Repositório RCAAP

The paper is the summary of lectures given in São Carlos, Brazil during the 2004 Summer School on Statistical Mechanics. My objective was to provide the students with some basic tools necessary to study the thermodynamics of Coulomb systems. I have restricted myself to simple models and techniques, which nevertheless, when used correctly can give a clear insight into the fundamental physics behind various complex phenomena that appear when the interactions between the system's constituents are dominated by the long ranged Coulomb force.

Since the discovery of superconductivity in palladium-hydrogen (PdH) and its isotopes (D,T) at low temperature, several efforts have been made to study the properties of this system. Superconductivity of PdH system has been initially claimed by resistance drop versus temperature and then confi rmed by dc magnetic susceptibility measurements. These studies have shown that the critical transition temperature is a function of the hydrogen concentration x in the PdHx system. In all these experiments, the highest concentration x of hydrogen in palladium was lower than the unit. In the last decade we defi ned a room temperature and room pressure technique to load hydrogen and its isotopes into palladium at levels higher than unit, using electrochemical set-up, followed by a stabilization process to maintain the hydrogen concentration in palladium lattice stable. In the meanwhile, several measurements of resistance versus temperature have been performed. These measurements have shown several resistive drops in the range of [18K<Tc< 273K] similar to the results presented in literature, when the superconducting phase has been discovered. Moreover, on PdH wires 6cm long the current-voltage characteristic with a current density greater than 6*104 Acm-2 has been measured at liquid nitrogen temperature. These measurements have the same behavior as superconducting I-V characteristic with sample resistivity, at 77K, of two orders of magnitude lower than copper or silver at the same temperature. The measurements of fi rst and third harmonic of ac magnetic susceptibility in PdHx system have been performed. These represent a good tool to understand the vortex dynamics, since the superconducting response is strongly non-linear. Clear ac susceptibility signals confi rming the literature data at low temperature (9K) and new signifi cant signals at high temperature (263K) have been detected. A phenomenological approach to describe the resistance behaviour of PdH versus stoichiometry x at room temperature has been developed. The value x=1.6 to achieve a macroscopic superconducting state in PdHx has been predicted.

A model potential depending on an effective core radius but otherwise parameter free is used for the comparative study of electrical resistivity of simple and non-simple liquid metals. In the present paper electrical resistivity of simple and non-simple liquid metals have been calculated using Ziman's formula, Ziman's formula modified and used by Khajil and Tomak (Self consistent approximation) and t-matrix formulation given by Evans and Evans et al. Previously no one have reported such comparative study using pseudopotentials. In the electrical resistivity calculations we have used structure factor derived through charge hard sphere approximation. The beauty of this approximation is that it needs pseudopotential form factor for the calculation of structure factor. So this gives the better explanation of structure factor than any other approximations. From present investigations it is found that self consistent formulation results are excellently agrees with the experimental findings. A successful application is an evidence that our potential can predict wide class of physical properties of d and f - shell metals as well as simple and non-simple metals.

Using a simple model described by a Hamiltonian of fermions coupled to bosons, we show that the relaxation function calculated via a low temperature approximation to the Mori memory function is similar, at least to lowest order, to the relaxation function calculated using a Green function formalism.

We analyze gauge theories based on abelian p-forms in real compact hyperbolic manifolds. The explicit thermodynamic functions associated with skew-symmetric tensor fields are obtained via zeta-function regularization and the trace tensor kernel formula. Thermodynamic quantities in the high-temperature expansions are calculated and the entropy/energy ratios are established.

We develop an adiabatic valence-bond theory of the positronium hydride, HPs, as a heteroisotopic diatomic molecule. Typical heteronuclear ionic behaviour comes out at bonding distances, yielded just by finite nuclear mass effects, but some interesting new features appears for short distances as well.

A model for the Universe is proposed where it is considered as a mixture of scalar and matter fields. The particle production is due to an irreversible transfer of energy from the gravitational field to the matter field and represented by a non-equilibrium pressure. This model can simulate three distinct periods of the Universe: (a) an accelerated epoch where the energy density of the scalar field prevails over that of the matter field, (b) a past decelerated period where the energy density of the matter field becomes larger than the scalar field energy density, and (c) a present acceleration phase where the scalar field energy density overcomes the energy density of the matter field.

ReO2 presents two crystalline variants, with monoclinic and orthorhombic structures. The former is metastable and irreversibly transforms to an orthorhombic structure above 460ºC. The structure of the latter was determined from studies on monocrystalline samples, whereas for the monoclinic variant there are no single crystals available so far. It was found only one monoclinic variant and the structure associated with this variant is based on studies on polycrystals. We analyzed a monoclinic oxide powder sample by X-ray diffraction and refined its pattern by means of the Rietveld Method. We obtained that the monoclinic variant belongs to space group P2(1)/c, with lattice parameters a = 5.615(3), b = 4.782(2), c = 5.574(2) Å, beta = 120.13(1)º.

