Searcharxiv⌕ Search

arXiv subjects

O. Bertolami

Publications and source records attributed to O. Bertolami.

At least 73 records · Page 4Linked to original sources
arXiv2008

Berry Phase in the Gravitational Quantum Well and the Seiberg-Witten map

We explicitly compute the geometrical Berry phase for the noncommutative gravitational quantum well for different SW maps. We find that they lead to different partial contributions to the Berry phase. For the most general map we obtain that $Δγ(S)\simη^3$, in a segment S of the path in the configuration space where $\sqrtη$ is the fundamental momentum scale for the noncommutative gravitational quantum well. For the full closed path, we find, through an explicit computation, that $γ(C)=0$. This result is consistent with the fact that physical properties are independent of the SW map and shows that these maps do not introduce degeneracies or level crossing in the noncommutative extensions of the gravitational quantum well.

gr-qc↗
arXiv2008

WMAP5 constraints on the unified model of dark energy and dark matter

We derive constraints on the parameter space of the unified model of dark energy and dark matter, the Generalized Chaplygin Gas (GCG), from the amplitudes and positions of the first few peaks and first trough of the cosmic microwave background radiation (CMBR) power spectrum, using the latest WMAP five year data.

astro-ph↗
arXiv2008

Lorentz violating extension of the Standard Model and the Beta-decay end-point

The Standard Model extension with additional Lorentz violating terms allows for redefining the equation of motion of a propagating left-handed fermionic particle. The obtained Dirac-type equation can be embedded in a generalized Lorentz-invariance preserving-algebra through the definition of Lorentz algebra-like generators with a light-like preferred axis. The resulting modification to the fermionic equation of motion introduces some novel ingredients to the phenomenological analysis of the cross section of the tritium $β$-decay. Assuming lepton number conservation, our formalism provides a natural explanation for the tritium $β$-decay end-point via an effective neutrino mass term without the need of a sterile right-handed state.

hep-ph↗
arXiv2008

Do f(R) theories matter?

We consider a modified action functional with a non-minimum coupling between the scalar curvature and the matter Lagrangian, and study its consequences on stellar equilibrium. Particular attention is paid to the validity of the Newtonian regime, and on the boundary and exterior matching conditions, as well as on the redefinition of the metric components. Comparison with solar observables is achieved through numerical analysis, and constraints on the non-minimum coupling are discussed.

astro-ph↗
arXiv2008

Solar system tests of scalar field models with an exponential potential

We consider a scenario where a scalar field has dynamics ruled by an exponential potential, such as those arising from some quintessence type models, and aim at obtaining phenomenological manifestations of this entity within our Solar System. To do so, we assume a perturbative regime, derive the perturbed Schwarzschild metric, and extract the relevant post-Newtonian parameters.

astro-ph↗
arXiv2008

Odyssey: a Solar System Mission

The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies. The mission proposes to perform a set of precision gravitation experiments from the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: i) test of the gravity force law in the Solar System up to and beyond the orbit of Saturn; ii) precise investigation of navigation anomalies at the fly-bys; iii) measurement of Eddington's parameter at occultations; iv) mapping of gravity field in the outer solar system and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13 AU, with the following components: a) a high-precision accelerometer, with bias-rejection system, measuring the deviation of the trajectory from the geodesics; b) Ka-band transponders, as for Cassini, for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; c) optional laser equipment, which would allow one to improve the range and Doppler measurement. In this baseline concept, the main spacecraft is designed to operate beyond the Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and fly-by phases allow the mission to achieve its baseline scientific objectives (i) to iii) in the above list). In addition to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in the outer Solar System.

gr-qc↗
arXiv2007

Galileo satellite constellation and extensions to General Relativity

We consider the impact of some known extensions of General Relativity in observables that will be available with the Galileo positioning systems, and draw conclusions as to the possibility of measuring them. We specifically address the effects of the presence of a cosmological constant, a Yukawa-like addition to the Newtonian potential, and the existence of an extra, constant acceleration. We also consider the phenomenological impact of a broad class of metric theories, which can be classified through the parameterized Post-Newtonian formalism.

gr-qc↗
arXiv2007

Dark Energy-Dark Matter Interaction and putative violation of the Equivalence Principle from the Abell Cluster A586

We show that the Abell Cluster A586 exhibits evidence of the interaction between dark matter and dark energy and argue that this interaction implies a violation of the Equivalence Principle. This violation is found in the context of two different models of dark energy-dark matter interaction. We also argue, based on the spherical symmetry of the Abell Cluster A586 that skewness is not the most general quantity to test the Equivalence Principle.

