27,590 research outputs found
Heavy Quark Production at High Energy
We report on QCD radiative corrections to heavy quark production valid at
high energy. The formulae presented will allow a matched calculation of the
total cross section which is correct at O(\as^3) and includes resummation of
all terms of order \as^3 [\as \ln (s/m^2)]^n. We also include asymptotic
estimates of the effect of the high energy resummation. A complete description
of the calculation of the heavy quark impact factor is included in an appendix.Comment: 32 pages (LaTeX) with three figures. Resubmission to agree with
published version, which contains a new note added in proof and modifications
of text of appendix
Scheme Dependence at Small x
We discuss the evolution of F_2^p at small x, emphasizing the uncertainties
related to expansion, fitting, renormalization and factorization scheme
dependence. We find that perturbative extrapolation from the measured region
down to smaller x and lower Q^2 may become strongly scheme dependent.Comment: 8 pages, LaTeX with epsfig, 2 uuencoded figure
The Regularization of the Fermion Determinant in Chiral Quark Models
The momentum dependence of the quark self energy gives a physically motivated
and consistent regularization of both the real and imaginary parts of the quark
loop contribution to the meson action. We show that the amplitudes for
anomalous processes are always reproduced correctly.Comment: 12/8 pages (b/l), plain TeX with harvmac, SphT93/13
The C-Theorem and Chiral Symmetry Breaking in Asymptotically Free Vectorlike Gauge Theories
We confront Cardy's suggested c-function for four-dimensional field theories
with the spontaneous breaking of chiral symmetries in asymptotically free
vectorlike gauge theories with fermions transforming according to different
representations under the gauge group. Assuming that the infrared limit of the
c-function is determined by the dimension of the associated Goldstone manifold,
we find that this c-function always decreases between the ultraviolet and
infrared fixed points.Comment: 8 pages, no figures, a few references adde
Incompatible sets of gradients and metastability
We give a mathematical analysis of a concept of metastability induced by
incompatibility. The physical setting is a single parent phase, just about to
undergo transformation to a product phase of lower energy density. Under
certain conditions of incompatibility of the energy wells of this energy
density, we show that the parent phase is metastable in a strong sense, namely
it is a local minimizer of the free energy in an neighbourhood of its
deformation. The reason behind this result is that, due to the incompatibility
of the energy wells, a small nucleus of the product phase is necessarily
accompanied by a stressed transition layer whose energetic cost exceeds the
energy lowering capacity of the nucleus. We define and characterize
incompatible sets of matrices, in terms of which the transition layer estimate
at the heart of the proof of metastability is expressed. Finally we discuss
connections with experiment and place this concept of metastability in the
wider context of recent theoretical and experimental research on metastability
and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea
BFKL at NNLO
We present a recent determination of an approximate expression for the
O(alpha_s^3) contribution chi_2 to the kernel of the BFKL equation. This
includes all collinear and anticollinear singular contributions and is derived
using duality relations between the GLAP and BFKL kernels.Comment: 8 pages. Talk presented at 12th International Conference on Elastic
and Diffractive Scattering: Forward Physics and QCD, Hamburg, DESY, Germany,
21-25 May 200
Singularity theory study of overdetermination in models for L-H transitions
Two dynamical models that have been proposed to describe transitions between
low and high confinement states (L-H transitions) in confined plasmas are
analysed using singularity theory and stability theory. It is shown that the
stationary-state bifurcation sets have qualitative properties identical to
standard normal forms for the pitchfork and transcritical bifurcations. The
analysis yields the codimension of the highest-order singularities, from which
we find that the unperturbed systems are overdetermined bifurcation problems
and derive appropriate universal unfoldings. Questions of mutual equivalence
and the character of the state transitions are addressed.Comment: Latex (Revtex) source + 13 small postscript figures. Revised versio
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