12,312 research outputs found
Massive gravity from descent equations
Both massless and massive gravity are derived from descent equations
(Wess-Zumino consistency conditions). The massive theory is a continuous
deformation of the massless one.Comment: 8 pages, no figur
Particle-Antiparticle Asymmetry Due to Non-Renormalizable Effective Interactions
We consider a model for generating a particle-antiparticle asymmetry through
out-of-equilibrium decays of a massive particle due to non-renormalizable,
effective interactions.Comment: preliminary version, 38 pages; LaTeX source, epsf.sty and EPS files
included in tar archiv
Pierre Auger Data, Photons, and Top-Down Cosmic Ray Models
We consider the ultra-high energy cosmic ray (UHECR) spectrum as measured by
the Pierre Auger Observatory. Top-down models for the origin of UHECRs predict
an increasing photon component at energies above about eV. Here we
present a simple prescription to compare the Auger data with a prediction
assuming a pure proton component or a prediction assuming a changing primary
component appropriate for a top-down model. We find that the UHECR spectrum
predicted in top-down models is a good fit to the Auger data. Eventually, Auger
will measure a composition-independent spectrum and will be capable of either
confirming or excluding the quantity of photons predicted in top-down models.Comment: 8 pages, 3 figure
Inflation, dark matter and dark energy in the string landscape
We consider the conditions needed to unify the description of dark matter,
dark energy and inflation in the context of the string landscape. We find that
incomplete decay of the inflaton field gives the possibility that a single
field is responsible for all three phenomena. By contrast, unifying dark matter
and dark energy into a single field, separate from the inflaton, appears rather
difficult.Comment: 4 pages RevTex4. Updated to include a toy model of reheating. Matches
version accepted by Phys Rev Let
New Upper Limits on the Tau Neutrino Mass from Primordial Helium Considerations
In this paper we reconsider recently derived bounds on tau neutrinos,
taking into account previously unaccounted for effects. We find that, assuming
that the neutrino life-time is longer than , the constraint
rules out masses in the range
for Majorana neutrinos and
for Dirac neutrinos. Given that the present
laboratory bound is 35 MeV, our results lower the present bound to and
for Majorana and Dirac neutrinos respectively.Comment: 9 pages (2 figures available upon request), UM-AC-93-0
Crypto-baryonic Dark Matter
It is proposed that dark matter could consist of compressed collections of
atoms (or metallic matter) encapsulated into, for example, 20 cm big pieces of
a different phase. The idea is based on the assumption that there exists at
least one other phase of the vacuum degenerate with the usual one. Apart from
the degeneracy of the phases we only assume Standard Model physics. The other
phase has a Higgs VEV appreciably smaller than in the usual electroweak vacuum.
The balls making up the dark matter are very difficult to observe directly, but
inside dense stars may expand eating up the star and cause huge explosions
(gamma ray bursts). The ratio of dark matter to ordinary baryonic matter is
expressed as a ratio of nuclear binding energies and predicted to be about 5.Comment: 9 pages. Published version with shorter abstract and new referenc
Energy-momentum diffusion from spacetime discreteness
We study potentially observable consequences of spatiotemporal discreteness
for the motion of massive and massless particles. First we describe some simple
intrinsic models for the motion of a massive point particle in a fixed causal
set background. At large scales, the microscopic swerves induced by the
underlying atomicity manifest themselves as a Lorentz invariant diffusion in
energy-momentum governed by a single phenomenological parameter, and we derive
in full the corresponding diffusion equation. Inspired by the simplicity of the
result, we then derive the most general Lorentz invariant diffusion equation
for a massless particle, which turns out to contain two phenomenological
parameters describing, respectively, diffusion and drift in the particle's
energy. The particles do not leave the light cone however: their worldlines
continue to be null geodesics. Finally, we deduce bounds on the drift and
diffusion constants for photons from the blackbody nature of the spectrum of
the cosmic microwave background radiation.Comment: 13 pages, 4 figures, corrected minor typos and updated to match
published versio
Resonant Leptogenesis with nonholomorphic R-Parity violation and LHC Phenomenology
In R-parity violating supersymmetric models both leptogenesis and the correct
neutrino masses are hard to achieve together. The presence of certain soft
nonholomorphic R-parity violating terms helps to resolve this problem. We
consider a scenario where the lightest and the second-lightest neutralino are
nearly degenerate in mass and enough CP-asymmetry can be produced through
resonant leptogenesis. In this model, the lighter chargino and the lightest
neutralino are highly degenerate. We have relatively lighter gauginos which can
be produced at the LHC leading to heavily ionizing charged tracks. At the same
time this model can also generate the correct neutrino mass scale. Thus our
scenario is phenomenologically rich and testable at colliders.Comment: 17 pages, 7 figures, Numerical results are improved and new plots are
added, Journal version. arXiv admin note: text overlap with
arXiv:hep-ph/0006173 by other author
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