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What is Munch?
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MeV Dark Matter and Small Scale Structure
Abstract: WIMPs with
electroweak scale masses (neutralinos, etc.) remain in kinetic
equilibrium with other particle species until temperatures
approximately in the
range of 10 MeV to 1 GeV, leading to the formation of dark matter
substructure
with masses as small as $10^{-4} M_{\odot}$ to $10^{-12} M_{\odot}$.
However,
if dark matter consists of particles with MeV scale masses, as
motivated by the
observation of 511 keV emission from the Galactic Bulge, such particles
are
naturally expected to remain in kinetic equilibrium with the cosmic
neutrino
background until considerably later times. This would lead to a strong
suppression of small scale structure with masses below about $10^7
M_{\odot}$
to $10^4 M_{\odot}$. This cutoff scale has important implications for
present
and future searches for faint Local Group satellite galaxies and for
the
missing satellites problem.
PDF
A discriminating probe of gravity at cosmological scales
Abstract: The standard
cosmological model is based on general relativity and includes
dark matter and dark energy. An important prediction of this model is a
fixed
relationship between the gravitational potentials responsible for
gravitational
lensing and the matter overdensity. Alternative theories of gravity
often make
different predictions for this relationship. We propose a set of
measurements
which can test the lensing/matter relationship, thereby distinguishing
between
dark energy/matter models and models in which gravity differs from
general
relativity. Planned optical, infrared and radio galaxy and lensing
surveys will
be able to measure $E_G$, an observational quantity whose expectation
value is
equal to the ratio of the Laplacian of the Newtonian potentials to the
peculiar
velocity divergence, to percent accuracy. We show that this will easily
separate alternatives such as $\Lambda$CDM, DGP, TeVeS and $f(R)$
gravity.
PDF Ultra-High
Energy Cosmic Rays and the GeV-TeV Diffuse Gamma-Ray Flux
(suggested by Pasquale)
Abstract: Ultra-high energy
cosmic ray protons accelerated in astrophysical objects
produce secondary electromagnetic cascades during propagation in the
cosmic
microwave and infrared backgrounds. We show that such cascades can
contribute
between ~1% and ~50% of the GeV-TeV diffuse photon flux measured by the
EGRET
experiment. The GLAST satellite should have a good chance to discover
this
flux.
PDF
Dark matter caustics and the enhancement of self-annihilation flux (suggested by Pasquale)
Abstract: Cold dark matter
haloes are populated by caustics, which are yet to be
resolved in N-body simulations or observed in the Universe. Secondary
infall
model provides a paradigm for the study of caustics in "typical" haloes
assuming that they have had no major mergers and have grown only by
smooth
accretion. This is a particular characteristic of the smallest dark
matter
haloes of about 10^{-5} Mo, which although "atypical" contain no
substructures
and could have survived until now with no major mergers. Thus using
this model
as the first guidline, we evaluate the neutralino self-annihilation
flux for
these haloes. Our results show that caustics could leave a distinct
sawteeth
signature on the differential and cumulative fluxes coming from the
outer
regions of these haloes. The total annihilation signal from the regions
away
from the centre can be boosted by about forty percents.
PDF
Fundamentalist physics: why Dark Energy is bad for Astronomy (suggested by several
group memebers)
Abstract: Astronomers carry out
observations to explore the diverse processes and
objects which populate our Universe. High-energy physicists carry out
experiments to approach the Fundamental Theory underlying space, time
and
matter. Dark Energy is a unique link between them, reflecting deep
aspects of
the Fundamental Theory, yet apparently accessible only through
astronomical
observation. Large sections of the two communities have therefore
converged in
support of astronomical projects to constrain Dark Energy. In this
essay I
argue that this convergence can be damaging for astronomy. The two
communities
have different methodologies and different scientific cultures. By
uncritically
adopting the values of an alien system, astronomers risk undermining
the
foundations of their own current success and endangering the future
vitality of
their field. Dark Energy is undeniably an interesting problem to attack
through
astronomical observation, but it is one of many and not necessarily the
one
where significant progress is most likely to follow a major investment
of
resources.
PDF
Redefining the Missing Satellites Problem
Abstract: Numerical simulations
of Milky-Way size Cold Dark Matter (CDM) halos predict
a steeply rising mass function of small dark matter subhalos and a
substructure
count that greatly outnumbers the observed satellites of the Milky Way.
Several
proposed explanations exist, but detailed comparison between theory and
observation in terms of the maximum circular velocity (Vmax) of the
subhalos is
hampered by the fact that Vmax for satellite halos is poorly
constrained. We
present comprehensive mass models for the well-known Milky Way dwarf
satellites, and derive likelihood functions to show that their masses
within
0.6 kpc (M_0.6) are strongly constrained by the present data. We show
that the
M_0.6 mass function of luminous satellite halos is flat between ~ 10^7
and 10^8
M_\odot. We use the ``Via Lactea'' N-body simulation to show that the
M_0.6
mass function of CDM subhalos is steeply rising over this range. We
rule out
the hypothesis that the 11 well-known satellites of the Milky Way are
hosted by
the 11 most massive subhalos. We show that models where the brightest
satellites correspond to the earliest forming subhalos or the most
massive
accreted objects both reproduce the observed mass function. A similar
analysis
with the newly-discovered dwarf satellites will further test these
scenarios
and provide powerful constraints on the CDM small-scale power spectrum
and warm
dark matter models.
