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What is Munch?
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Natural Dark Energy astro-ph/0703783 (suggested by
George W.)
Authors:
Douglas
Scott, Ali
Frolop
Comments: 2 pages, submitted to the new journal Physics in Progress
It is now well accepted that both Dark Matter and Dark Energy are
required in
any successful cosmological model. Although there is ample evidence
that both
Dark components are necessary, the conventional theories make no
prediction for
the contributions from each of them. Moreover, there is usually no
intrinsic
relationship between the two components, and no understanding of the
nature of
the mysteries of the Dark Sector. Here we suggest that if the Dark Side
is so
seductive then we should not be restricted to just 2 components. We
further
suggest that the most natural model has 5 distinct forms of Dark Energy
in
addition to the usual Dark Matter, each contributing precisely equally
to the
cosmic energy density budget.
The Stryngbohtyk Model of the Universe: a Solution to the
Problem of the Cosmological Constant astro-ph/0703774 (suggested by
George W.)
Authors:
Jordi
Miralda-Escude
Astronomical observations have shown that the expansion of the universe
is at
present accelerating, in a way consistent with the presence of a
positive
cosmological constant. This is a major puzzle, because we do not
understand:
why the cosmological constant is so small; why, being so small, it is
not
exactly zero; and why it has precisely the value it must have to make
the
expansion start accelerating just at the epoch when we are observing
the
universe. We present a new model of cosmology, which we call the
stryngbohtyk
model, that solves all these problems and predicts exactly the value
that the
cosmological constant must have. The predicted value agrees with the
observed
one within the measurement error. We show that in the stryngbohtyk
model, the
fact the cosmological constant starts being important at the present
epoch is
not a coincidence at all, but a necessity implied by our origin in a
planet
orbiting a star that formed when the age of the universe was of the
same order
as the lifetime of the star.
A Consistency Relation in Cosmology
astro-ph/0703347 (suggested by Miguel)
Authors: Takeshi
Chiba, Ryuichi
Takahashi
Comments: 8 pages, 1 figure
We provide a consistency relation between
cosmological observables in
general
relativity without relying on the equation of state of dark energy. The
consistency relation should be satisfied if general relativity is the
correct
theory of gravity and dark energy clustering is negligible. As an
extension, we
also provide the DGP counterpart of the relation.
Determining the WIMP mass using direct detection
experiments
hep-ph/0703217
Authors: Anne
M Green
Comments: 17 pages, 8 figures
We study the accuracy with which the WIMP mass could
be determined by a
superCDMS-like direct detection experiment, given optimistic
assumptions about
the detector set-up and WIMP properties. We consider WIMPs with an
interaction
cross-section of sigma_p = 10^{-7} pb (just below current exclusion
limits) and
assume, initially, that the local WIMP velocity distribution and
density are
known and that the experiment has zero background. For light WIMPs
(mass
significantly less than that of the target nuclei) small variations in
the WIMP
mass lead to significant changes in the energy spectrum. Conversely for
heavy
WIMPs the energy spectrum depends only weakly on the WIMP mass.
Consequently it
will be far easier to measure the WIMP mass if it is light than if it
is heavy.
With exposures of E= 3 x 10^{3}, 3 x 10^{4} and 3 x 10^{5} kg day
(corresponding, roughly, to the three proposed phases of SuperCDMS) it
will be
possible, given the optimistic assumptions mentioned above, to measure
the mass
of a light WIMP with an accuracy of roughly 25%, 15% and 2.5%
respectively.
These numbers increase with increasing WIMP mass, and for heavy WIMPs,
m_{\chi}
> O(500 GeV), even with a large exposure it will only be possible to
place a
lower limit on the mass. Finally we discuss the validity of the various
assumptions made, in particular regarding the smoothness of the small
scale
WIMP distribution, and the consequences if these assumptions are not
valid.
The galactic 511 keV line from electroweak scale WIMPs
hep-ph/0703128
Authors: Maxim
Pospelov, Adam
Ritz
Comments: 16 pages, 3 figures
We consider possible mechanisms via which electroweak
scale WIMPs
\chi^0
could provide the source of the INTEGRAL/SPI 511 keV photon flux from
the
galactic centre. We consider scenarios where the WIMP spectrum contains
near-degeneracies, with MeV-scale splitting, and focus on three
possible
production mechanisms for galactic positrons: (i) collisional
excitation of the
WIMP to a nearby charged state, \chi^0 + \chi^0 -> \chi^+ + \chi^-,
with the
subsequent decay producing positrons; (ii) capture of the WIMP by
nuclei in the
galactic interstellar medium, \chi^0 + N -> e^+ + (\chi^- N); and
(iii) the
decay of a nearby long-lived state surviving from the Big Bang,
\chi^0_2 ->
\chi_1^0 + e^+ + e^-. We find that process (i) requires a cross-section
which
is significantly larger than the unitarity bound, process (ii) is
allowed by
unitarity, but is impractical due to terrestrial bounds on the \chi-N
cross-section, while process (iii) is viable and we construct a simple
model
realization with singlet dark matter fields interacting with the
Standard Model
via the Higgs sector.
