arXiv subjects

Luca Bonanno

Publications and source records attributed to Luca Bonanno.

7 recordsLinked to original sources

arXiv2011

Holographic dark matter and dark energy with second order invariants

One of the main goals of modern cosmology remains to summon up a self consistent policy, able to explain, in the framework of the Einstein's theory, the cosmic speed up and the presence of Dark Matter in the Universe. Accordingly to the Holographic principle, which postulates the existence of a minimal size of a physical region, we argue, in this paper, that if this size exists for the Universe and it is accrued from the independent geometrical second order invariants, it would be possible to ensure a surprising source for Dark Matter and a viable candidate for explaining the late acceleration of the Universe. Along the work, we develop low redshift tests, such as Supernovae Ia and kinematical analysis complied by the use of Cosmography and we compare the outcomes with higher redshift tests, such as CMB peak and anisotropy of the cosmic power spectrum. All the results indicate that the models presented here can be interpreted as unified models that are capable to describe both the dark matter and the dark energy.

gr-qc↗

arXiv2011

Composition and stability of hybrid stars with hyperons and quark color-superconductivity

The recent measurement of a $1.97\pm 0.04$ solar-mass pulsar places a stringent lower bound on the maximum mass of compact stars and therefore challenges the existence of any agents that soften the equation of state of ultra-dense matter. We investigate whether hyperons and/or quark matter can be accommodated in massive compact stars by constructing an equation of state based on a combination of phenomenological relativistic hyper-nuclear density functional and an effective model of quantum chromodynamics (the Nambu-Jona-Lasinio model). Stable configurations are obtained with $M \ge 1.97 M_{\sun}$ featuring hyper-nuclear and quark matter in color superconducting state if the equation of state of nuclear matter is stiff above the saturation density, the transition to quark matter takes place at a few times the nuclear saturation density, and the repulsive vector interactions in quark matter are substantial.

astro-ph.SR↗

arXiv2011

Does nuclear matter bind at large $N_c$?

The existence of nuclear matter at large $N_{c}$ is investigated in the framework of effective hadronic models of the Walecka type. This issue is strongly related to the nucleon-nucleon attraction in the scalar channel, and thus to the nature of the light scalar mesons. Different scenarios for the light scalar sector correspond to different large $N_{c}$ scaling properties of the parameters of the hadronic models. In all realistic phenomenological scenarios for the light scalar field(s) responsible for the attraction in the scalar channel it is found that nuclear matter does not bind in the large $N_{c}$ world. We thus conclude that $N_{c}=3$ is in this respect special: 3 is fortunately not large at all and allows for nuclear matter, while large $N_{c}$ would not.

hep-ph↗

arXiv2011

Second order invariants and holography

Motivated by recent works on the role of the Holographic principle in cosmology, we relate a class of second order Ricci invariants to the IR cutoff characterizing the holographic Dark Energy density. The choice of second order invariants provides an invariant way to account the problem of causality for the correct cosmological cutoff, since the presence of event horizons is not an \emph{a priori} assumption. We find that these models work fairly well, by fitting the observational data, through a combined cosmological test with the use of SNeIa, BAO and CMB. This class of models is also able to overcome the fine-tuning and coincidence problems. Finally, to make a comparison with other recent models, we adopt the statistical tests AIC and BIC.

hep-th↗

arXiv2009

A chiral lagrangian with broken scale: a Fortran code with the thermal contributions of the dilaton field

The Chiral Dilaton Model is a chiral lagrangian in which the breaking of scale invariance is regulated by the expectation value of a scalar field, called dilaton. Here we provide a Fortran code \cite{epaps,ind}, as a tool to make calculations within the Chiral Dilaton Model at finite density and temperature. The calculations are improved respect to previous works [arXiv:0704.3707,arXiv:0805.4188] by including the thermal contributions of the dilaton field.

nucl-th↗

arXiv2009

A chiral lagrangian with Broken Scale: testing the restoration of symmetries in astrophysics and in the laboratory

We study matter at high density and temperature using a chiral lagrangian in which the breaking of scale invariance is regulated by the value of a scalar field, called dilaton \cite{Heide:1993yz,Carter:1995zi,Carter:1996rf,Carter:1997fn}. We provide a phase diagram describing the restoration of chiral and scale symmetries. We show that chiral symmetry is restored at large temperatures, but at low temperatures it remains broken at all densities. We also show that scale invariance is more easily restored at low rather than large baryon densities. The masses of vector mesons scale with the value of the dilaton and their values initially slightly decrease with the density but then they increase again for densities larger than $\sim 3 ρ_0$. The pion mass increases continuously with the density and at $ρ_0$ and T=0 its value is $\sim$ 30 MeV larger than in the vacuum. We show that the model is compatible with the bounds stemming from astrophysics, as e.g. the one associated with the maximum mass of a neutron star. The most striking feature of the model is a very significant softening at large densities, which manifests also as a strong reduction of the adiabatic index. While the softening has probably no consequence for Supernova explosion via the direct mechanism, it could modify the signal in gravitational waves associated with the merging of two neutron stars.

nucl-th↗

arXiv2007

Softening of the equation of state of matter at large densities and temperatures: chiral symmetry restoration vs. quark deconfinement

We discuss two models for describing the behavior of matter at large densities and intermediate temperatures. In both models a softening of the equation of state takes place due to the appearance of new degrees of freedom. The first is a hadronic model in which the softening is due to chiral symmetry restoration. In the second model the softening is associated with the formation of clusters of quarks in the mixed phase. We show that both models allow a significant softening but, in the first case the bulk modulus is mainly dependent on the density, while in the mixed phase model it also strongly depends on the temperature. We also show that the bulk modulus is not vanishing in the mixed phase due to the presence of two conserved charges, the baryon and the isospin one. Only in a small region of densities and temperatures the incompressibility becomes extremely small. Finally we compare our results with recent analysis of heavy ion collisions at intermediate energies.

hep-ph↗