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Detecting MeV Gauge Bosons With High-Energy Neutrino
Telescopes
hep-ph/0701194 (suggested
by Newton)
Authors:
Dan
Hooper
Comments: 4 pages, 3 figures
Report-no: FERMILAB-PUB-07-017-A
If annihilating MeV-scale dark matter particles are responsible for the
observed 511 keV emission from the Galactic bulge, then new light gauge
bosons
which mediate the dark matter annihilations may have other observable
consequences. In particular, if such a gauge boson exists and has even
very
small couplings to Standard Model neutrinos, cosmic neutrinos with ~TeV
energies will scatter with the cosmic neutrino background through
resonant
exchange, resulting in a distinctive spectral absorption line in the
high-energy neutrino spectrum. Such a feature could potentially be
detected by
future high-energy neutrino telescopes.
Fitting CMB data with cosmic strings and inflation
astro-ph/0702223
Authors:
Neil
Bevis, Mark
Hindmarsh, Martin
Kunz, Jon
Urrestilla
Comments: 4 pages, 3 figures, 1 table
We perform a multi-parameter likelihood analysis to compare
measurements of
the cosmic microwave background (CMB) power spectra with predictions
from
models involving cosmic strings. We explore the addition of strings to
the
inflationary concordance model, involving an adiabatic primordial power
spectrum with a power-law tilt n, as well as the Harrison-Zeldovich
(HZ) case
n=1. Using ACBAR, BOOMERANG, CBI, VSA and WMAP data we show that of the
models
investigated, the HZ case with strings provides the best fit to the
data
relative to the freedom in the model, having a moderately higher
Bayesian
evidence than the concordance model. For HZ plus strings, CMB data then
implies
a (10+/-3)% string contribution to the temperature power spectrum at
multipole
l=10. However, with non-CMB data included, finite tilt and finite
strings are
approximately on par with each other. Considering variable $\ns$, we
then find
a 95% upper limit of the string fraction of 11%, corresponding to
$G\mu<0.7\times 10^{-6}$ (where G is Newton's constant and $\mu$ is
the string
tension).
The Cold Dark Matter Halos of Local Group Dwarf Spheroidals
astro-ph/0701780
Authors:
Jorge
Penarrubia, Alan
McConnachie, Julio
F. Navarro (Uvic, Canada)
Comments: 10 pages, 10 figures, submitted to ApJ
We examine the dynamics of stellar systems embedded within cold dark
matter
(CDM) halos in order to assess observational constraints on the dark
matter
content of Local Group dwarf spheroidals (dSphs). Our analysis shows
that the
total mass within the luminous radius is reasonably well constrained
and
approximately independent of the luminosity of the dwarf, highlighting
the poor
correspondence between luminosity and halo mass. This result implies
that the
average density of dark matter is substantially higher in physically
small
systems such as Draco and Sculptor than in larger systems such as
Fornax. For
example, our results imply that Draco formed in a halo 5 times more
massive
than Fornax's despite being roughly 70 times fainter. Stellar velocity
dispersion profiles, sigma_p(R), provide further constraints; flat
sigma_p(R)
profiles imply that stars are deeply embedded within their cold dark
matter
halos and so quite resilient to tidal disruption. We estimate that
halos would
need to lose more than 90% of their original mass before tides begin
affecting
the kinematics of stars.
We estimate that V_max is about 3 times higher than the central
velocity
dispersion of the stars, which alleviates significantly the CDM
``substructure
crisis''.
We use these results to interpret the size differences between the M31
and
Milky Way (MW) dSph population. Our modeling indicates that this
difference
should be reflected in their kinematics, and predicts that M31 dwarfs
should
have velocity dispersions up to a factor of ~ 2 higher than their MW
counterparts. This CDM-motivated prediction may be verified with
present
observational capabilities.
21 cm radiation - a new probe of variation in the fine
structure constant
astro-ph/0701752
Authors:
Rishi
Khatri, Benjamin
D. Wandelt
Comments: 5 pages, 3 figures, Accepted for publication in Physical
Review Letters
We investigate the effect of variation in the value of the fine
structure
constant at high redshifts (recombination > z > 30) on the
absorption of the
cosmic microwave background (CMB) at 21 cm hyperfine transition of the
neutral
atomic hydrogen. We find that the 21 cm signal is very sensitive to the
variations in the fine structure constant and it is so far the only
probe of
the fine structure constant in this redshift range. A change in the
value of
the fine structure constant by 1% changes the mean brightness
temperature
decrement of the CMB due to 21 cm absorption by > 5% over the
redshift range z
< 45 and z > 120. There is an effect of similar magnitude on the
amplitude of
the fluctuations in the brightness temperature. The redshift of maximum
absorption also changes by more than 5%.
