6,923 research outputs found
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 -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
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