arXiv subjects

Alberto Rozas-Fernández

Publications and source records attributed to Alberto Rozas-Fernández.

9 recordsLinked to original sources

arXiv2026

Testing cosmological structure formation in a Unified Dark Matter-Energy model with fast transition

Unified Dark Matter-Energy models (UDM), a class of models where dark matter and dark energy exist as a single cosmological fluid, are an alternative approach to $Λ$CDM. In this work we focus on a model with a fast transition between dark matter-like and dark energy-like behaviour. The epoch and rapidity of the transition are the key features to enable the formation of structure in this model. We have studied its viability using CMB and Weak Lensing data with nested sampling inference methods. We found that the preferred region of the parameter space is the one with early and fast transition models, where it also lies the model's $Λ$CDM limit. Our study confirms that this UDM model is able to form cosmological structure compatible with the data used.

astro-ph.CO↗

arXiv2024

Kinetic coupled tachyon: A dynamical system analysis

We present and examine a kinetically coupled tachyon dark energy model, where a tachyon scalar field interacts with the matter sector. More specifically, we deduce this cosmological setting from a generalised interacting dark energy model that allows for the kinetic term of the scalar field to couple to the matter species a priori in the action. A thorough dynamical system analysis and its cosmological implications unveil the appearance of a scaling solution which is also an attractor of the system, thanks to a novel critical point, with a period of accelerated expansion thereafter. This new solution, not present in the uncoupled case, has the enticing consequence of alleviating the coincidence problem.

gr-qc↗

arXiv2017

Cosmological constraints on a unified dark matter-energy scalar field model with fast transition

We test the viability of a single fluid cosmological model containing a transition from a dark-matter-like regime to a dark-energy-like regime. The fluid is a k-essence scalar field with a well-defined Lagrangian. We constrain its model parameters with a combination of geometric probes and conclude that the evidence for this model is similar to the evidence for $Λ$CDM. In addition, we find a lower bound for the rapidity of the transition, implying that fast transitions are favored with respect to slow ones even at background level.

astro-ph.CO↗

arXiv2014

K-essential covariant holography

The holographic principle is applied to a flat Friedmann-Robertson-Walker space-time dominated by dark energy when this is due to the presence of a k-essence scalar field, both for dark energy and phantom scenarios. In this framework, a geometrical covariant approach permits the construction of holographic hypersurfaces. The resulting covariant preferred screens, both for phantom and non-phantom regions, are then compared with those obtained by using the holographic dark energy model with the future event horizon as the infrared cut-off. In the phantom case, one of the two obtained holographic screens is placed on the big rip hypersurface, both for the covariant holographic formalism and the holographic phantom model. It is also analysed whether this covariant formalism allows a mathematically consistent formulation of fundamental theories based on the existence of a S-matrix at infinite distances.

gr-qc↗

arXiv2014

Covariant holography of a tachyonic accelerating universe

We apply the holographic principle to a flat dark energy dominated Friedmann-Robertson-Walker spacetime filled with a tachyon scalar field with constant equation of state $w=p/ρ$, both for $w>-1$ and $w<-1$. By using a geometrical covariant procedure, which allows the construction of holographic hypersurfaces, we have obtained for each case the position of the preferred screen and have then compared these with those obtained by using the holographic dark energy model with the future event horizon as the infrared cutoff. In the phantom scenario, one of the two obtained holographic screens is placed on the big rip hypersurface, both for the covariant holographic formalism and the holographic phantom model. It is also analyzed whether the existence of these preferred screens allows a mathematically consistent formulation of fundamental theories based on the existence of a S matrix at infinite distances.

gr-qc↗

arXiv2014

Phenomenology of Unified Dark Matter models with fast transition

A fast transition between a standard matter-like era and a late $Λ$CDM-like epoch generated by a single Unified Dark Matter component can explain the observed acceleration of the Universe. UDM models with a fast transition should be clearly distinguishable from $Λ$CDM (and alternatives) through observations. Here we focus on a particularly simple model and analyse its viability by studying features of the background model and properties of the adiabatic UDM perturbations.

astro-ph.CO↗

arXiv2010

Interacting non-minimally coupled canonical, phantom and quintom models of holographic dark energy in non-flat universe

Motivated by our recent work \cite{set1}, we generalize this work to the interacting non-flat case. Therefore in this paper we deal with canonical, phantom and quintom models, with the various fields being non-minimally coupled to gravity, within the framework of interacting holographic dark energy. We employ the holographic model of interacting dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named $L$.

hep-th↗

arXiv2010

Interacting holographic tachyon model of dark energy

We propose a holographic tachyon model of dark energy with interaction between the components of the dark sector. The correspondence between the tachyon field and the holographic dark energy densities allows the reconstruction of the potential and the dynamics of the tachyon scalar field in a flat Friedmann-Robertson-Walker universe. We show that this model can describe the observed accelerated expansion of our universe with a parameter space given by the most recent observational results.

gr-qc↗

arXiv2008

Quantum cosmic models and thermodynamics

The current accelerating phase of the evolution of the universe is considered by constructing most economical cosmic models that use just general relativity and some dominating quantum effects associated with the probabilistic description of quantum physics. Two of such models are explicitly analyzed. They are based on the existence of a sub-quantum potential and correspond to a generalization of the spatially flat exponential model of de Sitter space. The thermodynamics of these two cosmic solutions is discussed, using the second principle as a guide to choose which among the two is more feasible. The paper also discusses the relativistic physics on which the models are based, their holographic description, some implications from the classical energy conditions, and an interpretation of dark energy in terms of the entangled energy of the universe.

gr-qc↗