Diffraction in Charged Current DIS

We present the QCD calculation of the diffractive structure function for charged current DIS. In particular we analyse the perturbatively tractable excitation of heavy quarks. We emphasize the peculiarities of the Regge factorization breaking in excitation of open charm.Comment: 16 pages LateX, 5 eps figures include

A combinatorial proof of tree decay of semi-invariants

We consider finite range Gibbs fields and provide a purely combinatorial proof of the exponential tree decay of semi--invariants, supposing that the logarithm of the partition function can be expressed as a sum of suitable local functions of the boundary conditions. This hypothesis holds for completely analytical Gibbs fields; in this context the tree decay of semi--invariants has been proven via analyticity arguments. However the combinatorial proof given here can be applied also to the more complicated case of disordered systems in the so called Griffiths' phase when analyticity arguments fail

Renormalization Group in the uniqueness region: weak Gibbsianity and convergence

We analyze the block averaging transformation applied to lattice gas models with short range interaction in the uniqueness region below the critical temperature. We prove weak Gibbsianity of the renormalized measure and convergence of the renormalized potential in a weak sense. Since we are arbitrarily close to the coexistence region we have a diverging characteristic length of the system: the correlation length or the critical length for metastability, or both. Thus, to perturbatively treat the problem we have to use a scale-adapted expansion. Moreover, such a model below the critical temperature resembles a disordered system in presence of Griffiths' singularity. Then the cluster expansion that we use must be graded with its minimal scale length diverging when the coexistence line is approached

Quark fragmentation into vector and pseudoscalar mesons at LEP

Some data on the ratio of vector to vector + pseudoscalar mesons, V/(V+P), and the probability of helicity zero vector states, rho_00, are now available from LEP. A possible relation between these two quantities and their interpretation in terms of polarized fragmentation functions are discussed; numerical estimates are given for the relative occupancies of K and K*, D and D*, B and B* states.Comment: 5 pages, no figure

Off-diagonal helicity density matrix elements for vector mesons produced in polarized e+e- processes

Final state quark-antiquark interactions give origin to non zero values of the off-diagonal element rho_{1,-1} of the helicity density matrix of vector mesons produced in e+e- annihilations, as confirmed by recent OPAL data on Phi, D^* and K^*'s. New predictions are given for rho_{1,-1} of several mesons produced at large x_E and small p_T -- i.e. collinear with the parent jet -- in the annihilation of polarized e+ and e-; the results depend strongly on the elementary dynamics and allow further non trivial tests of the Standard Model.Comment: LaTeX, 20 pages, 6 ps figures, uses epsfig.st

Charged Current Diffractive Structure Functions

We present our study of the diffraction in charged current DIS. We analyse the perturbatively tractable excitation of heavy quarks, emphasizing the peculiarities of the Regge factorization breaking in excitation of open charm.Comment: Proceeding of LISHEP98 workshop on diffractive physic

The Pomeron in Elastic and Deep Inelastic Scattering

We discuss some properties of the Pomeron in high energy elastic hadron-hadron and deep inelastic lepton-hadron scattering. A number of issues concerning the nature and the origin of the Pomeron are briefly recalled here. The novelty in this paper resides essentially in its presentation; we strive at discussing all these various issues in the following unifying perspective : it is our contention that the Pomeron is one and the same in all reactions. Various examples will be provided illustrating why we do not believe that one should invoke additional tools to describe the data. For pedagogical convenience, we list below the topics to be covered in the following. -- 1. Introduction. How many Pomerons? -- 2. The Pomeron in the $S$-matrix theory -- 3. The Pomeron in QCD -- 4. The Pomeron in deep inelastic scattering -- 5. The Pomeron structure -- 6. (Temporary?) ConclusionsComment: 32 pages in TeX; 27 figures (available on request from [email protected]

Towards a nonequilibrium thermodynamics: a self-contained macroscopic description of driven diffusive systems

In this paper we present a self-contained macroscopic description of diffusive systems interacting with boundary reservoirs and under the action of external fields. The approach is based on simple postulates which are suggested by a wide class of microscopic stochastic models where they are satisfied. The description however does not refer in any way to an underlying microscopic dynamics: the only input required are transport coefficients as functions of thermodynamic variables, which are experimentally accessible. The basic postulates are local equilibrium which allows a hydrodynamic description of the evolution, the Einstein relation among the transport coefficients, and a variational principle defining the out of equilibrium free energy. Associated to the variational principle there is a Hamilton-Jacobi equation satisfied by the free energy, very useful for concrete calculations. Correlations over a macroscopic scale are, in our scheme, a generic property of nonequilibrium states. Correlation functions of any order can be calculated from the free energy functional which is generically a non local functional of thermodynamic variables. Special attention is given to the notion of equilibrium state from the standpoint of nonequilibrium.Comment: 21 page

Off-diagonal helicity density matrix elements for heavy vector mesons inclusively produced in N-N, gamma-N, l-N interactions

Final state interactions in quark fragmentation may give origin to non zero values of the off-diagonal element rho_(1,-1) of the helicity density matrix of vector mesons V produced in current jets, with a large energy fraction x_E; the value of rho_(1,-1)(V) is related to the hard constituent dynamics and tests unusual properties of it. Some recent data on phi, K^* and D^* produced in e^+ e^- annihilations at LEP show such effects. Predictions are given here for rho_(1,-1) of heavy mesons produced in nucleon-nucleon, gamma-nucleon and lepton-nucleon interactions.Comment: LaTeX, 10 pages, 1 postscript figure, uses epsfig.sty. Revised version, to be published on Phys. Lett. B. Some statements added to clarify tex