Scielo RSS <![CDATA[Brazilian Journal of Physics]]> http://www.scielo.br/rss.php?pid=0103-973320070001&lang=en vol. 37 num. 1A lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<B>Foreword</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100001&lng=en&nrm=iso&tlng=en <![CDATA[<B>Yogiro Hama</B>: <B>a life in time and space</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100002&lng=en&nrm=iso&tlng=en In this article we write a biographical note about Yogiro Hama. It is quite an amazing life story, as you will read in the pages below. In the second part of this article we include many messages and letters sent by several of his friends and collaborators for the celebration of his 70th birthday. <![CDATA[<B>Learning hydrodynamics with Yogiro Hama</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100003&lng=en&nrm=iso&tlng=en As part of the celebration of his 70th birthday, I review the works done in collaboration with Prof. Yogiro Hama and try to recover the history of some of his ideas concerning the formation of a fluid in high energy hadronic collisions, its expansion and dissociation. I show how these ideas evolved and how they are relevant for understanding the present experimental data. <![CDATA[<B>Working in hydrodynamics with Yogiro Hama</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100004&lng=en&nrm=iso&tlng=en I present a brief overview on the motivation for performing relativistic nuclear collisions and the justification for using hydrodynamics to describe them. The contribution of Prof. Hama to the field of hydrodynamics and his efforts to form a group working on this subject are outlined. <![CDATA[<B>On the França and Hama analysis of elastic hadron scattering</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100005&lng=en&nrm=iso&tlng=en After reviewing the main aspects of the model-independent analysis on elastic proton-proton scattering, developed by França and Hama in the seventies, we argue that the work can be considered a paradigm for empirical analysis on elastic hadron interactions (the inverse problem). We discuss some further developments, consequences and results that have been recently obtained on the subject and which have been based on the original strategy by França and Hama. <![CDATA[<B>Tunneling and the Vacuum Zero-Point Radiation</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100006&lng=en&nrm=iso&tlng=en We make a brief review of the Kramers escape rate theory for the probabilistic motion of a particle in a potential well U(x), and under the influence of classical fluctuation forces. The Kramers theory is extended in order to take into account the action of the thermal and zero-point random electromagnetic fields on a charged particle. The result is physically relevant because we get a non null escape rate over the potential barrier at low temperatures (T -> 0). It is found that, even if the mean energy is much smaller than the barrier height, the classical particle can escape from the potential well due to the action of the zero-point fluctuating fields. These stochastic effects can be used to give a classical interpretation to some quantum tunneling phenomena. Relevant experimental data are used to illustrate the theoretical results. <![CDATA[<B>Space-time and hadrons</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100007&lng=en&nrm=iso&tlng=en The hadronic structure is investigated in terms of a recently proposed theory which considers the effect of the strong interaction in the space-time description. From the equations, the masses of the particles may be calculated, and quark confinement appears as a natural result, without the need of confining potentials. Some properties of the considered particles, such as the topponium size, are also estimated. <![CDATA[<B>Color flavor locked phase transition in strange quark matter</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100008&lng=en&nrm=iso&tlng=en We discuss macroscopic aspects of quark matter phase transition in cold dense stellar matter, considering global charge neutrality and baryonic charge conservation. We determine the critical condition for the phase transition between the strange quark matter, SQM, and the color-flavor locked, CFL, superconducting phase. We also discuss the sensitivity of our results to variations in the gap energy, delta, and in the current strange quark mass, m s0. The phase transition is calculated taking into account the baryonic density dependence of the quark masses in dense baryonic medium. <![CDATA[<B>Yang-Mills effective action from QCD at finite chemical potential</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100009&lng=en&nrm=iso&tlng=en We present a construction of an effective Yang-Mills action for QCD, from the expansion of the fermionic determinant in terms of powers of the chemical potential at high temperature for the case of massless quarks. We analyze this expansion in the perturbative region and find that it gives extra spurious information. We propose for the non-perturbative sector a simplified effective action which, in principle, contains only the relevant information. <![CDATA[<B>Cold and dense perturbative Yukawa theory with massive fermions</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100010&lng=en&nrm=iso&tlng=en Recent results for the two-loop thermodynamic potential of QCD at finite density have shown that nonzero quark mass corrections to the pressure are relevant and can dramatically affect the structure of compact stars. Motivated by these