710 research outputs found
Conformal Scalar Propagation on the Schwarzschild Black-Hole Geometry
The vacuum activity generated by the curvature of the Schwarzschild
black-hole geometry close to the event horizon is studied for the case of a
massless, conformal scalar field. The associated approximation to the unknown,
exact propagator in the Hartle-Hawking vacuum state for small values of the
radial coordinate above results in an analytic expression which
manifestly features its dependence on the background space-time geometry. This
approximation to the Hartle-Hawking scalar propagator on the Schwarzschild
black-hole geometry is, for that matter, distinct from all other. It is shown
that the stated approximation is valid for physical distances which range from
the event horizon to values which are orders of magnitude above the scale
within which quantum and backreaction effects are comparatively pronounced. An
expression is obtained for the renormalised in the
Hartle-Hawking vacuum state which reproduces the established results on the
event horizon and in that segment of the exterior geometry within which the
approximation is valid. In contrast to previous results the stated expression
has the superior feature of being entirely analytic. The effect of the
manifold's causal structure to scalar propagation is also studied.Comment: 34 pages, 2 figures. Published on line on October 16, 2009 and due to
appear in print in Gen.Rel.Gra
On Free Quotients of Complete Intersection Calabi-Yau Manifolds
In order to find novel examples of non-simply connected Calabi-Yau
threefolds, free quotients of complete intersections in products of projective
spaces are classified by means of a computer search. More precisely, all
automorphisms of the product of projective spaces that descend to a free action
on the Calabi-Yau manifold are identified.Comment: 39 pages, 3 tables, LaTe
Free Fermions and Extended Conformal Algebras
A class of algebras is constructed using free fermions and the invariant
antisymmetric tensors associated with irreducible holonomy groups. (This
version contains minor typographical corrections and some additional
references. )Comment: 7 pages, KCL-Th-94-1
One-loop effective multi-gluon Lagrangian in arbitrary dimensions
We exhibit the one-loop multi-gluon effective Lagrangian in any dimension for
a field theory with a quasilocal background, using the background-field
formalism. Specific results, including counter terms (up to 12 spacetime
dimensions), have been derived, applied to the Yang-Mills theory and found to
be in agreement with other string-inspired approaches.Comment: 16 pages, LaTe
The Rotating Quantum Thermal Distribution
We show that the rigidly rotating quantum thermal distribution on flat
space-time suffers from a global pathology which can be cured by introducing a
cylindrical mirror if and only if it has a radius smaller than that of the
speed-of-light cylinder. When this condition is met, we demonstrate numerically
that the renormalized expectation value of the energy-momentum stress tensor
corresponds to a rigidly rotating thermal bath up to a finite correction except
on the mirror where there are the usual Casimir divergences.Comment: 8 pages, 2 PostScript figure
Chains of N=2, D=4 heterotic/type II duals
We report on a search for heterotic strings that are dual candidates of
type II compactifications on Calabi-Yau threefolds described as
fibrations. We find many new heterotic duals by using standard orbifold
techniques. The associated type II compactifications fall into chains in which
the proposed duals are heterotic compactifications related one another by a
sequential Higgs mechanism. This breaking in the heterotic side typically
involves the sequence , while in the type II side the weights of the complex hypersurfaces and the
structure of the quotient singularities also follow specific patterns.Comment: Latex, 21 pages, 2 table
La educación no formal de alumnos de primaria mediante la teoría de las situaciones didácticas : el caso del ludión
La teoría de situaciones didácticas de Guy Brousseau que se desarrolló en el área de las matemáticas ahora se está aplicando a todas las ciencias experimentales. Se presenta aquí su adaptación al programa de educación no formal «Niñ@s Talento» para alumnos de nivel primaria al emplear el experimento del ludión o buzo cartesiano. Una ventaja de esta teoría es que no exige llegar a los conocimientos científicos escolares (fase de institucionalización) para explicar diversos experimentos realizados. De esta manera los alumnos que participaron en esta actividad lúdica disfrutan realmente las situaciones didácticas y generan conocimiento que les permite explicar lo observado, a su nivel de conocimiento
Vacuum Polarization and Energy Conditions at a Planar Frequency Dependent Dielectric to Vacuum Interface
The form of the vacuum stress-tensor for the quantized scalar field at a
dielectric to vacuum interface is studied. The dielectric is modeled to have an
index of refraction that varies with frequency. We find that the stress-tensor
components, derived from the mode function expansion of the Wightman function,
are naturally regularized by the reflection and transmission coefficients of
the mode at the boundary. Additionally, the divergence of the vacuum energy
associated with a perfectly reflecting mirror is found to disappear for the
dielectric mirror at the expense of introducing a new energy density near the
surface which has the opposite sign. Thus the weak energy condition is always
violated in some region of the spacetime. For the dielectric mirror, the mean
vacuum energy density per unit plate area in a constant time hypersurface is
always found to be positive (or zero) and the averaged weak energy condition is
proven to hold for all observers with non-zero velocity along the normal
direction to the boundary. Both results are found to be generic features of the
vacuum stress-tensor and not necessarily dependent of the frequency dependence
of the dielectric.Comment: 16 pages, 4 figures, Revtex style Minor typographic corrections to
equations and tex
Heterotic strings on G_2 orbifolds
We study compactification of heterotic strings to three dimensions on
orbifolds of G_2 holonomy. We consider the standard embedding and show that the
gauge group is broken from E_8 x E_8 or SO(32) to F_4 x E_8 or SO(25)
respectively. We also compute the spectrum of massless states and compare with
the results obtained from reduction of the 10-dimensional fields. Non-standard
embeddings are discussed briefly. For type II compactifications we verify that
IIB and IIA have equal massless spectrum.Comment: LaTex, 21 page
- …