International Journal of Modern Physics: Conference Series

We study the compact stars internal structure and observable characteristics alterations due to the quark deconfinement phase transition. To proceed with, we investigate the properties of isospin- asymmetric nuclear matter in the improved relativistic mean-field (RMF) theory, including a scalar-isovector δ-meson effective field. In order to describe the quark phase, we use the improved version of the MIT bag model, in which the interactions between u, d and s quarks inside the bag are taken into account in the one-gluon exchange approximation. We compute the amount of energy released by the corequake for both cases of deconfinement phase transition scenarios, corresponding to the Maxwellian type ordinary first-order phase transition and the phase transition with formation of a mixed quark-hadron phase (Glendenning scenario).

We investigate a double extension to the Standard Model (SM). A first extension introduces, via minimal coupling, a massive Z′ boson. This enlarged SM is coupled to a dark matter sector through the Stueckelberg mechanism by a A′ boson. However, the A′ boson does not interact directly with the SM fermions. In our study, we found that the A′ is a massless photon-like particle in dark sector. Constraints on the mass for Z′ and corrections to Z mass are obtained.

In this contribution, we discuss quantum effects on relic gravitons described by the Friedmann-Robertson-Walker (FRW) spacetime background by reducing the problem to that of a generalized time-dependent harmonic oscillator, and find the corresponding Schrödinger states with the help of the dynamical invariant method. Then, by considering a quadratic time-dependent invariant operator, we show that we can obtain the geometric phases and squeezed quantum states for this system. Furthermore, we also show that we can construct Gaussian wave packet states by considering a linear time-dependent invariant operator. In both cases, we also discuss the uncertainty product for each mode of the quantized field.

We compute the holonomy transformation for circles on the equatorial plane in the Lense-Thirring spacetime taking into account the appropriate modification of this quantity due to the rotation of the source. In parallel transporting vectors we examine how the rotation affects the holonomy transformation.

In this paper we use the Generalized Uncertainty Principle in order to obtain the corrections to the fine structure constant in (D + 1)-dimensional global monopole spacetime. We also discuss the case D = 3 corresponding to the (3+1)-dimensional global monopole spacetime.

We obtain approximate solutions of the Dirac equation in the gravitational fields of vacuumless defects. In all obtained solutions we show the role played by the presence of these defects.

The creation of ultra-light dark particles in the late-time FLRW spacetime provides a cosmological model in accordance with precise observational tests. The matter creation backreaction implies in this context a vacuum energy density scaling linearly with the Hubble parameter H, which is consistent with the vacuum expectation value of the QCD condensate in a low-energy expanding spacetime. Both the cosmological constant and coincidence problems are alleviated in this scenario. We also explore the opposite, high energy limit of the particle creation process. We show that it leads to a non-singular primordial universe where an early inflationary era takes place, with natural reheating and exit. The generated primordial spectrum is scale invariant and, by supposing that inflation lasts for 60 e-folds, we obtain a scalar expectral index n ≈ 0.97.

We study the non-radial oscillations of relativistic neutron stars, in particular the (fundamental) f-modes, which are believed to be the most relevant for the gravitational wave emission of perturbed isolated stars. The expected frequencies of the f-modes are compared to the sensitivity range of Mario Schenberg, the Brazilian gravitational wave spherical detector.

HD 87643 is one of the B[e] stars that still defy our understanding to better classify it. The spectroscopic observations of HD 87643 performed in the Astronomical Observatory of La Silla (ESO) between December 1998 and April 2000 show an object far more complex than was already known, with profiles of the Balmer series showing variability on different time scales. This work examine the formation of Hα and Hβ profiles with the SEI method (Sobolev approximation with Exact Integration of the transfer equation), as well as their spectral energy distribution by means of codes Cloudy and Dusty. For a homogeneous and spherically symmetric nebula around a star with T_ef ~ 15, 000 K and log L/L_⊙ > 4.2, the reproduction of the profiles mentioned was only achieved for Hβ and to some extent, considering two distinct regions with different laws for the expansion of the wind and with different rates of mass loss.

It is well established that there is a breakdown in the curve of specific angular momentum as a function of mass for stars on the main sequence Ref. 5. Stars earlier than F5 and more massive than the sun, rotate rapidly over a large mass range. For spectral type F5 and later, including the Sun, much smaller rotational velocities are found. We revisit this question from a new sample to shed a light on the basis of a sample solar twins and analogs recently observed by interferometric measurements of stellar radius. Our results clearly show that, as the Sun, the solar twins present similar global behavior from their specific angular momentum. 18 Sco and HIP 100963 have a specific angular momentum one order higher than the solar value, and HIP 55459 and HIP 56948 have a specific angular momentum one order lower than the solar value.

