|
FAQ
What is Munch?
Munch Archive
---------
13 Mar 2006
6 Mar 2006
|
Implications of Direct Dark Matter Searches for MSSM Higgs
Searches at the Tevatron
Authors:
Marcela
Carena, Dan
Hooper, Peter
Skands
Comments: 4 pages, 3 figures
Report-no: FERMILAB-PUB-06-032-A
Searches for the Minimal Supersymmetric Standard Model (MSSM) Higgs
bosons
are among the most promising channels for exploring new physics at the
Tevatron. In particular, interesting regions of large $\tan \beta$ and
small
$m_A$ are probed by searches for heavy neutral Higgs bosons, A and H,
when they
decay to $\tau^+ \tau^-$ and $b\bar{b}$. At the same time, direct
searches for
dark matter, such as CDMS, attempt to observe neutralino dark matter
particles
scattering elastically off nuclei. This can occur through t-channel
Higgs
exchange, which has a large cross section in the case of large $\tan
\beta$ and
small $m_A$. As a result, there is a natural interplay between the
heavy,
neutral Higgs searches at the Tevatron and the region of parameter
space
explored by CDMS. We show that if the lightest neutralino makes up the
dark
matter of our universe, current limits from CDMS strongly constrain the
prospects of heavy, neutral MSSM Higgs discovery at the Tevatron (at 3
sigma
with 4 fb^-1 per experiment) unless $|\mu| \gsim$ 400 GeV. The limits
of CDMS
projected for 2007 will increase this constraint to $|\mu| \gsim$ 800
GeV. On
the other hand, if CDMS does observe neutralino dark matter in the near
future,
it will make the discovery of heavy, neutral MSSM Higgs bosons far more
likely
at the Tevatron.
Challenges in Detecting Gamma-Rays From Dark Matter
Annihilations in the Galactic Center
Authors:
Gabrijela
Zaharijas, Dan
Hooper
Comments: 8 pages, 10 figures
Report-no: FERMILAB-PUB-06-048-A
Atmospheric Cerenkov Telescopes, including HESS and MAGIC, have
detected a
spectrum of gamma-rays from the galactic center region which extends
from
$\sim$200 GeV or lower, to at least $\sim$10 TeV. Although the source
of this
radiation is not yet known, the spectrum appears to behave as a simple
power-law, which is not the expectation for gamma-rays generated
through the
annihilation of dark matter particles. If instead we conclude that the
source
of these gamma-rays is astrophysical in origin, this spectrum will
constitute a
background for future dark matter searches using gamma-rays from this
region.
In this paper we study how this background will affect the prospects
for
experiments such as GLAST to detect dark matter in the galactic center.
We find
that only a narrow range of dark matter annihilation rates are
potentially
observable by GLAST given this newly discovered background and
considering
current constraints from EGRET and HESS. We also find that a detection
of line
emission, while not completely ruled out, is only possible for a very
narrow
range of dark matter models and halo profiles.
Updating reionization scenarios after recent data
Authors:
T.
Roy Choudhury, A.
Ferrara
Comments: 5 pages, 1 figure
The recent release of data on (i) high redshift source counts from
NICMOS
HUDF, and (ii) electron scattering optical depth from 3-year WMAP,
require a
re-examination of reionization scenarios. Using an improved
self-consistent
model, based on Choudhury & Ferrara (2005), we determine the range
of
reionization histories which can match a wide variety of data sets
simultaneously. From this improved analysis we find that hydrogen
reionization
starts around z = 15, driven by the metal-free stars (with normal
Salpeter-like
IMF), and is 90% complete by z = 10. The photoionizing power of PopIII
stars
fades for z < 10 because of the concomitant action of radiative and
chemical
feedbacks, which causes the reionization process to stretch
considerably and to
end only by z = 6. The combination of different data sets still favours
a
non-zero contribution from metal-free stars, forming with efficiencies
> 2%.
Small Scale Anisotropy Predictions for the Auger Observatory
Authors:
Daniel
De Marco, Pasquale
Blasi, Angela
V. Olinto
Comments: 15 pages, 6 figures, 6 tables, submitted to JCAP
We study the small scale anisotropy signal expected at the Pierre Auger
Observatory in the next 1, 5, 10, and 15 years of operation, from
sources of
ultra-high energy (UHE) protons. We numerically propagate UHE protons
over
cosmological distances using an injection spectrum and normalization
that fits
current data up to $\sim 10^{20}\eV$. We characterize possible sources
of
ultra-high energy cosmic rays (UHECRs) by their mean density in the
local
Universe, $\bar{\rho} = 10^{-r}$ Mpc$^{-3}$, with $r$ between 3 and 6.