Dark matter maps reveal cosmic scaffolding
astro-ph/0701594
Authors:
Richard
Massey, Jason
Rhodes, Richard
Ellis, Nick
Scoville, Alexie
Leauthaud, Alexis
Finoguenov, Peter
Capak, David
Bacon, Herve
Aussel, Jean-Paul
Kneib, Anton
Koekemoer, Henry
McCracken, Bahram
Mobasher, Sandrine
Pires, Alexandre
Refregier, Shunji
Sasaki, Jean-Luc
Starck, Yoshi
Taniguchi, Andy
Taylor, James
Taylor
Comments: 10 pages, 5 figures... plus 6 pages, 7 figures of
supplementary information. An officially typset version is available
from the Nature website at this
http URL and the front cover of Nature featuring the mass map is
available in PDF format from this
http URL
Journal-ref: Nature 445 (2007) 286
Ordinary baryonic particles (such as protons and neutrons) account for
only
one-sixth of the total matter in the Universe. The remainder is a
mysterious
"dark matter" component, which does not interact via electromagnetism
and thus
neither emits nor reflects light. As dark matter cannot be seen
directly using
traditional observations, very little is currently known about its
properties.
It does interact via gravity, and is most effectively probed through
gravitational lensing: the deflection of light from distant galaxies by
the
gravitational attraction of foreground mass concentrations. This is a
purely
geometrical effect that is free of astrophysical assumptions and
sensitive to
all matter -- whether baryonic or dark. Here we show high fidelity maps
of the
large-scale distribution of dark matter, resolved in both angle and
depth. We
find a loose network of filaments, growing over time, which intersect
in
massive structures at the locations of clusters of galaxies. Our
results are
consistent with predictions of gravitationally induced structure
formation, in
which the initial, smooth distribution of dark matter collapses into
filaments
then into clusters, forming a gravitational scaffold into which gas can
accumulate, and stars can be built.
The Sunyaev-Zel'dovich Effect from Quasar Feedback
astro-ph/0701750
Authors:
Suchetana
Chatterjee (University of Pittsburgh), Arthur
Kosowsky (University of Pittsburgh)
Comments: 4 pages, 2 figures, Submitted to ApJ Letters
The observed relationship between X-ray luminosity and temperature of
the
diffuse intercluster medium clearly shows the effect of
nongravitational
heating on the formation of galaxy clusters. Quasar feedback into the
intergalactic medium can potentially be an important source of heating,
and can
have significant impact on structure formation. This feedback process
is a
source of thermal Sunyaev-Zel'dovich distortions of the cosmic
microwave
background. Using a simple one-dimensional Sedov-Taylor model of energy
outflow, we calculate the angular power spectrum of the temperature
distortion,
which has an amplitude on the order of one micro-Kelvin. This signal
will be
below the noise limit of upcoming arcminute-scale microwave background
experiments, including the Atacama Cosmology Telescope and the South
Pole
Telescope, but will be directly detectable with deep exposures by the
Atacama
Large Millimeter Array or by stacking many microwave images.
The Sunyaev-Zel'dovich effects from a cosmological
hydrodynamical simulation: large-scale properties and correlation with
the soft X-ray signal astro-ph/0701680
Authors:
M.
Roncarelli, L.
Moscardini, S.
Borgani, K.