The study of solar twins offers a unique opportunity to investigating the solar magnetic field over longer timescales. Supported by the new generation of stellar spectropolarimeters (ESPaDOnS@CFHT, NARVAL@TBL), we are able to measure the large-scale magnetic field solar twins. Studying the behavior of solar magnetic field, we are able to learn about the mechanisms of magnetic field generation in the dynamo process. Besides convection, various physical parameters affect the dynamo operation, in particular the rotation and mass. We collected signature of the stellar large-scale magnetic field for solar twins and we present here a analysis of seven candidates.

We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity, which is based on a modification of the usual matter conservation law. We show that, besides its application to the generalized Chaplygin gas model, other cosmological models based on Rastall's theory have many interesting and unexpected new features.

The Friedman-Lemaître-Robertson-Walker cosmological models are based on the assumptions of large-scale homogeneity and isotropy of the distribution of matter and energy. They are usually taken to have spatial sections that are simply connected; they have finite volume in the positive curvature case, and infinite volume in the null and negative curvature ones. I want to call the attention to the existence of an infinite number of models, which are based on these same metrics, but have compact, finite volume, multiply connected spatial sections. Some observational implications are briefly mentioned.

The quark gluon plasma (QGP) at zero temperature and high baryon number is a strongly interacting system that may exist in the core of dense stars. Using an equation of state based on a mean-field approximation of QCD to describe this cold QGP, we study the structure of compact stars and obtain masses which are compatible with recent astrophysical data.

To show the important role that geometry may play in the problem of confining particles to our four-dimensional spacetime, we consider a five-dimensional model where fermions are confined in a hypersurface due to an interaction with geometric fields. We use two different fields which appear in non-Riemannian geometries, namely, the Weyl one-form and the torsion two-form. We show that for suitable choices of these fields one manages to confine fermions in our brane (our four-dimensional world). It turns out that this confinement is independent of the energy and the mass of the fermions.

Using an equation of state based on a mean-field approximation for QCD (MQCD) to describe the cold quark gluon plasma we study the stellar structure of compact stars.

Some of the most interesting types of astrophysical objects that have been intensively studied in the recent years are the Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) seen usually as neutron stars pulsars with super strong magnetic fields. However, in the last two years two SGRs with low magnetic fields have been detected. Moreover, fast and very magnetic white dwarf pulsars have also been observed in the last years. Based on these new pulsar discoveries, white dwarf pulsars have been proposed as an alternative explanation to the observational features of SGRs and AXPs. Here we present several properties of these SGRs/AXPs as WD pulsar, in particular the surface magnetic field and the magnetic dipole momentum.

In this short communication, we study the Landau levels in the non-relativistic quantum dynamics of a neutral particle which possesses a permanent magnetic dipole moment interacting with an external electric field in curved spacetime background with the presence or absence of a torsion field. We show that the presence of the topological defect breaks the infinite degeneracy of the Landau levels.

In this work we investigate the adiabatic radial oscillations of hybrid stars. We use a relativistic-mean-field model equation of state (EOS) to describe the hadron phase and the Nambu-Jona-Lasinio (NJL) model for the quark matter phase. We integrate the equations of relativistic radial oscillations using different parameterizations for the NJL model and investigate the effect of a first order hadron-quark phase transition on the fundamental oscillation mode. The results show that the period τ of the fundamental mode is characterized by a cusp on the maximum mass and is finite for some configurations beyond the maximum mass. We conclude that for hybrid stars with sharp discontinuities the standard stability criterion ∂M/∂ε_c > 0 is not coincident with the stability criterion based on the finiteness of τ.

It is shown that topological changes in space-time are necessary to make General Relativity compatible with the Newtonian limit and to solve the hierarchy of the fundamental interactions. We detail how topology and topological changes appear in General Relativity and how it leaves an observable footprint in space-time. In cosmology we show that such topological observable is the cosmic radiation produced by the acceleration of the universe. The cosmological constant is a very particular case which occurs when the expansion of the universe into the vacuum occurs only in the direction of the cosmic time flow.

