arXiv subjects

Ruben Cordero

Publications and source records attributed to Ruben Cordero.

At least 19 recordsLinked to original sources

arXiv2022

Perturbations and stability conditions of k-essence and kinetic gravity braiding models in two-field measure theory

We study cosmological perturbations for k-essence and kinetic gravity braiding models in the context of the two-field measure theory (TMT). Considering scalar perturbations and the uniform field gauge, we obtain the sound speed of the fields and present a stability analysis by means of the kinetic matrix and the mass eigenvalues. For k-essence models, in the two-field measure theory, the speed of propagation of the field is modified completely due to the new measure field and it gives rise to crucial differences with respect to the case without new measure. The stability analysis gives a physical viable model for the Universe. For the kinetic gravity braiding models in the two-field measure theory we get that, in general, the speed of perturbations is equal to the speed of light which is a consequence of the properties of the new measure field. In the later case, there is always a ghost field. Furthermore, we calculate general expressions for the mass eigenvalues and find, for an explicit example, the existence of tachyonic instabilities.

gr-qc↗

arXiv2020

New Exact Supersymmetric Wave Functions for a Massless Scalar Field and Axion-Dilaton String Cosmology in a FRWL Metric

We study the quantum cosmology of the 2D Hawking-Page massless scalar-field model and the homogeneous and isotropic dilation-axion string cosmology.For both models we find new exact solutions for the Wheeler-DeWitt equation and for the supersymmetric wave function equations. We show that the Wheeler-DeWitt equations for the Hawking-Page model and the axion-dilaton string cosmology are invariant under a one-parameter and two-parameter squeezed transformations, respectively. These results allow to find new solutions for the wave functions of these systems at the quantum cosmology level. Also, we apply the same squeezed transformations to solve the supersymmetric wave equations and find new supersymmetric solutions for the 2D Hawking-Page massless scalar-field model and the homogeneous and isotropic dilation-axion fields. Besides, for the former case, with the help of separation of variables we find new supersymmetric wave functions.

gr-qc↗

arXiv2019

A phase space description of the FLRW quantum cosmology in Ho$\check{\rm r}$ava-Lifshitz type gravity

Quantum cosmology of the Friedmann-Lemaître-Robertson-Walker model with cosmological constant in the Ho$\check{\rm r}$ava-Lifshitz type gravity is studied in the phase space by means of the Wigner function. The modification of the usual general relativity description by the Ho$\check{\rm r}$ava-Lifshitz type gravity induces a new scenario for the origin of the Universe with an embryonic era where the Universe can exist classically before the tunneling process takes place and which gives rise to the current evolution of the Universe. The Wigner functions corresponding to the Hartle-Hawking, Vilenkin and Linde boundary conditions are obtained by means of numerical calculations. In particular three cases were studied for the potential of the Wheeler-DeWitt equation: tunneling barrier with and without embryonic era and when the potential barrier is not present. The quantum behavior of these three cases are analyzed using the Wigner function for the three boundary conditions considered.

gr-qc↗

arXiv2018

Radiation Damping of a Yang-Mills Particle Revisited

The problem of a color-charged point particle interacting with a four dimensional Yang-Mills gauge theory is revisited. The radiation damping is obtained inspired in the Dirac's computation. The difficulties in the non-abelian case were solved by using an ansatz for the Liénard-Wiechert potentials, already used in the literature for finding solutions to the Yang-Mills equations. Three non-trivial examples of radiation damping for the non-abelian particle are discussed in detail.

hep-th↗

arXiv2016

An equation of state for purely kinetic k-essence inspired by cosmic topological defects

We investigate the physical properties of a purely kinetic k-essence model with an equation of state motivated in superconducting membranes. We compute the equation of state parameter $w$ and discuss its physical evolution via a nonlinear equation of state. Using the adiabatic speed of sound and energy density, we restrict the range of parameters of the model in order to have an acceptable physical behavior. Furthermore, we analyze the evolution of the luminosity distance $d_{L}$ with redshift $z$ by comparing (normalizing) it with the $Λ$CDM model. Since the equation of state parameter is $z$-dependent the evolution of the luminosity distance is also analyzed using the Alcock-Paczyński test.

