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We ask the question of how angular momentum is conserved in electroweak interaction processes. To introduce the problem with a minimum of mathematics, we first raise the same issue in elastic scattering of a circularly polarized photon by an atom, where the scattered photon has a different spin direction than the original photon, and note its presence in scattering of a fully relativistic spin-1/2 particle by a central potential. We then consider inverse beta decay in which an electron is emitted following the capture of a neutrino on a nucleus. While both the incident neutrino and final electron spins are antiparallel to their momenta, the final spin is in a different direction than that of the neutrino -- an apparent change of angular momentum. However, prior to measurement of the final particle, in all these cases angular momentum is indeed conserved, The apparent non-conservation of angular momentum arises in the quantum measurement process in which the measuring apparatus does not have an initially well-defined angular momentum, but is localized in the outside world. We generalize the discussion to massive neutrinos and electrons, and examine nuclear beta decay and electron-positron annihilation processes through the same lens, enabling physically transparent derivations of angular and helicity distributions in these reactions., Comment: 9 pages, 1 figure. Expanded version

We re-introduce, in light of our modern understanding of neutrinos, the concept of ``macroscopic neutrinoless double beta decay" (MDBD) for Majorana neutrinos. In this process an antineutrino produced by a nucleus undergoing beta decay, $X\to Y + e^- + \bar \nu_e$, is absorbed as a neutrino by another identical $X$ nucleus via the inverse beta decay reaction, $\nu_e + X \to e^-+Y$. The distinct signature of MDBD is that the total kinetic energy of the two electrons equals twice the endpoint energy of single beta decay. The amplitude for MDBD, a coherent sum over the contribution of different mass states of the intermediate neutrinos, reflects quantum coherence over macroscopic distances, and is a new macroscopic quantum effect. We evaluate the rate of MDBD for a macroscopic sample of ``$X$" material, e.g., tritium, acting both as the source and the target. The accidental background for MDBD originating from two separate single beta decays, which contains two final state neutrinos, can be readily rejected by measuring the energy of the detected two electrons. We discuss the similarities and differences between the MDBD and conventional neutrinoless double beta decay., Comment: 11 pages, 6 figures, final version

Since the release of the 2015 Long Range Plan in Nuclear Physics, major events have occurred that reshaped our understanding of quantum chromodynamics (QCD) and nuclear matter at large densities, in and out of equilibrium. The US nuclear community has an opportunity to capitalize on advances in astrophysical observations and nuclear experiments and engage in an interdisciplinary effort in the theory of dense baryonic matter that connects low- and high-energy nuclear physics, astrophysics, gravitational waves physics, and data science, Comment: 70 pages, 3 figures, White Paper for the Long Range Plan for Nuclear Science

The inverse tritium beta decay (ITBD) reaction, $\nu_e + ^3$H $\to e^- + ^3$He, is a promising experimental tool for observing relic neutrinos created in the early Universe. This reaction has been selected by the PTOLEMY experiment for the search of relic neutrinos. Despite its potential, the ITBD reaction induced by any sources of neutrinos has yet to be observed. We show that an intense $^{51}$Cr radioactive neutrino source is suitable for observing the ITBD reaction for the first time. As the Sun is another source of intense electron neutrinos, we also examine the ITBD reaction rate from solar neutrinos. Based on our recent studies on the evolution of the helicity of relic neutrinos, we further present the ITBD rate for capturing relic neutrinos as a function of neutrino mass hierarchy, the Dirac versus Majorana nature of neutrino, and the mass of the lightest neutrino., Comment: 5 pages, 4 figures, final version to appear in PRD

We obtain the superfluid transition temperature of equal Rashba-Dresselhaus spin-orbit and Rabi-coupled Fermi superfluids, from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in three dimensions for tunable $s$-wave interactions. In the presence of Rabi coupling, we find that spin-orbit coupling enhances (reduces) the critical temperature in the BEC (BCS) limit. For fixed interactions, we show that spin-orbit coupling can convert a first-order (discontinuous) phase transition into a second-order (continuous) phase transition, as a function of Rabi coupling. We derive the Ginzburg-Landau free energy to sixth power in the superfluid order parameter to describe both continuous and discontinuous phase transitions as a function of spin-orbit and Rabi couplings. Lastly, we develop a time-dependent Ginzburg-Landau fluctuation theory for an arbitrary mixture of Rashba and Dresselhaus spin-orbit couplings at any interaction strength., Comment: arXiv admin note: text overlap with arXiv:1709.07042