findings, we consider a simple toy model - cold and dense Yukawa theory - to study the effects of finite fermion masses on the pressure. The role of renormalization group running of the coupling and mass is also discussed. Results within this simple model might be useful in the description of condensates in the core of neutron stars. <![CDATA[<B>Semiclassical approximation for the partition function in QFT</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100011&lng=en&nrm=iso&tlng=en In this paper we discuss the semiclassical approximation for the thermodynamics of scalar fields. We construct a semiclassical propagator in terms of two solutions of an ordinary differential equation. The main result is an analytic (non-perturbative) expression for the partition function written in terms of known quantities. <![CDATA[<B>Linear sigma model at finite baryonic density and symmetry breakings</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100012&lng=en&nrm=iso&tlng=en The linear sigma model at finite baryonic density with a massive vector field is investigated considering that all the bosonic fields develop non zero expected classical values, eventually associated with condensates and corresponding to dynamical symmetry breakings which might occur in the QCD phase diagram. A modified equation for the classical vector field is proposed with its respective solution. Some in medium properties of the model (mainly masses) are investigated within reasonable prescriptions. In particular the behavior of the in medium pion and sigma masses and a particular way of calculating in medium coupling to baryons is investigated. A symmetry radius for finite baryonic densities is proposed and calculated in different ways in terms of the other variables of the model and these different ways of calculating it agree quite well. However, assuming that the pion and sigma masses go to zero close to the restoration of chiral symmetry a too high value for the critical density is obtained rhoc <FONT FACE=Symbol>@</FONT> 4.3 rho0. <![CDATA[<B>Numerical simulation of Ginzburg-Landau-Langevin equations</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100013&lng=en&nrm=iso&tlng=en This work is concerned with non-equilibrium phenomena, with focus on the numerical simulation of the relaxation of non-conserved order parameters described by stochastic kinetic equations known as Ginzburg-Landau-Langevin (GLL) equations. We propose methods for solving numerically these type of equations, with additive and multiplicative noises. Illustrative applications of the methods are presented for different GLL equations, with emphasis on equations incorporating memory effects. <![CDATA[<B>Effects of nucleus initialization on event-by-event observables</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100014&lng=en&nrm=iso&tlng=en In this work we present a study of the influence of nucleus initializations on the event-by-event elliptic flow coefficient, v2. In most Monte-Carlo models, the initial positions of the nucleons in a nucleus are completely uncorrelated, which can lead to very high density regions. In a simple, yet more realistic model where overlapping of the nucleons is avoided, fluctuations in the initial conditions are reduced. However, v2 distributions are not very sensitive to the initialization choice. <![CDATA[<B>Role of global and local strangeness neutrality in an inhomogeneous freeze-out approach to relativistic heavy ion collisions</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100015&lng=en&nrm=iso&tlng=en An inhomogeneous decoupling surface of hadrons produced in relativistic heavy-ion collisions may occur, if the expanding hot and dense matter passes through a first order phase transition. We show that due to the non-linear dependence of the particle densities on the temperature and baryon-chemical potential such inhomogeneities should be visible even in the integrated, inclusive abundances. We analyze experimental data from Pb+Pb collisions at CERN-SPS and Au+Au collisions at BNL-RHIC to determine the amplitude of inhomogeneities and the role of local and global strangeness neutrality. <![CDATA[<B>Dark matter halos and the anisotropy of ultra-high energy cosmic rays in the Pierre Auger observatory</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100016&lng=en&nrm=iso&tlng=en We analyze the cosmic ray arrival direction map that would be observed if the source of ultra high energy cosmic rays were the decay of dark matter particles in the halos of our galaxy and of the Andromeda galaxy (M31). To model the dark matter distribution throughout the halos we use two different density profiles, the Moore et al. and the Navarro-Frenk-White profile. The results show what would be seen by the Pierre Auger experiment, since we take into account its exposure. We evaluate the dipole and quadrupole terms for the resulting maps in the two density profiles cases and compare them with the terms expected for an isotropic sky. <![CDATA[<B>Contribution from Drell-Yan processes to the emission spectrum in solar flares</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100017&lng=en&nrm=iso&tlng=en The recent discovery of a new and intense solar flare radiation spectral component with a maximum in the terahertz range has raised a great deal of interest. The origin of this component is still unknown, constituting a problem that goes beyond the application of canonical models used to describe the well-known microwave spectrum. In this work, we present preliminary results on the