isospin of the former.

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Y. Pehlivan, A. Subasi, N. Ghazanfari, et. al.
Tue, 22 Mar 16
59/72

Comments: 5 pages, 3 figures

Equation of state of imbalanced cold matter from chiral perturbation theory [CL]

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http://arxiv.org/abs/1602.01317


We study the thermodynamic properties of matter at vanishing temperature for non-extreme values of the isospin chemical potential and of the strange quark chemical potential. From the leading order pressure obtained by maximizing the static chiral Lagrangian density we derive a simple expression for the equation of state in the pion condensed phase and in the kaon condensed phase. We find an analytical expression for the maximum of the ratio between the chiral perturbation energy density and the Stefan-Boltzmann energy density as well as for the isospin chemical potential at the peak in good agreement with lattice simulations of quantum chromodynamics. We speculate on the location of the crossover from the Bose-Einstein condensate state to the Bardeen-Cooper-Schrieffer state by a simple analysis of the thermodynamic properties of the system. For $\mu_I \gtrsim 2 m_\pi$ the leading order chiral perturbation theory breaks down; as an example it underestimates the energy density of the system and leads to a wrong asymptotic behavior.

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S. Carignano, A. Mammarella and M. Mannarelli
Thu, 4 Feb 16
11/50

Comments: 6 pages, 4 figures

Static Response of Neutron Matter [CL]

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http://arxiv.org/abs/1510.06417


We generalize the problem of strongly interacting neutron matter by adding a periodic external modulation. This allows us to study from first principles a neutron system that is extended and inhomogeneous, with connections to the physics of both neutron-star crusts and neutron-rich nuclei. We carry out fully non-perturbative microscopic Quantum Monte Carlo calculations of the energy of neutron matter at different densities, as well as different strengths and periodicities of the external potential. In order to remove systematic errors, we examine finite-size effects and the impact of the wave function ansatz. We also make contact with energy-density functional theories of nuclei and disentangle isovector gradient contributions from bulk properties. Finally, we calculate the static density-density linear response function of neutron matter and compare it with the response of other physical systems.

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M. Buraczynski and A. Gezerlis
Fri, 23 Oct 15
25/63

Comments: 5 pages, 3 figures

Instabilities in relativistic two-component (super)fluids [CL]

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http://arxiv.org/abs/1510.01982


We study two-fluid systems with nonzero fluid velocities and compute their sound modes, which indicate various instabilities. For the case of two zero-temperature superfluids we employ a microscopic field-theoretical model of two coupled bosonic fields, including an entrainment coupling and a non-entrainment coupling. We analyse the onset of the various instabilities systematically and point out that the dynamical two-stream instability can only occur beyond Landau’s critical velocity, i.e., in an already energetically unstable regime. A qualitative difference is found for the case of two normal fluids, where certain transverse modes suffer a two-stream instability in an energetically stable regime if there is entrainment between the fluids. Since we work in a fully relativistic setup, our results are very general and of potential relevance for (super)fluids in neutron stars and, in the non-relativistic limit of our results, in the laboratory.

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A. Haber, A. Schmitt and S. Stetina
Thu, 8 Oct 15
54/58

Comments: 25 pages, 7 figures

Bose-Einstein condensates in neutron stars [CL]

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http://arxiv.org/abs/1507.05839


In the two decades since the appearance of the book “Bose-Einstein Condensation” in 1995, there have been a number of developments in our understanding of dense matter. After a brief overview of neutron star structure and the Bose-Einstein condensed phases that have been proposed, we describe selected topics, including neutron and proton pairing gaps, the physics of the inner crust of neutron stars, where a neutron fluid penetrates a lattice of nuclei, meson condensates, and pairing in dense quark matter. Especial emphasis is placed on basic physical effects and on connections to the physics of cold atomic gases.

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C. Pethick, T. Schaefer and A. Schwenk
Wed, 22 Jul 15
1/59

Comments: 22 pages, 2 figures, to appear in “Universal Themes of Bose-Einstein Condensation”, edited by D.W. Snoke, N.P. Proukakis and P.B. Littlewood (Cambridge University Press)

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

Multiple Period States of the Superfluid Fermi Gas in an Optical Lattice [CL]

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http://arxiv.org/abs/1503.07976


We study multiple period states of a superfluid Fermi gas in an optical lattice along the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover. The existence of states whose period is a multiple of the lattice spacing is a consequence of the non-linear behavior of the gas, which is due to the presence of the order parameter associated with superfluidity. By solving Bogoliubov-de Gennes equations we find that, in the BCS side of the crossover, the multiple period states can be energetically favorable compared to the normal Bloch states and their survival time against dynamical instability drastically increases, suggesting that these states can be accessible in current experiments with ultracold gases. This is in sharp contrast to the situation in BECs.

