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