investigation of a possible contribution from electron-positron pairs produced in a Drell-Yan process to the emission of the terahertz component observed in solar flares. <![CDATA[<B>Investigating the tetraquark structure of the new mesons</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100018&lng=en&nrm=iso&tlng=en Using the QCD sum rule approach we investigate the vertex associated with the decay D0(0+)-> D+pi-, where the scalar meson D0(0+) is considered as a four-quark state $(cd)(\bar{u}\bar{d})$. Although our results for the mass and partial decay width are smaller than the mass and the total decay width of the broad scalar meson D0*0(2308) reported by BELLE Collaboration, we can not discard the possibility that the BELLE's resonance can be interpreted as the four-quark state studied here. <![CDATA[<B>Coupling constants of <I>D<SUP>*</SUP>D<SUB>s</SUB>K</I> and <I>D<SUB>s</SUB><SUP>*</SUP>DK</I> processes</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100019&lng=en&nrm=iso&tlng=en We calculate the coupling constants of D*Ds K and Ds*DK vertices using the QCD sum rules technique. We compare our results with results obtained in the limit of SU(4) symmetry and we found that the symmetry is broken at the order of 40%. <![CDATA[<B>X (3872) in QCD sum rules</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100020&lng=en&nrm=iso&tlng=en QCD spectral sum rules is used to test the nature of the meson X(3872), assumed to be an exotic four-quark $(c\bar{c}q\bar{q})$ state with J PC = 1++. For definiteness, the current proposed recently by Maiani et al [1] is used, at leading order in alphas, considering the contributions of higher dimension condensates. The value M X = (3.94±0.11) GeV is found which is compatible, within the errors, with the experimental candidate X(3872). The uncertainties of our estimates are mainly due to the one from the c quark mass. <![CDATA[<B>Charmed scalar mesons masses within the QCD sum rules framework</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100021&lng=en&nrm=iso&tlng=en In this work, we evaluate the D+sJ(2317), D(0)0(2308), D(0)0(2407) and D+0(2403) masses. These are scalar mesons recently discovered in the BABAR, BELLE and FOCUS Collaborations. The nature of these particles is intensely discussed nowadays. We treat them as a diquark-antidiquark configuration and treat the problem using the QCD sum rules (QCDSR) approach. <![CDATA[<B>The NJL interaction from <I>q</I>-deformed inspired transformations</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100022&lng=en&nrm=iso&tlng=en From the mass term for q-deformed quark fields, we obtain effective contact interactions of the NJL type. The parameters of the model that maps a system of non-interacting deformed fields into quarks interacting via NJL contact terms is discussed. <![CDATA[<B>Brazilian relativistic <I>O</I>(<I>q</I><SUP>4</SUP>) two-pion exchange nucleon-nucleon potential</B>: <B>parametrized version</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100023&lng=en&nrm=iso&tlng=en In our recent works we derived a chiral O(q4) two-pion exchange nucleon-nucleon potential (TPEP) formulated in a relativistic baryon (RB) framework, expressed in terms of the so called low energy constants (LECs) and functions representing covariant loop integrations. In order to facilitate the use of the potential in nuclear applications, we present a parametrized version of our configuration space TPEP. <![CDATA[<B>On the slope of the elastic differential cross sections</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100024&lng=en&nrm=iso&tlng=en Making use of a model-independent analytical fit for the elastic hadron-hadron amplitude, recently developed, we investigate the slope of the proton-proton and antiproton-proton differential cross sections, as a function of the energy and the momentum transfer. We show that the predictions for these quantities are in agreement with the experimental data available and discuss the effect of the slope position as function of the momentum transfer. <![CDATA[<B>Diffraction and an infrared finite gluon propagator</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100025&lng=en&nrm=iso&tlng=en We discuss some phenomenological applications of an infrared finite gluon propagator characterized by a dynamically generated gluon mass. In particular we compute the effect of the dynamical gluon mass on pp and ${\bar{p}}p$ diffractive scattering. We also show how the data on gammap photoproduction and hadronic <FONT FACE=Symbol>gg</FONT> reactions can be derived from the pp and ${\bar{p}}p$ forward scattering amplitudes by assuming vector meson dominance and the additive quark model. <![CDATA[<B>Nucleon and delta sigma-terms</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100026&lng=en&nrm=iso&tlng=en We evaluate nucleon and delta sigma-terms and obtain the results 43 MeV < sigmaN < 49 MeV and 28 MeV < <FONT FACE=Symbol>sD</FONT> < 32 MeV, depending on the coupling constants used, which are compatible with values extracted from experiment and produced by other groups. We show that the decay <FONT FACE=Symbol>D ® p</FONT>N explains the relation <FONT FACE=Symbol>sD</FONT> < sigmaN. <![CDATA[<B>On the existence of Korteweg</B>: <B>de Vries solitons in relativistic hydrodynamics</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100027&lng=en&nrm=iso&tlng=en We study the conditions for the formation and propagation of Korteweg-de Vries solitons in relativistic fluid dynamics using an appropriate equation of state. The