arXiv subjects

S. del Campo

Publications and source records attributed to S. del Campo.

16 recordsLinked to original sources

arXiv2017

Is the cosmological dark sector better modeled by a generalized Chaplygin gas or by a scalar field?

Both scalar fields and (generalized) Chaplygin gases have been widely used separately to characterize the dark sector of the Universe. Here we investigate the cosmological background dynamics for a mixture of both these components and quantify the fractional abundances that are admitted by observational data from supernovae of type Ia and from the evolution of the Hubble rate. Moreover, we study how the growth rate of (baryonic) matter perturbations is affected by the dark-sector perturbations.

astro-ph.CO↗

arXiv2014

Cosmology with Ricci-type dark energy

We consider the dynamics of a cosmological substratum of pressureless matter and holographic dark energy with a cutoff length proportional to the Ricci scale. Stability requirements for the matter perturbations are shown to single out a model with a fixed relation between the present matter fraction $Ω_{m0}$ and the present value $ω_{0}$ of the equation-of-state parameter of the dark energy. This model has the same number of free parameters as the $Λ$CDM model but it has no $Λ$CDM limit. We discuss the consistency between background observations and the mentioned stability-guaranteeing parameter combination.

astro-ph.CO↗

arXiv2006

Tachyon warm inflationary universe models

Warm inflationary universe models in a tachyon field theory are studied. General conditions required for these models to be realizable are derived and discussed. We describe scalar perturbations (in the longitudinal gauge) and tensor perturbations for these scenarios. We develop our models for a constant dissipation parameter $Γ$ in one case and one dependent on $ϕ$ in the other case. We have been successful in describing such of inflationary universe models. We use recent astronomical observations for constraining the parameters appearing in our model. Also, our results are compared with their analogous found in the cool inflationary case.

astro-ph↗

arXiv2005

Curvaton reheating in tachyonic inflationary models

The curvaton reheating in a tachyonic inflationary universe model with an exponential potential is studied. We have found that the energy density in the kinetic epoch, has a complicated dependencies of the scale factor. For different scenarios, the temperature of reheating is computed. These temperature result to be analogous to those obtained in the standard case of the curvaton scenario.

gr-qc↗

arXiv2004

Hamiltonian treatment of Collapsing Thin Shells in Lanczos-Lovelock's theories

The Hamiltonian treatment for the collapse of thin shells for a family of Lanczos-Lovelock theories is studied. This formalism allows us to carry out a concise analysis of these theories. It is found that the black holes solution can be created by collapsing a thin shell. Naked singularities cannot be formed by this mechanism. Among the different Lanczos-Lovelock's theories, the Chern-Simons' theory corresponds to an exceptional case, because naked singularities can emerge from the collapse of a thin shell. This kind of theory does not possess a gravitational self-interaction analogous to the Newtonian case.

hep-th↗

arXiv2004

On Magnetic solution to 2+1 Einstein--Maxwell gravity

The three--dimensional magnetic solution to the Einstein--Maxwell field equations have been considered by some authors. Several interpretations have been formulated for this magnetic spacetime. Up to now this solution has been considered as a two--parameter self--consistent field. We point out that the parameter related to the mass of this solution is just a pure gauge and can be rescaled to minus one. This implies that the magnetic metric has really a simple form and it is effectively one-parameter solution, which describes a distribution of a radial magnetic field in a 2+1 anti--de Sitter background space--time. We consider an alternative interpretation to the Dias--Lemos one for the magnetic field source.

hep-th↗

arXiv2003

A causal model for a closed universe

We study a closed model of a universe filled with viscous fluid and quintessence matter components. The dynamical equations imply that the universe might look like an accelerated flat Friedmann-Robertson-Walker (FRW) universe at low redshift. We consider here dissipative processes which obey a causal thermodynamics. Here, we account for the entropy production via causal dissipative inflation.

hep-th↗

arXiv2003

Relationship between (2+1) and 3+1)--Friedmann--Robertson--Walker cosmologies

In this work we establish the correspondence between solutions to the Friedmann--Robertson--Walker cosmologies for perfect fluid and scalar field sources, where both ones fulfill state equations of the form $p+ρ=γf(ρ)$, not necessarily linear ones. Such state equations are of common use in the case of matter--fluids, nevertheless, for a scalar field, they introduce relationships on the potential and kinetic scalar field energies which restrict the set of solutions. A theorem on this respect is demonstrated: From any given (3+1)--cosmological solution, obeying the quoted state equations, one can derive its (2+1)--cosmological counterpart or vice-versa. Some applications are given.