The recent NICER measurement of the radius of the neutron star PSR J0740+6620, and the inferred small variation of radii from 1.4$M_\odot$ to 2.1$M_\odot$, reveal key features of the equation of state of neutron star matter. The pressure rises rapidly in the regime of baryon density $n \sim$ 2-4 times nuclear saturation density, $n_0$ -- the region where we expect hadronic matter to be undergoing transformation into quark matter -- and the pressure in the nuclear regime is greater than predicted by microscopic many-body variational calculations of nuclear matter. To incorporate these insights into the microscopic physics from the nuclear to the quark matter regimes, we construct an equation of state, QHC21, within the framework of quark-hadron crossover (QHC). We include nuclear matter results primarily based on the state-of-the-art chiral effective field theory, but also note results of using nuclear matter variational calculations based on empirical nuclear forces. We employ explicit nuclear degrees of freedom only up to $n \sim 1.5n_0$, in order to explore the possibility of further physical degrees of freedom than nucleonic here. The resulting QHC21, which has a peak in sound velocity in $\sim 2$-$4 n_0$, is stiffer than the earlier QHC19 below 2$n_0$, predicting larger radii in substantial agreement with the NICER data., Comment: 10 pages, 11 figures; v2) 12 pages, 11 figures

We provide a brief commentary on recent work by Hammer and Son on the scaling behavior of nuclear reactions involving the emission of several loosely bound neutrons. In this work they discover a regime, termed unnuclear physics, in which these reactions are governed by an approximate conformal symmetry of the nuclear force. Remarkably, the scaling exponents that govern nuclear reactions can be related to the energies of ultracold atomic drops confined in harmonic potentials. We also comment on the importance and the limitations of this approximate symmetry in the physics of neutron stars., Comment: 7 pages, 1 figure

Relic neutrinos from the Big Bang decoupled from the hot plasma predominantly in helicity eigenstates. Their subsequent propagation through gravitational inhomogeneities of the Universe alters the helicities of both Dirac and Majorana neutrinos, thus providing an independent probe of the evolving universe. We determine here the probability that relic neutrinos flip their helicity, in terms of the spectrum of density inhomogeneities measured in the Cosmic Microwave Background. As we find, for Dirac neutrinos the gravitational helicity modifications are intermediate between the effects of magnetic fields if the neutrino magnetic moment is of the magnitude predicted in the Standard Model and the much larger effects if the magnetic moment is of the scale consistent with the excess of low energy electron events seen by the XENON1T experiment. We give succinct derivations, within general relativity, of the semi-classical response of a spinning particle to a weak gravitational field in an expanding universe, and estimate the helicity modifications of neutrinos emitted by the Sun caused by the Sun's gravity., Comment: Typographical error corrected in Appendix A

Since decoupling in the early universe in helicity states, primordial neutrinos propagating in astrophysical magnetic fields precess and undergo helicity changes. In view of the XENON1T experiment possibly finding a large magnetic moment of solar neutrinos, we estimate the helicity flipping for relic neutrinos in both cosmic and galactic magnetic fields. The flipping probability is sensitive both to the neutrino magnetic moment and the structure of the magnetic fields, thus potentially a probe of the fields. As we find, even a magnetic moment well below that suggested by XENON1T could significantly affect relic neutrino helicities and their detection rate via inverse tritium beta decay., Comment: 7 pages, 1 figure, typos corrected, references added, to be published in Phys. Rev. Lett

We consider the scattering of dark matter particles from superfluid liquid $^4$He, which has been proposed as a target for their direct detection. Focusing on dark matter masses below ~1 MeV, we demonstrate from sum-rule arguments the importance of the production of single phonons with energies $\omega \lesssim 1$ meV. We show further that the anomalous dispersion of phonons in liquid $^4$He at low pressures [i.e., $d^2\omega(q)/dq^2>0$, where $q$ and $\omega(q)$ are the phonon momentum and energy] has the important consequence that a single phonon will decay over a relatively short distance into a shower of lower energy phonons centered on the direction of the original phonon. Thus the experimental challenge in this regime is to detect a shower of low energy phonons, not just a single phonon. Additional information from the distribution of phonons in such a shower could enhance the determination of the dark matter mass., Comment: 17 pages, 12 figures; Updated with correction to 2-phonon integration limits, Equations 55-59

Stirling Colgate was a remarkably imaginative physicist, an independent thinker with a wide breadth of interests and contagious enthusiasm, a born leader with enduring drive to attack fundamental problems in science. Among his many achievements, he founded the quantitative theory of stellar collapse and supernova explosions, and introduced numerical simulation into the astrophysical toolbox. He brought strong physical intuition to both theory and experiment, in the sciences of nuclear weapons, magnetic and inertial fusion, as well as astrophysics., Comment: 10 pages, 11 figures. Memoir of Stirling Colgate (1925-2013) for the U.S. National Academy of Sciences Biographical Memoirs series

A moderately strong vector repulsion between quarks in dense quark matter is needed to explain how a quark core can support neutron stars heavier than two solar masses. We study this repulsion, parametrized by a four-fermion interaction with coupling g_V, in terms of non-perturbative gluon exchange in QCD in the Landau gauge. Matching the energy of quark matter, g_V n_q^2 (where n_q is the number density of quarks) with the quark exchange energy calculated in QCD with a gluon propagator parametrized by a finite gluon mass m_g and a frozen coupling alpha_s, at moderate quark densities, we find that gluon masses m_g in the range 200 - 600 MeV and alpha_s = 2 - 4 lead to a g_V consistent with neutron star phenomenology. Estimating the effects of quark masses and a color-flavor-locked (CFL) pairing gap, we find that g_V can be well approximated by a flavor-symmetric, decreasing function of density. We briefly discuss similar matchings for the isovector repulsion and for the pairing attraction., Comment: 9 pages, 6 figures

