Repositório RCAAP

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Main features of nonlocal chiral quark models are discussed, focusing on the description of low energy phenomenology and the analysis of phase transitions at finite temperature and/or chemical potential. Applications to compact stars are commented.

We review in these notes the recent results of the Pierre Auger Observatory related to ultra high energy cosmic rays. We describe the components of the observatory and the status of its operation. The observations related here cover the correlation with astrophysical sources and its implications, as well as the determination of the spectrum at the higher end of energy, and the detemination of the primary cosmic rays being photons. We also report on the limit of the neutrino flux. It is described the next steps in the layout of the Observatory, which includes extending the capabilities of the Southern observatory to lower energies and, in the Northen Hemisphere the construction of a new observatory in Colorado, USA.

In this contribution results from a phenomenological analysis for the diffractive hadroproduction of heavy flavors at high energies are reported. Diffractive production of charm, bottom and top are calculated using the Regge factorization, taking into account recent experimental determination of the diffractive parton density functions in Pomeron by the H1 Collaboration at DESY-HERA. In addition, multiple-Pomeron corrections are considered through the rapidity gap survival probability factor. We give numerical predictions for single diffractive as well as double Pomeron exchange (DPE) cross sections, which agree with the available data for diffractive production of charm and beauty. We make estimates which could be compared to future measurements at the LHC.

We analyse the possibilities to detect a new Z' boson in di-electron events at LHC in the framework of the 331 model with right-handed neutrinos. For an integrated luminosity of 100fb-1 at LHC, and considering a central value Mz' = 1500 GeV, we obtain the invariant mass distribution in the process pp → Z' → e+e-, where a huge peak, corresponding to 800 signal events, is found above the SM background. The number of di-electron events vary from 10000 to 1 in the mass range of Mz' = 1000 - 5000 GeV.

The return of the cosmological constant A to explain the accelerated stage of the universe has brought back many puzzles and misteries surrounding this constant. These enigmas touch upon the scales set by Λ, the cosmological aspect, the astrophysical effects of Λ and its role in quantum gravity. We will briefly discuss all these aspects putting the emphasis on issues not commonly known.

We present and discuss our recent study of an eikonal two channel model, in which we reproduce the soft total, integrated elastic and diffractive cross sections, and the corresponding forward differential slopes in the ISR-Tevatron energy range. Our study is extended to provide predictions at the LHC and Cosmic Rays energies. These are utilized to assess the role of unitarity at ultra high energies, as well as predict the implied survival probability of exclusive diffractive central production of a light Higgs. Our approach is critically examined so as to estimate the margins of error of the calculated survival probability for diffractive Higgs production.

The thermal behaviour of the mass, leptonic decay constant, and width of heavy-light quark peseudoscalar and vector mesons is analized in the framework of thermal Hilbert moment QCD sum rules. In all the cases, the meson leptonic decay constants decrease with increasing T, and vanish at a critical temperature Tc, while the mesons develop a width which increases dramatically, diverging when T → Tc, where Tc is the temperature for chiral-symmetry restoration. The spectral function becomes a smooth function of the energy. This is interpreted as a signal for deconfinement at T = Tc. In contrast, the thermal masses are stable, except when T → Tc, where the pseudoscalar meson mass increases slightly by 10-20 %, and the vector meson mass decreases by some 20-30 %.

The azimuthal asymmetry of direct photons originating from primary hard scatterings between partons is calculated. This can be accounted for by the inclusion of the color dipole orientation, which is sensitive to the rapid variation of the nuclear profile. To this end we introduce the dipole orientation within the saturation model of Golec-Biernat and Wusthoff, while preserving all its features at the cross-section level. We show that the direct photon elliptic anisotropy v2 coming from this mechanism changes sign and becomes negative for peripheral collisions, albeit it is quite small for nuclear collisions at the RHIC energy.

We present results for the photoproduction helicity amplitudes of excited baryons obtained in the context of the 1 /Nc expansion of QCD. The results show that, in order to get a satisfactory description of the observed photoproduction amplitudes, the sub-leading corrections in 1/Nc are important. We also find that, while one-body effective operators are dominant, there is some evidence for the need of two-body effects which, in general, are not included in quark model calculations.

By using the Cheng, Sher and Yuan's anzats, we study the light Higgs Boson production associated with b quark production at TEVATRON using the 2HDM type III. We compare the simulations with experimental results coming from TEVATRON, finding valid ranges for the bb coupling. By using these results, we calculate the cross section for the process pp → bbh(bb) for the LHC collider.

We revisited the calculation of the effective potential for self-interacting scalar field with U (1) charge at one loop approximation. We show that high charge densities can induce important changes in the phase structure of the theory. A class of very interesting phenomena appear when we introduce finite density effects, e.g. symmetry nonrestoration, inverse symmetry breaking and anticipation of the high temperature symmetry restoration. The extension of these calculations in the context of multi-scalar field theory is outlined, with the objectives of studying the effects of a finite charge on the symmetry breaking phase transition, and to learn how these effects change the number of phases allowed by the system symmetries.

