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Papers by Orfeu Bertolami
We study the effect of higher-curvature terms in the string low-energy effective actions on the c... more 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,
Journal of Physics: Conference Series, 2015
Quantumness and separability criteria for continuous variable systems are discussed for the case ... more Quantumness and separability criteria for continuous variable systems are discussed for the case of a noncommutative (NC) phase-space. In particular, the quantum nature and the entanglement configuration of NC two-mode Gaussian states are examined. Two families of covariance matrices describing standard quantum mechanics (QM) separable states are deformed into a NC QM configuration and then investigated through the positive partial transpose criterium for identifying quantum entanglement. It is shown that the entanglement of Gaussian states may be exclusively induced by switching on the NC deformation. Extensions of some preliminary results are presented.
In the last few years, the so-called flyby anomaly has been widely discussed, but remains still a... more In the last few years, the so-called flyby anomaly has been widely discussed, but remains still an illusive topic. This is due to the harsh conditions experienced during an Earth flyby as well as due to the limited data available. In this work, we assess the possibility of confirming and characterizing this anomaly by resorting to the scientific capabilities of
Physics Letters B, 1999
Spontaneous breaking of Lorentz invariance compatible with observational limits may realistically... more Spontaneous breaking of Lorentz invariance compatible with observational limits may realistically take place in the context of string theories, possibly endowing the photon with a mass.
Astrophysics and Space Science Library, 2008
The nature of gravity is fundamental to our understanding of our own solar system, the galaxy and... more The nature of gravity is fundamental to our understanding of our own solar system, the galaxy and the structure and evolution of the Universe. Einstein's general theory of relativity is the standard model that is used for almost ninety years to describe gravitational phenomena on these various scales. We review the foundations of general relativity, discuss the recent progress in the tests of relativistic gravity, and present motivations for high-accuracy gravitational experiments in space. We also summarize the science objectives and technology needs for the laboratory experiments in space with laboratory being the entire solar system. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential for the recently proposed gravitational experiments.
General Relativity and Gravitation, 2014
In this work we study how a non-minimal coupling between matter and gravity can modify the struct... more In this work we study how a non-minimal coupling between matter and gravity can modify the structure of a homogeneous spherical body. The physical relevance of the adopted Lagrangian density is ascertained, with results obtained for two different choices of the latter.
International Journal of Modern Physics D, 1996
We study the phenomenological consequences of the recently proposed idea of a running gravitation... more We study the phenomenological consequences of the recently proposed idea of a running gravitational coupling on macroscopic scales. When applied to the rotation curves of galaxies, we find that their flatness requires the presence of baryonic dark matter. Bounds on the variation of the gravitational coupling from primordial nucleosynthesis and the change of the period of binary pulsars are analysed. We also study constraints on the variations of G with scale from gravitational lensing and the cosmic virial theorem, as well as briefly discuss the implications of such a scenario for structure formation.
Physical Review D, 2015
Ozawa's measurement-disturbance relation is generalized to a phase-space noncommutative extension... more Ozawa's measurement-disturbance relation is generalized to a phase-space noncommutative extension of quantum mechanics. It is shown that the measurement-disturbance relations have additional terms for backaction evading quadrature amplifiers and for noiseless quadrature transducers. Several distinctive features appear as a consequence of the noncommutative extension: measurement interactions which are noiseless, and observables which are undisturbed by a measurement, or of independent intervention in ordinary quantum mechanics, may acquire noise, become disturbed by the measurement, or no longer be an independent intervention in noncommutative quantum mechanics. It is also found that there can be states which violate Ozawa's universal noise-disturbance trade-off relation, but verify its noncommutative deformation.
Physics Letters B, 1997
We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. U... more We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. Under suitable circumstances, certain CPTviolating terms can produce a large baryon asymmetry at the grandunified scale that reduces to the observed value via sphaleron or other dilution mechanisms.
Nuclear Physics B - Proceedings Supplements, 1996
We investigate the astrophysical and cosmological implications of the recently proposed idea of a... more We investigate the astrophysical and cosmological implications of the recently proposed idea of a running gravitational coupling on macroscopic scales. We find that when applied to the rotation curves of galaxies, their flatness requires still the presence of dark matter. Bounds on the variation of the gravitational coupling from primordial nucleosynthesis, change of the period of binary pulsars, gravitational lensing and the cosmic virial theorem are analysed.