We present a much improved equation of state for neutron star matter, QHC19, with a smooth crossover from the hadronic regime at lower densities to the quark regime at higher densities. We now use the Togashi et al.~equation of state (Togashi:2017), a generalization of the Akmal-Pandharipande-Ravenhall equation of state of uniform nuclear matter, in the entire hadronic regime; the Togashi equation of state consistently describes non-uniform as well as uniform matter, and matter at beta equilibrium without the need for an interpolation between pure neutron and symmetric nuclear matter. We describe the quark matter regime at higher densities with the Nambu--Jona--Lasinio model, now identifying tight constraints on the phenomenological universal vector repulsion between quarks and the pairing interaction between quarks arising from the requirements of thermodynamic stability and causal propagation of sound. The resultant neutron star properties agree very well with the inferences of the LIGO/Virgo collaboration, from GW170817, of the pressure vs. baryon density, neutron star radii, and tidal deformabilities. The maximum neutron star mass allowed by QHC19 is 2.35 $M_\odot$, consistent with all neutron star mass determinations., Comment: 8 pages, 11 figures; v3) published version, appendix was added

Neutron stars were first posited in the early thirties, and discovered as pulsars in late sixties; however, only recently are we beginning to understand the matter they contain. This talk describes the continuing development of a consistent picture of the liquid interiors of neutron stars, driven by four advances: observations of two heavy neutron stars with masses $\simeq$ 2.0 solar masses; inferences of masses and radii simultaneously for an increasing number of neutron stars in low mass X-ray binaries, and future determinations via the NICER observatory; the observation of the binary neutron star merger, GW170817, through gravitational waves as well as across the electromagnetic spectrum; and an emerging understanding in QCD of how nuclear matter can turn into deconfined quark matter in the interior. We describe the modern quark-hadron crossover equation of state, QHC18, and the corresponding neutron stars, which agree well with current observations., Comment: 6 pages, 6 figures, Proceedings, 8th Intl. Conference on Quarks and Nuclear Physics 2018 (Tsukuba, Japan), Nov. 2018

We study how vortices in dense superfluid hadronic matter can connect to vortices in superfluid quark matter, as in rotating neutron stars, focusing on the extent to which quark-hadron continuity can be maintained. As we show, a singly quantized vortex in three-flavor symmetric hadronic matter can connect smoothly to a singly quantized non-Abelian vortex in three-flavor symmetric quark matter in the color-flavor locked (CFL) phase, without the necessity for boojums appearing at the transition., Comment: 10 pages, 2 figures; discussions on flavor non-singlet vortices elaborated; comments on color flux and center vortices added

We demonstrate that the observation of neutron stars with masses greater than one solar mass places severe demands on any exotic neutron decay mode that could explain the discrepancy between beam and bottle measurements of the neutron lifetime. If the neutron can decay to a stable, feebly-interacting dark fermion, the maximum possible mass of a neutron star is 0.7 solar masses, while all well-measured neutron star masses exceed one solar mass. The survival of $2 M_\odot$ neutron stars therefore indicates that any explanation beyond the Standard Model for the neutron lifetime puzzle requires dark matter to be part of a multi-particle dark sector with highly constrained interactions., Comment: 4 pages, 7 figures. v2: relativistic corrections added, results shown for wider range of dark fermion masses, conclusions unchanged

We obtain the superfluid transition temperature of equal Rashba-Dresselhaus spin-orbit and Rabi coupled Fermi superfluids, from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in three dimensions. Spin-orbit coupling enhances the critical temperature in the BEC limit, and can convert a first order phase transition in the presence of Rabi coupling into second order, as a function of the Rabi coupling for fixed interactions. We derive the Ginzburg-Landau equation to sixth power in the superfluid order parameter to describe both first and second order transitions as a function of spin-orbit and Rabi couplings.

