57 research outputs found
Massive scalar field on (A)dS space from a massless conformal field in
We show how the equations for the scalar field (including the massive,
massless, minimally and conformally coupled cases) on de Sitter and Anti-de
Sitter spaces can be obtained from both the SO-invariant equation
in and two geometrical constraints defining
the (A)dS space. Apart from the equation in , the results only
follow from the geometry.Comment: Revtex 4.1, 6 pages. In v3: New material added (references, relation
with mass ladder operator), accepted in JM
A toy model of a fake inflation
Discontinuities in non linear field theories propagate through null geodesics
in an effective metric that depends on its dynamics and on the background
geometry. Once information of the geometry of the universe comes mostly from
photons, one should carefully analyze the effects of possible nonlinearities on
Electrodynamics in the cosmic geometry. Such phenomenon of induced metric is
rather general and may occurs for any nonlinear theory independently of its
spin properties. We limit our analysis here to the simplest case of non linear
scalar field. We show that a class of theories that have been analyzed in the
literature, having regular configuration in the Minkowski space-time background
is such that the field propagates like free waves in an effective deSitter
geometry. The observation of these waves would led us to infer, erroneously,
that we live in a deSitter universe
Conformally covariant quantization of Maxwell field in de Sitter space
In this article, we quantize the Maxwell ("massless spin one") de Sitter
field in a conformally invariant gauge. This quantization is invariant under
the SO group and consequently under the de Sitter group. We obtain a
new de Sitter invariant two-points function which is very simple. Our method
relies on the one hand on a geometrical point of view which uses the
realization of Minkowski, de Sitter and anti-de Sitter spaces as intersections
of the null cone in \setR^6 and a moving plane, and on the other hand on a
canonical quantization scheme of the Gupta-Bleuler type.Comment: v2 is is the definitive (improved compare to v1) versio
Fuzzy de Sitter space-times via coherent states quantization
ISBN 0-954946-8-4International audienceA construction of the 2d and 4d fuzzy de Sitter hyperboloids is carried out by using a (vector) coherent state quantization. We get a natural discretization of the dS "time" axis based on the spectrum of Casimir operators of the respective maximal compact subgroups SO(2) and SO(4) of the de Sitter groups SO_0(1,2) and SO_0(1,4). The continuous limit at infinite spins is examined
Conformally related massless fields in dS, AdS and Minkowski spaces
In this paper we write down the equation for a scalar conformally coupled
field simultaneously for de Sitter (dS), anti-de Sitter (AdS) and Minkowski
spacetime in d-dimensions. The curvature dependence appears in a very simple
way through a conformal factor. As a consequence the process of curvature free
limit, including wave functions limit and two-points functions, turns to be a
straightforward issue. We determine a set of modes, that we call de Sitter
plane waves, which become ordinary plane waves when the curvature vanishes.Comment: 7 pages, 1 figur
A natural fuzzyness of de Sitter space-time
A non-commutative structure for de Sitter spacetime is naturally introduced
by replacing ("fuzzyfication") the classical variables of the bulk in terms of
the dS analogs of the Pauli-Lubanski operators. The dimensionality of the fuzzy
variables is determined by a Compton length and the commutative limit is
recovered for distances much larger than the Compton distance. The choice of
the Compton length determines different scenarios. In scenario I the Compton
length is determined by the limiting Minkowski spacetime. A fuzzy dS in
scenario I implies a lower bound (of the order of the Hubble mass) for the
observed masses of all massive particles (including massive neutrinos) of spin
s>0. In scenario II the Compton length is fixed in the de Sitter spacetime
itself and grossly determines the number of finite elements ("pixels" or
"granularity") of a de Sitter spacetime of a given curvature.Comment: 16 page
New Integrable Sectors in Skyrme and 4-dimensional CP^n Model
The application of a weak integrability concept to the Skyrme and
models in 4 dimensions is investigated. A new integrable subsystem of the
Skyrme model, allowing also for non-holomorphic solutions, is derived. This
procedure can be applied to the massive Skyrme model, as well. Moreover, an
example of a family of chiral Lagrangians providing exact, finite energy
Skyrme-like solitons with arbitrary value of the topological charge, is given.
In the case of models a tower of integrable subsystems is obtained. In
particular, in (2+1) dimensions a one-to-one correspondence between the
standard integrable submodel and the BPS sector is proved. Additionally, it is
shown that weak integrable submodels allow also for non-BPS solutions.
Geometric as well as algebraic interpretations of the integrability conditions
are also given.Comment: 23 page
Oesophageal adenocarcinoma is associated with a deregulation in the MYC/MAX/MAD network
Oesophageal adenocarcinoma, which arises from an acquired columnar lesion, Barrett's metaplasia, is rising in incidence more rapidly than any other cancer in the Western world. Elevated expression of c-MYC has been demonstrated in oesophageal adenocarcinoma; however, the expression of other members of the MYC/MAX/MAD network has not been addressed. The aims of this work were to characterise the expression of c-MYC, MAX and the MAD family in adenocarcinoma development and assess the effects of overexpression on cellular behaviour. mRNA expression in samples of Barrett's metaplasia and oesophageal adenocarcinoma were examined by qRT–PCR. Semi-quantitative immunohistochemistry and western blotting were used to examine cellular localisation and protein levels. Cellular proliferation and mRNA expression were determined in SEG1 cells overexpressing c-MYCER or MAD1 using a bromodeoxyuridine assay and qRT–PCR, respectively. Consistent with previous work expression of c-MYC was deregulated in oesophageal adenocarcinoma. Paradoxically, increased expression of putative c-MYC antagonists MAD1 and MXI1 was observed in tumour specimens. Overexpression of c-MYC and MAD proteins in SEG1 cells resulted in differential expression of MYC/MAX/MAD network members and reciprocal changes in proliferation. In conclusion, the expression patterns of c-MYC, MAX and the MAD family were shown to be deregulated in the oesophageal cancer model
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