gr-qc↗

arXiv2015

The Wentzel - Kramers - Brillouin approximation method applied to the Wigner function

An adaptation of the WKB method in the deformation quantization formalism is presented with the aim to obtain an approximate technique of solving the eigenvalue problem for energy in the phase space quantum approach. A relationship between the phase $σ(\vec{r})$ of a wave function $\exp \left(\frac{i}{\hbar} σ(\vec{r}) \right)$ and its respective Wigner function is derived. Formulas to calculate the Wigner function of a product and of a superposition of wave functions are proposed. Properties of a Wigner function of interfering states are also investigated. Examples of this quasi - classical approximation in deformation quantization are analysed. A strict form of the Wigner function for states represented by tempered generalised functions has been derived. Wigner functions of unbound states in the Poeschl - Teller potential have been found.

quant-ph↗

arXiv2015

On the flat spacetime Galileons and the Born-Infeld type structures

We show how the flat spacetime Galileon field theories (FSGFT) in arbitrary dimensions can be obtained through a Born-Infeld type structure. This construction involves a brane metric and non-linear combinations of derivatives of a scalar field. Our setup gives rise to some Galileon tensors and vectors useful for the variational analysis which are related to the momentum density of the probe Lovelock branes floating in a $N$-dimensional flat bulk. We find further that the Noether currents associated to these Galileon theories may be written in terms of such tensors.

hep-th↗

arXiv2012

Cosmological constraints in a two branes system for a vacuum bulk

We present the study of a two 3-branes system embedded in a 5-dimensional space-time in which the fifth dimension is compacted on a $S^{1}/Z_{2}$ orbifold and the space between the two branes is vacuum. Assuming isotropic and homogeneous space time, we probe that the dynamics of the visible brane is affected by the dynamics of the hidden brane and the possible components which fills it. We study two different cases: assuming a constant equation of state and inflationary scalar field, and its possible consequences in the brane evolution.

gr-qc↗

arXiv2012

Two-brane system in a vacuum bulk with a single equation of state

We study the cosmology of a two-brane model in a five-dimensional spacetime, where the extra spatial coordinate is compactifed on an orbifold. Additionally, we consider the existence on each brane of matter fields that evolve in time. Solving the Einstein equations in a vacuum bulk, we can show how the matter fields in both branes are connected and they do not evolve independently

gr-qc↗

arXiv2012

Cosmological constraints for a two brane-world system with single equation of state

We present the study of two 3-brane system embedded in a 5-dimensional space-time in which the fifth dimension is compactified on a $S^{1}/Z_{2}$ orbifold. Assuming isotropic, homogeneous, and static branes, it can be shown that the dynamics of one brane is dominated by the other one when the metric coefficients have a particular form. We study the resulting cosmologies when one brane is dominated by a given single-fluid component.

gr-qc↗

arXiv2011

Quantum string cosmology in the phase space

Deformation quantization is applied to quantize gravitational systems coupled with matter. This quantization procedure is performed explicitly for quantum cosmology of these systems in a flat minisuper(phase)space. The procedure is employed in a quantum string minisuperspace corresponding to an axion-dilaton system in an isotropic FRW Universe. The Wheeler-DeWitt-Moyal equation is obtained and its corresponding Wigner function is given analytically in terms of Meijer's functions. Finally, this Wigner functions is used to extract physical information of the system.

hep-th↗

arXiv2011

Novel Complete Non-compact Symmetries for the Wheeler-DeWitt Equation in a Wormhole Scalar Model and Axion-Dilaton String Cosmology

We find the full symmetries of the Wheeler-DeWitt equation for the Hawking and Page wormhole model and an axion-dilaton string cosmology. We show that the Wheeler-DeWitt Hamiltonian admits an U(1,1) hidden symmetry for the Hawking and Page model and U(2,1) for the axion-dilaton string cosmology. If we consider the existence of matter-energy renormalization, for each of these models we find that the Wheeler-DeWitt Hamiltonian accept an additional SL(2,R) dynamical symmetry. In this case, we show that the SL(2,R) dynamical symmetry generators transform the states from one energy Hilbert eigensubspace to another. Some new wormhole type-solutions for both models are found.

