1,565 research outputs found
Partially Massless Spin 2 Electrodynamics
We propose that maximal depth, partially massless, higher spin excitations
can mediate charged matter interactions in a de Sitter universe. The proposal
is motivated by similarities between these theories and their traditional
Maxwell counterpart: their propagation is lightlike and corresponds to the same
Laplacian eigenmodes as the de Sitter photon; they are conformal in four
dimensions; their gauge invariance has a single scalar parameter and actions
can be expressed as squares of single derivative curvature tensors. We examine
this proposal in detail for its simplest spin 2 example. We find that it is
possible to construct a natural and consistent interaction scheme to conserved
vector electromagnetic currents primarily coupled to the helicity 1 partially
massless modes. The resulting current-current single ``partial-photon''
exchange amplitude is the (very unCoulombic) sum of contact and shorter-range
terms, so the partial photon cannot replace the traditional one, but rather
modifies short range electromagnetic interactions. We also write the gauge
invariant fourth-derivative effective actions that might appear as effective
corrections to the model, and their contributions to the tree amplitude are
also obtained.Comment: 15 pages, LaTe
Quantum Cosmology and Conformal Invariance
According to Belinsky, Khalatnikov and Lifshitz, gravity near a space-like
singularity reduces to a set of decoupled one-dimensional mechanical models at
each point in space. We point out that these models fall into a class of
conformal mechanical models first introduced by de Alfaro, Fubini and Furlan
(DFF). The deformation used by DFF to render the spectrum discrete corresponds
to a negative cosmological constant. The wave function of the universe is the
zero-energy eigenmode of the Hamiltonian, also known as the spherical vector of
the representation of the conformal group SO(1,2). A new class of conformal
quantum mechanical models is constructed, based on the quantization of
nilpotent coadjoint orbits, where the conformal group is enhanced to an ADE
non-compact group for which the spherical vector is known.Comment: 4 pages, latex2e, uses revtex
BRST Detour Quantization
We present the BRST cohomologies of a class of constraint (super) Lie
algebras as detour complexes. By giving physical interpretations to the
components of detour complexes as gauge invariances, Bianchi identities and
equations of motion we obtain a large class of new gauge theories. The pivotal
new machinery is a treatment of the ghost Hilbert space designed to manifest
the detour structure. Along with general results, we give details for three of
these theories which correspond to gauge invariant spinning particle models of
totally symmetric, antisymmetric and K\"ahler antisymmetric forms. In
particular, we give details of our recent announcement of a (p,q)-form K\"ahler
electromagnetism. We also discuss how our results generalize to other special
geometries.Comment: 43 pages, LaTeX, added reference
Xrn1/Pacman affects apoptosis and regulates expression of hid and reaper
Programmed cell death, or apoptosis, is a highly conserved cellular process that is crucial for tissue homeostasis under normal development as well as environmental stress. Misregulation of apoptosis is linked to many developmental defects and diseases such as tumour formation, autoimmune diseases and neurological disorders. In this paper, we show a novel role for the exoribonuclease Pacman/Xrn1 in regulating apoptosis. Using Drosophila wing imaginal discs as a model system, we demonstrate that a null mutation in pacman results in small imaginal discs as well as lethality during pupation. Mutant wing discs show an increase in the number of cells undergoing apoptosis, especially in the wing pouch area. Compensatory proliferation also occurs in these mutant discs, but this is insufficient to compensate for the concurrent increase in apoptosis. The phenotypic effects of the pacman null mutation are rescued by a deletion that removes one copy of each of the pro-apoptotic genes reaper, hid and grim, demonstrating that pacman acts through this pathway. The null pacman mutation also results in a significant increase in the expression of the pro-apoptotic mRNAs, hid and reaper, with this increase mostly occurring at the post-transcriptional level, suggesting that Pacman normally targets these mRNAs for degradation. Our results uncover a novel function for the conserved exoribonuclease Pacman and suggest that this exoribonuclease is important in the regulation of apoptosis in other organisms
BPS black holes, quantum attractor flows and automorphic forms
We propose a program for counting microstates of four-dimensional BPS black
holes in N >= 2 supergravities with symmetric-space valued scalars by
exploiting the symmetries of timelike reduction to three dimensions. Inspired
by the equivalence between the four dimensional attractor flow and geodesic
flow on the three-dimensional scalar manifold, we radially quantize stationary,
spherically symmetric BPS geometries. Connections between the topological
string amplitude, attractor wave function, the Ooguri-Strominger-Vafa
conjecture and the theory of automorphic forms suggest that black hole
degeneracies are counted by Fourier coefficients of modular forms for the
three-dimensional U-duality group, associated to special "unipotent"
representations which appear in the supersymmetric Hilbert space of the quantum
attractor flow.Comment: 9 pages, revtex; v2: references added and typos correcte
