arXiv subjects

J. L. Cervantes-Cota

Publications and source records attributed to J. L. Cervantes-Cota.

24 records · Page 2Linked to original sources

arXiv2009

The influence of scalar fields in protogalactic interactions

We present simulations within the framework of scalar-tensor theories, in the Newtonian limit, to investigate the influence of massive scalar fields on the dynamics of the collision of two equal spherical clouds. We employ a SPH code modified to include the scalar field to simulate two initially non-rotating protogalaxies that approach each other, and as a result of the tidal interaction, intrinsic angular momentum is generated. We have obtained sufficient large values of J/M to suggest that intrinsic angular momentum can be the result of tidal interactions.

astro-ph.CO↗

arXiv2007

Newtonian limit of scalar-tensor theories and galactic dynamics: isolated and interacting galaxies

We use the Newtonian limit of a general scalar-tensor theory around a background field to study astrophysical effects. The gravitational theory modifies the standard Newtonian potential by adding a Yukawa term to it, which is quantified by two theoretical parameters: $λ$, the lenghtscale of the gravitational interaction and its strength, $α$. Within this formalism we firstly present a numerical study on the formation of bars in isolated galaxies. We have found for positive $α$ that the modified gravity destabilizes the galactic discs and leads to rapid bar formation in isolated galaxies. Values of $λ$ in the range $\approx 8$ -- 14 kpc produce strongest bars in isolated models. Then, we extent this work by considering tidal effects due to interacting galaxies. We send two spirals to collide and study the bar properties of the remnant. We characterize the bar kinematical properties in terms of our parameters ($λ, α$).

astro-ph↗

arXiv1998

Can induced gravity isotropize Bianchi I, V, or IX Universes?

We analyze if Bianchi I, V, and IX models in the Induced Gravity (IG) theory can evolve to a Friedmann--Roberson--Walker (FRW) expansion due to the non--minimal coupling of gravity and the scalar field. The analytical results that we found for the Brans-Dicke (BD) theory are now applied to the IG theory which has $ω\ll 1$ ($ω$ being the square ratio of the Higgs to Planck mass) in a cosmological era in which the IG--potential is not significant. We find that the isotropization mechanism crucially depends on the value of $ω$. Its smallness also permits inflationary solutions. For the Bianch V model inflation due to the Higgs potential takes place afterwads, and subsequently the spontaneous symmetry breaking (SSB) ends with an effective FRW evolution. The ordinary tests of successful cosmology are well satisfied.

gr-qc↗

arXiv1995

Induced gravity inflation in the standard model of particle physics

We are considering the cosmological consequences of an induced gravity theory coupled to the minimal standard model of particle physics. The non-minimal coupling parameter between gravity and the Higgs field must then be very large, yielding some new cosmological consequences for the early Universe and new constraints on the Higgs mass. As an outcome, new inflation is only possible for very special initial conditions producing first a short contraction era after which an inflationary expansion automatically follows; a chaotic inflationary scenario is successfully achieved. The contrast of density perturbations required to explain the seed of astronomic structures are obtained for very large values of the Higgs mass ($M_{H} >> G_{F}^{-1/2}$), otherwise the perturbations have a small amplitude; in any case, the spectral index of scalar perturbations agrees with the observed one.

astro-ph↗

arXiv1995

Isotropization of Bianchi-Type Cosmological Solutions in Brans-Dicke Theory

The cosmic, general analitic solutions of the Brans--Dicke Theory for the flat space of homogeneous and isotropic models containing perfect, barotropic, fluids are seen to belong to a wider class of solutions --which includes cosmological models with the open and the closed spaces of the Friedmann--Robertson--Walker metric, as well as solutions for models with homogeneous but anisotropic spaces corresponding to the Bianchi--Type metric clasification-- when all these solutions are expressed in terms of reduced variables. The existence of such a class lies in the fact that the scalar field, $ϕ$, times a function of the mean scale factor or ``volume element'', $a^3 = a_1 a_2 a_3$, which depends on time and on the barotropic index of the equation of state used, can be written as a function of a ``cosmic time'' reduced in terms of another function of the mean scale factor depending itself again on the barotropic index but independent of the metrics here employed. This reduction procedure permites one to analyze if explicitly given anisotropic cosmological solutions ``isotropize'' in the course of their time evolution. For if so can happen, it could be claimed that there exists a subclass of solutions that is stable under anisotropic perturbations.

gr-qc↗

arXiv1994

Induced gravity inflation in the SU(5) GUT

We investigate the cosmological consequences of a theory of induced gravity in which the scalar field is identified with the Higgs field of the first symmetry breaking of a mi\-ni\-mal SU(5) GUT. The mass of the X-boson determines a great value for the coupling constant of gravity-particle physics. Because of this fact, a "slow" rollover dynamics for the Higgs field is not possible in a "new" inflation scenario and, moreover, a contraction era for the scale factor in the early universe exists, \-after\- which inflation follows automatically; "chaotic" inflation is performed without problems. Inflation is successfully achieved due to the relationship among the masses of particle physics at that scale: The Higgs-, X-boson- and Planck-masses. As a result the particle physics pa\-ra\-me\-ter $λ$ is not fine-tuned as usual in order to predict acceptable values of re-heating temperature and density and gravitational wave perturbations. Moreover, if the coherent Higgs oscillations didn't decay they could explain the missing mass problem of cosmology.

astro-ph↗