2,137 research outputs found
Chain Inflation in the Landscape: "Bubble Bubble Toil and Trouble"
In the model of Chain Inflation, a sequential chain of coupled scalar fields
drives inflation. We consider a multidimensional potential with a large number
of bowls, or local minima, separated by energy barriers: inflation takes place
as the system tunnels from the highest energy bowl to another bowl of lower
energy, and so on until it reaches the zero energy ground state. Such a
scenario can be motivated by the many vacua in the stringy landscape, and our
model can apply to other multidimensional potentials. The ''graceful exit''
problem of Old Inflation is resolved since reheating is easily achieved at each
stage. Coupling between the fields is crucial to the scenario. The model is
quite generic and succeeds for natural couplings and parameters. Chain
inflation succeeds for a wide variety of energy scales -- for potentials
ranging from 10MeV scale inflation to GeV scale inflation.Comment: 31 pages, 3 figures, one reference adde
Dark matter powered stars: Constraints from the extragalactic background light
The existence of predominantly cold non-baryonic dark matter is unambiguously
demonstrated by several observations (e.g., structure formation, big bang
nucleosynthesis, gravitational lensing, and rotational curves of spiral
galaxies). A candidate well motivated by particle physics is a weakly
interacting massive particle (WIMP). Self-annihilating WIMPs would affect the
stellar evolution especially in the early universe. Stars powered by
self-annihilating WIMP dark matter should possess different properties compared
with standard stars. While a direct detection of such dark matter powered stars
seems very challenging, their cumulative emission might leave an imprint in the
diffuse metagalactic radiation fields, in particular in the mid-infrared part
of the electromagnetic spectrum. In this work the possible contributions of
dark matter powered stars (dark stars; DSs) to the extragalactic background
light (EBL) are calculated. It is shown that existing data and limits of the
EBL intensity can already be used to rule out some DS parameter sets.Comment: Accepted for publication in ApJ; 7 pages, 5 figure
Are we seeing the beginnings of Inflation?
Phantom Cosmology provides an unique opportunity to "connect" the phantom
driven (low en- ergy meV scale) dark energy phase to the (high energy GUT
scale) inflationary era. This is possible because the energy density increases
in phantom cosmology. We present a concrete model where the energy density, but
not the scale factor, cycles through phases of standard radiation/matter domi-
nation followed by dark energy/inflationary phases, and the pattern repeating
itself. An interesting feature of the model is that once we include
interactions between the "phantom fluid" and ordinary matter, the Big rip
singularity is avoided with the phantom phase naturally giving way to a near
exponential inflationary expansion.Comment: 17 pages, 1 figur
On an easy transition from operator dynamics to generating functionals by Clifford algebras
Clifford geometric algebras of multivectors are treated in detail. These
algebras are build over a graded space and exhibit a grading or multivector
structure. The careful study of the endomorphisms of this space makes it clear,
that opposite Clifford algebras have to be used also. Based on this
mathematics, we give a fully Clifford algebraic account on generating
functionals, which is thereby geometric. The field operators are shown to be
Clifford and opposite Clifford maps. This picture relying on geometry does not
need positivity in principle. Furthermore, we propose a transition from
operator dynamics to corresponding generating functionals, which is based on
the algebraic techniques. As a calculational benefit, this transition is
considerable short compared to standard ones. The transition is not injective
(unique) and depends additionally on the choice of an ordering. We obtain a
direct and constructive connection between orderings and the explicit form of
the functional Hamiltonian. These orderings depend on the propagator of the
theory and thus on the ground state. This is invisible in path integral
formulations. The method is demonstrated within two examples, a non-linear
spinor field theory and spinor QED. Antisymmetrized and normal-ordered
functional equations are derived in both cases.Comment: 23p., 76kB, plain LaTeX, [email protected]
Effects of vertical vibration on hopper flows of granular material
The discharge of granular material from a hopper subject to vertical sinusoidal oscillations was investigated using experiments and discrete element computer simulations. With the hopper exit closed, side-wall convection cells are observed, oriented such that particles move up along the inclined walls of the hopper and down at the center line. The convection cells are a result of the granular bed dilation during free fall and the subsequent interaction with the hopper walls. The mass discharge rate for a vibrating hopper scaled by the discharge rate without vibration reaches a maximum value at a dimensionless velocity amplitude just greater than 1. Further increases in the velocity decrease the discharge rate. The decrease occurs due to a decrease in the bulk density of the discharging material when vibration is applied
The Sensitivity of the IceCube Neutrino Detector to Dark Matter Annihilating in Dwarf Galaxies
In this paper, we compare the relative sensitivities of gamma-ray and
neutrino observations to the dark matter annihilation cross section in
leptophilic models such as have been designed to explain PAMELA data. We
investigate whether the high energy neutrino telescope IceCube will be
competitive with current and upcoming searches by gamma-ray telescopes, such as
the Atmospheric Cerenkov Telescopes (ACTs) (HESS, VERITAS and MAGIC), or the
Fermi Gamma Ray Space Telescope, in detecting or constraining dark matter
particles annihilating in dwarf spheroidal galaxies. We find that after ten
years of observation of the most promising nearby dwarfs, IceCube will have
sensitivity comparable to the current sensitivity of gamma-ray telescopes only
for very heavy (m_X > 7 TeV) or relatively light (m_X < 200 GeV) dark matter
particles which annihilate primarily to mu+mu-. If dark matter particles
annihilate primarily to tau+tau-, IceCube will have superior sensitivity only
for dark matter particle masses below the 200 GeV threshold of current ACTs. If
dark matter annihilations proceed directly to neutrino-antineutrino pairs a
substantial fraction of the time, IceCube will be competitive with gamma-ray
telescopes for a much wider range of dark matter masses.Comment: 7 pages, 3 figures. v2: references added and minor revisions. v3: as
published in PRD
High-Energy Neutrino Signatures of Dark Matter Decaying into Leptons
Decaying dark matter has previously been proposed as a possible explanation
for the excess high energy cosmic ray electrons and positrons seen by PAMELA
and the Fermi Gamma-Ray Space Telescope (FGST). To accommodate these signals
however, the decays must be predominantly leptonic, to muons or taus, and
therefore produce neutrinos, potentially detectable with the IceCube neutrino
observatory. We find that, with five years of data, IceCube (supplemented by
DeepCore) will be able to significantly constrain the relevant parameter space
of decaying dark matter, and may even be capable of discovering dark matter
decaying in the halo of the Milky Way.Comment: 4 pages, 1 figur
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