Martín G. Richarte

Interacting dark matter and modified holographic Ricci dark energy induce a relaxed Chaplygin gas

We investigate a model of interacting dark matter and dark energy given by a modified holographic Ricci’s cutoff in a spatially flat Friedmann-Robertson-Walker (FRW) space-time. We consider a non linear interaction consisting of a significant rational function of the total energy density and its first derivative homogeneous of degree one and show that the effective one-fluid obeys the equation of state of a relaxed Chaplygin gas. So that, the universe is dominated by pressureless dark matter at early times and undergoes an accelerated expansion in the far future driven by a strong negative pressure. We apply the � 2 -statistical method to the observational Hubble data for constraining the cosmological parameters and analyze the feasibility of the modified holographic Ricci’s cutoff. Finally, by using the new Om diagnostic method, we find that the effective model differs substantially from the �-CDM one, because it gets the accelerated expansion faster than the �-CDM model.

Interacting dark matter and modified holographic Ricci dark energy plus a noninteracting cosmic component

We investigate a spatially flat Friedmann-Robertson-Walker universe that has an interacting dark matter, a modified holographic Ricci dark energy (MHRDE), plus a third, decoupled component that behaves as a radiation term. We consider a nonlinear interaction in the dark component densities and their derivatives up to second order. We apply the

Thin-shell wormholes in Brans-Dicke gravity

\chi^{2}

Traversable wormholes in a string cloud

method to the observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era for both MHRDE and holographic Ricci dark energy models. The former is consistent with the bound

Black holes in Einstein–Gauss–Bonnet gravity with a string cloud background

\Omega_{x}(z\simeq 1100)<0.1

Enhanced Inflation in the Dirac-Born-Infeld framework

reported for the behavior of dark energy at early times while the latter does not fulfill it.

Cylindrical wormholes in DGP gravity

Abstract Spherically symmetric thin-shell wormholes are constructed within the framework of Brans–Dicke gravity. It is shown that, for appropriate values of the Brans–Dicke constant, these wormholes can be supported by matter satisfying the energy conditions.

Self-interacting holographic dark energy

We study spherically symmetric thin shell wormholes in a string cloud background in (3 + 1)-dimensional space–time. The amount of exotic matter required for the construction, the traversability and the stability of such wormholes under radial perturbations are analyzed as functions of the parameters of the model. In addition, in the appendices a nonperturbative approach to the dynamics and a possible extension of the analysis to a related model are briefly discussed.

Dark radiation and dark matter coupled to holographic Ricci dark energy

Abstract We obtain a black hole solution in the Einstein–Gauss–Bonnet theory for the string cloud model in a five-dimensional spacetime. We analyze the event horizons and naked singularities. Later, we compute the Hawking temperature T H , the specific heat C , the entropy S , and the Helmholtz free energy F of the black hole. The entropy was computed using the Wald formulation. In addition, the quantum correction to the Walds entropy is considered for the string cloud source. We mainly explore the thermodynamical global and local stability of the system with vanishing or non-vanishing cosmological constant. The global thermodynamic phase structure indicates that the Hawking–Page transition is achieved for this model. Further, we observe that there exist stable black holes with small radii and that these regions are enlarged when choosing small values of the string cloud density and of the Gauss–Bonnet parameter. Besides, the rate of evaporation for these black holes are studied, determining whether the evaporation time is finite or not. Then, we concentrate on the dynamical stability of the system, studying the effective potential for s-waves propagating on the string cloud background.

Interacting dark sector with variable vacuum energy

We consider the Einstein equations within the Dirac-Born-Infield (DBI) scenario for a spatially flat Friedmann-Robertson-Walker (FRW) spacetime without a cosmological constant. We derive the inflationary scenario by applying the symmetry transformations which preserve the form of the Friedmann and conservation equations. These form invariance transformations generate a symmetry group parametrized by the Lorentz factor {gamma}. We explicitly obtain an inflationary scenario by the cooperative effect of adding energy density into the Friedmann equation. For the case of a constant Lorentz factor, and under the slow roll assumption, we find the transformation rules for the scalar and tensor power spectra of perturbations as well as their ratio under the action of the form invariance symmetry group. Within this case and due to its relevance for the inflationary paradigm, we find the general solution of the dynamical equations for a DBI field driven by an exponential potential and show a broad set of inflationary solutions. The general solution can be split into three subsets and all these behave asymptotically as a power-law solution at early and at late times.