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Ramon Herrera

Publications and source records attributed to Ramon Herrera.

At least 55 records · Page 3Linked to original sources
arXiv2013

General dissipative coefficient in warm intermediate and logamediate inflation

We study a general form for the dissipative coefficient $Γ(T,ϕ)=C_ϕ\,T^{m}/ϕ^{m-1}$ in the context of warm intermediate and logamediate inflationary universe models. We analyze these models in the weak and strong dissipative regimes. In the slow-roll approximation, we describe in great detail the characteristics of these models. In both regimes, we use recent data from the WMAP nine-year data and Planck data to constrain the parameters appearing in our models.

gr-qc↗
arXiv2013

Intermediate inflation on the brane and warped DGP models

Brane and warped Dvali-Gabadadze-Porrati inflationary universe models in the context of intermediate inflation are studied. In both models we consider that the energy density is a standard scalar field and we discuss the evolution of the universe during the slow-roll inflation. Also, we describe the conditions for these models. The corresponding Wilkinson Microwave Anisotropy Probe seven year data are utilized to fix some parameters in our models. Our results are compared to those found in General Relativity.

gr-qc↗
arXiv2013

Intermediate-Generalized Chaplygin Gas inflationary universe model

An intermediate inflationary universe model in the context of a generalized Chaplygin gas is considered. For the matter we consider two different energy densities; a standard scalar field and a tachyon field, respectively. In general, we discuss the conditions of an inflationary epoch for these models. We also, use recent astronomical observations from Wilkinson Microwave Anisotropy Probe seven year data for constraining the parameters appearing in our models.

astro-ph.CO↗
arXiv2012

Three thermodynamically-based parametrizations of the deceleration parameter

We propose, and constrain with the latest observational data, three model-independent parametrizations of the cosmic deceleration parameter $q(z)$. They are well behaved and stay finite at all redshifts. We construct them by fixing the value of $q$ at high redshift, $q(z \gg 1) = 1/2$ (as demanded by cosmic structure formation), and at the far future, $q(z = -1) = -1$, and smoothly interpolating $q(z)$ between them. The fixed point at $z = -1$ is not arbitrarily chosen; it readily follows from the second law of thermodynamics. This fairly reduces the ample latitude in parameterizing $q(z)$.

gr-qc↗
arXiv2012

Warm-Logamediate inflationary universe model

Warm inflationary universe models in the context of logamediate expansion are studied. General conditions required for these models to be realizable and discussed. This study is done in the weak and strong dissipative regimes. The parameters of our models are constrained from the observational data.

gr-qc↗
arXiv2011

The generalized second law in the emergent universe

This paper studies whether the generalized second law of thermodynamics is fulfilled in the transition from a generic initial Einstein static phase to the inflationary phase, with constant Hubble rate, and from the end of the latter to the conventional era of thermal radiation dominated expansion. As it turns out, the said law is satisfied provided the radiation component does not largely contribute to the total energy of the static phase.

gr-qc↗
arXiv2011

Warm-Intermediate inflationary universe model in braneworld cosmologies

Warm-intermediate inflationary universe models in the context of braneworld cosmologies, are studied. This study is done in the weak and strong dissipative regimes. We find that, the scalar potentials and dissipation coefficients in terms of the scalar field, evolves as type-power-law and powers of logarithms, respectively. General conditions required for these models to be realizable are derived and discussed. We also study the scalar and tensor perturbations for each regime. We use recent astronomical observations to constraint the parameters appearing in the braneworld models.

gr-qc↗
arXiv2011

Emergent Universe from Scale Invariant Two Measures Theory

The dilaton-gravity sector of a linear in the scalar curvature, scale invariant Two Measures Field Theory (TMT), is explored in detail in the context of closed FRW cosmology and shown to allow stable emerging universe solutions. The model possesses scale invariance which is spontaneously broken due to the intrinsic features of the TMT dynamics. We study the transition from the emerging phase to inflation, and then to a zero cosmological constant phase. We also study the spectrum of density perturbations and the constraints that impose on the parameters of the theory.

