Resumo em Inglês:

What is the shape of space is a long-standing question in cosmology. I review recent advances in cosmic topology since it has entered a new era of experimental tests. High redshift surveys of astronomical sources and accurate maps of the Cosmic Microwave Background radiation (CMB) are beginning to hint at the shape of the universe, or at least to limit the wide range of possibilities. Among those possibilites are surprising "wrap around" universe models in which space, whatever its curvature, may be smaller than the observable universe and generate topological lensing effects on a detectable cosmic scale. In particular, the recent analysis of CMB data provided by the WMAP satellite suggest a finite universe with the topology of the Poincaré dodecahedral spherical space. Such a model of a "small universe", the volume of which would represent only about 80 % the volume of the observable universe, offers an observational signature in the form of a predictable topological lens effect on one hand, and rises new issues on the early universe physics on the other hand.

Resumo em Inglês:

At nonzero temperature, it is expected that QCD undergoes a phase transition to a deconfined, chirally symmetric phase, the Quark-Gluon Plasma (QGP). I review what we expect theoretically about this possible transition, and what we have learned from heavy ion experiments at RHIC. I argue that while there are unambiguous signals for qualitatively new behavior at RHIC, versus experiments at lower energies, that in detail, no simple theoretical model can explain all salient features of the data.

Resumo em Inglês:

A natural and very important development of constrained system theory is a detail study of the relation between the constraint structure in the Hamiltonian formulation with specific features of the theory in the Lagrangian formulation, especially the relation between the constraint structure with the symmetries of the Lagrangian action. An important preliminary step in this direction is a strict demonstration, and this is the aim of the present article, that the symmetry structures of the Hamiltonian action and of the Lagrangian action are the same. This proved, it is sufficient to consider the symmetry structure of the Hamiltonian action. The latter problem is, in some sense, simpler because the Hamiltonian action is a first-order action. At the same time, the study of the symmetry of the Hamiltonian action naturally involves Hamiltonian constraints as basic objects. One can see that the Lagrangian and Hamiltonian actions are dynamically equivalent. This is why, in the present article, we consider from the very beginning a more general problem: how the symmetry structures of dynamically equivalent actions are related. First, we present some necessary notions and relations concerning infinitesimal symmetries in general, as well as a strict definition of dynamically equivalent actions. Finally, we demonstrate that there exists an isomorphism between classes of equivalent symmetries of dynamically equivalent actions.

Resumo em Inglês:

We consider the gravitational fields generated by a cosmic string, a global monopole and a tubular matter with interior magnetic field (Safko-Witten space-time), and examine some classical and quantum effects due to these fields. We investigate the Aharonov-Bohm effect in the space-time of a cosmic string, using the loop variables. In the space-time of a global monopole, we calculate the total energy radiated by a uniformly moving charged scalar particle, for small solid angle deficit. We show that the radiated energy is proportional to the cube of the velocity of the particle and to the cube of the Lorenz factor, in the non-relativistic and ultra-relativistic cases, respectively. In the Safko-Witten space-time, we investigate the existence of an electrostatic self-force on a charged particle. We also consider a hydrogen atom in the background space-time generated by a cosmic string and we find the solutions of the corresponding Dirac equation and we determine the energy levels of the atom. We investigate how the topological features of this space-time lead to shifts in the energy levels as compared with the flat Minkowski space-time. We study the behavior of non-relativistic quantum particles interacting with a Kratzer potential in the space-time generated by a global monopole and we find the energy spectrum in the presence of this topological defect. In the Safko-Witten space-time, an investigation is also made concerning the interaction of an harmonic oscillator with this background gravitational field.

Resumo em Inglês:

We discuss a few recent results for the equation of state of strongly interacting matter and the dynamics of chiral phase transition. First, we consider the cases of very high densities, where weak-coupling approaches may in principle give reasonable results, and very low densities, where we use the framework of heavy-baryon chiral perturbation theory. We also speculate on the nature of the chiral transition and present possible astrophysical implications. Next, we discuss the kinetics of phase conversion, through the nucleation of bubbles and spinodal decomposition, after a chiral transition within an effective field theory approach to low-energy QCD. We study possible effects resulting from the finite size of the expanding system for both the initial and the late-stage growth of domains, as well as those effects due to inhomogeneities in the chiral field which act as a background for the fermionic motion. We also argue how dissipation effects might dramatically modify the picture of explosive hadronization.

Resumo em Inglês:

The effect of experimentally observed hot atom mechanism on the phase diagram using Pt (111) surface of the monomer-dimer reaction has been studied. While using this mechanism, whenever O2 molecule hits the randomly vacant selected site, it breaks up into atomic form and then executes ballistic flight. The path of the two oxygen atoms is taken exactly opposite to each other i.e. anti-parallel and range of the atoms is taken equal i.e. they may fly upto 1 and 1.73 atomic spacing from the site of impact . Two cases have been studied on the basis of the range of hot atoms. The steady reactive window is observed and the continuous transition disappears. As soon as the CO partial pressure departs from zero the production of CO2 is observed, which clearly verifies the experimental observation.