Dolag
Comments: 11 pages, 15 figures. Submitted to MNRAS
Using the results of a cosmological hydrodynamical simulation of the
concordance LambdaCDM model, we study the global properties of the
Sunyaev-Zel'dovich (SZ) effects, both considering the thermal (tSZ) and
the
kinetic (kSZ) component. The simulation follows gravitation and gas
dynamics
and includes also several physical processes that affect the baryonic
component, like a simple reionization scenario, radiative cooling, star
formation and supernova feedback. Starting from the outputs of the
simulation
we create mock maps of the SZ signals due to the large structures of
the
Universe integrated in the range 0 < z < 6. We predict that the
Compton
y-parameter has an average value of (1.19 +/- 0.32) 10^-6 and is
lognormally
distributed in the sky; half of the whole signal comes from z < 1
and about 10
per cent from z > 2. The Doppler b-parameter shows approximately a
normal
distribution with vanishing mean value and a standard deviation of 1.6
10^-6,
with a significant contribution from high-redshift (z > 3) gas. We
find that
the tSZ is expected to dominate the primary CMB anisotropies for l
>~ 3000 in
the Rayleigh-Jeans limit, while interestingly the kSZ dominates at all
frequencies at very high multipoles (l >~ 7 10^4). We also analyse
the
cross-correlation between the two SZ effects and the soft (0.5-2 keV)
X-ray
emission from the intergalactic medium and we obtain a strong
correlation
between the three signals, especially between X-ray emission and tSZ
effect
(r_l ~ 0.8-0.9) at all angular scales.
The behavior of $f(R)$ gravity in the solar system, galaxies
and clusters
astro-ph/0701662
Authors:
Pengjie
Zhang (SHAO)
Comments: 4 pages, no figure. Submitted to PRD. Comments welcome
Cosmologically interesting $f(R)$ gravity models are in general
strongly
environment dependent. For these models, we derive the complete sets of
the
linearized field equations in the Newtonian gauge, under environments
of the
solar system, galaxies and clusters respectively. Approximating the
solar
system as the Sun embedded in a uniform background with density
$\bar{\rho}$,
we find that {\it the constant curvature solution with the PPN
parameter
$\gamma=1$ is the only solution}. When $\bar{\rho}\to 0$, this solution
approaches to the Schwarzschild-de Sitter vacuum solution found in the
literature. In the solar system, the matter density is much higher than
the
cosmological critical density. This results in significant suppression
on
corrections to the general relativity (GR) induced by $f(R)$ gravity.
We show
that the behavior of $f(R)$ gravity in the solar system is virtually
identical
to that of GR.
Although the environments in galaxies and clusters differ from that in
the
solar system, we find that gravitational lensing of galaxies and
clusters are
virtually identical to that in GR. Fortunately, galaxy rotation curve
and
intra-cluster gas pressure profile may contain valuable information to
distinguish between $f(R)$ gravity and GR.
Testing cosmic homogeneity astro-ph/0702229
Authors:
Antonio
Enea Romano
Comments: 12 pages, 4 figures
We analyze the compatibility of astrophysical catalogs data with
inhomogeneous cosmological models. In particular we observe that
previous
spatial homogeneity tests were based on the analysis of a limited
redshift
range, and as such should be considered tests of isotropy, i.e. of
homogeneity
of the corresponding spherical shell. We introduce a radial homogeneity
measure
called redshift spherical shell mass (RSSM) which can be used to test
in the
redshift space the radial inhomogeneity of an isotropic universe,
providing
additional constraints for LTB models, and a more general test of
cosmic
homogeneity.
Measuring dark energy with the shear triplet statistics
astro-ph/0702078
Authors:
Mauro
Sereno
Comments: 5 pages, 3 figures, accepted for publication in MNRAS
The shear triplet statistics is a geometric method to measure
cosmological
parameters with observations in the weak gravitational lensing regime
towards
massive haloes. Here, this proposal is considered to probe the dark
energy
equation of state and its time derivative in view of future wide-field
galaxy
surveys. A survey with a median redshift of nearly 0.7 and a total area
of
nearly 10000 square degrees would be pretty effective in determining
the dark
matter cosmological density and in putting useful constraints on the
dark
energy properties.
Information criteria for astrophysical model selection
astro-ph/0701113
Authors: Andrew
R Liddle
Comments: 5 pages, no figures
Model selection is the problem of distinguishing
competing models,
perhaps
featuring different numbers of parameters. The statistics literature
contains
two distinct sets of tools, those based on information theory such as
the
Akaike Information Criterion (AIC), and those on Bayesian inference
such as the
Bayesian evidence and Bayesian Information Criterion (BIC). The
Deviance
Information Criterion combines ideas from both heritages; it is readily
computed from Monte Carlo posterior samples and, unlike the AIC and
BIC, allows
for parameter degeneracy. I describe the properties of the information
criteria, and as an example compute them from WMAP3 data for several
cosmological models. I find that at present the information theory and
Bayesian
approaches give significantly different conclusions from that data.
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