Search

The gluon self-energies and dispersion laws in the color superconducting phase of QCD with two massless flavors are calculated using the effective theory near the Fermi surface. These quantities are calculated at zero temperature for all the eight gluons, those of the remaining SU(2) color group and those corresponding to the broken generators. The construction of the effective interaction is completed with the one loop calculation of the three- and four-point gluon interactions.

Abstract.: Using a QCD relativistic potential model, previously applied to the calculation of the heavy meson leptonic constants, we evaluate the form factors governing the exclusive decays , and . In our approach the heavy meson is described as a bound state, whose wave function is solution of the relativistic Salpeter equation, with an instantaneous potential displaying Coulombic behaviour at small distances and linear behaviour at large distances. The light vector meson is described by using a vector current interpolating field, according to the Vector Meson Dominance assumption. A Pauli-Villars regularized propagator is assumed for the quarks not constituting the heavy meson. Our procedure allows to avoid the description of the light meson in terms of wave function and constituent quarks, and consequently the problem of boosting the light meson wave function. Assuming as an input the experimental results on , we evaluate all the form factors describing the semileptonic and rare transitions. The overall comparison with the data, whenever available, is satisfactory.

We propose a model of polarized partonic densities based on Regge behaviour, quark counting rules,U(1)A Goldberger-Treiman relation and positivity constraints. The resulting polarized proton structure function is found to be in agreement with EMC and SLAC data. From this input we compute double helicity asymmetries for 1 and 2 jet inclusive production in polarized proton proton scattering at high energies. We obtain asymmetries of 10–20% at energies GeV.

We estimate the rates ofB0 decays into neutral charmed final states , by considering factorizable, vector meson dominance and long distance contributions. We also discuss the role of these decay modes as a source of background events in the search for exclusiveb?s? transitions in very high energy experiments, e.g. at LEP.

Using parity violating nucleon wave function effects we make predictions for spin asymmetries inpp and p scattering at moderate and high energies

We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of GeV is analyzed in detail.

We estimate long distance corrections to radiativeB →K*γ and to non leptonicB→Kπ,B→K*π,B→Kσ,B→K*σ,B→KΦ andB→K*Φ decays generated by the ( c) ( s) part of the non leptonic weak Hamiltonian. While vanishing in the vacuum saturation approximation, these corrections are finite if one includes single particle charmed states between the currents in the Hamiltonian. We find small effects in radiative decays, but significant contributions to several non leptonic processes.

We analyse an artificial neural network which deviates from biological behaviour in two aspects. First, the process of activation of a generic neuron is not described by a monotone increasing output function. This means that, while artificial neurons modelled on biological behaviour are active when the sum of the postsynaptic potentials is larger than a given threshold and quiescent in the opposite case, in our model the state of the neuron depends non-monotonically on its argument, i.e. the activation function is not an increasing function, but has a more complicated behaviour which reduces to the usual (step or sigmoid) function for some particular values of the parameters describing its shape. Second, they assume as a learning rule of the network a modification of the Hebb rule, namely they choose an iterative algorithm (Edinburgh algorithm) that constructs a synaptic matrix with a given set of stored memories and given retrieval properties, i.e. given domains of attraction of the stored patterns. The non-monotonicity of the output function results, for some values of the parameters, in a larger storage capacity than in conventional models, whereas the choice of the learning rule allows to control the domains of attraction of the memories.

In the framework of a QCD inspired relativistic potential model, we evaluate radiative decay rates of heavy mesons and their coupling with soft pions. The agreement with the existing experimental data is satisfactory. In the limit mQ→ ∞ one obtains results in agreement with the Heavy Quark Effective Theory and is able to predict the values of the relevant couplings; in particular, for the scaled B*Bπ strong coupling constant g, we find that the non relativistic constituent quark model prediction g=1 is modified, by the inclusion of the relativistic effects due to the light quarks, to the value g=1/3, in agreement with recent QCD sum rules determination.

Deep inelastic scattering on a photon target has been calculated in the framework of the Massive Quark Model (MQM). Precise predictions are given for the longitudinal and transverse structure function, and a comparison with the calculation of Quark Parton Model and of perturbative QCD is carried out.

Weapply WKB techniques to a Schrödinger equation modified for relativistic kinematics. We show that a potential consisting of linear and logarithmic terms accounts for different aspects of quarkonium phenomenology. Using an Extended Vector Meson Dominance model we calculateRe+e- and we derive the Quark Parton Model result.

We calculate the ratioR in the framework of Anisotropic Chromo-Dynamics (ACD), a recently proposed approach to strong interactions, and we show that asymptotically the Quark Parton Model value is recovered. Scaling violations due to the quark-masses and to the structure of the -potential are also calculated.

Long-distance, nonperturbative effects in the parity-violating pion-nucleon coupling constantEπare calculated. Our result isEπ= (2.1-5.5) .10-7in agreement with the present experimental data

The new experimental results on v¯pdeep inelastic scattering show that we possess a good numerical understanding of this important class of phenomena. We argue that among the different descriptions of deep inelastic scattering, the MQM clearly qualifies as the most predective, economical and realistic approach to this fascinating area of physics.

A glance at fig. 9–18 shows that the MQM gives a very accurate and economical description of all relevant deep inelastic processes. What conclusion should we draw from our study?