240 research outputs found
Relativistic Quantum Scattering of High Energy Fermions in the Presence of Phase Transition
We study the high energy behaviour of fermions hitting a general wall caused
by a first-order phase transition. The wall profile is introduced through a
general analytic function. The reflection coefficient is computed in the high
energy limit and expressed in terms of the poles of the wall profile function.
It is shown that the leading singularity gives the high energy behaviour.Comment: 10 page
Scaling Properties of the Probability Distribution of Lattice Gribov Copies
We study the problem of the Landau gauge fixing in the case of the SU(2)
lattice gauge theory. We show that the probability to find a lattice Gribov
copy increases considerably when the physical size of the lattice exceeds some
critical value , almost independent of the lattice
spacing. The impact of the choice of the copy on Green functions is presented.
We confirm that the ghost propagator depends on the choice of the copy, this
dependence decreasing for increasing volumes above the critical one. The gluon
propagator as well as the gluonic three-point functions are insensitive to
choice of the copy (within present statistical errors). Finally we show that
gauge copies which have the same value of the minimisation functional () are equivalent, up to a global gauge transformation, and
yield the same Green functions.Comment: replaced with revised version; 23 pages, 7 figures, 27 table
Standard Model Baryogenesis
Simply on CP arguments, we argue against a Standard Model explanation of
baryogenesis via the charge transport mechanism. A CP-asymmetry is found in the
reflection coefficients of quarks hitting the electroweak phase boundary
created during a first order phase transition. The problem is analyzed both in
an academic zero temperature case and in the realistic finite temperature one.
At finite temperature, a crucial role is played by the damping rate of
quasi-quarks in a hot plasma, which induces loss of spatial coherence and
suppresses reflection on the boundary even at tree-level. The resulting baryon
asymmetry is many orders of magnitude below what observation requires. We
comment as well on related works.Comment: 10 pages, CERN-TH. 7368/94, LPTHE Orsay-94/71, HD-THEP-94-2
Semileptonic decays in Lattice QCD : a feasibility study and first results
We compute the decays and with finite
masses for the and quarks. We first discuss the spectral properties of
both the meson as a function of its momentum and of the and
at rest. We compute the theoretical formulae leading to the decay
amplitudes from the three-point and two-point correlators. We then compute the
amplitudes at zero recoil of which turns out not to be
vanishing contrary to what happens in the heavy quark limit. This opens a
possibility to get a better agreement with experiment. To improve the continuum
limit we have added a set of data with smaller lattice spacing. The vanishes at zero recoil and we show a convincing signal but only
slightly more than 1 sigma from 0. In order to reach quantitatively significant
results, we plan to fully exploit smaller lattice spacings as well as another
lattice regularization.Comment: 31 pages with 15 figures ; sections 5 and 6 revised and update
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