Effects of Cosmic Infrared Background on High Energy Delayed
Gamma-Rays from Gamma-Ray Bursts astro-ph/0703759
Authors: Kohta
Murase, Katsuaki
Asano, Shigehiro
Nagataki
Comments: 10 pages, 14 figures, submitted to ApJ
Regenerated high energy emissions from gamma-ray
bursts (GRBs) are
studied in
detail. If the primary emission spectrum extends to TeV range, these
very high
energy photons will be absorbed by the cosmic infrared background
(CIB). The
created high energy electron-positron pairs up-scatter not only cosmic
microwave background (CMB) photons but also CIB photons, and secondary
photons
are generated in the GeV-TeV range. These secondary delayed photons may
be
observed in the near future, and useful for a consistency check for the
primary
spectra and GRB physical parameters. The up-scattered CIB photons
cannot be
neglected for low redshift bursts and/or GRBs with a relatively low
maximum
photon energy. The secondary gamma-rays also give us additional
information on
the CIB, which is uncertain in observations so far.
Note on Varying Speed of Light Cosmologies
astro-ph/0703751
(suggested by Miguel)
Authors: George
F R Ellis (Mathematics Department and Applied Mathematics,
University of Cape Town, South Africa)
Comments: 6 pages; to appear in the GRG Journal
The various requirements on a consistent varying
speed of light (`VSL')
theory are surveyed, giving a short check-list of issues that should be
satisfactorily handled by such theories.
`Eppur Si Muove': On The Motion of the Acoustic Peak in the
Correlation Function astro-ph/0703620 (suggested by
Emiliano)
Authors: Robert
E. Smith (UPenn), Roman
Scoccimarro (NYU), Ravi
K. Sheth (UPenn)
Comments: 19 Pages, 8 Figures. For submission to PRD
The baryonic acoustic signature in the large-scale
clustering pattern
of
galaxies has been detected in the two-point correlation function. Its
precise
spatial scale has been forwarded as a rigid-rod ruler test for the
space-time
geometry, and hence as a probe for tracking the evolution of Dark
Energy.
Percent-level shifts in the measured position can bias such a test and
erode
its power to constrain cosmology. This paper addresses some of the
systematic
effects that might induce shifts: namely non-linear corrections from
matter
evolution, redshift space distortions and biasing. We tackle these
questions
through analytic methods and through a large battery of numerical
simulations,
with total volume of the order 105 [Gpc/h]^3. A toy-model calculation
shows
that if the non-linear corrections simply smooth the acoustic peak,
then this
gives rise to an `apparent' shifting to smaller scales. However if
tilts in the
broad band power spectrum are induced, then this gives rise to more
pernicious
`physical' shift. Our numerical simulations show evidence of both: in
real
space and at z=0, we find that for the dark matter the shift is of
order a few
percent; for haloes the shifts depend on halo mass, with larger shifts
being
found for the most biased samples, roughly 3-5%. In redshift space
these
effects are exacerbated, but at higher redshifts are slightly
alleviated. We
develop an analytical model to understand this, based on solutions to
the pair
conservation equation using characteristic curves. When combined with
modeling
of pairwise velocities the model reproduces the main trends found in
the data.
The model may also help to unbias the acoustic peak.
Gamma-Rays from Dark Matter Mini-Spikes in M31
astro-ph/0703757
Authors: Mattia
Fornasa, Marco
Taoso, Gianfranco
Bertone
Comments: 9 pages, 5 figures
The existence of a population of wandering
Intermediate Mass Black
Holes
(IMBHs) is a generic prediction of scenarios that seek to explain the
formation
of Supermassive Black Holes in terms of growth from massive seeds. The
growth
of IMBHs may lead to the formation of DM overdensities called
"mini-spikes",
recently proposed as ideal targets for indirect DM searches. Current
ground-based gamma-ray experiments, however, cannot search for these
objects
due to their limited field of view, and it might be challenging to
discriminate
mini-spikes in the Milky Way from the many astrophysical sources that
GLAST is
expected to observe. We show here that gamma-ray experiments can
effectively
search for IMBHs in the nearby Andromeda galaxy (also known as M31),
where
mini-spikes would appear as a distribution of point-sources,
isotropically
distributed in a \thickapprox 3^{\circ} circle around the galactic
center. For
a neutralino-like DM candidate with a mass m_{\chi}=150 GeV, up to 20
sources
would be detected with GLAST (at 5\sigma, in 2 months). With Air
Cherenkov
Telescopes such as MAGIC and VERITAS, up to 10 sources might be
detected,
provided that the mass of neutralino is in the TeV range or above.