In this paper we evaluate the Wightman functions associated with a massive quantum scalar field in de Sitter and anti-de Sitter spacetimes in the presence of a cosmic string. Having these functions we calculate the corresponding renormalized vacuum expectation values of the field squared and present the behavior of the contributions induced by the cosmic string as function of the proper distance to it for different values of the parameter which codify the presence of this linear topological defect.

We investigate the topology of Schwarzschild's black holes through the immersion of this space-time in space of higher dimension. Through the immersions of Kasner and Fronsdal we calculate the extension of the Schwarzschilds black hole.

Magnetic field in the Sun is produced through the dynamo process in a way that is not yet completely understood. The question whether the Sun is peculiar as compared with other stars has been the subject of active investigation over the past 5 decades, but no studies have been focused on the properties of rotation and surface magnetic fields. The availability of ESPaDOnS offers an exceptional possibility to study the specificity of rotation and magnetic properties of Sun-like stars by means of spectropolarimetric observations. In this review, we present some results concerning the investigation of magnetic fields and dynamo evolution in cool active solar-like stars. Our results are based on the systematic searching for genuine solar analogs and observation of a sample of bona fide solar twins and solar analogs, whose fundamental parameters and evolutionary stage was determined in our previous studies. Our main aim is to investigate how rotation and magnetism evolve and how the depth of the convection zone may influence the global-scale toroidal magnetic fields at the stellar surface.

The present work is devoted to the detection of monochromatic gravitational waves signals from pulsars using the ALLEGRO's data detector. In this work we will present the region (in frequency) of millisecond pulsars of the 47 Tucanae (NGC 104) in the band of detector. According with this result was possible to analyse the frequency of the pulsar J1342+2822c, searching annual Doppler variations using power spectrum estimates for the year 1999. We tested this method injecting a simulated signal in real data and we were able to detect it.

In this work we investigate classical and quantum properties of light propagating in curved spacetimes determined by the Robertson-Walker metric. As a special case we consider the classical de Sitter spacetime. Afterwards, based on a quadratic invariant and the dynamical invariant method, we solve the Schrödinger equation for this problem and write the corresponding wave functions in terms of solutions of the Milne-Pinney equation. In addition, we construct coherent states for the quantized light and employ them to study quantum properties of light in curved spacetimes. In particular, we show that the product of the quantum fluctuations of the coordinate and the momentum space does not attain its minimum value.

We discuss the consistency of the Gödel metric within the Chern-Simons modified gravity, both for external and dynamical Chern-Simons coefficients.

There are many cosmological scenarios that try to explain the observed current accelerated expansion. They are based or on the existence of new fields in nature or on the modification of the gravitation theory. This work investigates the observational viability of a modified gravity f(R) = R - α/ Rⁿ within the Palatine approach, in the light of 32 age measurements of passively evolving galaxies and the baryonic acoustic oscillation peak scale. By using information-criteria model selection, this scenario is compared with the DGP alternative cosmological model as well the adjustable components of energy based in the general relativity based int the observational data set.

A detection or non detection of primordial non–Gaussianity (NG) by using the cosmic microwave background radiation (CMB) is a possible way to break the degeneracy of early universe models. Since a single statistical estimator hardly can be sensitive to all possible forms of NG which may be present in the data, it is important to use different statistical estimators to study NG in CMB. Recently, two new large-angle NG indicators based on skewness and kurtosis of spherical caps or spherical cells of CMB sky have been proposed and used in both CMB data and simulated maps. Here, we make a comparative study of these two different procedures by examining the NG in the WMAP seven years ILC map. We show that the spherical cells procedure detects a higher level of NG than that obtained by the method with overlapping spherical caps.

Vacuum energy density and stresses are investigated for a scalar field in de Sitter spacetime with an arbitrary number of toroidally compactified spatial dimensions and in anti-de Sitter spacetime with two parallel branes. On the branes the field obeys the Robin boundary conditions. The behavior of the vacuum expectation values is discussed in various asymptotic regions of the parameters. Applications are given to Randall-Sundrum type braneworlds.

Binary stars are important for understanding stellar structure and evolution. Binary systems with an evolved component give us an important constraint about the role played by convection on the characteristic time for tidal synchronization and circularization. On this study, we discuss about the role of convection in binary stars with evolved components. Base on a stellar sample composed by 260 binary stars with surface convective mass determined from evolutionary models computed with the Toulouse-Geneva Evolution Code (TGEC) as in do Nascimento et al. (2009). The stars with different convective deepening are represented in the Hertzsprung-Russell diagram (HR diagram). We are focused on the important question of how convection influence the evolution of the tidal synchronization and circularization of binary systems with an evolved component.