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S. Yoon, F. Dalfovo, T. Nakatsukasa, et. al.
Mon, 30 Mar 15
40/65

Comments: 5 pages, 5 figures

Neutron Matter from Low to High Density [CL]

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http://arxiv.org/abs/1501.05675


Neutron matter is an intriguing nuclear system with multiple connections to other areas of physics. Considerable progress has been made over the last two decades in exploring the properties of pure neutron fluids. Here we begin by reviewing work done to explore the behavior of very low density neutron matter, which forms a strongly paired superfluid and is thus similar to cold Fermi atoms, though at energy scales differing by many orders of magnitude. We then increase the density, discussing work that ties the study of neutron matter with the determination of the properties of neutron-rich nuclei and neutron-star crusts. After this, we review the impact neutron matter at even higher densities has on the mass-radius relation of neutron stars, thereby making contact with astrophysical observations.

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S. Gandolfi, A. Gezerlis and J. Carlson
Mon, 26 Jan 15
40/46

Comments: 30 pages, 11 figures; prepared for Annual Review of Nuclear and Particle Science

Quantum Monte Carlo methods for nuclear physics [CL]

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http://arxiv.org/abs/1412.3081


Quantum Monte Carlo methods have proved very valuable to study the structure and reactions of light nuclei and nucleonic matter starting from realistic nuclear interactions and currents. These ab-initio calculations reproduce many low-lying states and transition moments in light nuclei, and simultaneously predict many properties of light nuclei and neutron matter over a rather wide range of energy and momenta. We review the nuclear interactions and currents, and describe the continuum Quantum Monte Carlo methods used in nuclear physics. These methods are similar to those used in condensed matter and electronic structure but naturally include spin-isospin, tensor, spin-orbit, and three-body interactions. We present a variety of results including the low-lying spectra of light nuclei, nuclear form factors, and transition matrix elements. We also describe low-energy scattering techniques, studies of the electroweak response of nuclei relevant in electron and neutrino scattering, and the properties of dense nucleonic matter as found in neutron stars. A coherent picture of nuclear structure and dynamics emerges based upon rather simple but realistic interactions and currents.

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J. Carlson, S. Gandolfi, F. Pederiva, et. al.
Wed, 10 Dec 14
30/61

Comments: 53 pages, 38 figures, review article

BCS-BEC crossovers and unconventional phases in dilute nuclear matter. II [CL]

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http://arxiv.org/abs/1410.1053


We study the phase diagram of isospin-asymmetrical nuclear matter in the density-temperature plane, allowing for four competing phases of nuclear matter: (i) the unpaired phase, (ii) the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, (iii) the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell phase, and (iv) the heterogeneous phase-separated phase. The phase diagram of nuclear matter composed of these phases features two tri-critical points in general, as well as crossovers from the asymmetrical BCS phase to a BEC of deuterons plus a neutron gas, both for the homogeneous superfluid phase (at high temperatures) and for the heterogeneous phase (at low temperatures). The BCS-BEC type crossover in the condensate occurs as the density is reduced. We analyze in detail some intrinsic properties of these phases, including the Cooper-pair wave function, the coherence length, the occupation numbers of majority and minority nucleonic components, and the dispersion relations of quasiparticle excitations about the ground state. We show by explicit examples that the physics of the individual phases and the transition from weak to strong coupling can be well understood by tracing the behavior of these quantities.

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M. Stein, A. Sedrakian, X. Huang, et. al.
Tue, 7 Oct 14
60/69

Comments: 14 pages, 16 figures, uses RevTex 4

Doppler Shift of de Broglie Waves- Black body System of Fermions and Massive Bosons [CL]

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http://arxiv.org/abs/1408.3538


The Doppler shift of de Broglie wave is obtained for fermions and massive bosons in a many body Fermi gas or in a Bose gas using the Lorentz transformations for momentum and energy of the particles. A formalism is developed to obtain the variation of de Broglie waves with temperature using the classic idea of Wien. It has been noticed that unlike the photon gas or electromagnetic waves in a black body chamber, where the variation is determined by the Wien’s displacement law, for Fermi gas the de Borglie wavelength increases with temperature and at a critical temperature it becomes infinity. This is the quantum to classical transition temperature for fermions. On the other hand for bosons, the de Broglie wavelength decreases with the increase in temperature. There is a minimum possible temperature at which condensation takes place. At the minimum of thr temperature the de Broglie wavelength of bosons become infinitely large. Unlike a transition from quantum to classical world this is indirectly related to the large value of coherence length for the bosons in the condensed phase.

