Altas Energias

K. Tsushima

Phys. Rev. D 99, 014026 – Published 17 January 2019

Abstract

In-medium properties of the low-lying strange, charm, and bottom baryons in symmetric nuclear matter are studied in the quark-meson coupling (QMC) model. Results for the Lorentz-scalar effective masses, mean field potentials felt by the light quarks in the baryons, in-medium bag radii, and the lowest mode bag eigenvalues are presented for those calculated using the updated data. This study completes the in-medium properties of the low-lying baryons in symmetric nuclear matter in the QMC model, for the strange, charm, and bottom baryons which contain one or two strange, one charm, or one bottom quark, as well as at least one light quark. The highlight is the prediction of the bottom baryon Lorentz-scalar effective masses; namely, the Lorentz-scalar effective mass of Σb becomes smaller than that of Ξb at moderate nuclear matter density, m∗Σb<m∗Ξb, although in vacuum mΣb>mΞb. We study further the effects of the repulsive Lorentz-vector potentials on the excitation (total) energies of these bottom baryons.

10.1103/PhysRevD.99.014026

Fábio L. Braghin

Fábio L. Braghin

Phys. Rev. D 99, 014001

Abstract

Form factors for pion interactions with constituent quarks are investigated as the leading effective couplings obtained from a one-loop background field method applied to a global color model. Two pion field definitions are considered and the resulting eleven form factors are expressed in terms of components of the quark and gluon propagators that compose only two momentum-dependent functions. A momentum-dependent Goldberger-Treiman relation is also obtained as one of the ratios between the form factors. The resulting form factors with pion momenta up to 1.5 GeV are exhibited for different quark effective masses and two different nonperturbative gluon propagators and they present similar behavior to fittings of experimental data from nucleons form factors. The corresponding pseudoscalar averaged quadratic radii (a.q.r.) and correction to the axial a.q.r. are presented as functions of the sea quark effective mass, being equal, respectively, to the scalar and vector ones at the present level of calculation.

10.1103/PhysRevD.99.014001

Fábio S. Bemfica, Marcelo M. Disconzi, and Jorge Noronha

Phys. Rev. D 98, 104064

Abstract

A new approach is described to help improve the foundations of relativistic viscous fluid dynamics and its coupling to general relativity. Focusing on neutral conformal fluids constructed solely in terms of hydrodynamic variables, we derive the most general viscous energy-momentum tensor yielding equations of motion of second order in the derivatives, which is shown to provide a novel type of generalization of the relativistic Navier-Stokes equations for which causality holds. We show how this energy-momentum tensor may be derived from conformal kinetic theory. We rigorously prove local existence, uniqueness, and causality of solutions of this theory (in the full nonlinear regime) both in a Minkowski background and also when the fluid is dynamically coupled to Einstein’s equations. Linearized disturbances around equilibrium in Minkowski spacetime are stable in this causal theory. A numerical study reveals the presence of an out-of-equilibrium hydrodynamic attractor for a rapidly expanding fluid. Further properties are also studied, and a brief discussion of how this approach can be generalized to nonconformal fluids is presented.

10.1103/PhysRevD.98.104064

B. B. Brandt, G. Endrődi, E. S. Fraga, M. Hippert, J. Schaffner-Bielich, and S. Schmalzbauer

Phys. Rev. D 98, 094510

Abstract

We investigate the viability of a new type of compact star whose main constituent is a Bose-Einstein condensate of charged pions. Several different setups are considered, where a gas of charged leptons and neutrinos is also present. The pionic equation of state is obtained from lattice QCD simulations in the presence of an isospin chemical potential and requires no modeling of the nuclear force. The gravitationally bound configurations of these systems are found by solving the Tolman-Oppenheimer-Volkoff equations. We discuss weak decays within the pion condensed phase and elaborate on the generation mechanism of such objects.

10.1103/PhysRevD.98.094510

J. P. B. C. De Melo and Kazuo Tsushima

Physics Letters B, Volume 788, p. 137-146.

Abstract

Properties of ρ-meson in symmetric nuclear matter are investigated in a light-front constituent quark model (LFCQM), using the in-medium inputs calculated by the quark-meson coupling (QMC) model. The LFCQM used in this study was already applied for the studies of the electromagnetic properties of ρ-meson in vacuum, namely, the charge G0, magnetic G1, and quadrupole G2 form factors, electromagnetic charge radius, and electromagnetic decay constant. Using the two different density dependence of the regulator mass in medium, we predict that the charge radius, and quadrupole moment are enhanced as increasing the nuclear matter density, while the magnetic moment is slightly quenched. Furthermore, we predict the value Qzero2 , which crosses zero of the charge form factor, G0 (Qzero2) = 0 (Q2 = -q2 > 0 with q being the four-momentum transfer), decreases as increasing the nuclear matter density by the two different density dependence of the regulator mass. On the other hand, for the electromagnetic decay constant of the ρ-meson, the two different density dependence of the regulator mass predict the opposite density dependence. Namely, as increasing the nuclear matter density, the naive treatment with the density independent regulator mass as in the vacuum, predicts the increase of the decay constant, while the other that assumes the same density dependence of the regulator mass as that of the in-medium constituent quark mass, predicts the decrease of the decay constant. Thus, although the other physical quantities are predicted to have similar density dependence by the two different density dependence of the regulator mass applied, the density dependence of the ρ-meson electromagnetic decay constant is predicted to have opposite density dependence, and the facts suggest that the in-medium ρ-meson decay constant needs to be investigated further in the future.

10.1016/j.physletb.2018.10.059

G. S. Denicol; X. Huang; E. MOLNÁR; G. M. MONTEIRO; H. Niemi; J. Noronha; D. H. Rischke; Q. WANG

PHYSICAL REVIEW D., v.98, p. 076009

Abstract

We derive the equations of motion of relativistic, nonresistive, second-order dissipative magnetohydrodynamics from the Boltzmann equation using the method of moments. We assume the fluid to be composed of a single type of point-like particles with vanishing dipole moment or spin, so that the fluid has vanishing magnetization and polarization. In a first approximation, we assume the fluid to be nonresistive, which allows to express the electric field in terms of the magnetic field. We derive equations of motion for the irreducible moments of the deviation of the single-particle distribution function from local thermodynamical equilibrium. We analyze the Navier-Stokes limit of these equations, reproducing previous results for the structure of the first-order transport coefficients. Finally, we truncate the system of equations for the irreducible moments using the 14-moment approximation, deriving the equations of motion of relativistic, nonresistive, second-order dissipative magnetohydrodynamics. We also give expressions for the new transport coefficients appearing due to the coupling of the magnetic field to the dissipative quantities.

10.1103/PhysRevD.98.076009