59,850 research outputs found
Enhanced Gauge Symmetry in Three-Moduli Models of Type-II String and Hypergeometric Series
The conifold singularities in the type-II string are considered as the points
of phase transition. In some cases, these singularities can be understood in
the framework of the conventional fields theores as the points of enhanced
gauge symmetry. We consider a class of three moduli Type-II strings. It is
shown the periods can be written in the form of hypergeometric series around
the singular points in these models. The leading expansion around the conifold
locus turns out to be described by Appell functions. In one singular point, we
observe the enhanced gauge symmetry of independent of the
models. Around another conifold locus, however, the resulting expression of the
Appell functions depends on the models. We examine the result by considering a
relation between these Appell functions and underlying Riemann surfaces.Comment: 20 pages, Late
Quantum gauge boson propagators in the light front
Gauge fields in the light front are traditionally addressed via the
employment of an algebraic condition in the Lagrangian density,
where is the gauge field (Abelian or non-Abelian) and is the
external, light-like, constant vector which defines the gauge proper. However,
this condition though necessary is not sufficient to fix the gauge completely;
there still remains a residual gauge freedom that must be addressed
appropriately. To do this, we need to define the condition with . The implementation of this
condition in the theory gives rise to a gauge boson propagator (in momentum
space) leading to conspicuous non-local singularities of the type where . These singularities must be conveniently
treated, and by convenient we mean not only matemathically well-defined but
physically sound and meaningfull as well. In calculating such a propagator for
one and two noncovariant gauge bosons those singularities demand from the
outset the use of a prescription such as the Mandelstam-Leibbrandt (ML) one. We
show that the implementation of the ML prescription does not remove certain
pathologies associated with zero modes. However we present a causal,
singularity-softening prescription and show how to keep causality from being
broken without the zero mode nuisance and letting only the propagation of
physical degrees of freedom.Comment: 10 page
Negative dimensional approach for scalar two-loop three-point and three-loop two-point integrals
The well-known -dimensional Feynman integrals were shown, by Halliday and
Ricotta, to be capable of undergoing analytic continuation into the domain of
negative values for the dimension of space-time. Furthermore, this could be
identified with Grassmannian integration in positive dimensions. From this
possibility follows the concept of negative dimensional integration for loop
integrals in field theories. Using this technique, we evaluate three two-loop
three-point scalar integrals, with five and six massless propagators, with
specific external kinematic configurations (two legs on-shell), and four
three-loop two-point scalar integrals. These results are given for arbitrary
exponents of propagators and dimension, in Euclidean space, and the particular
cases compared to results published in the literature.Comment: 6 pages, 7 figures, Revte
Excited state TBA and functional relations in spinless Fermion model
The excited state thermodynamic Bethe ansatz (TBA) equations for the spinless
Fermion model are presented by the quantum transfer matrix (QTM) approach. We
introduce a more general family called T-functions and explore functional
relations among them (T-system) and their certain combinations (Y-system).
{}From their analytical property, we derive a closed set of non-linear integral
equations which characterize the correlation length of at
any finite temperatures. Solving these equations numerically, we explicitly
determine the correlation length, which coincides with earlier results with
high accuracy.Comment: 4 page
Diffractive heavy pseudoscalar-meson productions by weak neutral currents
A first theoretical study for neutrino-induced diffractive productions of
heavy pseudoscalar-mesons, \eta_c and \eta_b, off a nucleon is performed based
on factorization formalism in QCD. We evaluate the forward diffractive
production cross section in perturbative QCD in terms of the light-cone wave
functions of Z boson and \eta_{c,b} mesons, and the gluon distribution of the
nucleon. The diffractive production of \eta_c is governed by the axial vector
coupling of the longitudinally polarized Z boson to Q\bar{Q} pair, and the
resulting \eta_c production cross section is larger than the J/\psi one by one
order of magnitude. The bottomonium \eta_b production, which shows up for
higher beam energy, is also discussed.Comment: 5 pages with 3 embedded figures. Talk presented at the 15th
International Spin Physics Symposium, Spin 2002, Brookhaven National
Laboratory, September 9-14, 200
Prepotential of Supersymmetric Yang-Mills Theories in the Weak Coupling Region
We show how to obtain the explicite form of the low energy quantum effective
action for supersymmetric Yang-Mills theory in the weak coupling region
from the underlying hyperelliptic Riemann surface. This is achieved by
evaluating the integral representation of the fields explicitly. We calculate
the leading instanton corrections for the group SU(\nc), SO(N) and
and find that the one-instanton contribution of the prepotentials for the these
group coincide with the one obtained recently by using the direct instanton
caluculation.Comment: 13 pages, LaTe
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