Resumo em Inglês:

We perform a theoretical analysis of a setup intended to measure the repulsive(outward) Casimir forces predicted to exist inside of perfectly conducting rectangular cavities. We consider the roles of the conductivity of the real metals, of the temperature and surface roughness. The possible use of this repulsive force to reduce friction and wear in micro and nanoelectromechanical systems (MEMS and NEMS) is also considered.

Resumo em Inglês:

We consider a preferred-frame bimetric theory in which the scalar gravitational field both influences the metric and has direct dynamical effects. A modified version ("v2") is built, by assuming now a locally-isotropic dilation of physically measured distances, as compared with distances evaluated with the Euclidean space metric. The dynamical equations stay unchanged: they are based on a consistent formulation of Newton's second law in a curved space-time. To obtain a local conservation equation for energy with the new metric, the equation for the scalar field is modified: now its l.h.s. is the flat wave operator. Fluid dynamics is formulated and the asymptotic scheme of post-Newtonian approximation is adapted to v2. The latter also explains the gravitational effects on light rays, as did the former version (v1). The violation of the weak equivalence principle found for gravitationally-active bodies at the point-particle limit, which discarded v1, is proved to not exist in v2. Thus that violation was indeed due to the anisotropy of the space metric assumed in v1.

Resumo em Inglês:

In this work, we discuss the preliminary analysis of some disruptive plasma discharges with a moveable graphite limiter on the HT-7 tokamak, which has been developed in order to investigate the influence of the horizontal plasma position on the density limit. What we have observed is that the m=2, MHD component dominates during almost the whole discharge duration, when the density limit is approached at values of the edge safety factor 3 < q(a) < 3.5. For the poloidal-magnetic-field fluctuations observed at the Mirnov coils, Mirnov-coil analysis shows that the m = 2 mode is unstable, which finally causes disruption.

Resumo em Inglês:

In this work we examine noncommutativity of position coordinates in classical symplectic mechanics and its quantisation. In coordinates {q i,p k} the canonical symplectic two-form is omega0 = dq i

Resumo em Inglês:

We review the implementation of a q-deformed fermionic algebra in the Nambu-Jona-Lasinio model (NJL). The gap equations obtained from a deformed condensate as well as from the deformation of the NJL Hamiltonian are discussed. The effect of both temperature and deformation in the chiral symmetry restoration process as well as in the pion properties is studied.

Resumo em Inglês:

We determined, by numerical simulations, the critical behavior one-dimensional systems with infinitely many absorbing states. These models are modified versions of the conserved lattice gas model in which two adjacent active particles instead of just one can jump to their neighboring sites. The models studied here are examples of systems with many absorbing states and order parameter coupled to a nondiffusive conserved field that show nontrivial critical behavior.

Resumo em Inglês:

The dynamical mass generation for gluons is discussed in Euclidean Yang-Mills theories supplemented with a renormalizable mass term. The mass parameter is not free, being determined in a self-consistent way through a gap equation which obeys the renormalization group. The example of the Landau gauge is worked out explicitly at one loop order. A few remarks on the issue of the unitarity are provided.

Resumo em Inglês:

The level schemes and transition rates B(E2; $\uprrow$) of eve-even 48-56Ti isotopes were studied by performing large-scale shell model calculations with FPD6 and GXPF1 effective interactions. Excellent agreement were obtained by comparing the first 2+ level for all isotopes with the recently available experimental data, but studying the transition strengths B(E2; 0+g.s. ->2(1)+) for all Ti isotopes using constant proton-neutron effective charges prove the limitations of the present large-scale calculations to reproduce the experiment in detail.

Resumo em Inglês:

A disordered medium is often constructed by N random points independently and identically distributed in a d-dimensional hyperspace. Characteristics related to the statistics of this system are known as the random point problem. As d <FONT FACE=Symbol>® ¥</FONT>, the distances between two points become independent random variables, leading to its mean field description: the random link model. While the numerical treatment of large random point problems poses no major difficulty, due to Euclidean restrictions the same is not true for large random link systems. Exploring the deterministic nature of the pseudo-random number generators, we present techniques which allow to consider models with memory consumption of O(N), instead of O(N²) obtained by a naive implementation, but with the same time dependence O(N²).

Resumo em Inglês:

In this paper we give a method that removes the Wess Zumino fields of the BFFT formalism. Consequently, we derive a gauge invariant system written only in terms of the original second class phase space variables where important physical properties can be raised. Here, the Wess Zumino fields are considered only as auxiliary variables that permit us to reveal the underlying symmetries present in a second class system. We apply our formalism in three important and nontrivial constrained systems which are the Abelian Proca model, the Chern Simons Proca theory and the reduced SU(2) Skyrme model.