The electromagnetic form factors of light and heavy pseudoscalar mesons are calculated within two covariant constituent-quark models, viz., a light-front and a dispersion relation approach. We investigate the details and physical origins of the model dependence of various hadronic observables: the weak decay constant, the charge radius and the elastic electromagnetic form factor.

We obtain through a Matrix Product Ansatz the exact solution of the most general inhomogeneous spin chain with nearest neighbor interaction and with U(1)² and U(1)³ symmetries. These models are related to the one loop mixing matrix of the Leigh-Strassler deformed N = 4 SYM theory, dual to type IIB string theory in the generalized Lunin-Maldacena backgrounds, in the sectors of two and three kinds of fields, respectively. The solutions presented here generalizes the results obtained by the author in a previous work for homogeneous spins chains with U(1)N symmetries in the sectors of N = 2 and N = 3.

We study three different variables that can be useful for Z' model discrimination: the forward-backward asymmetry, the rapidity ratio and the associated production. We also present two approaches to correct the Forward-Backward Asymmetry, which is affected by the unknown initial quark direction in the proton-proton collision. The study is performed for six different Z' models, using Monte Carlo events and a fast detector simulation. It is shown that the models studied here are distinguishable for a Z' mass of 1 TeV after one year of data taking in high luminosity.

We extend a recently proposed dipole model which relates the virtual photon-proton cross section to the dipole-proton forward scattering amplitude in momentum space investigating the effects of the gluon number fluctuations. The model interpolates between well known asymptotic behaviours predicted by perturbative QCD from the Balitsky-Kovchegov equation, which describes the rapidity evolution of the dipole-proton scattering amplitude in the mean field approximation. The model was shown to be successful in describing the last HERA data for the case where the strong coupling constant αs is fixed, showing also some important advantages when compared with other dipole models - all of them in coordinate space - in the literature. Based on the fact that the fluctuations may be important in the small-x evolution and on recent results obtained in coordinate space beyond the mean field approximation, we use this model to parametrize the proton structure function and confront it to HERA data using the average (physical) amplitude - then including fluctuations - within the momentum space framework.

The rate for inclusive charm production in neutral current neutrino-nucleus interactions is calculated. The interaction of high energy neutrinos on hadron targets is an outstanding probe to test Quantum Chromodynamics (QCD) and shed light in the understanding of the parton properties of hadron structure. We have considered the QCD color dipole picture for such an interaction and have in addition used parton saturation models. In particular, the dipole cross section is taken from recent phenomenology on deep inelastic scattering (DIS) at DESY-HERA. The theoretical predictions are compared to available theoretical predictions and experimental results from NuTeV detector at Fermilab. Moreover, we compute the relative rate of the associated cross section in deep inelastic neutrino-nucleus interactions, σ(ccv)σNCtot, from CHORUS Collaboration. As a byproduct, a QCD analysis of the F2, F L and F3 structure functions for the neutral current case also is presented.

The slow convergence of chiral perturbation theory for heavy baryons (HBChPT) suggests that any attempt to unitarize the amplitude following from this method will fail to describe the experimental phase shifts. However, it was possible to obtain a ChPT pion nucleon amplitudes respecting exact unitarity relation by using the Inverse Amplitude Method (IAM), but the resulting total amplitude violates the important property of crossing symmetry [1] . On the other hand, the use of a dispersive calculation, starting directly from a result at second order in the pion momentum, is an alternative approach to get unitarized scattering amplitude. By this method it was possible to fit, with two parameters, the P33 partial wave to the experimental low energy phase shifts, and to present the resulting S and P partial wave phase shifts [2]. This was done with a crossing symmetric amplitude, that respect approximate elastic unitarity relation. In the present exercise, we do not impose crossing symmetry for the amplitude obtained in the previous work, in order to verify the role played by crossing symmetry in the dispersive approach. As in the previous work, our strategy was to perform a fit of the P33 amplitude to the experimental phase shifts and then use the fixed parameters in the S and P partial waves to compare them with the corresponding experimental phase shifts. We conclude that, when we do not impose crossing symmetry for the total amplitude, more parameters are needed in the fitting procedure for P33, moreover the theoretical results for S11, S31, P11, P31 and P13 are quite far from the experimental points.

Our aim is to establish some signatures of the extra neutral gauge boson X0, predicted in a version of the SU(3)c x SU(3)L x U(1)x model with right-handed neutrinos, by considering the process p+p → X0 + X0* + X. In this work, we show some results concerning the LHC energy regime (√s = 14 TeV) and projected luminosity. Some distributions are shown and the X0 width is calculated. We conclude that hadron colliders can show a clear signature for the existence of X0 by comparing its production with Z pair production.

The nonequilibrium dynamics of an homogeneous scalar field is studied using Langevin equations. Microscopic derivations based on quantum field theory methods can lead to complicated nonlocal equations of motion. Here we study, numerically, the results obtained by appropriately approximating these equations in a local form (the Markovian approximation) and compare with results obtained with suitable prescriptions for accounting for the nonlocal terms, i.e. the non-Markovian form. We use a prescription for the nonlocal equations motivated by the results obtained from previous derivations using nonequilibrium quantum field theory methods.