KdV equation is obtained from the relativistic version of the Euler and continuity equations. <![CDATA[<B>Hydrodynamic evolution near QCD critical point</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100028&lng=en&nrm=iso&tlng=en Some consequences of the presence of critical point in the equation of state on the hydrodynamical evolution of the strongly interacting matter are discussed. For this purpose, we apply the low energy effective theory of QCD, the Nambu-Jona-Lasinio model and show some examples. <![CDATA[<B>A study of <FONT FACE=Symbol>á</FONT>v<SUB>2</SUB><FONT FACE=Symbol>ñ</FONT> with NeXSPheRIO</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100029&lng=en&nrm=iso&tlng=en Elliptic flow at RHIC is computed event by event with NeXSPheRIO. Reasonable agreement with experimental data on v2(eta) and v2(pt) is obtained. Various effects are studied as well: equation of state (with or without critical point), emission mechanism (Cooper-Frye prescription or continuous emission), type of the initial conditions (average or fluctuating initial conditions). <![CDATA[<B>Causal structure of relativistic dissipative hydrodynamics</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100030&lng=en&nrm=iso&tlng=en We present a new formalism for the relativistic dissipative hydrodynamics consistent with causality. We start from the physical analysis of the irreversible currents according to the Landau-Lifshitz theory. Then, the irreversible currents are given by integral expressions which take into account the relaxation time. Only one additional parameter was introduced, the relaxation time, tauR. We verified that the linearized equation of motion for small perturbations in the homogeneous, static background coincides with Hiscock-Lindblom. <![CDATA[<B>Small-<I>x</I> physics at coherent <I>pA/AA</I> interactions at LHC</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100031&lng=en&nrm=iso&tlng=en We report on our recent investigations in photonuclear production of heavy quarks and vector mesons in ultraperipheral collisions at nucleus-nucleus and proton-nucleus reactions. They are initiated by quasi-real photons coming from one of the nuclei or hadron in interactions taking place at large impact parameter. We focus on the role played by the high energy theoretical/phenomenological approaches in photon-nuclei scattering, namely the strength of parton saturation phenomenon and high energy nuclear shadowing. In particular, our theoretical predictions are compared with the recent experimental measurements on coherent r (STAR) and J/Y (PHENIX) photoproduction at RHIC and estimates for LHC are given. <![CDATA[<B>Gluon saturation and proton</B>: <B>anti-proton cross sections</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100032&lng=en&nrm=iso&tlng=en We study proton - anti-proton cross sections in the framework of an updated minijet eikonal model. We propose a different scheme for fixing the parameters, in which we make use of the measured minijet cross section. We compare the results obtained with the GRV98, MRST98, CTEQ6-L and KLN gluon distributions. The latter includes gluon saturation effects. We conclude that in the very high energy regime the use of the KLN distribution improves significantly the behavior of the cross sections. However this improvement is due to the shape of the KLN gluon density and has little to do with saturation effects. <![CDATA[<B><I>J</I>/<FONT FACE=Symbol>y</FONT> production in the saturation regime</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100033&lng=en&nrm=iso&tlng=en In this work we calculate the J/psi production in the initial stage of proton-proton, proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies, taking into account the high parton density regime of QCD, where the physics of parton saturation is expected to be dominant. We perform a quantitative analysis of the xF distributions in these collisions with the Color Glass Condensate (CGC) approach. The ratio between distributions with or without saturated gluons shows that this mechanism produces a suppression on the J/psi yield in the forward region and presents a dip in intermediate values of xF, which is visible only at LHC energies. <![CDATA[<B>Nuclear dependence of the saturation scale and its consequences for the electron-ion collider</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100034&lng=en&nrm=iso&tlng=en We study the predictions of CGC physics for electron-ion collisions at high energies. The nucleus at high energies acts as an amplifier of saturation effects. We have investigated some observables, using a generalization for nuclear targets of the Iancu-Itakura-Munier model, and our results indicate that the experimental analysis of these observables in the future electron-ion collider could discriminate between linear and saturation physics, as well as constrain the behavior of the saturation scale. <![CDATA[<B>Gluon saturation and leading particle spectra in pp collisions</B>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332007000100035&lng=en&nrm=iso&tlng=en In this work we use the IGM, a model that describes well the energy flux in hadronic collisions, to study the leading particle spectrum when saturation effects on the gluon distribution function are included. The leading particle spectrum is calculated for several center of mass energies (<FONT FACE=Symbol>Ö</FONT>s). In the very high energy limit we compare our results with the predictions made in a recent paper, which also addresses the same problem.