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Antonio Campos

Publications and source records attributed to Antonio Campos.

15 recordsLinked to original sources
arXiv2005

Asymptotic cosmological solutions for string/brane gases with solitonic fluxes

We present new cosmological solutions for brane gases with solitonic fluxes that can dynamically explain the existence of three large spatial dimensions. This reasserts the importance of fluxes for understanding the full space of solutions in a potential implementation of the Brandenberger-Vafa mechanism with M2-branes. Additionally, we study a particular example in which the cosmological dynamics supported by a string gas with a NS flux in the ten-dimensional dilaton gravity framework is asymptotically equivalent to that of a M2-brane gas with a certain wrapping configuration in eleven-dimensional supergravity. We speculate that this connection between the ten- and eleven-dimensional implementations of the Brandenberger-Vafa mechanism could be a general feature.

hep-th↗
arXiv2004

Dynamical decompactification from brane gases in eleven-dimensional supergravity

Brane gas cosmology provides a dynamical decompactification mechanism that could account for the number of spacetime dimensions we observe today. In this work we discuss this scenario taking into account the full bosonic sector of eleven-dimensional supergravity. We find new cosmological solutions that can dynamically explain the existence of three large spatial dimensions characterised by an universal asymptotic scaling behaviour and a large number of initially unwrapped dimensions. This type of solutions enlarge the possible initial conditions of the Universe in the Hagedorn phase and consequently can potentially increase the probability of dynamical decompactification from anisotropically wrapped backgrounds.

hep-th↗
arXiv2003

Late cosmology of brane gases with a two-form field

We consider the effects of a two-form field on the late-time dynamics of brane gas cosmologies. Assuming thermal equilibrium of winding states, we find that the presence of a form field allows a late stage of expansion of the Universe even when the winding degrees of freedom decay into a pressureless gas of string loops. Finally, we suggest to understand the dimensionality of the Universe not as a result of the thermal equilibrium condition but rather as a consequence of the symmetries of the geometry.

hep-th↗
arXiv2003

Braneworld cosmological models with anisotropy

For a cosmological Randall-Sundrum braneworld with anisotropy, i.e., of Bianchi type, the modified Einstein equations on the brane include components of the five-dimensional Weyl tensor for which there are no evolution equations on the brane. If the bulk field equations are not solved, this Weyl term remains unknown, and many previous studies have simply prescribed it ad hoc. We construct a family of Bianchi braneworlds with anisotropy by solving the five-dimensional field equations in the bulk. We analyze the cosmological dynamics on the brane, including the Weyl term, and shed light on the relation between anisotropy on the brane and Weyl curvature in the bulk. In these models, it is not possible to achieve geometric anisotropy for a perfect fluid or scalar field -- the junction conditions require anisotropic stress on the brane. But the solutions can isotropize and approach a Friedmann brane in an anti-de Sitter bulk.

hep-th↗
arXiv2003

Braneworld physics from the analog-gravity perspective: finiteness effects

We study Randall-Sundrum brane models from the viewpoint of condensed matter/quantum optics. Following the idea of analog gravity we obtain effective metrics in fluid and Bose-Einstein-condensate systems mimicking those in the brane framework. We find that the effect of warp factors in the bulk geometry translates into finiteness of the analog systems. As an illustration of this identification we give a new interpretation of the peculiar behaviour of the critical temperature for the splitting of thick branes in warped spacetimes.

hep-th↗
arXiv2003

Late-time dynamics of brane gas cosmology

Brane gas cosmology is a scenario inspired by string theory which proposes a simple resolution to the initial singularity problem and gives a dynamical explanation for the number of spatial dimensions of our universe. In this work we have studied analytically and numerically the late-time behaviour of these type of cosmologies taking a proper care of the annihilation of winding modes. This has help us to clarify and extend several aspects of their dynamics. We have found that the decay of winding states into non-winding states behaving like a gas of ordinary non-relativistic particles precludes the existence of a late expansion phase of the universe and obstructs the growth of three large spatial dimensions as we observe today. We propose a generic solution to this problem by considering the dynamics of a gas of non-static branes. We have also obtained a simple criterion on the initial conditions to ensure the small string coupling approximation along the whole dynamical evolution, and consequently, the consistency of an effective low-energy description. Finally, we have reexamined the general conditions for a loitering period in the evolution of the universe which could serve as a mechanism to resolve the {\sl brane problem} - a problem equivalent to the {\sl domain wall problem} in standard cosmology - and discussed the scaling properties of a self-interacting network of winding modes taking into account the effects of the dilaton dynamics.

hep-th↗
arXiv2002

Critical phenomena of thick branes in warped spacetimes

We have investigated the effects of a generic bulk first-order phase transition on thick Minkowski branes in warped geometries. As occurs in Euclidean space, when the system is brought near the phase transition an interface separating two ordered phases splits into two interfaces with a disordered phase in between. A remarkable and distinctive feature is that the critical temperature of the phase transition is lowered due to pure geometrical effects. We have studied a variety of critical exponents and the evolution of the transverse-traceless sector of the metric fluctuations.