Fokker-Planck and Landau-Lifshitz-Bloch Equations for Classical Ferromagnets
A macroscopic equation of motion for the magnetization of a ferromagnet at
elevated temperatures should contain both transverse and longitudinal
relaxation terms and interpolate between Landau-Lifshitz equation at low
temperatures and the Bloch equation at high temperatures. It is shown that for
the classical model where spin-bath interactions are described by stochastic
Langevin fields and spin-spin interactions are treated within the mean-field
approximation (MFA), such a ``Landau-Lifshitz-Bloch'' (LLB) equation can be
derived exactly from the Fokker-Planck equation, if the external conditions
change slowly enough. For weakly anisotropic ferromagnets within the MFA the
LLB equation can be written in a macroscopic form based on the free-energy
functional interpolating between the Landau free energy near T_C and the
``micromagnetic'' free energy, which neglects changes of the magnetization
magnitude |{\bf M}|, at low temperatures.Comment: 9 pages, no figures, a small error correcte
Common genetic and environmental contributions to post-traumatic stress disorder and alcohol dependence in young women
BACKGROUND: The few genetically informative studies to examine post-traumatic stress disorder (PTSD) and alcohol dependence (AD), all of which are based on a male veteran sample, suggest that the co-morbidity between PTSD and AD may be attributable in part to overlapping genetic influences, but this issue has yet to be addressed in females. METHOD: Data were derived from an all-female twin sample (n=3768) ranging in age from 18 to 29 years. A trivariate genetic model that included trauma exposure as a separate phenotype was fitted to estimate genetic and environmental contributions to PTSD and the degree to which they overlap with those that contribute to AD, after accounting for potential confounding effects of heritable influences on trauma exposure. RESULTS: Additive genetic influences (A) accounted for 72 % of the variance in PTSD ; individual-specific environmental (E) factors accounted for the remainder. An AE model also provided the best fit for AD, for which heritability was estimated to be 71 %. The genetic correlation between PTSD and AD was 0.54. CONCLUSIONS: The heritability estimate for PTSD in our sample is higher than estimates reported in earlier studies based almost exclusively on an all-male sample in which combat exposure was the precipitating traumatic event. However, our findings are consistent with the absence of evidence for shared environmental influences on PTSD and, most importantly, the substantial overlap in genetic influences on PTSD and AD reported in these investigations. Additional research addressing potential distinctions by gender in the relative contributions of genetic and environmental influences on PTSD is merited
Massive Spin 3/2 Electrodynamics
We study the general non-minimally coupled charged massive spin 3/2 model
both for its low energy phenomenological properties and for its unitarity,
causality and degrees of freedom behaviour. When the model is viewed as an
effective theory, its parameters (after ensuring the correct excitation count)
are related to physical characteristics, such as the magnetic moment g factor,
by means of low energy theorems. We also provide the corresponding higher spin
generalisation. Separately, we consider both low and high energy unitarity, as
well as the causality aspects of our models. None (including truncated N=2
supergravity) is free of the minimal model's acausality.Comment: 23 pages, 1 figure, LaTeX and axodraw.sty, novel Majorana-type term
included; results unaltere
The magnetic field and the location of the TeV emitter in Cygnus X-1 and LS 5039
Cygnus X-1 and LS 5039 are two X-ray binaries observed at TeV energies. Both
sources are compact systems, contain jet-like (radio) structures, and harbor
very luminous O stars. A TeV signal has been found around the superior
conjunction of the compact object in both objects, when the highest gamma-ray
opacities are expected. We investigate the implications of finding TeV emission
from Cygnus X-1 and LS 5039 around the superior conjunction, since this can
give information on the system magnetic field and the location of the TeV
emitter. Using the very high-energy spectra and fluxes observed around the
superior conjunction in Cygnus X-1 and LS 5039, we compute the absorbed
luminosity that is caused by pair creation in the stellar photon field for
different emitter positions with respect to the star and the observer line of
sight. The role of the magnetic field and electromagnetic cascading are
discussed. For the case of inefficient electromagnetic cascading, the expected
secondary synchrotron fluxes are compared with the observed ones at X-ray
energies. We find that, in Cygnus X-1 and LS 5039, either the magnetic field in
the star surroundings is much smaller than the one expected for O stars or the
TeV emitter is located at a distance >10^12 cm from the compact object. Our
results strongly suggest that the TeV emitters in Cygnus X-1 and LS 5039 are
located at the borders of the binary system and well above the orbital plane.
This would not agree with those models for which the emitter is well inside the
system, like the innermost-jet region (Cygnus X-1 and LS 5039; microquasar
scenario), or the region between the pulsar and the primary star (LS 5039;
standard pulsar scenario).Comment: A&A, in press, 4 pages, 3 figures, 1 table (minor changes
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