In the Sun-as-a-star Project, the sun was observed spectroscopically and photometrically for more than 25 years in order to determine variability and luminosity changes. This project detected systematic longterm decrease in the total irradiance as a consequence of the solar magnetic activity cycle (scale of years) and variability on solar activity from a time scale of days-months. The solar magnetic activity cycles could mimic the radial velocity modulation signal of a long-period companion in several spectral lines. This effect is an important limitation for the exoplanet searches programs using the radial velocity technique. The Lomb-Scargle periodogram analysis of the Sun-as-a-star spectroscopic data shows that the photospheric line C I 5380 Å and other 11 lines seems to not show significant influence from the rotational or cromospheric magnetic activity modulation. Thus, our analysis suggest that C I 5380 Å line could be used in programs that require extremely line stability.

Nuclear science has developed many excellent descriptions that embody various properties of the nucleus, and nuclear matter at low, medium and high densities. However, a full microscopic understanding of nuclear systems is still lacking. The aim of our theoretical research group is to shed some light on such challenges and particularly on open questions facing the high density nuclear many-body problem. Here we focus our attention on the conceptual issue of naturalness and its role in shaping the baryon-meson phase space dynamics in the description of the equation of state (EoS) of nuclear matter. In particular, in order to stimulate possible new directions of research, we discuss relevant aspects of a recently developed relativistic effective theory for nuclear matter with natural parametric couplings and genuine many-body forces. Among other topics we discuss in this work the connection of this theory with other known effective QHD models of the literature and its potentiality in describing a new physics for dense matter.

The form factor and the coupling constant of the vertex J/ψD_s D_s was calculated using the QCD Sum Rules. We have considered the cases where the J/ψ and D_s mesons are off-shell.

The Fock-Tani formalism is a successful mapping technique that has been used in hadron physics to describe hadron interaction and decay. In this one can obtain the ³P₀ model with bound state corrections. In this work we applay this technique for decay, where the amplitude and its respective decay rates are evaluated.

The Fock-Tani representation, is a field theoretic formalism to treat problems involving both composite particles and their constituents. The application of the Fock-Tani transformation to a pair creation Hamiltonian produces the characteristic expansion in powers of the wave function. In lowest order of this expansion, we obtain the model known in the literature: the ³P₀ model. In higher orders, the Corrected ³P₀ model (C³P₀) is obtained by introducing the bound state kernel. In this work, we use the C³P₀ model to calculate the J/ψ decay rates in the following channels: ρ π, ω η, ω η′, K^*+ K^-, , ϕ η, ϕ η′. We consider that the J/ψ is a mixture given by .

Using relativistic conformal hydrodynamics coupled to the linear σ model we study the evolution of matter created in heavy–ion collisions. We focus the study on the influence of the dynamics of the chiral fields on the charged-hadron elliptic flow v₂ for a temperature–independent as well as for a temperature–dependent η/s that is calculated from kinetic theory. We find that v₂ is not very sensitive to the coupling of chiral fields to the hydrodynamic evolution, but the temperature dependence of η/s plays a much bigger role on this observable.

In this work we use a mapping technique to derive in the context of a constituent gluon model an effective Hamiltonian that involves explicit gluon degrees of freedom. We study glueballs with two gluons using the Fock-Tani formalism. In the present work we calculate the glueball-glueball potential, in the context of the constituent gluon model, with gluon interchange.

We use a self-consistent chiral-hydrodynamic formalism which combines the linear σ model with second-order hydrodynamics in 2 + 1 dimensions to compute the spectrum of thermal photons produced in Au+Au collisions at . The temperature-dependent shear viscosity of the model, η, is calculated from the linearized Boltzmann equation. We compare the results obtained in the chiral-hydrodynamic model to those obtained in the second-order theory with a Lattice QCD equation of state and a temperature-independent value of η/s. We find that the thermal photon production is significantly larger in the latter model due to a slower evolution and larger dissipative effects.

We present the status and the recent measurements from the Pierre Auger Observatory. The energy spectrum is described and its features discussed. We report searches for anisotropy of cosmic rays arrival directions in large scales and through correlation with catalogues of celestial objects. The measurement of the cross section proton-air is discussed. Finally, the mass composition is addressed with the measurements of the variation of the depth of shower maximum with energy and with the muon density at ground.