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S. De and S. Chakrabarty
Fri, 29 Aug 14
48/51

Comments: Five pages REVTEX file, no figures

Pairing and superfluidity of nucleons in neutron stars [CL]

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http://arxiv.org/abs/1406.6109


We survey the current status of understanding of pairing and superfluidity of neutrons and protons in neutron stars from a theoretical perspective, with emphasis on basic physical properties. During the past two decades, the blossoming of the field of ultracold atomic gases and the development of quantum Monte Carlo methods for solving the many-body problem have been two important sources of inspiration, and we shall describe how these have given insight into neutron pairing gaps. The equilibrium properties and collective oscillations of the inner crust of neutron stars, where neutrons paired in a $^1$S$_0$ state coexist with a lattice of neutron-rich nuclei, are also described. While pairing gaps are well understood at densities less than one tenth of the nuclear saturation density, significant uncertainties exist at higher densities due to the complicated nature of nucleon-nucleon interactions, the difficulty of solving the many-body problem under these conditions, and the increasing importance of many-nucleon interactions. We also touch more briefly on the subject of pairing of neutrons in other angular momentum states, specifically the $^3$P$_2$ state, as well as pairing of protons.

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A. Gezerlis, C. Pethick and A. Schwenk
Wed, 25 Jun 14
64/67

Comments: 48 pages, 13 figures; chapter in “Novel Superfluids, Volume 2”, edited by K. H. Bennemann and J. B. Ketterson (Oxford University Press)

A theory of finite-temperature Bose-Einstein condensates in neutron stars [CL]

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http://arxiv.org/abs/1403.3812


We investigate the possible occurrence of a Bose-Einstein condensed phase of matter within neutron stars due to the formation of Cooper pairs among the superfluid neutrons. To this end we study the condensation of bosonic particles under the influence of both a short-range contact and a long-range gravitational interaction in the framework of a Hartree-Fock theory. We consider a finite-temperature scenario, generalizing existing approaches, and derive macroscopic and astrophysically relevant quantities like a mass limit for neutron stars.

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C. Gruber and A. Pelster
Tue, 18 Mar 14
21/62

Quantum Monte Carlo calculations of neutron matter with non-local chiral interactions [CL]

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http://arxiv.org/abs/1402.1576


We present fully non-perturbative quantum Monte Carlo calculations with non-local chiral effective field theory (EFT) interactions for the ground state properties of neutron matter. The equation of state, the nucleon chemical potentials and the momentum distribution in pure neutron matter up to one and a half times the nuclear saturation density are computed with a newly optimized chiral EFT interaction at next-to-next-to-leading order. This work opens the way to systematic order by order benchmarking of chiral EFT interactions, and \emph{ab initio} prediction of nuclear properties while respecting the symmetries of quantum chromodynamics.

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A. Roggero, A. Mukherjee and F. Pederiva
Mon, 10 Feb 14
38/49

Self-gravitating Bose-Einstein condensates and the Thomas-Fermi approximation [CL]

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http://arxiv.org/abs/1402.0600


Self-gravitating Bose-Einstein condensates have been proposed in various astrophysical contexts, including Bose-stars and BEC dark matter halos. These systems are described by a combination of the Gross-Pitaevskii and Poisson equations (the GPP system). In the analysis of these hypothetical objects, the Thomas-Fermi (TF) approximation is widely used. This approximation is based on the assumption that in the presence of a large number of particles, the kinetic term in the Gross-Pitaevskii energy functional can be neglected, yet this assumption is violated near the condensate surface. We also show that the total energy of the self-gravitating condensate in the TF-approximation is positive. The stability of a self-gravitating system is dependent on the total energy being negative. Therefore, the TF approximation is ill suited to formulate initial conditions in numerical simulations. As an alternative, we offer an approximate solution of the full GPP system.

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Wed, 5 Feb 14
41/61

The amazing properties of crystalline color superconductors [CL]

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http://arxiv.org/abs/1401.7551


This paper is a brief journey into the amazing realm of crystalline color superconductors. Starting from a qualitative description of superfluids, superconductors and supersolids, we show how inhomogeneous phases may arise when the system is under stress. These basic concepts are then extended to quark matter, in which a richer variety of phases can be realized. Then, the most interesting properties of the crystalline color superconductors are presented. This brief journey ends with a discussion of crystalline color superconductors in compact stars and related astrophysical observables. We aim at providing a pedagogical introduction for nonexpert in the field to a few interesting properties of crystalline color superconductors, without discussing the methods and the technicalities. Thus, the results are presented without a proof. However, we try to give a qualitatively clear description of the main concepts, using standard quantum field theory and analogies with condensed matter systems.

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Thu, 30 Jan 14
9/59