hep-th↗

arXiv2003

Supergravity with cosmological constant and the AdS group

It is shown that the supersymmetric extension of the Stelle-West formalism permits the construction of an action for $(3+1)$-dimensional N=1 supergravity with cosmological constant genuinely invariant under the $OSp(4/1).$ Since the action is invariant under the supersymmetric extension of the $AdS$ group, the supersymmetry algebra closes off shell without the need for auxiliary fields. The limit case $m\to 0$, i.e.$(3+1)$ -dimensional N=1 supergravity invariant under the Poincaré supergroup is also discussed.

hep-th↗

arXiv2002

Higher dimensional gravity invariant under the Poincare group

It is shown that the Stelle-West Grignani-Nardelli-formalism allows, both when odd dimensions and when even dimensions are considered, constructing actions for higher dimensional gravity invariant under local Lorentz rotations and under local Poincarè translations. It is also proved that such actions have the same coefficients as those obtained by Troncoso and Zanelli in ref. Class. Quantum Grav. 17 (2000) 4451.

gr-qc↗

arXiv2001

Supergravity and the Poincare group

An action for 3+1-dimensional supergravity genuinely invariant under the Poincare supergroup is proposed. The construction of the action is carried out considering a bosonic lagrangian invariant under both local Lorentz rotations and local Poincare translations as well as under diffeomorphism, and therefore the Poincare algebra closes off-shell. Since the lagrangian is invariant under the Poincare supergroup, the supersymmetry algebra closes off shell without the need of auxiliary fields.

gr-qc↗

arXiv2000

Viscous cosmologies in scalar-tensor theories for Kasner type metrics

In a viscous Bianchi type I metric of the Kasner form, it is well known that it is not possible to describe an anisotropic physical model of the universe, which satisfies the second law of thermodynamics and the dominant energy condition (DEC) in Einstein's theory of gravity. We examine this problem in scalar-tensor theories of gravity. In this theory we show that it is possible to describe the growth of entropy, keeping the thermodynamics and the dominant energy condition.

gr-qc↗

arXiv2000

(2+1)-Dimensional Black Hole with Coulomb-like Field

A (2+1)-static black hole solution with a nonlinear electric field is derived. The source to the Einstein equations is a nonlinear electrodynamics, satisfying the weak energy conditions, and it is such that the energy momentum tensor is traceless. The obtained solution is singular at the origin of coordinates. The derived electric field E(r) is given by $E(r)=q/r^2$, thus it has the Coulomb form of a point charge in the Minkowski spacetime. This solution describes charged (anti)--de Sitter spaces. An interesting asymptotically flat solution arises for $Λ=0$.

hep-th↗

arXiv2000

A critical-density closed Universe in Brans-Dicke theory

In a Brans-Dicke (BD) cosmological model, the energy density associated with some scalar field decreases as $\displaystyle a^{{-2}(\frac{ω_{o}+ {\frac12}%}{ω_{o}+1})} $ with the scale factor $a(t)$ of the Universe, giving a matter with an Equation of state $\displaystyle p=-{1/3}(\frac{2+ω_{o}}{1+ω_{o}}) ρ$. In this model, the Universe could be closed but still have a nonrelativistic-matter density corresponding to its critical value, $Ω_{o}=1$. Different cosmological expressions, such as, luminosity distance, angular diameter, number count and ratio of the redshift tickness-angular size, are determined in terms of the redshift for this model.

astro-ph↗

arXiv2000

Comment on "Viscous cosmology in the Kasner metric"

We show in this comment that in an anisotropic Bianchi type I model of the Kasner form, it is not possible to describe the growth of entropy, if we want to keep the thermodynamics together with the dominant energy conditions. This consequence disagrees with the results obtained by Brevik and Pettersen [Phys. Rev. D 56, 3322 (1997)].

gr-qc↗

arXiv2000

BTZ black hole from (3+1) gravity

We propose an approach for constructing spatial slices of (3+1) spacetimes with cosmological constant but without a matter content, which yields (2+1) vacuum with $Λ$ solutions. The reduction mechanism from (3+1) to (2+1) gravity is supported on a criterion in which the Weyl tensor components are required to vanish together with a dimensional reduction via an appropriate foliation. By using an adequate reduction mechanism from the Plebański-Carter[A] solution in (3+1) gravity, the (2+1) BTZ solution can be obtained.

gr-qc↗