Effects of Baryons and Dissipation on the Matter Power
Spectrum astro-ph/0703741
Authors: Douglas
H. Rudd, Andrew
R. Zentner, Andrey
V. Kravtsov (KICP, U.Chicago)
Comments: 14 pages, 8 figures. Submitted to ApJ
We study the importance of baryonic physics on
predictions of the
matter
power spectrum as it is relevant for forthcoming weak lensing surveys.
We
quantify the impact of baryonic physics using a set of three
cosmological
numerical simulations. Each simulation has the same initial density
field, but
models a different set of physical processes. The first simulation
evolves the
density field using gravity alone, the second includes non-radiative
gasdynamics, and the third includes radiative heating and cooling of
baryons,
star formation, and supernova feedback. We find that baryonic processes
alter
predictions for the matter power spectrum significantly relative to
models that
include only gravitational interactions. Our results imply that future
weak
lensing experiments such as LSST and SNAP will be very sensitive to the
poorly-understood physics governing the nonlinear evolution of the
baryonic
component of the universe. The net effect is significantly larger in
the case
of the model with cooling and star formation, in which case our results
imply
that contemporary surveys such as the CFHT Wide survey may also be
sensitive to
baryonic processes. In particular, this effect could be important for
forecasts
of the constraining power of future surveys if information from scales
larger
than l ~ 1000 is included in the analysis. We find that deviations are
caused
primarily by the rearrangement of matter within individual dark matter
halos
relative to the gravity-only case, rather than a large-scale
rearrangement of
matter. Consequently, we propose a simple model, based on the
phenomenological
halo model of dark matter clustering, for baryonic effects that can be
used to
aid in the interpretation of forthcoming weak lensing data.
Anisotropy Studies of the Unresolved Far-infrared
Background
astro-ph/0703592
Authors: Alexandre
Amblard, Asantha
Cooray
Comments: 4 pages, 3 figures, submitted to ApJL
Dusty, starforming galaxies and active galactic
nuclei that contribute
to the
integrated background intensity at far-infrared wavelengths trace the
large-scale structure. Below the point source detection limit,
correlations in
the large-scale structure lead to clustered anisotropies in the
unresolved
component of the far-infrared background (FIRB). The angular power
spectrum of
the FIRB anisotropies can be measured in surveys with the Spectral and
Photometric Imaging Receiver (SPIRE) on the upcoming Herschel
observatory. To
study statistical properties of these anisotropies, the confusion from
foreground Galactic dust emission needs to be reduced even in the
``cleanest''
regions of the sky. The multi-frequency coverage of SPIRE allows
foreground
dust to be partly separated from extragalactic anisotropies. The
separation
improves for fields with sizes greater than about 500 deg.$^2$ when
combined
with Planck data, while an area of about 1000 degrees$^2$ provides
maximal
information on the anisotropy power spectrum. We discuss scientific
studies
that can be done with anisotropy measurements of the unresolved FIRB.
Search for gravitational wave radiation associated with the
pulsating tail of the SGR 1806-20 hyperflare of 27 December 2004 using
LIGO astro-ph/0703419
Authors:
The LIGO
Scientific Collaboration
Comments: 13 pages, 2 tables, 3 figures
Report-no: LIGO-P040055-01-Z
We have searched for Gravitational Waves (GWs)
associated with the SGR
1806-20 hyperflare of 27 December 2004. This event, originating from a
Galactic
neutron star, displayed exceptional energetics. Recent investigations
of the
X-ray light curve's pulsating tail revealed the presence of
Quasi-Periodic
Oscillations (QPOs) in the 30 - 2000 Hz frequency range, most of which
coincides with the bandwidth of the LIGO detectors. These QPOs, with
well-characterized frequencies, can plausibly be attributed to seismic
modes of
the neutron star which could emit GWs. Our search targeted potential
quasi-monochromatic GWs lasting for tens of seconds and emitted at the
QPO
frequencies. We have observed no candidate signals above a
pre-determined
threshold and our lowest upper limit was set by the 92.5 Hz QPO
observed in the
interval from 150 s to 260 s after the start of the flare. This bound
corresponds to a (90% confidence) root-sum-squared amplitude
h_rssdet^90% =
4.5e-22 strain Hz^-1/2 on the GW waveform strength in the detectable
polarization state reaching our Hanford (WA) 4 km detector. We
illustrate the
astrophysical significance of the result via an estimated
characteristic energy
in GW emission that we would expect to be able to detect. The above
result
corresponds to 7.7e46 erg (= 4.3e-8 M_sun c^2), which is of the same
order as
the total (isotropic) energy emitted in the electromagnetic spectrum.
This
result provides a means to probe the energy reservoir of the source
with the
best upper limit on the GW waveform strength published and represents
the first
broadband asteroseismology measurement using a GW detector.
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