The Eleventh Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG11 Meeting on General Relativity, 2008
We consider the mechanism of spontaneous symmetry breaking of a bulk vector field to study signat... more We consider the mechanism of spontaneous symmetry breaking of a bulk vector field to study signatures of bulk dimensions invisible to the standard model confined to the brane. By assigning a non-vanishing vacuum expectation value to the vector field, a direction is singled out in the bulk vacuum, thus breaking the bulk Lorentz symmetry. We present the condition for induced Lorentz symmetry on the brane, as phenomenologically required, noting that it is related to the value of the observed cosmological constant.
Physics Letters B, 1991
We study the solutions of a string-inspired cosmological model after supersymmetry breaking using... more We study the solutions of a string-inspired cosmological model after supersymmetry breaking using the methods of the qualitative theory of dynamical systems. The model exhibits solutions corresponding to a period of chaotic inflation followed by an "old" inflationary GUT scenario. The usual graceful exit problem associated to the latter period is naturally solved.
The Tenth Marcel Grossmann Meeting, On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG10 Meeting, 2005
CMBR CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS MODEL.
The Tenth Marcel Grossmann Meeting, On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG10 Meeting, 2005
BRANE INFLATION:
Physics Letters B, 1994
We establish the main features of homogeneous and isotropic dilaton, metric and Yang-Mills field ... more 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.
Springer Handbook of Spacetime, 2014
In this contribution we assess the current experimental status of Special and General Relativity.... more In this contribution we assess the current experimental status of Special and General Relativity. Particular emphasis is put on putative extensions of these theories and on how these could be detected experimentally.
It is shown that the spatially homogeneous Bianchi type I and Kantowski-Sachs cosmologies derived... more It is shown that the spatially homogeneous Bianchi type I and Kantowski-Sachs cosmologies derived from the Brans-Dicke theory of gravity admit a supersymmetric extension at the quantum level. A wide family of exact wavefunctions satisfying the supersymmetric constraints are found. A connection with quantum wormholes is briefly discussed.
We study the effect of higher-curvature terms in the string low-energy effective actions on the c... more 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,
Journal of Physics: Conference Series, 2015
Quantumness and separability criteria for continuous variable systems are discussed for the case ... more Quantumness and separability criteria for continuous variable systems are discussed for the case of a noncommutative (NC) phase-space. In particular, the quantum nature and the entanglement configuration of NC two-mode Gaussian states are examined. Two families of covariance matrices describing standard quantum mechanics (QM) separable states are deformed into a NC QM configuration and then investigated through the positive partial transpose criterium for identifying quantum entanglement. It is shown that the entanglement of Gaussian states may be exclusively induced by switching on the NC deformation. Extensions of some preliminary results are presented.
In the last few years, the so-called flyby anomaly has been widely discussed, but remains still a... more In the last few years, the so-called flyby anomaly has been widely discussed, but remains still an illusive topic. This is due to the harsh conditions experienced during an Earth flyby as well as due to the limited data available. In this work, we assess the possibility of confirming and characterizing this anomaly by resorting to the scientific capabilities of
Physics Letters B, 1999
Spontaneous breaking of Lorentz invariance compatible with observational limits may realistically... more Spontaneous breaking of Lorentz invariance compatible with observational limits may realistically take place in the context of string theories, possibly endowing the photon with a mass.
Astrophysics and Space Science Library, 2008
The nature of gravity is fundamental to our understanding of our own solar system, the galaxy and... more The nature of gravity is fundamental to our understanding of our own solar system, the galaxy and the structure and evolution of the Universe. Einstein's general theory of relativity is the standard model that is used for almost ninety years to describe gravitational phenomena on these various scales. We review the foundations of general relativity, discuss the recent progress in the tests of relativistic gravity, and present motivations for high-accuracy gravitational experiments in space. We also summarize the science objectives and technology needs for the laboratory experiments in space with laboratory being the entire solar system. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential for the recently proposed gravitational experiments.