We review the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. We focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. After discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the Nambu--Jona-Lasinio framework, in which gluonic processes are replaced by effective quark interactions. We turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. We review construction of unified equations of state that interpolate between the reasonably well understood nuclear matter regime at low densities and the quark matter regime at higher densities. The utility of such interpolations is driven by the present inability to calculate the dense matter equation of state in QCD from first principles. As we review, the parameters of effective quark models -- which have direct relevance to the more general structure of the QCD phase diagram of dense and hot matter -- are constrained by neutron star mass and radii measurements, in particular favoring large repulsive density-density and attractive diquark pairing interactions. We describe the structure of neutron stars constructed from the unified equations of states with crossover. Lastly we present the current equations of state -- called "QHC18" for quark-hadron crossover -- in a parametrized form practical for neutron star modeling., Comment: v2, 42 pages, 36 figures, 3 tables; to be published in Reports on Progress in Physics; new sections for cooling, X-ray analyses, and gravitational waves are added; the results for tidal deformability are included; equations of state and the numerical tables are updated; v3, typos corrected in eq.8

We develop a unified description, via the Boltzmann equation, of damping of gravitational waves by matter, incorporating collisions. We identify two physically distinct damping mechanisms -- collisional and Landau damping. We first consider damping in flat spacetime, and then generalize the results to allow for cosmological expansion. In the first regime, maximal collisional damping of a gravitational wave, independent of the details of the collisions in the matter is, as we show, significant only when its wavelength is comparable to the size of the horizon. Thus damping by intergalactic or interstellar matter for all but primordial gravitational radiation can be neglected. Although collisions in matter lead to a shear viscosity, they also act to erase anisotropic stresses, thus suppressing the damping of gravitational waves. Damping of primordial gravitational waves remains possible. We generalize Weinberg's calculation of gravitational wave damping, now including collisions and particles of finite mass, and interpret the collisionless limit in terms of Landau damping. While Landau damping of gravitational waves cannot occur in flat spacetime, the expansion of the universe allows such damping by spreading the frequency of a gravitational wave of given wavevector., Comment: 9 pages (10 pages in journal), published version

Anisotropy in heavy-ion collisions leads to polarization of both direct and virtual photons, the latter detected via internal conversion to dileptons pairs. Thus measurement of photon polarization probes the anisotropy at all stages of collisions. In order to characterize the polarization of virtual photons, we derive here the general structure of the photon polarization operator, rho^(mu nu), in an anisotropic medium, in terms of the four spectral functions, two transverse and one longitudinal, as usual, plus a new spectral function that reflects anisotropy in asymmetric collisions; and derive the local production rate of dilepton pairs in terms of these four functions., Comment: 4 pages, 4 figures; proceedings contribution for Quark Matter 2017

Chiral symmetry is always broken in cold, dense matter, by chiral condensation at low densities and by diquark condensation at high density. We construct here, within a schematic Nambu-Jona-Lasinio (NJL) model, the corresponding generalized Nambu-Goldstone pion, $\pi_G$. As we show, the $\pi_G$ mode naturally emerges as a linear combination of the $\langle \bar{q}q\rangle$ vacuum pion $\pi$ and the $\langle qq \rangle$ diquark condensate pion $\tilde{\pi}$, with $q$ the quark field, and continuously evolves with increasing density from being $\pi$-like in the vacuum to $\tilde{\pi}$-like in the high density diquark pairing phase. We calculate the density-dependent mass, decay constant, and coupling to quarks of the $\pi_G$, and derive a generalized Gell-Mann--Oakes--Renner (GMOR) relation in the presence of a finite bare quark mass $m_q$. We briefly discuss the implications of the results to possible Bose condensation of $\pi_G$ in more realistic models., Comment: 15 pages, 7 figures, 1 table

The polarization of direct photons produced in an ultrarelativistic heavy-ion collision reflects the momentum anisotropy of the quark-gluon plasma created in the collision. This paper presents a general framework, based on the photon spectral functions in the plasma, for analyzing the angular distribution and thus the polarization of dileptons in terms of the plasma momentum anisotropies. The rates of dilepton production depend, in general, on four independent spectral functions, corresponding to two transverse polarizations, one longitudinal polarization, and -- in plasmas in which the momentum anisotropy is not invariant under parity in the local rest frame of the matter -- a new spectral function, $\rho_n$, related to the anisotropy direction in the collision. The momentum anisotropy appears in the difference of the two transverse spectral functions, as well as in $\rho_n$. As an illustration, we delineate the spectral functions for dilepton pairs produced in the lowest order Drell-Yan process of quark-antiquark annihilation to a virtual photon., Comment: 6 pages, 3 figures

I first review the early history of the ultrarelativistic heavy ion program, starting with the 1974 Bear Mountain Workshop, and the 1983 Aurora meeting of the U.S. Nuclear Science Committee, just one billion seconds ago, which laid out the initial science goals of an ultrarelativistic collider. The primary goal, to discover the properties of nuclear matter at the highest energy densities, included finding new states of matter -- the quark-gluon plasma primarily -- and to use collisions to open a new window on related problems of matter in cosmology, neutron stars, supernovae, and elsewhere. To bring out how the study of heavy ions and hot, dense matter in QCD has been fulfilling these goals. I concentrate on a few topics, the phase diagram of matter in QCD, and connections of heavy ion physics to cold atoms, cosmology, and neutron stars., Comment: Opening talk at QM2015, Kobe, 10 pages, 5 figures