These densities span a wide range of extragalactic sites for UHECR
sources,
from common to rare galaxies or even clusters of galaxies. We simulate
100
realizations for each model and calculate the two point correlation
function
for events with energies above $4 \times 10^{19}\eV$ and above
$10^{20}\eV$, as
specialized to the case of the Auger telescope. We find that for $r\ga
4$,
Auger should be able to detect small scale anisotropies in the near
future.
Distinguishing between different source densities based on cosmic ray
data
alone will be more challenging than detecting a departure from isotropy
and is
likely to require larger statistics of events. Combining the angular
distribution studies with the spectral shape around the GZK feature
will also
help distinguish between different source scenarios.
What mass are the smallest protohalos?
Authors:
Stefano
Profumo (Caltech), Kris
Sigurdson (IAS), Marc
Kamionkowski (Caltech)
Comments: 5 pages, 4 figures, submitted to Phys. Rev. Lett
We calculate the kinetic-decoupling temperature for weakly interacting
massive particles (WIMPs) in supersymmetric (SUSY) and
universal-extra-dimension (UED) models that can account for the
cold-dark-matter abundance determined from cosmic microwave background
measurements. Depending on the parameters of the particle-physics
model, a wide
variety of decoupling temperatures is possible, ranging from several
MeV to a
few GeV. These decoupling temperatures imply a range of masses for the
smallest
protohalos much larger than previously thought -- ranging from 10^{-6}
earth
masses to 10^{2} earth masses. We expect the range of protohalos masses
derived
here to be characteristic of most particle-physics models that can
thermally
accommodate the required relic abundance of WIMP dark matter, even
beyond SUSY
and UED.
Inflation models after WMAP year three
Authors:
Laila
Alabidi, David
H. Lyth
Comments: 4 pages
The survey of models in astro-ph/0510441
is updated. For the first time, a
large fraction of the models are ruled out at more than $3\sigma$.
Higher order contributions to the primordial non-gaussianity
Authors:
Ignacio
Zaballa, Yeinzon
Rodriguez, David
H. Lyth
Comments: 6 pages. 2 figures
In this paper we calculate additional contributions to that part of the
non-Gaussianity of the curvature perturbation, which come from the
three-point
correlator of the field perturbations. We estimate this contribution in
the
following models for its origin: single-component inflation,
multi-component
chaotic inflation, a two-component "hybrid" inflationary model, and the
curvaton scenario. In all of these models, the additional contributions
to the
primordial non-gaussianity considered here, are too small to be ever
detected.
Was Star-Formation Suppressed in High-Redshift Minihalos?
Authors:
Zoltan
Haiman, Greg
L. Bryan (Columbia University)
Comments: ApJL, submitted
The primordial gas in the earliest dark matter halos, collapsing at
redshifts
around z=20, with masses M_halo=10^6 M_sun, and virial temperatures
T_vir<10^4K, relied on the presence of molecules for cooling.
Several
theoretical studies have suggested that gas contraction and
star-formation in
these minihalos was suppressed by radiative, chemical, thermal, and
dynamical
feedback processes. The recent measurement by the Wilkinson Microwave
Anisotropy Probe (WMAP) of the optical depth to electron scattering,
tau=0.09+/-0.03, provides the first empirical evidence for this
suppression.
The new WMAP result is consistent with vanilla models of reionization,
in which
ionizing sources populate cold dark matter (CDM) halos down to a virial
temperature of T_vir=10^4K. On the other hand, we show that in order to
avoid
overproducing the optical depth, the efficiency for the production of
ionizing
photons in minihalos must have been about an order of magnitude lower
than
expected and lower than the efficiency in large halos that can cool via
atomic
hydrogen (T_vir > 10^4K). This conclusion is insensitive to
assumptions about
the efficiency of ionizing photon production in the large halos, as
long as
reionization ends by z=6, as required by the spectra of bright quasars
at z<6.
Our conclusion is strengthened if the clumping of the ionized gas
evolves with
redshift, as suggested by semi-analytical predictions and
three-dimensional
numerical simulations.
