59 research outputs found
Cosmological horizons and reconstruction of quantum field theories
As a starting point, we state some relevant geometrical properties enjoyed by
the cosmological horizon of a certain class of Friedmann-Robertson-Walker
backgrounds. Those properties are generalised to a larger class of expanding
spacetimes admitting a geodesically complete cosmological horizon \scrim
common to all co-moving observers. This structure is later exploited in order
to recast, in a cosmological background, some recent results for a linear
scalar quantum field theory in spacetimes asymptotically flat at null infinity.
Under suitable hypotheses on , encompassing both the cosmological de Sitter
background and a large class of other FRW spacetimes, the algebra of
observables for a Klein-Gordon field is mapped into a subalgebra of the algebra
of observables \cW(\scrim) constructed on the cosmological horizon. There is
exactly one pure quasifree state on \cW(\scrim) which fulfils a
suitable energy-positivity condition with respect to a generator related with
the cosmological time displacements. Furthermore induces a preferred
physically meaningful quantum state for the quantum theory in the
bulk. If admits a timelike Killing generator preserving \scrim, then the
associated self-adjoint generator in the GNS representation of has
positive spectrum (i.e. energy). Moreover turns out to be invariant
under every symmetry of the bulk metric which preserves the cosmological
horizon. In the case of an expanding de Sitter spacetime, coincides
with the Euclidean (Bunch-Davies) vacuum state, hence being Hadamard in this
case. Remarks on the validity of the Hadamard property for in more
general spacetimes are presented.Comment: 32 pages, 1 figure, to appear on Comm. Math. Phys., dedicated to
Professor Klaus Fredenhagen on the occasion of his 60th birthda
Topological features of massive bosons on two dimensional Einstein space-time
In this paper we tackle the problem of constructing explicit examples of
topological cocycles of Roberts' net cohomology, as defined abstractly by
Brunetti and Ruzzi. We consider the simple case of massive bosonic quantum
field theory on the two dimensional Einstein cylinder. After deriving some
crucial results of the algebraic framework of quantization, we address the
problem of the construction of the topological cocycles. All constructed
cocycles lead to unitarily equivalent representations of the fundamental group
of the circle (seen as a diffeomorphic image of all possible Cauchy surfaces).
The construction is carried out using only Cauchy data and related net of local
algebras on the circle.Comment: 41 pages, title changed, minor changes, typos corrected, references
added. Accepted for publication in Ann. Henri Poincare
Conformal generally covariant quantum field theory: The scalar field and its Wick products
In this paper we generalize the construction of generally covariant quantum
theories given in the work of Brunetti, Fredenhagen and Verch to encompass the
conformal covariant case. After introducing the abstract framework, we discuss
the massless conformally coupled Klein Gordon field theory, showing that its
quantization corresponds to a functor between two certain categories. At the
abstract level, the ordinary fields, could be thought as natural
transformations in the sense of category theory. We show that, the Wick
monomials without derivatives (Wick powers), can be interpreted as fields in
this generalized sense, provided a non trivial choice of the renormalization
constants is given. A careful analysis shows that the transformation law of
Wick powers is characterized by a weight, and it turns out that the sum of
fields with different weights breaks the conformal covariance. At this point
there is a difference between the previously given picture due to the presence
of a bigger group of covariance. It is furthermore shown that the construction
does not depend upon the scale mu appearing in the Hadamard parametrix, used to
regularize the fields. Finally, we briefly discuss some further examples of
more involved fields.Comment: 21 pages, comments added, to appear on Commun. Math. Phy
Thermal partition function of photons and gravitons in a Rindler wedge
The thermal partition function of photons in any covariant gauge and
gravitons in the harmonic gauge, propagating in a Rindler wedge, are computed
using a local -function regularization approach. The correct Planckian
leading order temperature dependence is obtained in both cases. For the
photons, the existence of a surface term giving a negative contribution to the
entropy is confirmed, as earlier obtained by Kabat, but this term is shown to
be gauge dependent in the four-dimensional case and, therefore is discarded. It
is argued that similar terms could appear dealing with any integer spin in the massless case and in more general manifolds. Our conjecture is
checked in the case of a graviton in the harmonic gauge, where different
surface terms also appear, and physically consistent results arise dropping
these terms. The results are discussed in relation to the quantum corrections
to the black hole entropy.Comment: 29 pages, RevTeX, no figures. Minor errors corrected and a few
comments changed since first submission. To be published on Phys.Rev.
Functional determinants for general self-adjoint extensions of Laplace-type operators resulting from the generalized cone
In this article we consider the zeta regularized determinant of Laplace-type
operators on the generalized cone. For {\it arbitrary} self-adjoint extensions
of a matrix of singular ordinary differential operators modelled on the
generalized cone, a closed expression for the determinant is given. The result
involves a determinant of an endomorphism of a finite-dimensional vector space,
the endomorphism encoding the self-adjoint extension chosen. For particular
examples, like the Friedrich's extension, the answer is easily extracted from
the general result. In combination with \cite{BKD}, a closed expression for the
determinant of an arbitrary self-adjoint extension of the full Laplace-type
operator on the generalized cone can be obtained.Comment: 27 pages, 2 figures; to appear in Manuscripta Mathematic
Listeriose e AIDS: relato de caso e revisão de literatura
A listeriose é uma infecção não incomum, geralmente associada com recém-nascidos e pacientes imunodeprimidos que tem sido poucas vezes encontrada em pacientes com AIDS. Esta escassez de relatos despertou o interesse de diversos investigadores. Neste artigo, os autores relatam um caso de septicemia e meningite por Listeria monocytogenes em paciente com AIDS e fazem uma revisão da literatura. Novos conhecimentos sobre a interação agente - hospedeiro nas infecções por listeria, como o papel do fator de necrose tumoral e da integralina, estão permitindo novas interpretações da aparente escassez de infecções por listeria em pacientes com AIDS. O número de relatos vem crescendo em período recente, sugerindo que a associação pode ser mais freqüente do que aparenta ser, em parte explicada por inadequação no diagnóstico.Listeriosis is a not uncommon infection in humans, usually associated with immunodeficient states and with newborns. However, relatively few cases have been reported in HIV-infected patients. This scarcity of reported cases has aroused interest in the association of listerosis and AIDS. In this paper we present a case of meningitis and septicemia caused by Listeria monocytogenes in a female patient with AIDS. A review of recent medical literature indicates that association of listeriosis and AIDS may be more common than it seems. Recent research in host-parasite interaction in listerial infection suggests an important role for tumor necrosis factor (TNF) and for integralin, a bacterial protein, in modulating listerial disease in AIDS patients. Inadequate diagnosis may be in part responsible for the scarcity of reports
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