The procedures used to obtain general expressions for the components of the effective dielectric tensor for electromagnetic waves in inhomogeneous magnetized plasmas are briefly reviewed, and the relationship between these expressions and their counterparts which can be obtained assuming electrostatic fluctuations is discussed. It is argued that a general formulation formerly available in the literature, which do not satisfy Onsager symmetry in the case of electrostatic fluctuations, is not the suitable form for description of dielectric properties in the electrostatic case, which require a dielectric constant. A general expression for an effective dielectric constant is therefore provided, obtained from the effective dielectric tensor, which satisfy Onsager symmetry.

We present a detailed derivation of the effective dielectric constant to be used in the dispersion relation for electrostatic waves in the case of a plasma immersed in a inhomogeneous magnetic field, with inhomogeneity perpendicular to the direction of the magnetic field.

We extend a Fokker-Planck formalism, previously used to describe the behavior of a cooling granular gas, with a Hertzian contact potential and viscoelastic radial friction, giving a velocity dependent coefficient of restitution. In the present work, we study the more general case of a steady-state with finite kinetic energy, far from equilibrium, due to the coupling to an external energy-feeding mechanism. Also from first-principles, we extend the validity of the former results.

We study nuclear reactions in collisions of unstable projectiles with heavy targets. For this purpose, we use a simple approximation for the breakup channel and treat two-neutron halos as a single particle. We then evaluate cross sections for collisions of 6He projectiles with targets of 238U and 209Bi. Comparing our results with recently measured fusion cross sections, we conclude that the large enhancement observed in 6He+238U fusion at sub-barrier energies cannot be explained by the coupling with the breakup channel. The effects of the halo on other reaction channels are also investigated. Coulomb-nuclear interference in the breakup channel is discussed.

In the present paper we consider the vortex lattice properties of a square superconductor such as the vortex patterns, the Gibbs free energy, the magnetization, and the depairing critical current density. We show that this last quantity shows a matching effect, that is, it shows a discontinuous behavior as a function of the applied magnetic field.

We discuss the one-loop quantum corrections to the mass M and central charge Z of supersymmetric (susy) solitons: the kink, the vortex and the monopole. Contrary to previous expectations and published results, in each of these cases there are nonvanishing quantum corrections to the mass. For the N = 1 kink and the N = 2 monopole a new anomaly in Z rescues BPS saturation (M = Z); for the N = 2 vortex, BPS saturation is rescued for two reasons: (i) the quantum fluctuations of the Higgs field acquire a nontrivial phase due to the winding of the classical solution, and (ii) a fermionic zero mode used in the literature is shown not to be normalizable.

Recent experimental measurements of high pT hadron spectra and jet correlation at RHIC are analyzed within a parton model which incoporates initial jet production and final propagation in heavy-ion collisions. The suppre-sion of single hadron spectra, back-to-back correlation, their centrality dependence and azimuthal anisotropy point to a dense matter with an initial parton density about 30 times of that in a cold heavy nucleus.

In the last few years experiments at B-factories have established CP violation in Bd decays. From 2007 onward new experiments will start to exploit the large <IMG SRC="/img/revistas/bjp/v34n4a/a04img21.gif">cross-section at the LHC to advance the understanding of CP violation by studying unprecedented large samples of all B-meson flavours. After a short review of the present status, the experimental challenges for the future experiments will be described. The emphasis will be on LHCb, a dedicated B-physics experiment at the LHC, and some examples of the projected physics results will be presented.

A brief review of inflation is presented. After having demonstrated the generality of the inflationary mechanism, the emphasis is put on its simplest realization, namely the single field slow-roll inflationary scenario. Then, it is shown how, concretely, one can calculate the predictions of a given model of inflation. Finally, a short overview of the most popular models is given and the implications of the recently released WMAP data are briefly (and partially) discussed.

We present a brief review of some applications of quantum field theory in condensed matter systems. These include isotropic and anisotropic antiferromagnetic chains, strongly correlated organic conductors, such as the Bechgaard salts, carbon nanotubes and high-Tc superconductors. The review is by no means exhaustive and points to a vast range of new interesting possible applications.

I try to explain why many high-energy theoretical physicists are studying superstrings.

Some of the motivations and basic properties of noncommutative field models are presented. I also comment on recent developments in the understanding of these peculiar and intriguing theories.