General Relativity and Gravitation, 2014
In this work we study how a non-minimal coupling between matter and gravity can modify the struct... more In this work we study how a non-minimal coupling between matter and gravity can modify the structure of a homogeneous spherical body. The physical relevance of the adopted Lagrangian density is ascertained, with results obtained for two different choices of the latter.
International Journal of Modern Physics D, 1996
We study the phenomenological consequences of the recently proposed idea of a running gravitation... more We study the phenomenological consequences of the recently proposed idea of a running gravitational coupling on macroscopic scales. When applied to the rotation curves of galaxies, we find that their flatness requires the presence of baryonic dark matter. Bounds on the variation of the gravitational coupling from primordial nucleosynthesis and the change of the period of binary pulsars are analysed. We also study constraints on the variations of G with scale from gravitational lensing and the cosmic virial theorem, as well as briefly discuss the implications of such a scenario for structure formation.
Physical Review D, 2015
Ozawa's measurement-disturbance relation is generalized to a phase-space noncommutative extension... more Ozawa's measurement-disturbance relation is generalized to a phase-space noncommutative extension of quantum mechanics. It is shown that the measurement-disturbance relations have additional terms for backaction evading quadrature amplifiers and for noiseless quadrature transducers. Several distinctive features appear as a consequence of the noncommutative extension: measurement interactions which are noiseless, and observables which are undisturbed by a measurement, or of independent intervention in ordinary quantum mechanics, may acquire noise, become disturbed by the measurement, or no longer be an independent intervention in noncommutative quantum mechanics. It is also found that there can be states which violate Ozawa's universal noise-disturbance trade-off relation, but verify its noncommutative deformation.
Physics Letters B, 1997
We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. U... more We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. Under suitable circumstances, certain CPTviolating terms can produce a large baryon asymmetry at the grandunified scale that reduces to the observed value via sphaleron or other dilution mechanisms.
Nuclear Physics B - Proceedings Supplements, 1996
We investigate the astrophysical and cosmological implications of the recently proposed idea of a... more We investigate the astrophysical and cosmological implications of the recently proposed idea of a running gravitational coupling on macroscopic scales. We find that when applied to the rotation curves of galaxies, their flatness requires still the presence of dark matter. Bounds on the variation of the gravitational coupling from primordial nucleosynthesis, change of the period of binary pulsars, gravitational lensing and the cosmic virial theorem are analysed.
The Eleventh Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG11 Meeting on General Relativity, 2008
We consider the mechanism of spontaneous symmetry breaking of a bulk vector field to study signat... more We consider the mechanism of spontaneous symmetry breaking of a bulk vector field to study signatures of bulk dimensions invisible to the standard model confined to the brane. By assigning a non-vanishing vacuum expectation value to the vector field, a direction is singled out in the bulk vacuum, thus breaking the bulk Lorentz symmetry. We present the condition for induced Lorentz symmetry on the brane, as phenomenologically required, noting that it is related to the value of the observed cosmological constant.
Physics Letters B, 1991
We study the solutions of a string-inspired cosmological model after supersymmetry breaking using... more We study the solutions of a string-inspired cosmological model after supersymmetry breaking using the methods of the qualitative theory of dynamical systems. The model exhibits solutions corresponding to a period of chaotic inflation followed by an "old" inflationary GUT scenario. The usual graceful exit problem associated to the latter period is naturally solved.
The Tenth Marcel Grossmann Meeting, On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG10 Meeting, 2005
CMBR CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS MODEL.
The Tenth Marcel Grossmann Meeting, On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG10 Meeting, 2005
BRANE INFLATION:
Physics Letters B, 1994
We establish the main features of homogeneous and isotropic dilaton, metric and Yang-Mills field ... more 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.
Springer Handbook of Spacetime, 2014
In this contribution we assess the current experimental status of Special and General Relativity.... more In this contribution we assess the current experimental status of Special and General Relativity. Particular emphasis is put on putative extensions of these theories and on how these could be detected experimentally.
It is shown that the spatially homogeneous Bianchi type I and Kantowski-Sachs cosmologies derived... more It is shown that the spatially homogeneous Bianchi type I and Kantowski-Sachs cosmologies derived from the Brans-Dicke theory of gravity admit a supersymmetric extension at the quantum level. A wide family of exact wavefunctions satisfying the supersymmetric constraints are found. A connection with quantum wormholes is briefly discussed.