The neutron, in addition to possibly having a permanent electric dipole moment as a consequence of violation of time-reversal invariance, develops an induced electric dipole moment in the presence of an external electric field. We present here a unified non-relativistic description of these two phenomena, in which the dipole moment operator, $\vec{\cal D}$, is not constrained to lie along the spin operator. Although the expectation value of $\vec{\cal D}$ in the neutron is less than $10^{-13}$ of the neutron radius, $r_n$, the expectation value of $\vec {\cal D}\,^2$ is of order $r_n^2$. We determine the spin motion in external electric and magnetic fields, as employed in past and future searches for a permanent dipole moment, and show that the neutron electric polarizability, although entering the neutron energy in an external electric field, does not affect the spin motion. In a simple non-relativistic model we show that the expectation value of the permanent dipole is, to lowest order, proportional to the product of the time reversal-violating coupling strength and the electric polarizability of the neutron.

We delineate the properties of QCD matter at baryon density n_B=1-10n_0 (n_0: nuclear saturation density), through the construction of neutron star equations of state that satisfy the neutron star mass-radius constraints as well as physical conditions on the speed of sound. The QCD matter is described in the 3-window modeling: at n_B < 2n_0 purely nuclear matter; at n_B > 5n_0 percolated quark matter; and at 2n_0 < n_B < 5n_0 matter intermediate between these two which are constructed by interpolation. Using a schematic quark model with effective interactions inspired from hadron and nuclear physics, we analyze the strength of interactions necessary to describe observed neutron star properties. Our finding is that the interactions should remain as strong as in the QCD vacuum, indicating that gluons at n_B =1-10 n_0 remain non-perturbative even after quark matter formation., Comment: 5 pages, 3 figures, proceedings of the XXV Quark Matter conference, Sep. 27 to Oct. 3 in 2015, Kobe (Japan)

We present a comprehensive study of spectroscopic radius measurements of twelve neutron stars obtained during thermonuclear bursts or in quiescence. We incorporate, for the first time, a large number of systematic uncertainties in the measurement of the apparent angular sizes, Eddington fluxes, and distances, in the composition of the interstellar medium, and in the flux calibration of X-ray detectors. We also take into account the results of recent theoretical calculations of rotational effects on neutron star radii, of atmospheric effects on surface spectra, and of relativistic corrections to the Eddington critical flux. We employ Bayesian statistical frameworks to obtain neutron star radii from the spectroscopic measurements as well as to infer the equation of state from the radius measurements. Combining these with the results of experiments in the vicinity of nuclear saturation density and the observations of ~2 Msun neutron stars, we place strong and quantitative constraints on the properties of the equation of state between approximately 2-8 times the nuclear saturation density. We find that around M=1.5 Msun, the preferred equation of state predicts radii between 10.1 - 11.1 km. When interpreting the pressure constraints in the context of high density equations of state based on interacting nucleons, our results suggest a relatively weak contribution of the three-body interaction potential., Comment: ApJ, in press. Revised version includes more expanded analyses and discussions of comparison to previous results

We calculate the effect of a heat current on transporting $^3$He dissolved in superfluid $^4$He at ultralow concentration, as will be utilized in a proposed experimental search for the electric dipole moment of the neutron (nEDM). In this experiment, a phonon wind will generated to drive (partly depolarized) $^3$He down a long pipe. In the regime of $^3$He concentrations $\tilde < 10^{-9}$ and temperatures $\sim 0.5$ K, the phonons comprising the heat current are kept in a flowing local equilibrium by small angle phonon-phonon scattering, while they transfer momentum to the walls via the $^4$He first viscosity. On the other hand, the phonon wind drives the $^3$He out of local equilibrium via phonon-$^3$He scattering. For temperatures below $0.5$ K, both the phonon and $^3$He mean free paths can reach the centimeter scale, and we calculate the effects on the transport coefficients. We derive the relevant transport coefficients, the phonon thermal conductivity and the $^3$He diffusion constants from the Boltzmann equation. We calculate the effect of scattering from the walls of the pipe and show that it may be characterized by the average distance from points inside the pipe to the walls. The temporal evolution of the spatial distribution of the $^3$He atoms is determined by the time dependent $^3$He diffusion equation, which describes the competition between advection by the phonon wind and $^3$He diffusion. As a consequence of the thermal diffusivity being small compared with the $^3$He diffusivity, the scale height of the final $^3$He distribution is much smaller than that of the temperature gradient. We present exact solutions of the time dependent temperature and $^3$He distributions in terms of a complete set of normal modes., Comment: NORDITA PREPRINT 2015-37, 9 pages, 6 figures