astro-ph.CO↗
arXiv2011

$H(z)$ diagnostics on the nature of dark energy

The two dominant components of the cosmic budget today, pressureles matter and dark energy, may or may not be interacting with each other. Currently, both possibilities appear compatible with observational data. We propose several criteria based on the history of the Hubble factor that can help discern whether they are interacting and whether dark energy is phantom or quintessence in nature.

astro-ph.CO↗
arXiv2010

The effect of curvature in thawing models

We study the evolution of spatial curvature for thawing class of dark energy models. We examine the evolution of the equation of state parameter, $w_ϕ$, as a function of the scale factor $a$, for the case in which the scalar field $ϕ$ evolve in nearly flat scalar potential. We show that all such models provide the corresponding approximate analytical expressions for $w_ϕ(Ω_ϕ,Ω_k)$ and $w_ϕ(a)$. We present observational constraints on these models.

astro-ph.CO↗
arXiv2010

Emerging Universe from Scale Invariance

We consider a scale invariant model which includes a $R^{2}$ term in action and show that a stable "emerging universe" scenario is possible. The model belongs to the general class of theories, where an integration measure independent of the metric is introduced. To implement scale invariance (S.I.), a dilaton field is introduced. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of S.I. After S.S.B. of S.I. in the model with the $R^{2}$ term (and first order formalism applied), it is found that a non trivial potential for the dilaton is generated. The dynamics of the scalar field becomes non linear and these non linearities are instrumental in the stability of some of the emerging universe solutions, which exists for a parameter range of the theory.

astro-ph.CO↗
arXiv2010

Warm inflationary model in loop quantum cosmology

A warm inflationary universe model in loop quantum cosmology is studied. In general we discuss the condition of inflation in this framework. By using a chaotic potential, $V(ϕ)\propto ϕ^2$, we develop a model where the dissipation coefficient $Γ=Γ_0=$ constant. We use recent astronomical observations for constraining the parameters appearing in our model.

astro-ph.CO↗
arXiv2010

Intermediate inflation in Gauss-Bonnet braneworld

In this article we study an intermediate inflationary universe models using the Gauss-Bonnet brane. General conditions required for these models to be realizable are derived and discussed. We use recent astronomical observations to constraint the parameters appearing in the model.

astro-ph.CO↗
arXiv2009

Curvaton reheating in logamediate inflationary model

In a logamediate inflationary universe model we introduce the curvaton field in order to bring this inflationary model to an end. In this approach we determine the reheating temperature. We also outline some interesting constraints on the parameters that describe our models. Thus, we give the parameter space in this scenario.

astro-ph.CO↗
arXiv2009

Closed inflationary universe in Patch Cosmology

In this article we study closed inflationary universe models using the Gauss-Bonnet Brane. We determine and characterize the existence of a universe with $Ω> 1$, with an appropriate period of inflation. We have found that this model is less restrictive in comparison with the standard approach where a scalar field is considered. We use recent astronomical observations to constrain the parameters appearing in the model.

gr-qc↗
arXiv2009

On the Stability of Jordan-Brans-Dicke Static Universe

In this work we study the stability of the Jordan-Brans-Dicke (JBD) static universe. This is motivated by the possibility that the universe might have started out in an asymptotically JBD static state, in the context of the so called emergent universe scenario. We extent our previous results on stability of JBD static universe by considering spatially homogeneous Bianchi type IX anisotropic perturbation modes and by including more general perfect fluids. Contrary to general relativity, we have found that the JBD static universe, dominated by a standard perfect fluid, could be stable against isotropic and anisotropic perturbations. The implications of these results for the initial state of the universe and its pre-inflationary evolution are discussed.

gr-qc↗
arXiv2009

Tachyon Field in Intermediate Inflation

The tachyonic inflationary universe model in the context of intermediate inflation is studied. General conditions for this model to be realizable are discussed. In the slow-roll approximation, we describe in great details the characteristics of this model.

astro-ph.CO↗