863 research outputs found
Factors associated with suicide among African American adult men: a systematic review of the literature
http://dx.doi.org/10.1016/j.jomh.2008.09.01
Unitarity Bounds for Gauged Axionic Interactions and the Green-Schwarz Mechanism
We analyze the effective actions of anomalous models in which a
four-dimensional version of the Green-Schwarz mechanism is invoked for the
cancellation of the anomalies, and we compare it with those models in which
gauge invariance is restored by the presence of a Wess-Zumino term. Some issues
concerning an apparent violation of unitarity of the mechanism, which requires
Dolgov-Zakharov poles, are carefully examined, using a class of amplitudes
studied in the past by Bouchiat-Iliopoulos-Meyer (BIM), and elaborating on
previous studies. In the Wess-Zumino case we determine explicitly the unitarity
bound using a realistic model of intersecting branes (the Madrid model) by
studying the corresponding BIM amplitudes. This is shown to depend
significantly on the St\"uckelberg mass and on the coupling of the extra
anomalous gauge bosons and allows one to identify Standard-Model-like regions
(which are anomaly-free) from regions where the growth of certain amplitudes is
dominated by the anomaly, separated by an inflection point which could be
studied at the LHC. The bound can even be around 5-10 TeV's for a mass
around 1 TeV and varies sensitively with the anomalous coupling. The results
for the WZ case are quite general and apply to all the models in which an
axion-like interaction is introduced as a generalization of the Peccei-Quinn
mechanism, with a gauged axion.Comment: 50 pages, 28 figure
Characteristic cohomology of -form gauge theories
The characteristic cohomology for an arbitrary set of free
-form gauge fields is explicitly worked out in all form degrees ,
where is the spacetime dimension. It is shown that this cohomology is
finite-dimensional and completely generated by the forms dual to the field
strengths. The gauge invariant characteristic cohomology is also computed. The
results are extended to interacting -form gauge theories with gauge
invariant interactions. Implications for the BRST cohomology are mentioned.Comment: Latex file, no figures, 44 page
One loop renormalization of the four-dimensional theory for quantum dilaton gravity.
We study the one loop renormalization in the most general metric-dilaton
theory with the second derivative terms only. The general theory can be divided
into two classes, models of one are equivalent to conformally coupled with
gravity scalar field and also to general relativity with cosmological term. The
models of second class have one extra degree of freedom which corresponds to
dilaton. We calculate the one loop divergences for the models of second class
and find that the arbitrary functions of dilaton in the starting action can be
fine-tuned in such a manner that all the higher derivative counterterms
disappear on shell. The only structures in both classical action and
counterterms, which survive on shell, are the potential (cosmological) ones.
They can be removed by renormalization of the dilaton field which acquire the
nontrivial anomalous dimension, that leads to the effective running of the
cosmological constant. For some of the renormalizable solutions of the theory
the observable low energy value of the cosmological constant is small as
compared with the Newtonian constant. We also discuss another application of
our result.Comment: 21 pages, latex, no figures
Gravitational excitons from extra dimensions
Inhomogeneous multidimensional cosmological models with a higher dimensional
space-time manifold are investigated under dimensional reduction. In the
Einstein conformal frame, small excitations of the scale factors of the
internal spaces near minima of an effective potential have a form of massive
scalar fields in the external space-time. Parameters of models which ensure
minima of the effective potentials are obtained for particular cases and masses
of gravitational excitons are estimated.Comment: Revised version --- 12 references added, Introduction enlarged, 20
pages, LaTeX, to appear in Phys.Rev.D56 (15.11.97
A High Statistics Search for Ultra-High Energy Gamma-Ray Emission from Cygnus X-3 and Hercules X-1
We have carried out a high statistics (2 Billion events) search for
ultra-high energy gamma-ray emission from the X-ray binary sources Cygnus X-3
and Hercules X-1. Using data taken with the CASA-MIA detector over a five year
period (1990-1995), we find no evidence for steady emission from either source
at energies above 115 TeV. The derived upper limits on such emission are more
than two orders of magnitude lower than earlier claimed detections. We also
find no evidence for neutral particle or gamma-ray emission from either source
on time scales of one day and 0.5 hr. For Cygnus X-3, there is no evidence for
emission correlated with the 4.8 hr X-ray periodicity or with the occurrence of
large radio flares. Unless one postulates that these sources were very active
earlier and are now dormant, the limits presented here put into question the
earlier results, and highlight the difficulties that possible future
experiments will have in detecting gamma-ray signals at ultra-high energies.Comment: 26 LaTeX pages, 16 PostScript figures, uses psfig.sty to be published
in Physical Review
The Proposed Dropping of the Genus \u3ci\u3eCrassostrea\u3c/i\u3e for All Pacific Cupped Oysters and Its Replacement by a New Genus \u3ci\u3eMagallana\u3c/i\u3e: A Dissenting View
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
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