Tracing early structure formation with massive starburst
galaxies and their implications for reionization
Authors: Kentaro
Nagamine (UCSD), Renyue
Cen (Princeton), Steven
R. Furlanetto (Caltech), Lars
Hernquist (Harvard), Christopher
Night (Harvard), Jeremiah
P. Ostriker (Princeton)
Comments: 9 pages, 4 figures. Summary of the talk given at the "First
Light & Reionization" workshop at UC Irvine, May 2005. The
published article is available from this http URL
Journal-ref: New Astron.Rev. 50 (2006) 29-34
DOI: 10.1016/j.newar.2005.11.002
Cosmological hydrodynamic simulations have
significantly improved over
the
past several years, and we have already shown that the observed
properties of
Lyman-break galaxies (LBGs) at z=3 can be explained well by the massive
galaxies in the simulations. Here we extend our study to z=6 and show
that we
obtain good agreement for the LBGs at the bright-end of the luminosity
function
(LF). Our simulations also suggest that the cosmic star formation rate
density
has a peak at z= 5-6, and that the current LBG surveys at z=6 are
missing a
significant number of faint galaxies that are dimmer than the current
magnitude
limit. Together, our results suggest that the universe could be
reionized at
z=6 by the Pop II stars in ordinary galaxies. We also estimate the LF
of
Lyman-alpha emitters (LAEs) at z=6 by relating the star formation rate
in the
simulation to the Ly-alpha luminosity. We find that the simulated LAE
LFs agree
with the observed data provided that the net escape fraction of
Ly-alpha photon
is f_{Ly-alpha} <= 0.1. We investigate two possible scenarios for
this effect:
(1) all sources in the simulation are uniformly dimmer by a factor of
10
through attenuation, and (2) one out of ten LAEs randomly lights up at
a given
moment. We show that the correlation strength of the LAE spatial
distribution
can possibly distinguish the two scenarios.
Gravitational Waves from the First Stars
Authors:
Pearl
Sandick, Keith
A. Olive, Frederic
Daigne, Elisabeth
Vangioni
Comments: 16 pages, 8 figures
Report-no: UMN-TH-2435/06, FTPI-MINN-06/07
We consider the stochastic background of gravitational waves produced
by an
early generation of Population III stars coupled with a normal mode of
star
formation at lower redshift. The computation is performed in the
framework of
hierarchical structure formation and is based on cosmic star formation
histories constrained to reproduce the observed star formation rate at
redshift
$z \la 6$, the observed chemical abundances in damped Lyman alpha
absorbers and
in the intergalactic medium, and to allow for an early reionization of
the
Universe at $z\sim 10-20$ as indicated by the first year results
released by
WMAP. We find that the normal mode of star formation produces a
gravitational
wave background which peaks at 300-500 Hz and is within LIGO III
sensitivity.
The Population III component peaks at lower frequencies (30-100 Hz
depending on
the model), and could be detected by LIGO III as well as the planned
BBO and
DECIGO interferometers.
Bursts from the very early universe
Authors:
J.
Silk, L.
Stodolsky
Comments: eight pages, no figures, typo in metadata corrected
Bursts of weakly interacting particles such as neutrinos or even more
weakly
interacting particles such as wimps and gravitons from the very early
universe
would offer a much deeper ``look back time'' to early epochs than is
possible
with photons.
We consider some of the issues related to the existence of such bursts
and
their detectability. Characterizing the burst rate by a probability
$\cal P$
per Hubble four-volume we find, for events in the radiation-dominated
era, that
the natural unit of description is the present intensity of the CMB
times $\cal
P$. The existence of such bursts would make the observation of
phenomena
associated with very early times in cosmology at least conceptually
possible.
One might even hope to probe the transplanckian epoch if complexes more
weakly
interacting than the graviton can exist. Other conceivable applications
include
the potential detectability of the formation of "pocket" universes'' in
a
multiverse.
Inflating in a Better Racetrack
Authors:
J.J.
Blanco-Pillado, C.P.
Burgess, J.M.
Cline, C.
Escoda, M.
Gomez-Reino, R.
Kallosh, A.
Linde, F.
Quevedo
Comments: 20 pages, 6 figures
Report-no: DAMTP-2006-20, SU-ITP-06-07
We present a new version of our racetrack inflation scenario which,
unlike
our original proposal, is based on an explicit compactification of type
IIB
string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The
axion-dilaton and
all complex structure moduli are stabilized by fluxes. The remaining 2
Kahler
moduli are stabilized by a nonperturbative superpotential, which has
been
explicitly computed. For this model we identify situations for which a
linear
combination of the axionic parts of the two Kahler moduli acts as an
inflaton.