astro-ph↗
arXiv2007

The Higgs portal and an unified model for dark energy and dark matter

We examine a scenario where the Higgs boson is coupled to an additional singlet scalar field which we identify with a quintessence field. We show that this results in an unified picture of dark matter and dark energy, where dark energy is the zero-mode classical field rolling the usual quintessence potential and the dark matter candidate is the quantum excitation (particle) of the field, which is produced in the universe due to its coupling to the Higgs boson.

hep-ph↗
arXiv2006

Brane Lorentz Symmetry from Lorentz Breaking in the Bulk

We propose the mechanism of spontaneous symmetry breaking of a bulk vector field as a way to generate the selection of bulk dimensions invisible to the standard model confined to the brane. By assigning a non-vanishing vacuum 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.

gr-qc↗
arXiv2006

Deformation quantization of noncommutative quantum mechanics and dissipation

We review the main features of the Weyl-Wigner formulation of noncommutative quantum mechanics. In particular, we present a $\star$-product and a Moyal bracket suitable for this theory as well as the concept of noncommutative Wigner function. The properties of these quasi-distributions are discussed as well as their relation to the sets of ordinary Wigner functions and positive Liouville probability densities. Based on these notions we propose criteria for assessing whether a commutative regime has emerged in the realm of noncommutative quantum mechanics. To induce this noncommutative-commutative transition, we couple a particle to an external bath of oscillators. The master equation for the Brownian particle is deduced.

hep-th↗
arXiv2006

The electromagnetic coupling and the dark side of the Universe

We examine the properties of dark energy and dark matter through the study of the variation of the electromagnetic coupling. For concreteness, we consider the unification model of dark energy and dark matter, the generalized Chaplygin gas model (GCG), characterized by the equation of state $p=-\frac{A}{ρ^α}$, where $p$ is the pressure, $ρ$ is the energy density and $A$ and $α$ are positive constants. The coupling of electromagnetism with the GCG's scalar field can give rise to such a variation. We compare our results with experimental data, and find that the degeneracy on parameters $α$ and $A_s$, $A_s \equiv A / ρ_{ch0}^{1+α}$, is considerable.

astro-ph↗
arXiv2006

Gravity Control Propulsion: Towards a General Relativistic Approach

Evaluation of gravity control concepts should be examined with respect to currently known physical theories. In this work we study the hypothetical conversion of gravitational potential energy into kinetic energy using the formalism of general relativity. We show that the energy involved in the process greatly exceeds the Newtonian estimate, given the nature of general relativity. We conclude that the impact of any gravity manipulation for propulsion greatly depends fundamentally on its exact definition.

physics.space-ph↗
arXiv2006

Chaplygin inspired Inflation

We discuss chaotic inflation in the context of a phenomenological modification of gravity inspired by the Chaplygin gas equation of state. We find that all observationalconstraints can be satisfied provided the Chaplygin scale is smaller than $6.9 \times 10^{-3} M$ and the inflaton mass is smaller than $4.7 \times 10^{-6} M$, respectively, where $M^2\equiv(8 πG)^{-1} is the reduced Planck mass.

astro-ph↗
arXiv2006

Pioneer Anomaly and the Kuiper Belt mass distribution

Pioneer 10 and 11 were the first probes sent to study the outer planets of the Solar System and Pioneer 10 was the first spacecraft to leave the Solar System. Besides their already epic journeys, Pioneer 10 and 11 spacecraft were subjected to an unaccounted effect interpreted as a constant acceleration toward the Sun, the so-called Pioneer anomaly. One of the possibilities put forward for explaining the Pioneer anomaly is the gravitational acceleration of the Kuiper Belt. In this work we examine this hypothesis for various models for the Kuiper Belt mass distribution. We find that the gravitational effect due to the Kuiper Belt cannot account for the Pioneer anomaly. Furthermore, we have also studied the hypothesis that drag forces can explain the the Pioneer anomaly; however we conclude that the density required for producing the Pioneer anomaly is many orders of magnitude greater than those of interplanetary and interstellar dust. Our conclusions suggest that only through a mission, the Pioneer anomaly can be confirmed and further investigated. If a mission with these aims is ever sent to space, it turns out, on account of our results, that it will be also a quite interesting probe to study the mass distribution of the Kuiper Belt.

astro-ph↗
arXiv2006

Observational constraints on modified gravity models and the Poincaré dodecahedral topology

We study the constraints that spatial topology may place on the parameters of models that account for the accelerated expansion of the universe via infrared modifications to general relativity, namely the Dvali-Gabadadze-Porrati braneworld model as well as the Dvali-Turner and Cardassian models. By considering the Poincaré dodecahedral space as the circles-in-the-sky observable spatial topology, we examine the constraints that can be placed on the parameters of each model using type Ia supernovae data together with the baryon acoustic peak in the large scale correlation function of the Sloan Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background Radiation shift parameter data. We show that knowledge of spatial topology does provide relevant constraints, particularly on the curvature parameter, for all models.

astro-ph↗