Altas Energias

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

M. Broilo, E. G. S. Luna, and M. J. Menon

Phys. Rev. D 98, 074006 – Published 5 October 2018

ABSTRACT

Recent data from LHC13 by the TOTEM Collaboration indicate an unexpected decrease in the value of the ρ parameter and a σtot value in agreement with the trend of previous measurements at 7 and 8 TeV. These data at 13 TeV are not simultaneously described by the predictions from Pomeron models selected by the COMPETE Collaboration but show agreement with the maximal Odderon dominance, as recently demonstrated by Martynov and Nicolescu. Here, we present a detailed analysis on the applicability of Pomeron dominance by means of a general class of forward scattering amplitude, consisting of even-under-crossing leading contributions associated with single, double, and triple poles in the complex angular momentum plane and subleading even and odd Regge contributions. The analytic connection between σtot and ρ is obtained by means of singly subtracted dispersion relations, and we carry out fits to pp and ¯pp data in the interval 5 GeV–13 TeV. The data set comprises all the accelerator data below 7 TeV, and we consider two independent ensembles by adding either only the TOTEM data or the TOTEM and ATLAS data at the LHC energy region. In the data reductions to each ensemble, the uncertainty regions are evaluated with both one and two standard deviations (∼68%and ∼95%  CL, respectively). Besides the general analytic model, we investigate four particular cases of interest, three of them typical of outstanding models in the literature. We conclude that, within the experimental and theoretical uncertainties and both ensembles, the general model and three particular cases are not able to describe the σtot and ρ data at 13 TeV simultaneously. However, if the discrepancies between the TOTEM and ATLAS data are not resolved, one Pomeron model, associated with double and triple poles and with only 7 free parameters, seems not to be excluded by the complete set of experimental information presently available.

DOI:10.1103/PhysRevD.98.074006

H.Medeiros, D.Lazzaro, T.Kodama

Planetary and Space Science, volume 160

Abstract

The distribution of the rotational frequencies of asteroids is believed to carry important information on their formation and the subsequent evolutionary processes (Burns, 1975). In particular, it is commonly considered that during their formation stage the larger asteroids in the Main Belt have attained a statistical equilibrium (canonical ensemble) in the 3-dimensional isotropic velocity vector space. Subsequently, especially the smaller objects, suffered from various dynamical processes, such as collisions, fragmentation and YORP effect, for example, which modified their spin velocity and direction. In this work we re-examine the spin distribution of asteroids using more recent data and focusing on its statistical aspects, in particular, the dimensionality of the phase space. We find that the presently observed spin distribution of asteroids of any diameter bin is clearly consistent with a 2-dimensional phase space, or even less for the smaller objects. This is true also for those objects with diameter larger than 50 km, whose distribution is usually believed to be consistent with isotropic 3-dimensional Maxwellian. The present result casts open questions on the origin of the asteroids spin.

10.1016/j.pss.2018.04.002

G. S. Denicol, C. Gale, S. Jeon, A. Monnai, B. Schenke, and C.Shen

Phys. Rev. C 98, 034916

Abstract

A hybrid (hydrodynamics + hadronic transport) theoretical framework is assembled to model the bulk dynamics of relativistic heavy-ion collisions at energies accessible in the beam energy scan program at the Relativistic Heavy-Ion Collider and the NA61/SHINE experiment at CERN. The system’s energy-momentum tensor and net-baryon current are evolved according to relativistic hydrodynamics with finite shear viscosity and nonzero net-baryon diffusion. Our hydrodynamic description is matched to a hadronic transport model in the dilute region. With this fully integrated theoretical framework, we present a pilot study of the hadronic chemistry, particle spectra, and anisotropic flow. Phenomenological effects of a nonzero net-baryon current and its diffusion on hadronic observables are presented for the first time. The importance of the hadronic transport phase is also investigated.

10.1103/PhysRevC.98.034916