arXiv subjects

M. C. Bento

Publications and source records attributed to M. C. Bento.

At least 37 records · Page 2Linked to original sources

arXiv2003

WMAP and Supergravity Inflationary Models

We study a class of N=1 Supergravity inflationary models in which the evolution of the inflaton dynamics is controlled by a single power in the inflaton field at the point where the observed density fluctuations are produced, in the context of the braneworld scenario, in light of WMAP results. In particular, we find that the bounds on the spectral index and its running constrain the parameter space both for models where the inflationary potential is dominated by a quadratic term and by a cubic term in the inflaton field. We also find that $α_s>0$ is required for the quadratic model whereas $α_s<0 $ for the cubic model. Moreover, we have determined an upper bound on the five-dimensional Planck scale, $M_5 \lsim 0.019$ M, for the quadratic model. On the other hand, a running spectral index with $n_s>1$ on large scales and $n_s<1$ on small scales is not possible in either case.

astro-ph↗

arXiv2003

WMAP Constraints on the Generalized Chaplygin Gas Model

The generalized Chaplygin gas (GCG) model explains the recent accelerated expansion of the Universe via an exotic background fluid whose equation of state is given by p=-A/ρ^α, where A is a positive constant and 0<α\le 1. The model is an interesting alternative to scenarios involving scalar field potentials, with the ensuing unnatural fine tuning conditions for the underlying particle physics theories. We derive constraints on the parameter space of the model from bounds on the location of the first few peaks and troughs of the the Cosmic Microwave Background Radiation (CMBR) power spectrum arising from recent WMAP and BOOMERanG data.

astro-ph↗

arXiv2003

Generalized Chaplygin Gas Model: Dark Energy - Dark Matter Unification and CMBR Constraints

The generalized Chaplygin gas (GCG) model allows for an unified description of the recent accelerated expansion of the Universe and the evolution of energy density perturbations. This dark energy - dark matter unification is achieved through an exotic background fluid whose equation of state is given by $p = - A/ρ^α$, where $A$ is a positive constant and $0 < α\le 1$. Stringent constraints on the model parameters can be obtained from recent WMAP and BOOMERanG bounds on the locations of the first few peaks and troughs of the Cosmic Microwave Background Radiation (CMBR) power spectrum as well as SNe Ia data.

gr-qc↗

arXiv2003

WMAP Constraints on Quintessence

We use recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) for the locations of peaks and troughs of the Cosmic Microwave Background (CMB) power spectrum, together with constraints from large-scale structure, to study a quintessence model in which the pure exponential potential is modified by a polynomial factor. We find that the model is compatible with all the recent data for a wide range of cosmological and potential parameters. Moreover, quintessence is favoured compared to $Λ$CDM for $n_s\approx 1$ and relatively high values of the average fraction of dark energy before last scattering (``early quintessence''); for $n_s<1$, quintessence and $Λ$CDM give similar results, except for high values of early quintessence, in which case $Λ$CDM is favoured.

astro-ph↗

arXiv2002

Supergravity Inflation on the Brane

We study N=1 Supergravity inflation in the context of the braneworld scenario. Particular attention is paid to the problem of the onset of inflation at sub-Planckian field values and the ensued inflationary observables. We find that the so-called $η$-problem encountered in supergravity inspired inflationary models can be solved in the context of the braneworld scenario, for some range of the parameters involved. Furthermore, we obtain an upper bound on the scale of the fifth dimension, $M_5 \lsim 10^{-3} M_P$, in case the inflationary potential is quadratic in the inflaton field, $ϕ$. If the inflationary potential is cubic in $ϕ$, consistency with observational data requires that $M_5 \simeq 9.2 \times 10^{-4} M_P$.

gr-qc↗

arXiv2002

Tachyonic Inflation in the Braneworld Scenario

We consider cosmological inflation driven by the rolling tachyon in the context of the braneworld scenario. We show that sufficient inflation consistent with the observational constraints can be achieved for well defined upper limits on the five-dimensional mass scale, string mass scale and the string coupling for the bosonic string.

hep-th↗

arXiv2002

Generalized Chaplygin gas and CMBR constraints

We study the dependence of the location of the Cosmic Microwave Background Radiation (CMBR) peaks on the parameters of the generalized Chaplygin gas model, whose equation of state is given by $p = - A/ρ^α$, where $A$ is a positive constant and $0 < α\le 1$. We find, in particular, that observational data arising from Archeops for the location of the first peak, BOOMERANG for the location of the third peak, supernova and high-redshift observations allow constraining significantly the parameter space of the model. Our analysis indicates that the emerging model is clearly distinguishable from the $α= 1$ Chaplygin case and the $Λ$CDM model.

astro-ph↗

arXiv2002

Generalized Chaplygin gas as a scheme for Unification of Dark Energy and Dark Matter

We study the cosmological scenario arising from the dynamics of a generalized Chaplygin gas. The equation of state of the system is given in terms of the energy density, $ρ$, and pressure, $p$, by the relationship $p = - A/ρ^α$, where $A$ is a positive constant and $0 < α\le 1$. The conditions under which homogeneity arises are discussed and it is shown that this equation of state describes a universe evolving from a phase dominated by non-relativistic matter to a phase dominated by a cosmological constant via an intermediate period where the effective equation of state is $p = αρ$.

astro-ph↗

arXiv2002

Generalized Chaplygin Gas, Accelerated Expansion and Dark Energy-Matter Unification

