Nuclear Theory·nucl-th

Thursday·June 17, 2021

9 papers—3 primary·6 cross-listed

01
Causality and stability analysis of first-order field redefinition in relativistic hydrodynamics from kinetic theory
Sukanya Mitra
In this work, the causality and stability of a first-order relativistic dissipative hydrodynamic theory, that redefines the hydrodynamic fields from a first principle microscopic estimation, have been analyzed. A generic approach of gradient expansion for solving the relativistic transport equation has been adopted using the Chapman-Enskog iterative method. Next, the momentum dependent relaxation time approximation (MDRTA) has been employed to quantify the collision term for analytical estimation of the field correction coefficients from kinetic theory. At linear regime, in local rest frame the dispersion relations are observed to produce a causal propagating mode. However, the acausality and instability reappear when a boosted background is considered for linear analysis. These facts point out relevant aspects regarding the methodology of extracting the causal and stable first order hydrodynamics from kinetic theory and indicate the appropriate approach to construct a valid first order theory with proper justification.
nucl-thPRC(2022)·11 citations
02
Shape of atomic nuclei in heavy ion collisions
Jiangyong Jia🇺🇸
In the hydrodynamic model description of heavy ion collisions, the final-state anisotropic flow $v_{n}$ are linearly related to the strength of the multi-pole shape of the distribution of nucleons in the transverse plane $ε_{n}$ , $v_{n} \propto ε_{n}$ . The $ε_{n}$ , for $n = 1, 2, 3, 4$ , are sensitive to the shape of the colliding ions, characterized by the quadrupole $β_{2}$ , octupole $β_{3}$ and hexadecapole $β_{4}$ deformations. This sensitivity is investigated analytically and also in a Monte Carlo Glauber model. One observes a robust linear relation, $⟨ ε_{n}^{2} ⟩ = a_{n}^{'} + b_{n}^{'} β_{n}^{2}$ , for events in a fixed centrality. The $⟨ ε_{1}^{2} ⟩$ has a contribution from $β_{3}$ and $β_{4}$ , and $⟨ ε_{3}^{2} ⟩$ from $β_{4}$ . In the ultra-central collisions, there are little cross contributions between $β_{2}$ and $ε_{3}$ and between $β_{3}$ and $ε_{2}$ , but clear cross contributions are present in non-central collisions. Additionally, $⟨ ε_{n}^{2} ⟩$ are insensitive to non-axial shape parameters such as the triaxiality. This is good news because the measurements of $v_{2}$ , $v_{3}$ and $v_{4}$ can be used to constrain simultaneously the $β_{2}$ , $β_{3}$ , and $β_{4}$ values. This is best done by comparing two colliding ions with similar mass numbers and therefore nearly identical $a_{n}^{'}$ , to obtain simple equation that relates the $β_{n}$ of the two species. This opens up the possibility to map the shape of the atomic nuclei at a timescale ( $< 1 0^{- 24}$ s) much shorter than probed by low-energy nuclear structure physics ( $< 1 0^{- 21}$ s), which ultimately may provide information complementary to those obtained in the nuclear structure experiments.
nucl-thhep-phnucl-exPRC(2022)·122 citations
03
Variational approximations to exact solutions in shell-model valence spaces: systematic calculations in the $s d$ -shell
Adrián Sánchez-Fernández · Benjamin Bally · Tomás R. Rodríguez
We study the ability of variational approaches based on self-consistent mean-field and beyond-mean-field methods to reproduce exact energies and electromagnetic properties of the nuclei defined within the $s d$ -shell valence space using the non-trivial USD Hamiltonian. In particular, Hartree-Fock-Bogoliubov (HFB), variation after particle-number projection (VAPNP) and projected generator coordinate methods (PGCM) are compared to exact solutions {obtained by} the full diagonalization of the Hamiltonian. We analyze the role played by the proton-neutron ( $p n$ ) mixing as well as the quadrupole and pairing degrees of freedom (including both isoscalar and isovector channels) in the description of the spectra of even-even, even-odd and odd-odd nuclei in the whole $s d$ -shell.
nucl-thPRC(2021)·24 citations
04
Exact equilibrium distributions in statistical quantum field theory with rotation and acceleration: Dirac field
Andrea Palermo🇮🇹 · Matteo Buzzegoli🇮🇹 · Francesco Becattini🇮🇹
We derive the general exact forms of the Wigner function, of mean values of conserved currents, of the spin density matrix, of the spin polarization vector and of the distribution function of massless particles for the free Dirac field at global thermodynamic equilibrium with rotation and acceleration, extending our previous results obtained for the scalar field. The solutions are obtained by means of an iterative method and analytic continuation, which leads to formal series in thermal vorticity. In order to obtain finite values, we extend to the fermionic case the method of analytic distillation introduced for bosonic series. The obtained mean values of the stress-energy tensor, vector and axial currents for the massless Dirac field are in agreement with known analytic results in the special cases of pure acceleration and pure rotation. By using this approach, we obtain new expressions of the currents for the more general case of combined rotation and acceleration and, in the pure acceleration case, we demonstrate that they must vanish at the Unruh temperature.
↳ hep-thcond-mat.stat-mechgr-qcmath-ph+2JHEP(2021)·52 citations
05
Quantum simulation of non-equilibrium dynamics and thermalization in the Schwinger model
Wibe A. de Jong🇺🇸 · Kyle Lee🇺🇸 · James Mulligan🇺🇸 · Mateusz Płoskoń🇺🇸 · Felix Ringer🇺🇸 · Xiaojun Yao🇺🇸
