864 research outputs found
Vacuum Structure of Two-Dimensional Theory on the Orbifold
We consider the vacuum structure of two-dimensional theory on
both in the bosonic and the supersymmetric cases. When the size
of the orbifold is varied, a phase transition occurs at , where
is the mass of . For , there is a unique vacuum, while for
, there are two degenerate vacua. We also obtain the 1-loop quantum
corrections around these vacuum solutions, exactly in the case of and
perturbatively for greater than but close to . Including the
fermions we find that the "chiral" zero modes around the fixed points are
different for . As for the quantum corrections, the
fermionic contributions cancel the singular part of the bosonic contributions
at L=0. Then the total quantum correction has a minimum at the critical length
.Comment: Revtex, 15 pages, 3 eps figure
The Effects of Alfalfa Silage Harvesting Systems on Dry Matter Intake of Friesland Dairy Ewes in Late Pregnancy
With the recent introduction of alfalfa in Chilean Patagonia (Aisén), its utilisation as silage has to be reviewed relative to animal performance. The effect of silage chop length on the voluntary intake has been evaluated in different species, with sheep being more sensitive to chop length than cattle (Dulphy et al., 1984). The objective of this experiment was to evaluate the effects of different alfalfa silage chop lengths on dry matter (DM) intake and eating behaviour of Friesland dairy ewes in late pregnancy
Effective action for in a region with borders
We study quantum effects due to a Dirac field in 2+1 dimensions, confined to
a spatial region with a non-trivial boundary, and minimally coupled to an
Abelian gauge field. To that end, we apply a path-integral representation,
which is applied to the evaluation of the Casimir energy and to the study of
the contribution of the boundary modes to the effective action when an external
gauge field is present. We also implement a large-mass expansion, deriving
results which are, in principle, valid for any geometry. We compare them with
their counterparts obtained from the large-mass `bosonized' effective theory.Comment: 15 pages, 1 figur
Effective Finite Temperature Partition Function for Fields on Non-Commutative Flat Manifolds
The first quantum correction to the finite temperature partition function for
a self-interacting massless scalar field on a dimensional flat manifold
with non-commutative extra dimensions is evaluated by means of dimensional
regularization, suplemented with zeta-function techniques. It is found that the
zeta function associated with the effective one-loop operator may be nonregular
at the origin. The important issue of the determination of the regularized
vacuum energy, namely the first quantum correction to the energy in such case
is discussed.Comment: amslatex, 14 pages, to appear in Phys. Rev.
Explicit Zeta Functions for Bosonic and Fermionic Fields on a Noncommutative Toroidal Spacetime
Explicit formulas for the zeta functions corresponding to
bosonic () and to fermionic () quantum fields living on a
noncommutative, partially toroidal spacetime are derived. Formulas for the most
general case of the zeta function associated to a quadratic+linear+constant
form (in {\bf Z}) are obtained. They provide the analytical continuation of the
zeta functions in question to the whole complex plane, in terms of series
of Bessel functions (of fast, exponential convergence), thus being extended
Chowla-Selberg formulas. As well known, this is the most convenient expression
that can be found for the analytical continuation of a zeta function, in
particular, the residua of the poles and their finite parts are explicitly
given there. An important novelty is the fact that simple poles show up at
, as well as in other places (simple or double, depending on the number of
compactified, noncompactified, and noncommutative dimensions of the spacetime),
where they had never appeared before. This poses a challenge to the
zeta-function regularization procedure.Comment: 15 pages, no figures, LaTeX fil
Dynamical Casimir Effect with Semi-Transparent Mirrors, and Cosmology
After reviewing some essential features of the Casimir effect and,
specifically, of its regularization by zeta function and Hadamard methods, we
consider the dynamical Casimir effect (or Fulling-Davis theory), where related
regularization problems appear, with a view to an experimental verification of
this theory. We finish with a discussion of the possible contribution of vacuum
fluctuations to dark energy, in a Casimir like fashion, that might involve the
dynamical version.Comment: 11 pages, Talk given in the Workshop ``Quantum Field Theory under the
Influence of External Conditions (QFEXT07)'', Leipzig (Germany), September 17
- 21, 200
Casimir Effect for Spherical Shell in de Sitter Space
The Casimir stress on a spherical shell in de Sitter background for massless
scalar field satisfying Dirichlet boundary conditions on the shell is
calculated. The metric is written in conformally flat form. Although the metric
is time dependent no particles are created. The Casimir stress is calculated
for inside and outside of the shell with different backgrounds corresponding to
different cosmological constants. The detail dynamics of the bubble depends on
different parameter of the model. Specifically, bubbles with true vacuum inside
expand if the difference in the vacuum energies is small, otherwise they
collapse.Comment: 9 pages, submitted to Class. Quantum Gra
Effective potential and stability of the rigid membrane
The calculation of the effective potential for fixed-end and toroidal rigid
-branes is performed in the one-loop as well as in the approximations.
The analysis of the involved zeta-functions (of inhomogeneous Epstein type)
which appear in the process of regularization is done in full detail.
Assymptotic formulas (allowing only for exponentially decreasing errors of
order ) are found which carry all the dependences on the basic
parameters of the theory explicitly. The behaviour of the effective potential
(specified to the membrane case ) is investigated, and the extrema of this
effective potential are obtained.Comment: 15 PAGE
Euler Polynomials and Identities for Non-Commutative Operators
Three kinds of identities involving non-commutating operators and Euler and
Bernoulli polynomials are studied. The first identity, as given by Bender and
Bettencourt, expresses the nested commutator of the Hamiltonian and momentum
operators as the commutator of the momentum and the shifted Euler polynomial of
the Hamiltonian. The second one, due to J.-C. Pain, links the commutators and
anti-commutators of the monomials of the position and momentum operators. The
third appears in a work by Figuieira de Morisson and Fring in the context of
non-Hermitian Hamiltonian systems. In each case, we provide several proofs and
extensions of these identities that highlight the role of Euler and Bernoulli
polynomials.Comment: 20 page
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