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Nuclear Theory·nucl-th

Monday·July 4, 2022

7 papers—3 primary·4 cross-listed

All7Primary3Cross-lists4
  1. 04

    Formation of Chiral Soliton Lattice

    Tetsutaro Higaki🇯🇵 · Kohei Kamada🇯🇵 · Kentaro Nishimura🇯🇵

    The Chiral Soliton Lattice (CSL) is a lattice structure composed of domain walls aligned in parallel at equal intervals, which is energetically stable in the presence of a background magnetic field and a finite (baryon) chemical potential due to the topological term originated from the chiral anomaly. We study its formation from the vacuum state, with describing the CSL as a layer of domain-wall disks surrounded by the vortex or string loop, based on the Nambu-Goto-type effective theory. We show that the domain wall nucleates via quantum tunneling when the magnetic field is strong enough. We evaluate its nucleation rate and determine the critical magnetic field strength with which the nucleation rate is no longer exponentially suppressed. We apply this analysis to the neutral pion in the two-flavor QCD as well as the axion-like particles (ALPs) with a finite (baryon) chemical potential under an external magnetic field. In the former case, even though the CSL state is more energetically stable than the vacuum state and the nucleation rate becomes larger for sufficiently strong magnetic field, it cannot be large enough so that the nucleation of the domain walls is not exponentially suppressed and promoted, without suffering from the tachyonic instability of the charged pion fluctuations. In the latter case, we confirm that the effective interaction of the ALPs generically includes the topological term required for the CSL state to be energetically favored. We show that the ALP CSL formation is promoted if the magnetic field strength and the chemical potential of the system is slightly larger than the scale of the axion decay constant.

    ↳ hep-thastro-ph.COcond-mat.mes-hallhep-ph+1PRD(2022)·29 citations
  2. 05

    Anomaly-induced Chiral Mixing in Cold and Dense Matter

    Chihiro Sasaki🇵🇱

    We construct the spectral functions for light vector mesons at finite density and temperature in the presence of a novel mixing between parity partners, induced by baryon density via the Wess-Zumino-Witten action. As the main origin of in-medium broadening, a set of baryon resonances that strongly couple to the vector mesons and the modifications of kaons and anti-kaons due to the Kaplan-Nelson term are included. It is shown that the vector spectra, even with the broadening effects, exhibit sizable signatures of chiral symmetry restoration thanks to the chiral mixing depending on three-momenta carried by the vector mesons. Those spectral functions are used to calculate the integrated production rates of lepton pairs, and a proper binning in momenta and potential decrease in the vector-meson masses due to chiral symmetry restoration are discussed in quantifying the signatures.

    ↳ hep-phnucl-thPRD(2022)·9 citations
  3. 06

    Emergence of microphysical bulk viscosity in binary neutron star post-merger dynamics

    Elias R. Most · Alexander Haber · Steven P. Harris · Ziyuan Zhang · Mark G. Alford · Jorge Noronha

    In nuclear matter in isolated neutron stars, the flavor content (e.g., proton fraction) is subject to weak interactions, establishing flavor (-)equilibrium. However, there can be deviations from this equilibrium during the merger of two neutron stars. We study the resulting out-of-equilibrium dynamics during the collision by incorporating direct and modified Urca processes (in the neutrino-transparent regime) into general-relativistic hydrodynamics simulations with a simplified neutrino transport scheme. We demonstrate how weak-interaction-driven bulk viscosity in post-merger simulations can emerge and assess the bulk viscous dynamics of the resulting flow. We further place limits on the impact on the post-merger gravitational wave strain. Our results show that weak-interaction-driven bulk viscosity can potentially lead to a phase shift of the post-merger gravitational wave spectrum, although the effect is currently on the same level as the numerical errors of our simulation.

    ↳ astro-ph.HEgr-qcnucl-thApJL(2024)·132 citations
  4. 07

    An introduction to Thermal Field Theory and Some of its Application

    Munshi G. Mustafa🇮🇳

    In this article an introduction to the thermal field theory within imaginary time has been discussed in details. The imaginary time formalism has been introduced through both the operatorial and the functional integration method. The prescription to perform frequency sum for boson and fermion has been discussed. Green's function both in Minkowski time as well as in Euclidean time has been derived. The tadpole diagram in theory and the self-energy in theory have been computed. The basic features of general two point functions for both fermions and bosons in presence of a heat bath have been discussed. Then the free partition functions for scalar, fermion and gauge field, and interacting scalar field have been obtained. The quantum electrodynamics (QED) and gauge fixing have been discussed in details. The one-loop self-energy for electron and photon in QED have been obtained in hard thermal loop (HTL) approximation. The dispersion properties and collective excitations of both electron and photon in a thermal medium have been presented. The spectral representation of fermion and gauge boson propagators have been obtained. In HTL approximation, the generalisation of QED results of two point functions to quantum chromodynamics (QCD) have been outlined that mostly involve group theoretical factors. As an effective field theory approach the HTL resummation and the HTL perturbation theory have been introduced. The leading order, next-to-leading order and next-to-next-leading order free energy and pressure for deconfined QCD medium created in heavy-ion collisions have been computed within HTLpt. The general features of the deconfined QCD medium have also been outlined with non-perturbative effects like gluon condensate and Gribov-Zwanziger action. The dilepton production rates from quark-gluon plasma with these non-perturbative effects have been computed.

    ↳ hep-phhep-latnucl-thEur.Phys.J.ST(2023)·41 citations

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first authorsco-authorsvia INSPIRE