arXiv subjects

Tonatiuh Matos

Publications and source records attributed to Tonatiuh Matos.

At least 91 records · Page 5Linked to original sources

arXiv2011

Braneworld Model of Dark Matter: Structure Formation

Following a previous work [Gen. Relativ. Gravit. 43 (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.

gr-qc↗

arXiv2011

Cosmic Bose dark matter

Cold and hot dark matter (CDM, HDM) imprint distinctive effects on the cosmological observables, naturally, they are often thought to be made of different kinds of particles. However, we point out that CDM and HDM could share a common origin, a Bose-Einstein condensate emerging with two components. In this framework, the mass and temperature constraints on HDM contain fundamental information of CDM, but also, the critical temperature of condensation shall be larger than the HDM temperature. We discuss two scenarios: a gas made of bosons and a gas made of boson-antiboson pairs. We use some cosmological data surveys to test the idea and constrain the bosonic DM parameters, including a forecast for the Planck mission. We find that the bosonic DM picture is consistent with data in the first scenario, although, the second one might be increasingly interesting for future data surveys.

astro-ph.CO↗

arXiv2011

Structure Formation with Scalar Field Dark Matter: The Fluid Approach

The properties of nearby galaxies that can be observed in great detail suggest that a better theory rather than cold dark matter (CDM) would describe in a better way a mechanism by which matter is more rapidly gathered into large-scale structure such as galaxies and groups of galaxies. In this work we develop and simulate a hydrodynamical approach for the early formation of structure in the Universe, this approach is based on the fact that dark matter is on the form of some kind of scalar field (SF) with a potential that goes as $μ^2Φ^2/2+λΦ^4/4$, we expect that the fluctuations coming from the SF will give us some information about the matter distribution we observe these days.

gr-qc↗

arXiv2010

Ultra light bosonic dark matter and cosmic microwave background

In this paper, we consider the hypothesis in which a species of ultra light bosonic dark matter (ULBDM) with mass $m_{B}\sim 10^{-22}$ eV could be the dominant dark matter (DM) in the Universe. As a first approach we work in the context of kinetic theory, where ULBDM is described by the phase space distribution function whose dynamics is dictated by the Boltzmann-Einstein equations. We investigate the effects that this kind of dark matter imprints in the acoustic peaks of the cosmic microwave background. We find that the effect of the Bose-Einstein statistics is small, albeit perceptible, and is equivalent to an increase of non-relativistic matter. It is stressed that in this approach, the mass-to-temperature ratio necessary for ULBDM to be a plausible DM candidate is about five orders of magnitude. We show that reionization is also necessary and we address a range of consistent values for this model. We find that the temperature of ULBDM is below the critical value, impliying that Bose-Einstein condensation is inherent to the ULBDM paradigm.

astro-ph.CO↗

arXiv2010

Testing DM halos using rotation curves and lensing: A warning on the determination of the halo mass

There are two observations of galaxies that can offer some insight into the nature of the dark matter (DM), namely the rotation curves and the gravitational lensing. While the first one can be studied using the Newtonian limit, the second one is completely relativistic. Each one separately can not determine the nature of DM, but both together give us key information about this open problem. In this work we use a static and spherically symmetric metric to model the DM halo in a galaxy or in a galaxy cluster. The metric contains two free functions, one associated with the distribution of mass and the other one with the gravitational potential. We use galactic, typical rotation curves to univocally determine the kinematics of the halos. We compute separately the mass functions for a perfect fluid and a scalar field, and demonstrate that both models can be fitted to the observations, though with different masses. We then employ lensing to discriminate between these models. This procedure represents a test of models using two measurements: rotation curves and lensing.

astro-ph.GA↗

arXiv2010

The Universe Dynamics from Topological Considerations

We explore the possibility that the dynamics of the universe can be reproduced choosing appropriately the initial global topology of the Universe. In this work we start with two concentric spherical three-dimensional branes S^3, with radius a_1<a_2 immersed in a five-dimensional space-time. The novel feature of this model is that in the interior brane there exist only spin-zero fundamental fields (scalar fields), while in the exterior one there exist only spin-one fundamental interactions. As usual, the bulk of the universe is dominated by gravitational interactions. In this model, like in the Ekpyrotic one, the Big Bang is consequence of the collision of the branes and causes the existence of the particles predicted by the standard model in the exterior brane (our universe). The scalar fields on the interior brane interact with the spin-one fields on the exterior one only through gravitation, they induce the effect of Scalar Field Dark Matter with an ultra-light mass on the exterior one. We discuss two different regimes where the energy density and the brane tension are compared, with the aim to obtain the observed dynamics of the universe after the collision of the branes.

gr-qc↗

arXiv2010

Scalar Field Dark Matter Quantum Effects as Dark Energy

Using very simple arguments we show that the quantum effects of an ultra-light particle as the Scalar Field Dark Matter $m_{SFDM}\sim10^{-22}$eV cannot be neglected at classical scales. We show that the effective density of this effect is constant in the space and for such a mass, it is of the order of magnitude of the critical mass of the universe. Thus, we can interpret the effective density of this quantum effect as the cosmological constant.

astro-ph.CO↗

arXiv2009

Dynamics of a Self-interacting Scalar Field Trapped in the Braneworld for a Wide Variety of Self-interaction Potentials

We apply the dynamical systems tools to study the linear dynamics of a self-interacting scalar field trapped in the braneworld, for a wide variety of self-interaction potentials. We focus on Randall-Sundrum (RS) and on Dvali-Gabadadze-Porrati (DGP) braneworld models exclusively. These models are complementary to each other: while the RS brane produces ultra-violet (UV) corrections to general relativity, the DGP braneworld modifies Einstein's theory at large scales, i. e., produces infra-red (IR) modifications of general relativity. This study of the asymptotic properties of both braneworld models, shows -- in the phase space -- the way the dynamics of a scalar field trapped in the brane departs from standard general relativity behaviour.

gr-qc↗

arXiv2009

Dynamics of Scalar Field Dark Matter With a Cosh-like Potential

The dynamics of a cosmological model fueled by scalar field dark matter with a cosh-like potential plus a cosmological constant is investigated in detail. It is revealed that the late-time attractor is always the de Sitter solution, and that, depending on the values of the free parameters, the oscillating solution of the scalar field -- modeling cold dark matter -- mediates between some early stage (say, the radiation-dominated solution) and the accelerating de Sitter attractor.

astro-ph.CO↗

arXiv2009

Class of Einstein-Maxwell-Dilaton-Axion Space-Times

We use the harmonic maps ansatz to find exact solutions of the Einstein-Maxwell-Dilaton-Axion (EMDA) equations. The solutions are harmonic maps invariant to the symplectic real group in four dimensions $Sp(4,\Rreal)\sim O(5)$. We find solutions of the EMDA field equations for the one and two dimensional subspaces of the symplectic group. Specially, for illustration of the method, we find space-times that generalise the Schwarzschild solution with dilaton, axion and electromagnetic fields.

gr-qc↗

arXiv2009

Class of Einstein-Maxwell Phantom Fields: Rotating and Magnetised Wormholes

Using a new ansatz for solving the Einstein equations with a scalar field with the sign of the kinetic term inverted, I find a series of formulae to derive axial symmetric stationary exact solutions of the Phantom scalar field in general relativity. We focus on the solutions which represent wormholes. The procedure presented in this work allows to derive new exact solutions up to very simple integrations. Among other results, I find exact rotating solutions containing magnetic monopoles, dipoles, etc., coupled to Phantom scalar and to gravitational multipole fields.

gr-qc↗

arXiv2008

Self accelerating solutions in a DGP brane with a scalar field trapped on it: the dynamical systems perspective

We apply the dynamical systems tools to study the linear dynamics of a self-interacting scalar field trapped on a DGP brane. The simplest kinds of self-interaction potentials are investigated: a) constant potential, and b) exponential potential. It is shown that the dynamics of DGP models can be very rich and complex. One of the most interesting results of this study shows that dynamical screening of the scalar field self-interaction potential, occuring within the Minkowski cosmological phase of the DGP model and mimetizing 4D phantom behaviour, is an attractor solution for a constant self-interaction potential but not for the exponential one. In the latter case gravitational screening is not even a critical point of the corresponding autonomous system of ordinary differential equations.

gr-qc↗

arXiv2008

Self-interacting Scalar Field Trapped in a Randall-Sundrum Braneworld: The Dynamical Systems Perspective

