Miguel A. Garcia-Aspeitia

Stellar models in brane worlds

We consider here a full study of stellar dynamics from the brane-world point of view in the case of constant density and of a polytropic fluid. We start our study cataloguing the minimal requirements to obtain a compact object with a Schwarzschild exterior, highlighting the low and high energy limit, the boundary conditions, and the appropriate behavior of Weyl contributions inside and outside of the star. Under the previous requirements we show an extensive study of stellar behavior, starting with stars of constant density and its extended cases with the presence of nonlocal contributions. Finally, we focus our attention to more realistic stars with a polytropic equation of state, especially in the case of white dwarfs, and study their static configurations numerically. One of the main results is that the inclusion of the Weyl functions from brane-world models allows the existence of more compact configurations than within general relativity.

Braneworld model of dark matter: structure formation

Following a previous work (García-Aspeitia in Gen Rel Grav 43:315–329, 2011), we further study the behavior of a real scalar field in a hidden brane in a configuration of two branes embedded in a five dimensional bulk. We find an expression for the equation of state for this scalar field in the visible brane in terms of the fields of the hidden one. Additionally, we investigated the perturbations produced by this scalar field in the visible brane with the aim to study their dynamical properties. Our results show that if the kinetic energy of the scalar field dominates during the early universe the perturbed scalar field could mimic the observed dynamics for the dark matter in the standard paradigm. Thus, the scalar field dark matter hypothesis in the context of braneworld theory could be an interesting alternative to the nature of dark matter in the Universe.

Probing dark energy with braneworld cosmology in the light of recent cosmological data

We investigate a brane model based on Randall–Sundrum scenarios with a generic dark energy component. The latter drives the accelerated expansion at late-times of the universe. In this scheme, extra terms are added into Einstein Field equations that are propagated to the Friedmann equations. To constrain the dark energy equation-of-state (EoS) and the brane tension we use observational data with different energy levels (Supernovae Type Ia, H(z), baryon acoustic oscillations, and cosmic microwave background radiation distance, and a joint analysis) in a background cosmology. Beside EoS being consistent with a cosmological constant at the 3σ confidence level for each dataset, the baryon acoustic oscillations probe favors an EoS consistent with a quintessence dark energy. Although we found different lower limit bounds on the brane tension for each dataset, being the most restricted for CMB, there is not enough evidence of modifications in the cosmological evolution of the universe by the existence of an extr...

Stellar Stability in the Braneworld

We study the properties of astrophysical systems in a Brane World scenario. In particular, the consequences of local terms that emerge from extra-dimensional gravity are explored through the modified Tolman-Oppenheimer-Volkoff equation. We compute the induced changes into mass, density and compactness of objects like white dwarfs and neutron stars. The main corrections in comparison with the known results of General Relativity are given in terms of the ratio ρ0/λ, where ρ0 is the central energy density of the stellar distribution and λ is the brane tension. As a result of these modifications, We obtain that the compactness of both, neutron stars and white dwarf decreases with respect to the value of General Relativity.

Cosmological solutions for a two-branes system in a vacuum bulk

We study the cosmology for a two branes model in a space-time of five dimensions where the extra coordinate is compactified on an orbifold. The hidden brane is filled with a real scalar field endowed with a quadratic potential that behaves as primordial dark matter field. This case is analyzed when the radion effects are negligible in comparison with the density energy; all possible solutions are found by means of a dynamical system approach.

Cosmic Braneworld and Ultralight Bosonic Dark Matter

In this paper we study a gas of ultra light bosons as a candidate for dark matter in a higher dimensional framework. We briefly introduce the formalism of brane theory (BN) and and relevant aspects of ultra light bosonic dark matter (ULBDM) with the aim to combine both ideas in a single model. In this model, we assume two branes (visible and hidden brane) inside of the bulk and study the behavior of ULBDM in the hidden brane for an observer in the visible one. We reformulate the Friedmann equations for our Universe and the Friedmann equation concerning to the hidden brane. Thus, we can stablish the mutual interaction between the branes through the Hubble parameter, which measures the rate of expansion of our Universe. Finllay, we discuss that the hypothesis of ULBDM in the context of the braneworld theory is an interesting idea regarding the nature of dark matter.

ULTRA LIGHT BOSONIC DARK MATTER AND CMB

We report the cosmological effects that a species of Ultra Light Bosonic Dark Matter imprints in the Acoustic Peaks of the CMB and some of its thermic features. We show that the effect of the Bose‐Einstein statistics is small albeit perceptible and is equivalent to an increase of non‐relativistic matter. It is noted the mass‐to‐temperature ratio necessary for being still a Dark Matter candidate. It is also needed a non‐zero optical depth of Reionization.

Cosmic Acceleration from Topological Considerations

In this work we explore the possibility that the dynamics of the universe can be reproduced choosing appropriately the global topology of the cosmos. We explore two concentric three‐dimensional spherical branes immersed in a five‐dimensional space‐time. Before to the collision, in the interior sphere there exist only a spin‐zero fundamental field (scalar field), in the exterior one there exist only fundamental spin‐one interactions and spin‐two interactions in the bulk. In this model, like in the Epkyrotic, the Big Bang is caused for the collision of the branes and generate all the fields predicted by the standard model in the exterior brane (our universe). In the interior brane the scalar field behaves like scalar field dark matter. We discuss two different regimens where the energy density and the brane tension are compared, with the aim to obtain the dynamics of the universe after and before the collision. Finally we discuse the perturbations in the modified Einstein equations of the scalar field dark ...