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O. Bertolami

Publications and source records attributed to O. Bertolami.

144 records · Page 8Linked to original sources
arXiv1998

Primordial Density Fluctuations in a Dual Supergravity Cosmology

We analyse the spectrum of energy density fluctuations of a dual supergravity model where the dilaton and the moduli are stabilized and sucessful inflation is achieved inside domain walls that separate different vacua of the theory. Constraints on the parameters of the superpotential are derived from the amplitude of the primordial energy density fluctuations as inferred from COBE and it is shown that the scale dependence of the tensor perturbations nearly vanishes.

gr-qc↗
arXiv1997

Quantum Cosmological Multidimensional Einstein-Yang-Mills Model in a $R \times S^3 \times S^d$ Topology

The quantum cosmological version of the multidimensional Einstein-Yang-Mills model in a $R \times S^3 \times S^d$ topology is studied in the framework of the Hartle-Hawking proposal. In contrast to previous work in the literature, we consider Yang-Mills field configurations with non-vanishing time-dependent components in both $S^3$ and $S^d$ spaces. We obtain stable compactifying solutions that do correspond to extrema of the Hartle-Hawking wave function of the Universe. Subsequently, we also show that the regions where 4-dimensional metric behaves classically or quantum mechanically (i.e. regions where the metric is Lorentzian or Euclidean) will depend on the number, $d$, of compact space dimensions.

gr-qc↗
arXiv1997

CPT, Strings and Baryogenesis

In the context of string field theory, the possibility exists for the spontaneous violation of Lorentz invariance and CPT. In this talk, we review its status and some experimental constraints. We discuss the possibility that stringy CPT violation could give rise to a mechanism in which baryogenesis occurs in the early Universe in thermal equilibrium and show that this can produce, under suitable circumstances, a baryon asymmetry equal to the observed value.

hep-ph↗
arXiv1996

CPT Violation and Baryogenesis

We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. Under suitable circumstances, certain CPT-violating terms can produce a large baryon asymmetry at the grand-unified scale that reduces to the observed value via sphaleron or other dilution mechanisms.

hep-ph↗
arXiv1996

Topological Inflation in Dual Superstring Models

We study the possibility of obtaining inflationary solutions from S-dual superstring potentials. We find, in particular, that such solutions occur at the core of domain walls separating degenerate minima whose positions differ by modular transformations.

gr-qc↗
arXiv1995

Constraints on Supergravity Chaotic Inflationary Models

We discuss, in the context of $N=1$ hidden sector non-minimal supergravity chaotic inflationary models, constraints on the parameters of a polynomial superpotential resulting from existing bounds on the reheating temperature and on the amplitude of the primordial energy density fluctuations as inferred from COBE. We present a specific two-parameter chaotic inflationary model which satisfies these constraints and discuss a possible scenario for adequate baryon asymmetry generation.

gr-qc↗
arXiv1995

String Theory and Cosmology

We discuss the main cosmological implications of considering string-loop effects and a potential for the dilaton in the lowest order string effective action. Our framework is based on the effective model arising from regarding homogeneous and isotropic dilaton, metric and Yang-Mills field configurations. The issues of inflation, entropy crisis and the Polonyi problem as well as the problem of the cosmological constant are discussed.

gr-qc↗
arXiv1995

Cosmological Solutions of Higher-Curvature String Effective Theories with Dilatons

We study the effect of higher-curvature terms in the string low-energy effective actions on the cosmological solutions of the theory, up to corrections quartic in the curvatures, for the bosonic and heterotic strings as well as the type II superstring. We find that cosmological solutions exist for all string types but they always disappear when the dilaton field is included, a conclusion that can be avoided if string-loop effects are taken into account.

gr-qc↗
arXiv1995

Decoherence Due to Massive Vector Fields with Global Symmetries

Retrieval of classical behaviour in quantum cosmology is usually discussed in the framework of minisuperspace models in the presence of scalar fields together with the inhomogeneous modes of gravitational or scalar fields. In this work we propose alternatively a model where the scalar field is replaced by a massive vector field with global U(1) or SO(3) internal symmetries.

gr-qc↗
arXiv1994

Scale Factor Duality: A Quantum Cosmological Approach

We consider the minisuperspace model arising from the lowest order string effective action containing the graviton and the dilaton and study solutions of the resulting Wheeler-Dewitt equation. The scale factor duality symmetry is discussed in the context of our quantum cosmological model.

gr-qc↗
arXiv1994

Decoherence of Friedmann-Robertson-Walker Geometries in the Presence of Massive Vector Fields with U(1) or SO(3) Global Symmetries

Retrieval of classical behaviour in quantum cosmology is usually discussed in the framework of {\em midi}superspace models in the presence of scalar fields and the inhomogeneous modes corresponding either to gravitational or scalar fields. In this work, we propose an alternative model to study the decoherence of homogeneous and isotropic geometries where the scalar field is replaced by a massive vector field with a global internal symmetry. We study here the cases with $U(1)$ and $SO(3)$ global internal symmetries. The presence of a mass term breaks the conformal invariance and allows for the longitudinal modes of the spin-1 field to be present in the Wheeler-DeWitt equation. In the case of the U(1) global internal symmetry, we have only one single ``classical'' degree of freedom while in the case of the SO(3) global symmetry, we are led to consider a simple two-dimensional minisuperspace model. These minisuperspaces are shown to be equivalent to a set of coupled harmonic oscillators where the kinetic term of the longitudinal modes has a coefficient proportional to the inverse of the scale factor. The conditions for a suitable decoherence process and correlations between coordinate and momenta are established. The validity of the semi-classical Einstein equations when massive vector fields (Abelian and non-Abelian) are present is also discussed.

gr-qc↗
arXiv1994

On a possible solution for the Polonyi problem in string cosmology

We establish the main features of homogeneous and isotropic dilaton, metric and Yang-Mills configurations in a cosmological framework. We identify a new energy exchange term between the dilaton and the Yang-Mills field which may lead to a possible solution to the Polonyi problem in 4-dimensional string models.

gr-qc↗
arXiv1994

Decoherence of Homogeneous and Isotropic Metrics in the Presence of Massive Vector Fields

Retrieval of classical behaviour in quantum cosmology is usually discussed in the framework of minisuperspace models in the presence of scalar fields together with the inhomogeneous modes either of the gravitational or of the scalar fields. In this work we propose alternatively a model where the scalar field is replaced by a massive vector field with global $U(1)$ or SO(3) symmetries.

gr-qc↗
arXiv1994

Decoherence of Homogeneous and Isotropic Geometries in the Presence of Massive Vector Fields

Decoherence of Friedmann-Robertson-Walker (FRW) geometries due to massive vector fields with $SO(3)$ global symmetry is discussed in the context of Quantum Cosmology. (Talk presented at the 3rd National Meeting of Astronomy and Astrophysics, July 1993, IST, Lisboa, Portugal. -- A more complete version will be presented at MG7 conference and in the report CERN-TH.7241/94 DAMTP R-94/22 by the same authors)

gr-qc↗
arXiv1994

General Cosmological Features of the Einstein-Yang-Mills-Dilaton System

We establish the main features of homogeneous and isotropic dilaton, metric and Yang-Mills field configurations in a cosmological framework. Special attention is paid to the energy exchange between the dilaton and the Yang-Mills field and, in particular, a new energy exchange term is identified. Implications for the Polonyi problem in 4-dimensional string models and in dynamical supersymmetry breaking scenarios are discussed.

gr-qc↗