hep-th↗

arXiv2011

Quantum charged rigid membrane

The early Dirac proposal to model the electron as a charged membrane is reviewed. A rigidity term, instead of the natural membrane tension, involving linearly the extrinsic curvature of the worldvolume swept out by the membrane is considered in the action modeling the bubble in the presence of an electromagnetic field. We set up this model as a genuine second-order derivative theory by considering a non-trivial boundary term which plays a relevant part in our formulation. The Lagrangian in question is linear in the bubble acceleration and by means of the Ostrogradski-Hamiltonian approach we observed that the theory comprises the management of both first- and second-class constraints. We show thus that our second-order approach is robust allowing for a proper quantization. We found an effective quantum potential which permits to compute bounded states for the system. We comment on the possibility of describing brane world universes by invoking this kind of second-order correction terms.

gr-qc↗

arXiv2011

Deformation quantization of cosmological models

The Weyl-Wigner-Groenewold-Moyal formalism of deformation quantization is applied to cosmological models in the minisuperspace. The quantization procedure is performed explicitly for quantum cosmology in a flat minisuperspace. The de Sitter cosmological model is worked out in detail and the computation of the Wigner functions for the Hartle-Hawking, Vilenkin and Linde wave functions are done numerically. The Wigner function is analytically calculated for the Kantowski-Sachs model in (non)commutative quantum cosmology and for string cosmology with dilaton exponential potential. Finally, baby universes solutions are described in this context and the Wigner function is obtained.

hep-th↗

arXiv2009

Ostrogradski approach for the Regge-Teitelboim type cosmology

We present an alternative geometric inspired derivation of the quantum cosmology arising from a brane universe in the context of {\it geodetic gravity}. We set up the Regge-Teitelboim model to describe our universe, and we recover its original dynamics by thinking of such field theory as a second-order derivative theory. We refer to an Ostrogradski Hamiltonian formalism to prepare the system to its quantization. Our analysis highlights the second-order derivative nature of the RT model and the inherited geometrical aspect of the theory. A canonical transformation brings us to the internal physical geometry of the theory and induces its quantization straightforwardly. By using the Dirac canonical quantization method our approach comprises the management of both first- and second-class constraints where the counting of degrees of freedom follows accordingly. At the quantum level our Wheeler-De Witt Wheeler equation agrees with previous results recently found. On these lines, we also comment upon the compatibility of our approach with the Hamiltonian approach proposed by Davidson and coworkers.

gr-qc↗

arXiv2007

Soliton Stability in a Generalized Sine-Gordon Potential

We study stability of a generalized sine-Gordon model with two coupled scalar fields in two dimensions. Topological soliton solutions are found from the first-order equations that solve the equations of motion. The perturbation equations can be cast in terms of a Schrodinger-like operators for fluctuations and their spectra are calculated.

hep-th↗

arXiv2007

Geometrical dynamics of Born-Infeld objects

We present a geometrical inspired study of the dynamics of $Dp$-branes. We focus on the usual nonpolynomial Dirac-Born-Infeld action for the worldvolume swept out by the brane in its evolution in general background spacetimes. We emphasize the form of the resulting equations of motion which are quite simple and resemble Newton's second law, complemented with a conservation law for a worldvolume bicurrent. We take a closer look at the classical Hamiltonian analysis which is supported by the ADM framework of general relativity. The constraints and their algebra are identified as well as the geometrical role they play in phase space. In order to illustrate our results, we review the dynamics of a $D1$-brane immersed in a $AdS_3 \times S^3$ background spacetime. We exhibit the mechanical properties of Born-Infeld objects paving the way to a consistent quantum formulation.

hep-th↗

arXiv2005

Supertubes versus superconducting tubes

In this paper we show the relationship between cylindrical D2-branes and cylindrical superconducting membranes described by a generic effective action at the bosonic level. In the first case the extended objects considered, arose as blown up type IIA superstrings to D2-branes, named supertubes. In the second one, the cosmological objects arose from some sort of field theories. The Dirac-Born-Infeld action describing supertubes is shown to be equivalent to the generic effective action describing superconducting membranes via a special transformation.

hep-th↗