We construct an equation of state for massive neutron stars based on quantum chromodynamics phenomenology. Our primary purpose is to delineate the relevant ingredients of equations of state that simultaneously have the required stiffness and satisfy constraints from thermodynamics and causality. These ingredients are: (i) a repulsive density-density interaction, universal for all flavors; (ii) the color-magnetic interaction active from low to high densities; (iii) confining effects, which become increasingly important as the baryon density decreases; (iv) non-perturbative gluons, which are not very sensitive to changes of the quark density. We use the following "3-window" description: At baryon densities below about twice normal nuclear density, 2n_0, we use the Akmal-Pandharipande-Ravenhall (APR) equation of state, and at high densities, > (4-7)n_0, we use the three-flavor Nambu-Jona-Lasinio (NJL) model supplemented by vector and diquark interactions. In the transition density region, we smoothly interpolate the hadronic and quark equations of state in the chemical potential-pressure plane. Requiring that the equation of state approach APR at low densities, we find that the quark pressure in non-confining models can be larger than the hadronic pressure, unlike in conventional equations of state. We show that consistent equations of state of stiffness sufficient to allow massive neutron stars are reasonably tightly constrained, suggesting that gluon dynamics remains non-perturbative even at baryon densities ~10n_0., Comment: 14 pages, 14 figures; v2 published version in PRD

We report microscopic calculations of the thermal conductivity, diffusion constant and thermal diffusion constant for classical solutions of $^3$He in superfluid $^4$He at temperatures $T \la 0.6$~K, where phonons are the dominant excitations of the $^4$He. We focus on solutions with $^3$He concentrations $\la \,10^{-3}$, for which the main scattering mechanisms are phonon-phonon scattering via 3-phonon Landau and Beliaev processes, which maintain the phonons in a drifting equilibrium distribution, and the slower process of $^3$He-phonon scattering, which is crucial for determining the $^3$He distribution function in transport. We use the fact that the relative changes in the energy and momentum of a $^3$He atom in a collision with a phonon are small to derive a Fokker-Planck equation for the $^3$He distribution function, which we show has an analytical solution in terms of Sonine polynomials. We also calculate the corrections to the Fokker-Planck results for the transport coefficients., Comment: 29 pages, 2 figures

We study, in the PNJL model, how the entropy of interacting quarks reflects the change in the effective degrees of freedom as the temperature increases through the quark-hadron phase transition. With inclusion of mesonic correlations, the effective degrees of freedom change from those of pi and sigma mesons at low temperatures to those of free quarks at high temperatures, with a resultant second order phase deconfinement transition in the chiral limit., Comment: 7 pages, 1 figure

We show how anisotropy in momentum of the gluon distribution in ultrarelativistic heavy ion collisions gives rise to polarization of direct photons produced via gluon-quark Compton scattering, as well as by quark-antiquark annihilation into a gluon-photon pair. We estimate the polarization asymmetry from the Compton process within a toy model where the polarized photons are produced from thermal gluons scattered by heavy-quark scattering centers moving with Bjorken boost-invariant flow, and find that it could be as large as 10%. We conclude that polarization measurements of directly produced photons can shed light on gluon pressure anisotropy in the early stages of collisions., Comment: 9 pages, 4 figures

We compute---at finite quark chemical potentials---the color screening of cold quark matter at the one-loop level, comparing the normal, BCS-paired U(1)em (or Higgs) phase and a singlet phase with color-singlet condensate near the Fermi surface. The latter phase is computed using the example of two-color QCD with a color-singlet diquark condensate. In contrast to the normal and Higgs phases, neither electric nor magnetic screening masses appear in the singlet phase. The absence of a magnetic mass, within a perturbative framework, is a consequence of the proper treatment of gauge invariance. While at large momenta the gluon self-energies approach those in the normal phase, the medium contributions to the infrared region below a scale of the mass gap are substantially suppressed. Infrared gluons at low quark density in the singlet phase appear protected from medium effects, unless the quark-gluon vertices are significantly enhanced in the infrared., Comment: 20 pages, 10 figures; v2 published version in PRD

We calculate the normal mass density of a paired Fermi gas at unitarity. The dominant contribution near the superfluid transition is from fermionic quasiparticle excitations, and is thus sensitive to the pairing gap. A comparison with the recent experiment of Sidorenkov et al. suggests that the superfluid gap near the transition temperature is larger than the BCS value, but the data do not permit a quantitative inference of the gap. Calculations of the quenched moment of inertia of a BCS superfluid in a harmonic trap are in reasonable agreement with the earlier experiment of Riedl et al., Comment: 6 pages, 2 figures, published version

We show how the configuration-space form of the Bogoliubov ground state wave function of a bosonic condensate with a single vortex in a harmonic trap can be described in terms of bosonic Jastrow correlations. We then generalize this result to study the first effects of such correlations on a mean-field vortex lattice state and show that the included correlations lower the energy below that of the mean-field state. Although the reduction is relatively small, it is a precursor of the more general expected effect of correlations in describing the melting of the vortex lattice at large angular momentum per particle.

