Altas Energias

J.C. Jiménez and E.S. Fraga

Physical Review D, vol. 97, Iss. 9

Abstract

We investigate protoneutron star matter using the state-of-the-art perturbative equation of state for cold and dense QCD in the presence of a fixed lepton fraction in which both electrons and neutrinos are included. Besides computing the modifications in the equation of state due to the presence of trapped neutrinos, we show that stable strange quark matter has a more restricted parameter space. We also study the possibility of nucleation of unpaired quark matter in the core of protoneutron stars by matching the lepton-rich QCD pressure onto a hadronic equation of state, namely TM1 with trapped neutrinos. Using the inherent dependence of perturbative QCD on the renormalization scale parameter, we provide a measure of the uncertainty in the observables we compute.

10.1103/PhysRevD.97.094023

Luiz Lopes and Debora Menezes

Journal of Cosmology and Astroparticle Physics, Volume 2018, May 2018

ABSTRACT

We study how the Λ hyperon threshold influences the radius of the canonical 1.4 M⊙ neutron star in the light of the measurements found in the recent literature. We show that the onset of a new degree of freedom not only causes the well known reduction of the maximum mass, but also compacts the neutron stars with high central density. With the help of the strange mesons phgr and σ*, we show that it is possible to simulate very compact neutron stars keeping realistic hyperon potentials, UΛ(n0)= −28 MeV and UΛΛ(n0/5) in agreement with recents measurements. In the end we generalize these results showing that the onset of a yet not known dark matter particle with mass of 1.04 GeV is able to produce simultaneously a 2 M⊙ neutron star and a canonical one with a radius of only 11.62 km.

DOI: 10.1088/1475-7516/2018/05/038

Thamirys de Oliveira, Débora P. Menezes, Marcus B. Pinto, and Francesca Gulminelli

Phys. Rev. C 97, 055205

ABSTRACT

We compare relativistic mean-field models with their low density expansion counterparts used to mimic nonrelativistic models by consistently expanding the baryonic scalar density in powers of the baryonic number density up to O(13/3), which goes two orders beyond the order considered in previous works. We show that, due to the nontrivial density dependence of the Dirac mass, the convergence of the expansion is very slow, and the validity of the nonrelativistic approximation is questionable even at subsaturation densities. In order to analyze the roles played by strangeness and isospin we consider n−Λ and n−p matter separately. Our results indicate that these degrees of freedom play quite different roles in the expansion mechanism and n−Λ matter can be better described by low density expansions than n−p matter in general.

DOI:10.1103/PhysRevC.97.055205

G. S. Denicol; J. Noronha

PHYSICAL REVIEW D, v. 97, p. 056021, 2018

Abstract

We find the general analytical solution of the viscous relativistic hydrodynamic equations (in the absence of bulk viscosity and chemical potential) for a Bjorken expanding fluid with an ideal gas equation of state and a constant shear viscosity relaxation time. We analytically determine the hydrodynamic attractor of this fluid and discuss its properties. We show for the first time that the slow-roll expansion, a commonly used approach to characterize the attractor, diverges. This is shown to hold also in a conformal plasma. The gradient expansion is found to converge in an example where causality and stability are violated.

10.1103/PhysRevD.97.056021

Fábio L. Braghin

Eur. Phys. J. A (2018) 54: 45

Abstract

An effective model with pions and constituent quarks in the presence of a weak external background electromagnetic field is derived by starting from a dressed one gluon exchange quark-quark interaction. By applying the auxiliary field and background field methods, the structureless pion limit is considered to extract effective pion and constituent quark couplings in the presence of a weak magnetic field. The leading terms of a large quark and gluon masses expansion are obtained by resolving effective coupling constants which turn out to depend on a weak magnetic field. Two pion field definitions are considered for that. Several relations between the effective coupling constants and parameters can be derived exactly or in the limit of very large quark mass at zero and weak constant magnetic field. Among these ratios, the Gell-Mann-Oakes-Renner and the quark level Goldberger-Treiman relations are obtained. In addition to that, in the pion sector, the leading terms of Chiral Perturbation Theory coupled to the electromagnetic field are recovered. Some numerical estimates are provided for the effective coupling constants and parameters.

