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Marcelo Chiapparini

Publications and source records attributed to Marcelo Chiapparini.

7 recordsLinked to original sources
arXiv2020

Thermodynamical and dynamical equilibrium of a self-gravitating uncharged thin shell

The dynamical stability of massive thin shells with a given equation of state (EOS) is here compared (both for the barotropic and non-barotropic case) with the results coming from thermodynamical stability. Our results show that the restrictions in the parameter space of equilibrium configurations of the shell following from thermodynamical stability are much more stringent that those obtained from dynamical stability. As a byproduct, we furnish evidence that the link between the maximum mass along a sequence of equilibrium configurations and the onset of dynamical stability is valid for EOS of the type $P=P(σ, R)$.

gr-qc↗
arXiv2018

An introductory study to white dwarfs

White dwarfs are compact objects that stand against gravitational collapse by their internal pressure of degenerate matter. In this work we aimed to perform an introductory study on these stars, using two equations of state (EOS): (I) an ideal Fermi gas and (II) the one by Baym Pethick and Sutherland (BPS). In addition, we analyzed these two equations of state in two scenarios, the Newtonian and the one from General Relativity, which allowed us to analyze the effects of curved space-time. We also studied a rotating white dwarf, finding a metric for this case. With these two cases, with rotation (J = cte) and static (J = 0) well determined, we introduced the concepts of instability by the turning point criterion and dynamic instability criterion. Finally, with the RNS program, we performed the numerical resolution with BPS equation of state in the rotating case in order to analyze the behavior of the turning point criterion in these two cases.

astro-ph.SR↗
arXiv2014

Gravitational wave generation from dynamical shape transition of protoneutron stars

We describe the dynamical behavior of newborn pulsars modeled as homogeneous rotating spheroids. The dynamical evolution is triggered by the escape of trapped neutrinos, provided the initial equilibrium configuration. It is shown that for a given set of values of the initial angular momentum a shape transition to a triaxial ellipsoid configuration occurs. Gravitational waves are then generated by the breaking of the axial symmetry, and some aspects of their observation are discussed. We found a narrow window for the initial values of the angular frequency and the eccentricity able to enable a dynamical shape transition, with the Kepler frequency of the rotating fluid determining the upper bound of the initial angular frequency and eccentricity. The loss of energy and angular momentum carried away by the gravitational wave is treated consistently with the solution of the equations of motion, which govern the dynamical evolution of the system. The transition in the shape of the core of the pulsar is weakly dependent on the time scale of the neutrino escape.

astro-ph.HE↗
arXiv2013

The $g_{J/ψD_s D_s}$ strong coupling constant from QCD Sum Rules

The coupling constant of the meson vertex $J/ψD_s D_s$ is calculated using the three point correlation function within the QCD Sum Rule formalism. We have considered alternately mesons $J/ψ$ and $D_s$ off-shell together with non-perturbative contributions up to the mixed quark-gluon condensates. When extrapolated, these two different form factors give the same coupling constant for the process $g_{J/ψD_s D_s} = 5.98^{+0.67}_{-0.58}$.

hep-ph↗
arXiv2013

Gravitational Wave Generation in Rotating Compact Stars

We present a simplified description of a rotating neutron star emitting gravitational waves. We describe the system by an uniformly rotating triaxial homogeneous ellipsoid to catch the main aspects of the evolution. We construct an effective Lagrangian model, in which the kinetic energy associated to the breath mode and rotation are explicitly determined. The rate of gravitational waves radiation is determined in the framework of the weak field limit approximation of Einstein equations. We then solve numerically the equations of motion for the nascent neutron star, incorporating the diffusion of neutrinos in the calculation.

astro-ph.SR↗
arXiv2012

A non-equilibrium picture of the chemical freeze-out in hadronic thermal models

Thermal models have proven to be an useful and simple tool used to make theoretical predictions and data analysis in relativistic and ultra-relativistic heavy ion collisions. A new version of these models is presented here, incorporating a non equilibrium feature to the description of the intermediate fireball state formed at the chemical freeze-out. Two different effective temperatures are attributed to the expanding fireball, regarding its baryonic and mesonic sectors. The proposal is not merely to include an additional degree of freedom to reach a better adjustment to the data, but to open a room in the model conception for considerations on the non-equilibrium scenario of the system evolution. A set of well consolidated data for particles production is used to validated the reformulated version of thermal models presented here. A rather good performance of the extended version was verified, both for the quality of particle ratio data fittings as well as for describing the asymptotic energy behavior of temperatures and baryochemical potential of the colliding nuclear system.

nucl-th↗