4,199 research outputs found
Unstable superheavy relic particles as a source of neutrinos responsible for the ultrahigh-energy cosmic rays
Decays of superheavy relic particles may produce extremely energetic
neutrinos. Their annihilations on the relic neutrinos can be the origin of the
cosmic rays with energies beyond the Greisen-Zatsepin-Kuzmin cutoff. The red
shift acts as a cosmological filter selecting the sources at some particular
value z_e, for which the present neutrino energy is close to the Z pole of the
annihilation cross section. We predict no directional correlation of the
ultrahigh-energy cosmic rays with the galactic halo. At the same time, there
can be some directional correlations in the data, reflecting the distribution
of matter at red shift z=z_e. Both of these features are manifest in the
existing data. Our scenario is consistent with the neutrino mass reported by
Super-Kamiokande and requires no lepton asymmetry or clustering of the
background neutrinos.Comment: 3 pages, revtex; references adde
Comments on ``A note on first-order formalism and odd-derivative actions'' by S. Deser
We argue that the obstacles to having a first-order formalism for
odd-derivative actions presented in a pedagogical note by Deser are based on
examples which are not first-order forms of the original actions. The general
derivation of an equivalent first-order form of the original second-order
action is illustrated using the example of topologically massive
electrodynamics (TME). The correct first-order formulations of the TME model
keep intact the gauge invariance presented in its second-order form
demonstrating that the gauge invariance is not lost in the Ostrogradsky
process.Comment: 6 pages, references are adde
Metastable Voltage States of Coupled Josephson Junctions
We investigate a chain of capacitively coupled Josephson junctions in the
regime where the charging energy dominates over the Josephson coupling,
exploiting the analogy between this system and a multi-dimensional crystal. We
find that the current-voltage characteristic of the current-driven chain has a
staircase shape, beginning with an (insulating) non-zero voltage plateau at
small currents. This behavior differs qualitatively from that of a single
junction, which should show Bloch oscillations with vanishing dc voltage. The
simplest system where this effect can be observed consists of three grains
connected by two junctions. The theory explains the results of recent
experiments on Josephson junction arrays.Comment: 5 pages, 4 figures include
Supersymmetric superheavy dark matter
We propose the lightest supersymmetric particle (LSP) as a well-suited
candidate for superheavy dark matter (SHDM). Various production mechanisms at
the end of inflation can produce SHDM with the correct abundance, , if its mass is sufficiently high. In particular, gravitational
production requires that the mass of the LSP is above . Weak interactions remain perturbative despite the large mass
hierarchy, , because of the special decoupling properties of
supersymmetry. As a result the model is predictive and we discuss the relevant
cosmological processes for the case of a superheavy neutralino within this
scheme.Comment: 9 pages; v2: references added, matches version to be publishe
Peculiarities of the Canonical Analysis of the First Order Form of the Einstein-Hilbert Action in Two Dimensions in Terms of the Metric Tensor or the Metric Density
The peculiarities of doing a canonical analysis of the first order
formulation of the Einstein-Hilbert action in terms of either the metric tensor
or the metric density along with the affine connection are discussed. It is shown that the
difference between using as opposed to
appears only in two spacetime dimensions. Despite there being a different
number of constraints in these two approaches, both formulations result in
there being a local Poisson brackets algebra of constraints with field
independent structure constants, closed off shell generators of gauge
transformations and off shell invariance of the action. The formulation in
terms of the metric tensor is analyzed in detail and compared with earlier
results obtained using the metric density. The gauge transformations, obtained
from the full set of first class constraints, are different from a
diffeomorphism transformation in both cases.Comment: 13 page
Neutron-antineutron Oscillations in the Trapping Box
We have reexamined the problem of oscillations for ultra-cold
neutrons (UCN) confined within a trap. We have shown that the growth of the
component with time is to a decent accuracy given by where is the mixing parameter,
sec in the neutron propagation time between subsequent collisions
with the trap walls. Possible corrections to this law and open questions are
discussed.Comment: 11 pages, LaTeX2
Neutrino cross sections at high energies and the future observations of ultrahigh-energy cosmic rays
We show that future detectors of ultrahigh-energy cosmic-ray neutrinos will
be able to measure neutrino-nucleon cross section at energies as high as
10^{11}GeV or higher. We find that the flux of up-going charged leptons per
unit surface area produced by neutrino interactions below the surface is
inversely proportional to the cross section. This contrasts with the rate of
horizontal air showers (HAS) due to neutrino interactions in the atmosphere,
which is proportional to the cross section. Thus, by comparing the HAS and
up-going air shower (UAS) rates, the neutrino-nucleon cross section can be
inferred. Taken together, up-going and horizontal rates ensure a healthy total
event rate, regardless of the value of the cross section.Comment: 4 pages, 2 figures, revtex; final draf
Instant preheating mechanism and UHECR
Top-down models assume that the still unexplained Ultra High Energy Cosmic
Rays (UHECR's) are the decay products of superheavy particles. Such particles
may have been produced by one of the post-inflationary reheating mechanisms and
may account for a fraction of the cold dark matter. In this paper, we assess
the phenomenological applicability of the simplest instant preheating framework
not to describe a reheating process, but as a mechanism to generate relic
supermassive particles as possible sources of UHECR's. We use cosmic ray flux
and cold dark matter observational data to constrain the parameters of the
model.Comment: 7 pages, 2 figures, submitted to PR
Light Lepton Number Violating Sneutrinos and the Baryon Number of the Universe
Recent results of neutrino oscillation experiments point to a nonvanishing
neutrino mass. Neutrino mass models favour Majorana-type neutrinos. In such
circumstances it is natural that the supersymmetric counterpart of the
neutrino, the sneutrino, bears also lepton number violating properties. On the
other hand, the fact that the universe exhibits an asymmetry in the baryon and
antibaryon numbers poses constraints on the extent of lepton number violation
in the light sneutrino sector if the electroweak phase transition is second or
weak first order. From the requirement that the Baryon Asymmetry of the
Universe should not be washed out by sneutrino induced lepton number violating
interactions and sphalerons below the critical temperature of the electroweak
phase transition we find that the mass splitting of the light sneutrino mass
states is compatible with the sneutrino Cold Dark Matter hypothesis only for
heavy gauginos and opposite sign gaugino mass parameters.Comment: 13 pages, 4 figure
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