hep-th↗
arXiv2001

Bulk effects in the cosmological dynamics of brane-world scenarios

In this paper we deal with the cosmological dynamics of Randall-Sundrum brane-world type scenarios in which the five-dimensional Weyl tensor has a non-vanishing projection onto the three-brane where matter fields are confined. Using dynamical systems techniques, we study how the state space of Friedmann-Lemaitre-Robertson-Walker (FLRW) and Bianchi type I cosmological models is affected by the bulk Weyl tensor, focusing in the differences that appear with respect to general relativity and also Randall-Sundrum cosmological scenarios without the Weyl tensor contribution.

hep-th↗
arXiv2001

Evolution of Cosmological Models in the Brane-world Scenario

In this work we consider Randall-Sundrum brane-world type scenarios, in which the spacetime is described by a five-dimensional manifold with matter fields confined in a domain wall or three-brane. We present the results of a systematic analysis, using dynamical systems techniques, of the qualitative behaviour of the Friedmann-Lemaitre-Robertson-Walker and the Bianchi I and V cosmological models in these scenarios. We construct the state spaces for these models and discuss how their structure changes with respect to the general-relativistic case, in particular, what new critical points appear and their nature, the occurrence of bifurcations and the dynamics of anisotropy.

hep-th↗
arXiv1998

Fluctuations in a Thermal Field and Dissipation of a Black Hole Spacetime: Far-Field Limit

We study the back reaction of a thermal field in a weak gravitational background depicting the far-field limit of a black hole enclosed in a box by the Close Time Path (CTP) effective action and the influence functional method. We derive the noise and dissipation kernels of this system in terms of quantities in quasi-equilibrium, and formally prove the existence of a Fluctuation-Dissipation Relation (FDR) at all temperatures between the quantum fluctuations of the thermal radiance and the dissipation of the gravitational field. This dynamical self-consistent interplay between the quantum field and the classical spacetime is, we believe, the correct way to treat back-reaction problems. To emphasize this point we derive an Einstein-Langevin equation which describes the non-equilibrium dynamics of the gravitational perturbations under the influence of the thermal field. We show the connection between our method and the linear response theory (LRT), and indicate how the functional method can provide more accurate results than prior derivations of FDRs via LRT in the test-field, static conditions. This method is in principle useful for treating fully non-equilibrium cases such as back reaction in black hole collapse.

gr-qc↗
arXiv1998

Non-equilibrium dynamics of a thermal plasma in a gravitational field

We introduce functional methods to study the non-equilibrium dynamics of a quantum massless scalar field at finite temperature in a gravitational field. We calculate the Close Time Path (CTP) effective action and, using its formal equivalence with the influence functional, derive the noise and dissipation kernels of the quantum open system in terms of quantities in thermodynamical equilibrium. Using this fact, we formally prove the existence of a Fluctuation-Dissipation Relation (FDR) at all temperatures between the quantum fluctuations of the plasma in thermal equilibrium and the energy dissipated by the external gravitational field. What is new is the identification of a stochastic source (noise) term arising from the quantum and thermal fluctuations in the plasma field, and the derivation of a Langevin-type equation which describes the non-equilibrium dynamics of the gravitational field influenced by the plasma. The back reaction of the plasma on the gravitational field is embodied in the FDR. From the CTP effective action the contribution of the quantum scalar field to the thermal graviton polarization tensor can also be derived and it is shown to agree with other techniques, most notably, Linear Response Theory (LRT). We show the connection between the LRT, which is applicable for near-equilibrium conditions and the functional methods used in this work which are useful for fully non-equilibrium conditions.

hep-ph↗
arXiv1995

Stochastic semiclassical equations for weakly inhomogeneous cosmologies

Semiclassical Einstein-Langevin equations for arbitrary small metric perturbations conformally coupled to a massless quantum scalar field in a spatially flat cosmological background are derived. Use is made of the fact that for this problem the in-in or closed time path effective action is simply related to the Feynman and Vernon influence functional which describes the effect of the ``environment'', the quantum field which is coarse grained here, on the ``system'', the gravitational field which is the field of interest. This leads to identify the dissipation and noise kernels in the in-in effective action, and to derive a fluctuation-dissipation relation. A tensorial Gaussian stochastic source which couples to the Weyl tensor of the spacetime metric is seen to modify the usual semiclassical equations which can be viewed now as mean field equations. As a simple application we derive the correlation functions of the stochastic metric fluctuations produced in a flat spacetime with small metric perturbations due to the quantum fluctuations of the matter field coupled to these perturbations.

gr-qc↗
arXiv1995

Back reaction in the formation of a straight cosmic string

A simple model for the formation of a straight cosmic string, wiggly or unperturbed is considered. The gravitational field of such string is computed in the linear approximation. The vacuum expectation value of the stress tensor of a massless scalar quantum field coupled to the string gravitational field is computed to the one loop order. Finally, the back-reaction effect on the gravitational field of the string is obtained by solving perturbatively the semiclassical Einstein's equations.

gr-qc↗
arXiv1993

Semiclassical Equations for Weakly Inhomogeneous Cosmologies

The in-in effective action formalism is used to derive the semiclassical correction to Einstein's equations due to a massless scalar quantum field conformally coupled to small gravitational perturbations in spatially flat cosmological models. The vacuum expectation value of the stress tensor of the quantum field is directly derived from the renormalized in-in effective action. The usual in-out effective action is also discussed and it is used to compute the probability of particle creation. As one application, the stress tensor of a scalar field around a static cosmic string is derived and the backreaction effect on the gravitational field of the string is discussed.

gr-qc↗