10.1140/epja/i2018-12485-6

Fábio L. Braghin

Phys. Rev. D 97, 054025

Abstract

Low-energy effective couplings of baryons’ constituent quarks to light vector and axial mesons are derived by considering quark polarization for a dressed one gluon–exchange quark interaction. The quark field is split into two components, one for background constituent quarks and another one for quark-antiquark states, light mesons, and the scalar chiral condensate. By considering a large quark effective mass derivative expansion, several effective coupling constants are resolved as functions of the original model parameters and of components of the quark and gluon propagators. Besides the leading single vector meson–constituent quark gauge–type effective coupling, several two-vector and axial meson–constituent quark couplings are also obtained in the next leading order. Among these, vector and axial mesons mixings induced by constituent quark currrents are found. Approximated and exact ratios between the effective coupling constants in the limit of very large quark effective mass and numerical estimates are exhibited. Numerical results of the corresponding form factors and of the (strong) vector mesons quadratic radius are also presented.

10.1103/PhysRevD.97.054025

S. RYU; J. PAQUET; C. SHEN; G. S. Denicol; B. SCHENKE; S. JEON; C. GALE

PHYSICAL REVIEW C, v. 97, p. 034910, 2018

Abstract

We describe ultrarelativistic heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider with a hybrid model using the IP-Glasma model for the earliest stage and viscous hydrodynamics and microscopic transport for the later stages of the collision. We demonstrate that within this framework the bulk viscosity of the plasma plays an important role in describing the experimentally observed radial flow and azimuthal anisotropy simultaneously. We further investigate the dependence of observables on the temperature below which we employ the microscopic transport description.

10.1103/PhysRevC.97.034910

Giuliano Giacalone, Jacquelyn Noronha-Hostler, Matthew Luzum, and Jean-Yves Ollitrault

Phys. Rev. C 97, 034904

Abstract

We argue that relativistic hydrodynamics is able to make robust predictions for soft particle production in Xe+Xe collisions at the CERN Large Hadron Collider (LHC). The change of system size from Pb+Pb to Xe+Xe provides a unique opportunity to test the scaling laws inherent to fluid dynamics. Using event-by-event hydrodynamic simulations, we make quantitative predictions for several observables: mean transverse momentum, anisotropic flow coefficients, and their fluctuations. Results are shown as a function of collision centrality.

10.1103/PhysRevC.97.034904

M. Strickland; J. Noronha; G. S. Denicol

PHYSICAL REVIEW D, v. 97, p. 036020, 2018

Abstract

We determine the dynamical attractors associated with anisotropic hydrodynamics (aHydro) and the DNMR equations for a 0+1d conformal system using kinetic theory in the relaxation time approximation. We compare our results to the nonequilibrium attractor obtained from the exact solution of the 0+1d conformal Boltzmann equation, the Navier-Stokes theory, and the second-order Mueller-Israel-Stewart theory. We demonstrate that the aHydro attractor equation resums an infinite number of terms in the inverse Reynolds number. The resulting resummed aHydro attractor possesses a positive longitudinal-to-transverse pressure ratio and is virtually indistinguishable from the exact attractor. This suggests that an optimized hydrodynamic treatment of kinetic theory involves a resummation not only in gradients (Knudsen number) but also in the inverse Reynolds number. We also demonstrate that the DNMR result provides a better approximation of the exact kinetic theory attractor than the Mueller-Israel-Stewart theory. Finally, we introduce a new method for obtaining approximate aHydro equations which relies solely on an expansion in the inverse Reynolds number. We then carry this expansion out to the third order, and compare these third-order results to the exact kinetic theory solution.

10.1103/PhysRevD.97.036020

Renato Critelli, Romulo Rougemont, Jorge Noronha

Journal of High Energy Physics

Abstract

We use holography to investigate the process of homogeneous isotropization and thermalization in a strongly coupled N=4 Super Yang-Mills plasma charged under a U(1) subgroup of the global SU(4) R-symmetry which features a critical point in its phase diagram. Isotropization dynamics at late times is affected by the critical point in agreement with the behavior of the characteristic relaxation time extracted from the analysis of the lowest non-hydrodynamic quasinormal mode in the SO(3) quintuplet (external scalar) channel of the theory. In particular, the isotropization time may decrease or increase as the chemical potential increases depending on whether one is far or close enough to the critical point, respectively. On the other hand, the thermalization time associated with the equilibration of the scalar condensate, which happens only after the system has relaxed to a (nearly) isotropic state, is found to always increase with chemical potential in agreement with the characteristic relaxation time associated to the lowest non-hydrodynamic quasinormal mode in the SO(3) singlet (dilaton) channel. These conclusions about the late dynamics of the system are robust in the sense that they hold for different initial conditions seeding the time evolution of the far-from-equilibrium plasma.

10.1007/JHEP12(2017)029