A unitary model for structure functions and diffractive production at small x

We propose a unified approach which describes both structure functions in the small-$x$ region and diffractive production in $\gamma^*p$-interactions. It is shown that the model, based on reggeon calculus and a quark-parton picture of the interaction, gives a good description of available experimental data in a broad region of $Q^2$ (including $Q^2 =0$) with a single Pomeron of intercept $\alpha_P(0) = 1.2$. Predictions for very small $x$ are given and the problem of saturation of parton densities is discussed.Comment: 43 pages, latex, 15 postscript figure

Double parton scatterings in high energy hadronic collisions

CDF has recently measured a large number of double parton scatterings. The observed value of $\sigma_{eff}$, the non perturbative parameter which characterizes the process, is considerably smaller as compared with the naive expectation. The small value of $\sigma_{eff}$ is likely to be an indication of the importance of the two-body parton correlations in the many-body parton distributions of the proton.Comment: 8 pages, latex file, no figures, contributions to the proceedings of the ISMD9

Centrality Dependence of Hadron Multiplicities in Nuclear Collisions in the Dual Parton Model

We show that, even in purely soft processes, the hadronic multiplicity in nucleus-nucleus interactions contains a term that scales with the number of binary collisions. In the absence of shadowing corrections, this term dominates at mid rapidities and high energies. Shadowing corrections are calculated as a function of impact parameter and the centrality dependence of mid-rapidity multiplicities is determined. The multiplicity per participant increases with centrality with a rate that increases between SPS and RHIC energies, in agreement with experiment.Comment: 15 pages, 4 postscript figure

On the electroweak phase transition in the Minimal Supersymmetric Standard Model

We study the finite-temperature effective potential of the Minimal Supersymmetric Standard Model, in the limit of only one light Higgs boson. Because of the large top Yukawa coupling, there can be significant differences with respect to the Standard Model case: for given values of the Higgs and top masses, little supersymmetry breaking in the stop sector can make the phase transition more strongly first-order. After including the full structure of the stop mass matrix, the most important experimental constraints and the leading plasma effects, we find that the present limits on Higgs and squark masses are still compatible with the scenario of electroweak baryogenesis, in a small region of parameter space corresponding to m_h \simlt 70 \gev and \msba \simlt 105 \gev.Comment: 10 A4 pages, 7 figures available upon request, CERN-TH.6833/93, IEM-FT-69/93 (one paragraph expanded for clarity

Physics of the Muon Spectrometer of the ALICE Experiment

The main goal of the Muon spectrometer of the ALICE experiment at LHC is the measurement of heavy quark production in p+p, p+A and A+A collisions at LHC energies, via the muonic channel. Physics motivations and expected performances have been presented in this talk.Comment: 10 pages and 4 figures. Talk presented in the ICPAQGP Conference, February 8-12, 2005, Salt Lake City, Kolkata, India. Web page of the conference : http://www.veccal.ernet.in/~icpaqgp

Temperature and Density Effects on the Nucleon Mass Splitting

The finite temperature and finite density dependence of the neutron-proton mass difference is analysed in a purely hadronic framework where the $\rho-\omega$ mixing is crucial for this isospin symmetry breakdown. The problem is handled within Thermo Field Dynamics. The present results, consistent with partial chiral and charge symmetry restoration, improve the experimental data fit for the energy difference between mirror nuclei.Comment: 17 pages, revtex fil

Minijets and the Two-Body Parton Correlation

A large number of double parton scatterings have been recently measured by CDF. The double parton scattering process measures $\sigma_{eff}$, a non perturbative quantity related to the hadronic transverse size and with the dimensions of a cross section. The actual value measured by CDF is considerably smaller as compared with the naive expectation, namely the value of the inelastic non diffractive cross section. The small value of $\sigma_{eff}$ may be an effect of the hadron structure in transverse plane. We discuss the problem by taking into account, at all orders, the two-body parton correlations in the many-body parton distributions.Comment: 19 pages, plane tex, no figure

Spontaneous CP Violation and Baryogenesis in the Minimal Supersymmetric Standard Model

We investigate the effects of the spontaneous CP violation at finite temperature in the Minimal Supersymmetric Standard Model on the baryogenesis at the weak scale. After a brief discussion of the case in which the electroweak phase transition is of the second order, we study in details the baryogenesis scenario when the transition proceeds via bubble nucleation. We show that the space-time dependent phase for the Higgs vacuum expectation values coming from the spontaneous CP violation can give rise to a efficient generation of baryon number inside the bubble walls if the superpotential parameters and the soft supersymmetry breaking ones are complex. However we find that in order to get the observed value for the baryon asymmetry of the universe the phases of such parameters can be as small as $10^{-5}$, giving rise to an electron dipole moment of the neutron well below the current experimental limit. Moreover a light Higgs pseudoscalar is needed, and an upper bound on its mass is obtained.Comment: 17 pages, LaTex, DFPD 93/TH/26 UTS-DFT 93/9 SISSA 93/50-