We present simulations of non-equilibrium dynamics of quantum field theories on digital quantum computers. As a representative example, we consider the Schwinger model, a 1+1 dimensional U(1) gauge theory, coupled through a Yukawa-type interaction to a thermal environment described by a scalar field theory. We use the Hamiltonian formulation of the Schwinger model discretized on a spatial lattice. With the thermal scalar fields traced out, the Schwinger model can be treated as an open quantum system and its real-time dynamics are governed by a Lindblad equation in the Markovian limit. The interaction with the environment ultimately drives the system to thermal equilibrium. In the quantum Brownian motion limit, the Lindblad equation is related to a field theoretical Caldeira-Leggett equation. By using the Stinespring dilation theorem with ancillary qubits, we perform studies of both the non-equilibrium dynamics and the preparation of a thermal state in the Schwinger model using IBM's simulator and quantum devices. The real-time dynamics of field theories as open quantum systems and the thermal state preparation studied here are relevant for a variety of applications in nuclear and particle physics, quantum information and cosmology.
↳ quant-phhep-lathep-phnucl-thPRD(2022)·145 citations
06
Regarding the distribution of glue in the pion
Lei Chang🇨🇳 · Craig D. Roberts🇨🇳
Understanding why the scale of emergent hadron mass is obvious in the proton but hidden in the pion may rest on mapping the distribution functions (DFs) of all partons within the pion and comparing them with those in the proton; and since glue provides binding in quantum chromodynamics, the glue DF could play a special role. Producing reliable predictions for the proton's DFs is difficult because the proton is a three valence-body bound-state problem. As sketched herein, the situation for the pion, a two valence-body problem, is much better, with continuum and lattice predictions for the valence-quark and glue DFs in agreement. This beginning of theory alignment is timely because experimental facilities now either in operation or planning promise to realise the longstanding goal of providing pion targets, thereby enabling precision experimental tests of rigorous theory predictions concerning Nature's most fundamental Nambu-Goldstone bosons.
↳ hep-phhep-exhep-latnucl-ex+1Chin.Phys.Lett.(2021)·31 citations
07
Transport coefficients of hyperonic neutron star cores
Peter Shternin🇷🇺 · Isaac Vidaña🇮🇹
We consider transport properties of the hypernuclear matter in neutron star cores. In particular, we calculate the thermal conductivity, the shear viscosity, and the momentum transfer rates for np $Σ^{-} Λ e μ$ composition of dense matter in $β$ --equilibrium for baryon number densities in the range $0.1 - 1$ ~fm $^{- 3}$ . The calculations are based on baryon interactions treated within the framework of the non-relativistic Brueckner-Hartree-Fock theory. Bare nucleon-nucleon (NN) interactions are described by the Argonne v18 phenomenological potential supplemented with the Urbana IX three-nucleon force. Nucleon-hyperon (NY) and hyperon-hyperon (YY) interactions are based on the \new{NSC97e and NSC97a models} of the Nijmegen group. We find that the baryon contribution to transport coefficients is dominated by the neutron one as in the case of neutron star cores containing only nucleons. In particular, we find that neutrons dominate the total thermal conductivity over the whole range of densities explored and that, due to the onset of $Σ^{-}$ which leads to the deleptonization of the neutron star core, they dominate also the shear viscosity in the high density region, in contrast with the pure nucleonic case where the lepton contribution is always the dominant one.
↳ astro-ph.HEnucl-thUniverse(2021)·5 citations
08
Langevin dynamics of heavy quarks in a soft-hard factorized approach
Shuang Li🇨🇳 · Fei Sun🇨🇳 · Wei Xie🇨🇳 · Wei Xiong🇨🇳
By utilizing a soft-hard factorized model, which combines a thermal perturbative description of soft scatterings and a perturbative QCD-based calculation for hard collisions, we study the energy and temperature dependence of the heavy quark diffusion coefficients in Langevin dynamics. The adjustable parameters are fixed from the comprehensive model-data comparison. We find that a small value of the spatial diffusion coefficient at transition temperature is preferred by data $2 π T D_{s} (T_{c}) ≃ 6$ . With the parameter-optimized model, we are able to describe simultaneously the prompt $D^{0}$ $R_{AA}$ and $v_{2}$ data at $p_{T} \leq 8$ GeV in Pb--Pb collisions at $s_{NN} = 2.76$ and $s_{NN} = 5.02$ TeV. We also make predictions for non-prompt $D^{0}$ meson for future experimental tests down to the low momentum region.
↳ hep-phnucl-thEPJC(2021)·7 citations
09
The Radial Excited Heavy Mesons
Muyang Chen🇨🇳
In this paper, the first radial excited heavy pseudoscalar and vector mesons ( $η_{c} (2 S)$ , $ψ (2 S)$ , $B_{c} (2 S)$ , $B_{c}^{*} (2 S)$ , $η_{b} (2 S)$ , $Υ (2 S)$ ) are studied in the Dyson-Schwinger equation and Bethe-Salpeter equation approach. It is showed that the effective interactions of the radial excited states are harder than that of the ground states. With the interaction well determined by fitting the masses and leptonic decay constants of $ψ (2 S)$ and $Υ (2 S)$ , the first radial excited heavy mesons could be quantitatively described in the rainbow ladder approximation. The masses and leptonic decay constants of $η_{c} (2 S)$ , $B_{c} (2 S)$ , $B_{c}^{*} (2 S)$ and $η_{b} (2 S)$ are predicted.
↳ hep-phnucl-thCPC(2021)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE