arXiv subjects

Miguel A. Garcia-Aspeitia

Publications and source records attributed to Miguel A. Garcia-Aspeitia.

At least 19 recordsLinked to original sources

arXiv2021

Testing noncommutativity-like model as a galactic density profile

Noncommutative-like model (NC-like) is an interesting alternative inspired by string theory to understand and describe the velocity rotation curves of galaxies without the inclusion of dark matter particles. In a natural way, a Gaussian density profile emerges and is characterized by a parameter θ, called the NC-like parameter. Hence we aim to confront the NC-like model with a galaxy sample of the SPARC catalogue to constrain the model parameters and compare statistically with the Einasto density profile using the Akaike and Bayesian information criteria. According to our results, some galaxies prefer the NC-like over the Einasto model while others do not support NC-like.

astro-ph.GA↗

arXiv2019

Compact objects in unimodular gravity

Unimodular gravity provides a theoretical framework that allows for non-conservation of energy-momentum, with possible implications for the cosmological constant problem. It is then important to study the predictions of unimodular gravity in other gravitational regimes. In this work we study stellar dynamics under the assumption of non-conserved energy-momentum. We find that constant density objects can be as compact as Schwarzschild black holes. For polytropic objects, we find modifications due to the non-conservation of energy-momentum that lead to sizeable effects that could be constrained with observational data. Additionally, we revisit and clarify the Reissner-Nordström solution in unimodular gravity. We also study gravitational collapse and discuss possible implications for the growth of structure.

gr-qc↗

arXiv2019

Asymptotically Equivalent Functions and Ultrafilters applied to Noncommutative Quantum Cosmology

Using the semi-classical approximation to the Wheeler-DeWitt equation obtained via Arnowitt-Deser-Misner (ADM) formalism in the Friedmann-Lemaitre-Robertson-Walker (FLRW) model coupled to a scalar field and positive cosmological constant, and in the Kantowski-Sachs (KS) Universe, we introduced a deformation on the commutation relation for the minisuperspace variables and find an explicit semiclassical expression equivalent, in an adequate limit, to the solution with the aid of asymptotically equal functions and the theory of Ultrafilters, offering a suggestive alternative to sketch the behavior of the dynamical system involved without the need to solve it numerically.

gr-qc↗

arXiv2018

Cosmological constraints on alternative model to Chaplygin fluid revisited

In this work we explore an alternative phenomenological model to Chaplygin gas proposed by H. Hova et. al., consisting on a modification of a perfect fluid, to explain the dynamics of dark matter and dark energy at cosmological scales immerse in a flat or curved universe. Adopting properties similar to a Chaplygin gas, the proposed model is a mixture of dark matter and dark energy components parameterized by only one free parameter denoted as $μ$. We focus on contrasting this model with the most recent cosmological observations of Type Ia Supernovae and Hubble parameter measurements. Our joint analysis yields a value $μ= 0.843^{+0.014}_{-0.015}\,$ ($0.822^{+0.022}_{-0.024}$) for a flat (curved) universe. Furthermore, with these constraints we also estimate the deceleration parameter today $q_0=-0.67 \pm 0.02\,(-0.51\pm 0.07)$, the acceleration-deceleration transition redshift $z_t=0.57\pm 0.04\, (0.50 \pm 0.06)$, and the universe age $t_A = 13.108^{+0.270}_{-0.260}\,\times (12.314^{+0.590}_{-0.430})\,$Gyrs. We also report a best value of $Ω_k = 0.183^{+0.073}_{-0.079}$ consistent at $3σ$ with the one reported by Planck Collaboration. Our analysis confirm the results by Hova et al, this Chaplygin gas-like is a plausible alternative to explain the nature of the dark sector of the universe.

astro-ph.CO↗

arXiv2018

Cosmological analysis of a DGP stable model with $H(z)$ observations a revision

In this paper, we will present a Dvali-Gabadadze-Porrati stable model in order to perform an observational test using $H(z)$ data and radial BAO scale in the galaxy distribution. In this vein, we study the tension between constraints on the cosmological constant $Λ$ and the crossover scale $r_c$, which is associated with the DGP model. Our results show that observations do not favor the DGP stable model as a possible candidate to fit the observations of the late cosmic acceleration.

gr-qc↗

arXiv2018

Brane with variable tension as a possible solution to the problem of the late cosmic acceleration

Braneworld models have been proposed as a possible solution to the problem of the accelerated expansion of the Universe. The idea is to dispense the dark energy (DE) and drive the late-time cosmic acceleration with a five-dimensional geometry. Here, we investigate a brane model with variable brane tension as a function of redshift called chrono-brane. We propose the polynomial $λ=(1+z)^{n}$ function inspired in tracker-scalar-field potentials. To constrain the $n$ exponent we use the latest observational Hubble data from cosmic chronometers, Type Ia Supernovae from the full JLA sample, baryon acoustic oscillations and the posterior distance from the cosmic microwave background of Planck 2015 measurements. A joint analysis of these data estimates $n\simeq6.19$ which generates a DE-like or cosmological-constant-like term, in the Friedmann equation arising from the extra dimensions. This model is consistent with these data and can drive the Universe to an accelerated phase at late times.

gr-qc↗

arXiv2018

The Cardassian expansion revisited: constraints from updated Hubble parameter measurements and Type Ia Supernovae data

Motivated by an updated compilation of observational Hubble data (OHD) which consist of 51 points in the redshift range 0.07<z<2.36, we study an interesting model known as Cardassian which drives the late cosmic acceleration without a dark energy component. Our compilation contains 31 data points measured with the differential age method by Jimenez & Loeb, and 20 data points obtained from clustering of galaxies. We focus on two modified Friedmann equations: the original Cardassian (OC) expansion and the modified polytropic Cardassian (MPC). The dimensionless Hubble, E(z), and the deceleration parameter, q(z), are revisited in order to constraint the OC and MPC free parameters, first with the OHD and then contrasted with modern observations of SN Ia using the compressed and full joint-light-analysis samples. We also perform a joint analysis using the combination OHD plus compressed JLA. Our results show that the OC and MPC models are in agreement with the standard cosmology and naturally introduce a cosmological-constant-like extra term in the canonical Friedmann equation with the capability of accelerating the Universe without dark energy.

astro-ph.CO↗

arXiv2017

The presence of a Phantom field in a Randall-Sundrum scenario

The presence of phantom dark energy in brane world cosmology generates important new effects, causing a premature Big Rip singularity when we increase the presence of extra dimension and considerably competing with the other components of our Universe. The idea is based first, in only considering a field with the characteristic equation $ω<-1$ and after that, consider the explicit form of the scalar field with a potential with a maximum (with the aim of avoid a Big Rip singularity). In both cases we study the dynamic in a robust form through the dynamical analysis theory, detailing in parameters like the deceleration $q$ and the vector field associated to the dynamical system. Results are discussed with the purpose of deeming the cosmology with a phantom field as dark energy in a Randall-Sundrum scenario.

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arXiv2017

Multistate scalar field dark matter and its correlation with galactic properties

In this paper, we search for correlations between the intrinsic properties of galaxies and the Bose-Einstein condensate (BEC) under a scalar field dark matter (SFDM) at temperature of condensation greater than zero. According to this paradigm the BEC is distributed in several states. Based on the galactic rotation curves collected in SPARC dataset, we observe that SFDM parameters present a weak correlation with most of the galaxy properties, having only a correlation with those related to neutral hydrogen emissions. In addition, we found evidence to support of self-interaction between the different BEC states, proposing that in future studies must be considered crossed terms in SFDM equations. Finally, we find a null correlation with galaxy distances giving support to non-hierarchy of SFDM formation.

astro-ph.GA↗

arXiv2017

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 data sets, 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 extra dimension within observational uncertainties. Nevertheless, these new bounds are complementary to those obtained by other probes like table-top experiments, Big Bang Nucleosynthesis, and stellar dynamics. Our results show that a further test of the braneworld model with appropriate correction terms or a profound analysis with perturbations, may be needed to improve the constraints provided by the current data.

astro-ph.CO↗

arXiv2017

Energy density profile inspired by noncommutativity

An important consequence which comes from noncommutativity (NC) is undoubtedly the energy density characterized by a microscopic free parameter; indeed a Trans-Planckian parameter. However, its functional form is an interesting and useful equation which can be analyzed in astrophysical scenarios giving now astrophysical constraints. In this sense, this paper is devoted to explore the astrophysical consequences of an energy density with the same functional form of NC; mainly in stellar dynamics and rotation curves of galaxies. We start exploring toy models of stars with incompressible and polytropic fluids respectively, with the addition and coexistence with this new fluid. In both cases, we propose an appropriate constriction based on the difference between a correct and an anomalous behavior. As a complement, we explore the rotation curves of galaxies assuming that the halo is a fluid with the same characteristic of a NC equation, obtaining the range of values for the free parameter through the analysis of eighteen LSB galaxies. Our results are compared with traditional models studied in literature like Pseudoisothermal (PISO), Navarro-Frenk-White (NFW), Burkert and WaveDM dark matter models. Finally, we have computed the surface density, $ρ_i r_i$ for each dark matter model, where $i$ is for PISO, NFW, Burkert, WaveDM and NC macroscopic version. In the later case, following the results found using SPARC galaxy catalog, we have found a theoretical value of $116.97 M_\odot$ pc$^{-2}$ while the data analysis gives us a value of $144.21 M_\odot$ pc$^{-2}$.

gr-qc↗

arXiv2016

Cosmological constant problem in a scenario with compactifications (RS-I model)

In this letter, we apply the Randall-Sundrum (RS) model, a scenario based on compactifications, to control the UV divergence of the zero-point energy density equation for the vacuum fluctuations, which has been unsuccessfully addressed to the cosmological constant (CC) due to a heavy discrepancy between theory and observation. Historically, the problem of CC has been shelved in the RS point of view, having few or non literature on the subject. In this sense and as done with the hierarchy problem, we apply the RS model to solve this difference via extra dimensions; we also describe how brane effects could be the solution to this substantial difference. It should be noticed that this problem is studied assuming first Minkoswki type branes, and then followed by cosmologically more realistic FLRW type branes. We finally find some remarkably interesting consequences in the RS scenario: The CC problem can be solved via compactification of the extra dimension and the compactification radius turns out to be approximately twice the one used to solve the hierarchy problem in the $βπr$ factor by Randall and Sundrum, suggesting that this subtle difference in both problems could be caused by corrections that comes from quantum gravity effects. We also estimate the corresponding scale where, according to this results, we should begin to notice subtle deviations to the inverse square law of gravitation due to the presence of the extra dimension.

gr-qc↗

arXiv2016

Gravitational collapse in brane-worlds revisited

This paper is dedicated to revisit the modifications caused by branes in the collapse of a stellar structure under the Snyder-Oppenheimer scheme. Due to the homogeneity and isotropy of the model, we choose study the case of a closed geometry described by $k=1$, through the tool of dynamical systems. We revisit the different components of the star and its evolution during the stellar collapse, paying particular attention to the non-local effects and the quadratic terms of the energy momentum tensor that come from branes corrections. In the same vein we realize a phase portrait together with a stability analysis with the aim of obtain information about the attractors or saddle points of the dynamical system under different initial conditions in the density parameters, remarking the parameters that come from branes contributions.

gr-qc↗

arXiv2015

Constraining brane tension using rotation curves of galaxies

We present in this work a study of brane theory phenomenology focusing on the brane tension parameter, which is the main observable of the theory. We show the modifications steaming from the presence of branes in the rotation curves of spiral galaxies for three well known dark matter density profiles: the Pseudo isothermal, Navarro-Frenk-White and Burkert dark matter density profiles. We estimate the brane tension parameter using a sample of high resolution observed rotation curves of low surface brightness spiral galaxies and a synthetic rotation curve for the three density profiles. Also, the fittings using the brane theory model of the rotation curves are compared with standard Newtonian models. We found that Navarro-Frenk-White model prefers lower values of the brane tension parameter, on the average $λ\sim 0.73\times 10^{-3}$ eV$^4$, therefore showing clear brane effects. Burkert case does prefer higher values of the tension parameter, on the average $λ\sim 0.93$ eV$^4$ -- $46$ eV$^4$, i.e., negligible brane effects. Whereas pseudo isothermal is an intermediate case. In this context, we found that our results show weaker bounds to the brane tension values in comparison with other bounds found previously.

gr-qc↗

arXiv2015

Branes constrictions with White Dwarfs

We consider here a robust study of stellar dynamics for White Dwarf Stars with polytropic matter in the weak field approximation using the Lane-Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze its stability and compactness, in order to show whether it is possible to be close to the conventional wisdom of white dwarfs dynamics. Our results predicts an average value of brane tension as: $\langleλ\rangle\gtrsim84.818\;\rm MeV^4$, with a standard deviation $σ\simeq82.021\;\rm MeV^4$ which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining above of cosmological results provided by nucleosynthesis among others.

gr-qc↗

arXiv2015

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 Schwarszchild 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, specially 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 braneworld models allow the existence of more compact configurations than within General Relativity.

gr-qc↗

arXiv2014

Gravitational Waves Bounds in Brane-Worlds

This paper is dedicated to investigate an astrophysical method to obtain the new dynamics generated by extra dimensions as well as bounds for the brane tension. Using the modified Einstein equations in the brane with a vanishing non-local effects, we study the contributions of the modified radiated power by gravitational waves and the stellar period modified by branes in a binary system composed by two neutron stars. Finally we propose two lower energy bounds, using these astrophysical methods.

gr-qc↗

arXiv2013

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.

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