PDF
Antiproton and Positron Signal Enhancement in Mini-Spikes Scenarios
Abstract: The annihilation of
dark matter in the Galaxy could be signed as specific
imprints on spectra of antimatter species in Galactic cosmic rays. Many
studies
are devoted to this topic, and in that context, an enhancement of the
signal is
often introduced and referred to as the so-called boost factor. Recent
studies
show that not only this factor does depend on energy, but it is
intrinsically a
statistical property of the distribution of DM substructures inside the
Milky
Way. Therefore a large variance affects the prediction of the signal
enhancement due to the clumpiness of the DM halo. We investigate a
scenario in
which substructures consist in a relatively small number of mini-spikes
formed
around intermediate-mass black holes, and find boosts of order a few
thousand,
with a high dispersion.
PDF
Sunyaev-Zel'dovich profiles and scaling relations: modelling effects
and observational biases
Abstract: We use
high-resolution hydrodynamic re-simulations to investigate the
properties of the thermal Sunyaev-Zel'dovich (SZ) effect from galaxy
clusters.
We compare results obtained using different physical models for the
intracluster medium (ICM), and show how they modify the SZ emission in
terms of
cluster profiles and scaling relations. We also produce realistic mock
observations to verify whether the results from hydrodynamic
simulations can be
confirmed. We find that SZ profiles depend marginally on the modelled
physical
processes, while they exhibit a strong dependence on cluster mass. The
central
and total SZ emission strongly correlate with the cluster X-ray
luminosity and
temperature. The logarithmic slopes of these scaling relations differ
from the
self-similar predictions by less than 0.2; the normalization of the
relations
is lower for simulations including radiative cooling. The observational
test
suggests that SZ cluster profiles are unlikely to be able to probe the
ICM
physics. The total SZ decrement appears to be an observable much more
robust
than the central intensity, and we suggest using the former to
investigate
scaling relations.
PDF
The Peculiar Velocities of Local Type Ia Supernovae and their Impact on
Cosmology
Abstract: We quantify the
effect of supernova Type Ia peculiar velocities on the
derivation of cosmological parameters. The published distant and local
Ia SNe
used for the Supernova Legacy Survey first-year cosmology report form
the
sample for this study. While previous work has assumed that the local
SNe are
at rest in the CMB frame (the No Flow assumption), we test this
assumption by
applying peculiar velocity corrections to the local SNe using three
different
flow models. The models are based on the IRAS PSCz galaxy redshift
survey, have
varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in
the CMB
frame. These datasets are then fit for w, Omega_m, and Omega_Lambda
using
flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to
examine
the effect of the velocity corrections on the quality of the fits. The
most
favored model is the beta=0.5 model, which produces a fit significantly
better
than the No Flow assumption, consistent with previous peculiar velocity
studies. By comparing the No Flow assumption with the favored models we
derive
the largest potential systematic error in w caused by ignoring peculiar
velocities to be Delta w = +0.04. For Omega_Lambda, the potential error
is
Delta Omega_Lambda = -0.04 and for Omega_m, the potential error is
Delta
Omega_m < +0.01. The favored flow model (beta=0.5) produces the
following
cosmological parameters: w = -1.08 (+0.09,-0.08), Omega_m = 0.27
(+0.02,-0.02)
assuming a flat cosmology, and Omega_Lambda = 0.80 (+0.08,-0.07) and
Omega_m =
0.27 (+0.02,-0.02) for a w = -1 (LambdaCDM) cosmology.
PDF
Higher-Order Angular Galaxy Correlations in the SDSS: Redshift and
Color Dependence of non-Linear Bias
Abstract: We present estimates
of the N-point galaxy, area-averaged, angular
correlation functions $\bar{\omega}_{N}$($\theta$) for $N$ = 2,...,7
for
galaxies from the fifth data release of the Sloan Digital Sky Survey.
Our
parent sample is selected from galaxies with $18 \leq r < 21$, and
is the
largest ever used to study higher-order correlations. We subdivide this
parent
sample into two volume limited samples using photometric redshifts, and
these
two samples are further subdivided by magnitude, redshift, and color
(producing
early- and late-type galaxy samples) to determine the dependence of
$\bar{\omega}_{N}$($\theta$) on luminosity, redshift, and galaxy-type.
We
measure $\bar{\omega}_{N}$($\theta$) using oversampling techniques and
use them
to calculate the projected, $s_{N}$. Using models derived from
theoretical
power-spectra and perturbation theory, we measure the bias parameters
$b_1$ and
$c_2$, finding that the large differences in both bias parameters
($b_1$ and
$c_2$) between early- and late-type galaxies are robust against changes
in
redshift, luminosity, and $\sigma_8$, and that both terms are
consistently
smaller for late-type galaxies. By directly comparing their
higher-order
correlation measurements, we find large differences in the clustering
of
late-type galaxies at redshifts lower than 0.3 and those at redshifts
higher
than 0.3, both at large scales ($c_2$ is larger by $\sim0.5$ at $z >
0.3$) and
small scales (large amplitudes are measured at small scales only for $z
> 0.3$,
suggesting much more merger driven star formation at $z > 0.3$).
Finally, our
measurements of $c_2$ suggest both that $\sigma_8 < 0.8$ and $c_2$
is negative.
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