As in our previous scenario, inflation begins at a saddle point of the
scalar
potential and proceeds as an eternal topological inflation. For a
certain range
of inflationary parameters, we obtain the COBE-normalized spectrum of
metric
perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We
discuss
possible changes of parameters of our model and argue that anthropic
considerations favor those parameters that lead to a nearly flat
spectrum of
inflationary perturbations, which in our case is characterized by the
spectral
index n_s = 0.95.
Towards a Cosmological Hubble Diagram for Type II-P Supernovae
Authors:
Peter
Nugent (1), Mark
Sullivan (2), Richard
Ellis (3), Avishay
Gal-Yam (3 and 4), Douglas
C. Leonard (3 and 5), D.
Andrew Howell (2), Pierre
Astier (6), Raymond
G. Carlberg (2), Alex
Conley (2), Sebastien
Fabbro (7), Dominique
Fouchez (8), James
D. Neill (9), Reynald
Pain (6), Kathy
Perrett (2), Chris
J. Pritchet (9), Nicolas
Regnault
(6) ((1) Lawrence Berkeley National Laboratory, (2) University of
Toronto, (3) California Institute of Technology, (4) Hubble
Postdoctoral Fellow, (5) NSF Astronomy and Astrophysics Postdoctoral
Fellow, (6) LPNHE, CNRS-IN2P3 and University of Paris VI & VII, (7)
CENTRA, (8) CPPM, CNRS-IN2P3 and University Aix Marseille II, (9)
University of Victoria)
Comments: 36 pages, 16 figures, accepted for publication in ApJ
We present the first high-redshift Hubble diagram for Type II-P
supernovae
(SNe II-P) based upon five events at redshift up to z~0.3. This diagram
was
constructed using photometry from the Canada-France-Hawaii Telescope
Supernova
Legacy Survey and absorption line spectroscopy from the Keck
observatory. The
method used to measure distances to these supernovae is based on recent
work by
Hamuy & Pinto (2002) and exploits a correlation between the
absolute brightness
of SNe II-P and the expansion velocities derived from the minimum of
the Fe II
516.9 nm P-Cygni feature observed during the plateau phases. We present
three
refinements to this method which significantly improve the practicality
of
measuring the distances of SNe II-P at cosmologically interesting
redshifts.
These are an extinction correction measurement based on the V-I colors
at day
50, a cross-correlation measurement for the expansion velocity and the
ability
to extrapolate such velocities accurately over almost the entire
plateau phase.
We apply this revised method to our dataset of high-redshift SNe II-P
and find
that the resulting Hubble diagram has a scatter of only 0.26
magnitudes, thus
demonstrating the feasibility of measuring the expansion history, with
present
facilities, using a method independent of that based upon supernovae of
Type
Ia.
On horizons and the cosmic landscape
Authors:
George
F R Ellis
Comments: Revised to clarify claims; essential substance unchanged
Susskind claims in his recent book The Cosmic Landscape that evidence
for the
existence and nature of `pocket universes' in a multiverse would be
available
in the detailed nature of the Cosmic Blackbody Background Radiation
that
constantly bathes all parts of our observable universe. I point out
that
acceptance of the complex chain of argument involved does not imply
possible
experimental verification of multiverses at the present time. Rather
this claim
relates only to theoretically possible observations in the very far
future of
the universe.
Abundance of Cosmological Relics in Low-Temperature Scenarios
Authors:
Manuel
Drees, Hoernisa
Iminniyaz, Mitsuru
Kakizaki
Comments: 25 pages, 8 figures
Report-no: KIAS-P06010, ICRR-Report-524-2005-7
We investigate the relic density n_\chi of non-relativistic long-lived
or
stable particles \chi in cosmological scenarios in which the
temperature T is
too low for \chi to achieve full chemical equilibrium. The case with a
heavier
particle decaying into \chi is also investigated. We derive approximate
solutions for n_\chi(T) which accurately reproduce numerical results
when full
thermal equilibrium is not achieved. If full equilibrium is reached,
our ansatz
no longer reproduces the correct temperature dependence of the \chi
number
density. However, it does give the correct final relic density, to an
accuracy
of about 3% or better, for all cross sections and initial temperatures.
|
|
