75,196 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
The light-cone gauge without prescriptions
Feynman integrals in the physical light-cone gauge are harder to solve than
their covariant counterparts. The difficulty is associated with the presence of
unphysical singularities due to the inherent residual gauge freedom in the
intermediate boson propagators constrained within this gauge choice. In order
to circumvent these non-physical singularities, the headlong approach has
always been to call for mathematical devices --- prescriptions --- some
successful ones and others not so much so. A more elegant approach is to
consider the propagator from its physical point of view, that is, an object
obeying basic principles such as causality. Once this fact is realized and
carefully taken into account, the crutch of prescriptions can be avoided
altogether. An alternative third approach, which for practical computations
could dispense with prescriptions as well as prescinding the necessity of
careful stepwise watching out of causality would be of great advantage. And
this third option is realizable within the context of negative dimensions, or
as it has been coined, negative dimensional integration method, NDIM for short.Comment: 9 pages, PTPTeX (included
Feynman integrals with tensorial structure in the negative dimensional integration scheme
Negative dimensional integration method (NDIM) is revealing itself as a very
useful technique for computing Feynman integrals, massless and/or massive,
covariant and non-covariant alike. Up to now, however, the illustrative
calculations done using such method are mostly covariant scalar integrals,
without numerator factors. Here we show how those integrals with tensorial
structures can also be handled with easiness and in a straightforward manner.
However, contrary to the absence of significant features in the usual approach,
here the NDIM also allows us to come across surprising unsuspected bonuses. In
this line, we present two alternative ways of working out the integrals and
illustrate them by taking the easiest Feynman integrals in this category that
emerges in the computation of a standard one-loop self-energy diagram. One of
the novel and as yet unsuspected bonus is that there are degeneracies in the
way one can express the final result for the referred Feynman integral.Comment: 9 pages, revtex, no figure
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
p-Wave superfluid and phase separation in atomic Bose-Fermi mixture
We consider a system of repulsively interacting Bose-Fermi mixtures of spin
polarized uniform atomic gases at zero temperature. We examine possible
realization of p-wave superfluidity of fermions due to an effective attractive
interaction via density fluctuations of Bose-Einstein condensate within
mean-field approximation. We find the ground state of the system by direct
energy comparison of p-wave superfluid and phase-separated states, and suggest
an occurrence of the p-wave superfluid for a strong boson-fermion interaction
regime. We study some signatures in the p-wave superfluid phase, such as
anisotropic energy gap and quasi-particle energy in the axial state, that have
not been observed in spin unpolarized superfluid of atomic fermions. We also
show that a Cooper pair is a tightly bound state like a diatomic molecule in
the strong boson-fermion coupling regime and suggest an observable indication
of the p-wave superfluid in the real experiment.Comment: 7 pages, 6 figur
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
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