We apply the dynamical systems tools to study the linear dynamics of a self-interacting scalar field trapped on a Randall-Sundrum brane. The simplest kinds of self-interaction potentials are investigated: a) constant potential, and b) exponential potential. It is shown that the dynamics of the Randall-Sundrum model significantly differs from the standard four-dimensional behavior at early times: in all cases of interest the (singular) empty universe is the past attractor for every trajectory in phase space, meanwhile the kinetic energy-dominated solution is always a saddle critical point. The late-time dynamics is not affected by the brane effects.

gr-qc↗

arXiv2008

Thick DGP braneworlds

We study Dvali-Gabadadze-Porrati braneworlds with finite thickness. In respect to standard (thin) DGP Friedmann equation, finite thickness of the brane causes a subtle modification of the cosmological equations that can lead to significant physical consequences. The resulting cosmology is governed by two length scales which are associated with the brane thickness and with the crossover length respectively. In this setup both early inflation and late-time acceleration of the expansion are a consequence of the 5D geometry. At early times, as well as at late times, 5D effects become dominant (gravity leaks into the extra dimension), while, at intermediate times, gravity is effectively 4D due to non-trivial physics occuring in standard (thin) DGP scenarios.

gr-qc↗

arXiv2008

$ϕ^2$ as Dark Matter

In this paper we consider $ϕ^2$ scalar field potential as a candidate to dark matter. If it is an ultralight boson particle, it condensates like a Bose-Einstein system at very early times and forms the basic structure of the Universe. Real scalar fields collapse in equilibrium configurations that oscillate in space-time (oscillatons).The cosmological behavior of the field equations are solved using the dynamical system formalism. We use the current cosmological parameters as constraints for the present value of the scalar field. We reproduce the cosmological predictions of the standard $Λ$CDM model with this model. Therefore, scalar field dark matter seems to be a good alternative to cold dark matter nature.

astro-ph↗

arXiv2008

Unification of cosmological scalar fields

We present a model where early inflation and late accelerating expansion of the Universe are driven by the real and imaginary parts of a single complex scalar field, which we identified as inflaton and phantom field, respectively. This inflaton-phantom unification is protected by an internal SO(1,1) symmetry, with the two cosmological scalars appearing as the degrees of freedom of a sole fundamental representation. The unification symmetry allows to build successful potentials. We observe that our theory provides a matter-phantom duality, which transforms scalar matter cosmological solutions into phantom solutions and vice versa. We also suggest that a complete unification of all scalar fields of cosmological interest is yet possible under a similar footing.

astro-ph↗

arXiv2008

An Alternative Interpretation for the Moduli Fields of the Cosmology Associated to Type IIB Supergravity with Fluxes

We start with a particular cosmological model derived from type IIB supergravity theory with fluxes, where usually the dilaton is interpreted as a Quintessence field. Instead of that, in this letter we interpret the dilaton as the dark matter of the universe. With this alternative interpretation we find that in this supergravity model gives a similar evolution and structure formation of the universe compared with the $Λ$CDM model in the linear regime of fluctuations of the structure formation. Some free parameters of the theory are fixed using the present cosmological observations. In the non-linear regimen there are some differences between the type IIB supergravity theory with the traditional CDM paradigm. The supergravity theory predicts the formation of galaxies earlier than the CDM and there is no density cusp in the center of galaxies. These differences can distinguish both models and can give a distinctive feature to the phenomenology of the cosmology coming from superstring theory with fluxes.

hep-th↗

arXiv2008

Flat Central Density Profiles from Scalar Field Dark Matter Halo

The scalar field endowed with a cosh scalar field potential, behaves exactly in the same way as cold dark matter (CDM) in the region where the scalar field oscillates around its minimum. Also, in the linear regime, the scalar field dark matter (SFDM) hypothesis predicts the same structure formation as the cold dark matter one. This means that CDM and SFDM are equivalent from the cosmological point of view. The free parameters of the SFDM model can be fixed using cosmological observations. In a previous work, we showed by solving the Einstein Klein Gordon equations, that if we use such parameters, the scalar field collapses forming stable objects with a mass around $10^{12}M_{\odot}$. In the present work we use analytical solutions of the flat and weak field limit of the Einstein- Klein-Gordon equations. With this solutions we show that its scalar field density profile corresponds to a halo with an almost flat central density and that this halo coincides with the CDM model in a large outer region. Such a result could solve the problem of the cusp DM halo in galaxies without extra hypothesis, adding to the viability of the SFDM model. Thus, the SFDM model can be seen as an alternative model to the CDM one, with a self interacting WIMP.

astro-ph↗