We investigate the effects of realistic quark masses and local color neutrality on quark pairing in the three-flavor Polyakov--Nambu--Jona-Lasinio model. While prior studies have indicated the presence of light flavor quark (2SC) or symmetric color-flavor-locked (CFL) pairing at low temperatures, we find that in the absence of a local color neutrality constraint the inclusion of the Polyakov loop gives rise to phases in which all quark colors and flavors pair, but with unequal magnitudes. We study this asymmetric color-flavor-locked (ACFL) phase, which can exist even for equal mass quarks, identifying its location in the phase diagram, the order of the associated phase transitions, and its symmetry breaking pattern, which proves to be the intersection of the symmetry groups of the 2SC and CFL phases. We also investigate the effects of the strange quark mass on this new phase and the QCD phase diagram generally. Finally, we analyze the effect of a local color neutrality constraint on these phases of asymmetric pairing. We observe that for massless quarks the neutrality constraint renders the 2SC phase energetically unfavorable, eliminating it at low temperatures, and giving rise to the previously proposed low temperature critical point, with associated continuity between the hadronic and ACFL phases. For realistic strange quark masses, however, the neutrality constraint shrinks the 2SC region of the phase diagram, but does not eliminate it, at T=0., Comment: 11 pages, 10 figures

A longstanding goal of Akira Tonomura was to observe Hanbury Brown--Twiss anti-correlations between electrons in a field-emission free electron beam. The experimental results were reported in his 2011 paper with Tetsuji Kodama and Nobuyuki Osakabe [Phys. Rev. A 83, 063616 (2011)]. An open issue in such a measurement is whether the observed anti-correlations arise from quantum statistics, or are simply produced by Coulomb repulsion between electrons. In this paper we describe a simple classical model of Coulomb effects to estimate their effects in electron beam interferometry experiments, and conclude that the experiment did indeed observe quantum correlations in the electron arrrival times., Comment: Contribution to the Memorial Publication in honor of Akira Tonomura, [eds. K. Fujikawa and Y. A. Ono] to be published by World Scientific Publishing

Motivated by a proposed experimental search for the electric dipole moment of the neutron (nEDM) utilizing neutron-$^3$He capture in a dilute solution of $^3$He in superfluid $^4 $He, we derive the transport properties of dilute solutions in the regime where the $^3$He are classically distributed and rapid $^3$He-$^3$He scatterings keep the $^3$He in equilibrium. Our microscopic framework takes into account phonon-phonon, phonon-$^3$He, and $^3$He-$^3$He scatterings. We then apply these calculations to measurements by Rosenbaum et al. [J.Low Temp.Phys. {\bf 16}, 131 (1974)] and by Lamoreaux et al. [Europhys.Lett. {\bf 58}, 718 (2002)] of dilute solutions in the presence of a heat flow. We find satisfactory agreement of theory with the data, serving to confirm our understanding of the microscopics of the helium in the future nEDM experiment., Comment: 10 pages, 5 figures, v2

We study the stability and dynamics of an ultra-cold bosonic gas trapped in a toroidal geometry and driven by rotation, in the absence of dissipation. We first delineate, via the Bogoliubov mode expansion, the regions of stability and the nature of instabilities of the system for both repulsive and attractive interaction strengths. To study the response of the system to variations in the rotation rate, we introduce a "disorder" potential, breaking the rotational symmetry. We demonstrate the breakdown of adiabaticity as the rotation rate is slowly varied and find forced tunneling between the system's eigenstates. The non-adiabaticity is signaled by the appearance of a swallow-tail loop in the lowest-energy level, a general sign of hysteresis. Then, we show that this system is in one-to-one correspondence with a trapped gas in a double-well potential and thus exhibits macroscopic quantum self-trapping. Finally, we show that self-trapping is a direct manifestation of the behavior of the lowest-energy level.

We review the history of neutron star physics in the 1930s that is related to L. Landau. According to recollections of Rosenfeld (1974, Proc. 16th Solvay Conference on Physics, p. 174), Landau improvised the concept of neutron stars in a discussion with Bohr and Rosenfeld just after the news of the discovery of the neutron reached Copenhagen in February 1932. We present arguments that the discussion took place in March 1931, before the discovery of the neutron, and that they in fact discussed the paper written by Landau in Zurich in February 1931 but not published until February 1932 (Phys. Z. Sowjetunion, 1, 285). In his paper Landau mentioned the possible existence of dense stars which look like one giant nucleus; this can be regarded as an early theoretical prediction or anticipation of neutron stars, prior to the discovery of the neutron. The coincidence of the dates of the neutron's discovery and the paper's publication has led to an erroneous association of the paper with the discovery of the neutron. In passing, we outline the contribution of Landau to the theory of white dwarfs and to the hypothesis of stars with neutron cores., Comment: 12 pages, 4 figures

We study the Bose-Einstein condensate phase transition of three-dimensional ultracold bosons with isotropic Rashba spin-orbit coupling. Investigating the structure of Ginzburg-Landau free energy as a function of the condensate density, we show, within the Bogoliubov approximation, that the condensate phase transition is first order with a jump in the condensate density. We calculate the transition temperature and the jump in the condensate density at the transition for large spin-orbit coupling, where the transition temperature depends linearly on the density of particles. Finally, we discuss the feasibility of producing the phase transition experimentally., Comment: 5 pages, 2 figures, published version

