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Angular Signatures of Dark Matter in the Diffuse Gamma Ray
Spectrum
astro-ph/0702328
Authors:
Dan
Hooper, Pasquale
D. Serpico
Comments: 12 pages, 5 figures
Report-no: FERMILAB-PUB-07-038-A
Dark matter annihilating in our Galaxy's halo and elsewhere in the
universe
is expected to generate a diffuse flux of gamma rays, potentially
observable
with next generation satellite-based experiments, such as GLAST. In
this
article, we study the signatures of dark matter in the angular
distribution of
this radiation. Pertaining to the extragalactic contribution, we
discuss the
effect of the motion of the solar system with respect to the
cosmological rest
frame and anisotropies due to the structure of our local universe. For
the
gamma ray flux from dark matter in our own Galactic halo, we discuss
the
effects of the offset position of the solar system, the Compton-Getting
effect,
the asphericity of the Milky Way halo, and the signatures of nearby
substructure. We explore the prospects for the detection of these
features by
the GLAST satellite and find that, if ~10% or more of the diffuse gamma
ray
background observed by EGRET is the result of dark matter
annihilations, then
GLAST should be sensitive to anisotropies down to the 0.1% level. Such
precision would be sufficient to detect many, if not all, of the
signatures
discussed in this paper.
Would Bohr be born if Bohm were born before Born?
physics/0702069 (Mark,
presumably for the title)
Authors:
H.
Nikolic
Comments: 7 pages
Subj-class: Physics and Society; History of Physics
I discuss a hypothetical historical context in which a Bohm-like
deterministic interpretation of the Schrodinger equation could have
been
proposed before the Born probabilistic interpretation and argue that in
such a
context the Copenhagen (Bohr) interpretation would probably have never
achieved
great popularity among physicists.
On the Possibility of Quantum Gravity Effects at
Astrophysical Scales
hep-th/0702051 (suggested
by Mark)
Authors:
M.
Reuter, H.
Weyer
Comments: LaTeX, 18 pages, 4 figures. Invited contribution to the Int.
J. Mod. Phys. D special issue on dark matter and dark energy
Report-no: MZ-TH/07-01
The nonperturbative renormalization group flow of Quantum Einstein
Gravity
(QEG) is reviewed. It is argued that at large distances there could be
strong
renormalization effects, including a scale dependence of Newton's
constant,
which mimic the presence of dark matter at galactic and cosmological
scales.
It's Never Too Late For Matter astro-ph/0702207 (suggested
by Pasquale)
Authors:
Lawrence
M. Krauss (Case Western Reserve University and Vanderbilt
University), Robert
J. Scherrer (Vanderbilt University)
Comments: several typos corrected, and references added, as well as a
closed form general result for annihilating dark matter to not be
overwhelmed by radiation in a universe with general equation of state.
submitted to PRL
We demonstrate that in a vacuum-energy-dominated expansion phase,
neither the
decay of matter nor matter-antimatter annihilation into relativistic
particles
can ever cause radiation to once again dominate over matter in the
future
history of the universe.
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).
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%.
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.
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