We consider the scenario emerging from the dynamics of a generalized $d$-brane in a $(d+1, 1)$ spacetime. The equation of state describing this system is given in terms of the energy density, $ρ$, and pressure, $p$, by the relationship $p = - A/ρ^α$, where $A$ is a positive constant and $0 < α\le 1$. We discuss the conditions under which homogeneity arises and show that this equation of state describes the evolution of a universe evolving from a phase dominated by non-relativistic matter to a phase dominated by a cosmological constant via an intermediate period where the effective equation of state is given by $p = αρ$.

gr-qc↗

arXiv2001

A Two-Field Quintessence Model

We study the dynamics of a quintessence model based on two interacting scalar fields. The model can account for the (recent) accelerated expansion of the Universe suggested by astronomical observations. Acceleration can be permanent or temporary and, for both scenarios, it is possible to obtain suitable values for the cosmological parameters while satisfying the nucleosynthesis constraint on the quintessence energy density. We argue that the model dynamics can be made consistent with a stable zero-energy relaxing supersymmetric vacuum.

astro-ph↗

arXiv2001

Cosmological Bounds on an Invisibly Decaying Higgs Boson

We derive bounds on the Higgs boson coupling $g^{\prime}$ to a stable light scalar which is regarded as a collisional dark matter candidate. We study the behaviour of this scalar, that we refer to as phion ($ϕ$), in the early Universe for different ranges of its mass. We find that a phion in the mass range of $100 \mev$ is excluded, while if its mass is about $1 \gev$, a rather large coupling constant, $g^{\prime} \gsim 2$, and $m_h \lsim 130 \gev$ are required in order to avoid overabundance. In the latter case, the invisible decay mode of the Higgs boson is dominant.

astro-ph↗

arXiv2001

Quintessence with Coupled Scalar Fields

We discuss the dynamics of a quintessence model involving two coupled scalar fields. The model presents two types of solutions, namely solutions that correspond to eternal and transient acceleration of the universe. In both cases, we obtain values for the cosmological parameters that satisfy current observational bounds as well as the nucleosynthesis constraint on the quintessence energy density.

gr-qc↗

arXiv2001

N=1 Supergravity Chaotic Inflation in the Braneworld Scenario

We study a N=1 Supergravity chaotic inflationary model, in the context of the braneworld scenario. It is shown that successful inflation and reheating consistent with phenomenological constraints can be achieved via the new terms in the Friedmann equation arising from brane physics. Interestingly, the model satisfies observational bounds with sub-Planckian field values, implying that chaotic inflation on the brane is free from the well known difficulties associated with the presence of higher order non-renormalizable terms in the superpotential. A bound on the mass scale of the fifth dimension, $M_5 \gsim 1.3 \times 10^{-6} M_P$, is obtained from the requirement that the reheating temperature be higher than the temperature of the electroweak phase transition.

astro-ph↗

arXiv2001

Cosmological Constraints on an Invisibly Decaying Higgs Boson

Working in the context of a proposal for collisional dark matter, we derive bounds on the Higgs boson coupling $g^{\prime}$ to a stable light scalar particle, which we refer to as phion ($ϕ$), required to solve problems with small scale structure formation which arise in collisionless dark matter models. We discuss the behaviour of the phion in the early universe for different ranges of its mass. We find that a phion in the mass range of 100 MeV is excluded and that a phion in the mass range of 1 GeV requires a large coupling constant, $g^{\prime} \gsim 2$, and $m_h \lsim 130$ GeV in order to avoid overabundance, in which case the invisible decay mode of the Higgs boson would be dominant.

hep-ph↗

arXiv2001

Self-Interacting Scalar Dark Matter and Higgs Decay

Self-interacting dark matter has been suggested in order to overcome the difficulties of the Cold Dark Matter model on galactic scales. We argue that a scalar gauge singlet coupled to the Higgs boson, leading to an invisibly decaying Higgs, is an interesting candidate for this self-interacting dark matter particle.

astro-ph↗

arXiv2000

Fitting BOOMERANG and MAXIMA-1 data with a Einstein-Yang-Mills Cosmological Model

We analyse the implications of recent Cosmic Microwave Background (CMB) data for a specific cosmological model, based on the higher-dimensional Einstein-Yang-Mills System compactified on a $R\times S^3\times S^d$ topology and conclude that the model parameters are tightly constrained by CMB spectra. Moreover, the model predicts a relationship between the deceleration parameter at present, $q_0$, and some characteristic features of CMB spectra, namely the height of the first peak and the location of the second peak, that is consistent with the observations and which can be further tested by future CMB and other experiments.

astro-ph↗

arXiv2000

Self-interacting Dark Matter and Invisibly Decaying Higgs

Self-interacting dark matter has been suggested in order to overcome the difficulties of the Cold Dark Matter model on galactic scales. We argue that a scalar gauge singlet coupled to the Higgs boson, which could lead to an invisibly decaying Higgs, is an interesting candidate for this self-interacting dark matter particle. We also present estimates on the abundance of these particles today as well as consequences to non-Newtonian forces.

astro-ph↗

arXiv1999

Compactification, Vacuum Energy and Quintessence

We study the possibility that the vacuum energy density of scalar and internal-space gauge fields arising from the process of dimensional reduction of higher dimensional gravity theories plays the role of quintessence. We show that, for the multidimensional Einstein-Yang-Mills system compactified on a $R \times S^3 \times S^d$ topology, there are classically stable solutions such that the observed accelerated expansion of the Universe at present can be accounted for without upsetting structure formation scenarios or violating observational bounds on the vacuum energy density.

gr-qc↗