The flow of a uniform Bose gas at speeds greater than the Landau critical velocity, v_c, does not necessarily destroy superfluidity, but rather need only lead to a decrease of the superfluid mass density, {\rho}_s. Analyzing a weakly interacting Bose gas with a finite range interparticle interaction that leads to a Landau critical velocity at non-zero quasiparticle momentum, we explicitly construct the (non-uniform) condensate for fluid flow faster than v_c and calculate the accompanying decrease in {\rho}_s. We briefly comment on the relation of the physics to other problems in superfluids, e.g., solitons, and vortices in Bose-Einstein condensates, and critical currents in superconductors., Comment: 5 pages, 1 figure

We show that an antiferrosmectic-C phase has lower energy at high densities than the non-magnetized Fermi gas and ferronematic phases in an ultracold gas of fermionic atoms, or molecules, with large magnetic dipole moments. This phase, which is analogous to meson condensation in dense nuclear matter, is a one-dimensional periodic structure in which the fermions localize in layers with their pseudospin direction aligned parallel to the layers, and staggered layer by layer., Comment: 4 pages, 3 eps figures. Title and abstract modified. Text is rearranged

The striped state of ultracold bosons with Rashba spin-orbit coupling in a homogeneous infinite system has, as we show, a constant particle flow, which in a finite-size system would accumulate particles at the boundaries; it is thus not a physical steady state of the system. We propose, as a variational ansatz, a condensate wave function for a weakly trapped system which behaves similarly to the striped state near the center, but does not have particle flow at the boundaries. This state has a line of unquantized coreless vortices. We show, by minimizing the total energy, that our modified striped state has lower energy than the conventional striped state and it is thus a physically appropriate starting point to analyze striped states in finite systems., Comment: 5 pages, 5 figures, minor errors corrected

We study the stability of Bose condensates with Rashba-Dresselhaus spin-orbit coupling in three dimensions against quantum and thermal fluctuations. The ground state depletion of the plane-wave condensate due to quantum fluctuations is, as we show, finite, and therefore the condensate is stable. We also calculate the corresponding shift of the ground state energy. Although the system cannot condense in the absence of interparticle interactions, we show by estimating the number of excited particles that interactions stabilize the condensate even at non-zero temperature. Unlike in the usual Bose gas, the normal phase is not kinematically forbidden at any temperature; calculating the free energy of the normal phase at finite temperature, and comparing with the free energy of the condensed state, we infer that generally the system is condensed at zero temperature, and undergoes a transition to normal at non-zero temperature., Comment: 4 pages, 2 figures

We investigate the phase structure of massless three-flavor QCD by extending the Nambu-Jona- Lasinio model to include the effects of confinement and the axial anomaly. We study the interplay between the chiral and diquark condensates induced by the axial anomaly, as well as their relationship with the Polyakov loop, which parameterizes confinement. By minimizing the thermodynamic potential we construct the QCD phase diagram and investigate the possibility of realizing a recently discovered low temperature critical point and an associated BEC-BCS crossover. We also perform a Ginzburg-Landau expansion of the thermodynamic potential, comparing our results to a prior analysis based purely on symmetry considerations, in order to assess the lowest-order effects of the condensate-confinement couplings., Comment: 13 pages, 14 figures

We study ultracold bosons in three dimensions with an anisotropic Rashba-Dresselhaus spin-orbit coupling. We first carry out the exact summation of ladder diagrams for the two-boson t-matrix at zero energy. Then, with the t-matrix as the effective interaction, we find the ground-state phase diagrams of bosons in mean field as a function of the spin-orbit coupling, the anisotropy, and the scattering lengths between particles in the same and in different pseudospin states. The resulting phase diagrams have much richer structures than those obtained using mean-field couplings, exhibiting three different phases: a plane-wave condensate, a striped condensate, and an unstable phase. The differences between the present approach using the t-matrix compared to using mean-field couplings is significant for large scattering lengths, large spin-orbit-coupling strength, or small anisotropy., Comment: 7 pages, 13 figures, published version

Interactions of ultracold atoms with Rashba spin-orbit coupling, currently being studied with simulated (artificial) gauge fields, have nontrivial ultraviolet and infrared behavior. Examining the ultraviolet structure of the Bethe-Salpeter equation, we show that the linear ultraviolet divergence in the bare interaction can be renormalized as usual in terms of low-energy scattering lengths, and that for both bosons and fermions ultraviolet logarithmic divergences are absent. Calculating the leading order effective interaction with full dependence on the spin-orbit coupling strength and the center-of-mass momentum of the colliding pair, we elucidate the relation between mean-field interactions and physical three-dimensional scattering lengths. As a consequence of infrared logarithmic divergences in the two-particle propagator, the effective interaction vanishes as the center-of-mass momentum approaches zero., Comment: 4 pages, 2 figures, published version