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6 Mar 2006
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A new cosmic microwave background constraint to primordial
gravitational waves
Authors: Tristan
L. Smith, Elena
Pierpaoli, Marc
Kamionkowski (Caltech)
Comments: 5 pages, 2 figures, submitted to Phys. Rev. Lett
Primordial gravitational waves (GWs) with frequencies
> 10^{-15} Hz
contribute to the radiation density of the Universe at the time of
decoupling
of the cosmic microwave background (CMB). The effects of this GW
background on
the CMB and matter power spectra are identical to those due to massless
neutrinos, unless the initial density-perturbation amplitude for the
gravitational-wave gas is non-adiabatic, as may occur if such GWs are
produced
during inflation or some post-inflation phase transition. In either
case,
current observations provide a constraint to the GW amplitude that
competes
with that from big-bang nucleosynthesis (BBN), although it extends to
much
lower frequencies (~10^{-15} Hz rather than the ~10^{-10} Hz lower
limit from
BBN): at 95% confidence-level, Omega_gw h^2 < 6.9 x 10^{-6} for
homogeneous
(i.e., non-adiabatic) initial conditions. Future CMB experiments, like
Planck
and CMBPol, should allow sensitivities to Omega_gw h^2 < 1.4 x
10^{-6} and
Omega_gw h^2 < 5 x 10^{-7}, respectively.
Impact of a non-Gaussian density field on Sunyaev-Zeldovich
observables
Authors: S.
Sadeh, Y.
Rephaeli, J.
Silk
Comments: 17 pages, 11 figures, accepted for publication in MNRAS
The main statistical properties of the
Sunyaev-Zeldovich (S-Z) effect -
the
power spectrum, cluster number counts, and angular correlation function
- are
calculated and compared within the framework of two density fields
which differ
in their predictions of the cluster mass function at high redshifts. We
do so
for the usual Press and Schechter mass function, which is derived on
the basis
of a Gaussian density fluctuation field, and for a mass function based
on a
chi^2 distributed density field. These three S-Z observables are found
to be
very significantly dependent on the choice of the mass function. The
different
predictions of the Gaussian and non-Gaussian density fields are probed
in
detail by investigating the behaviour of the three S-Z observables in
terms of
cluster mass and redshift. The formation time distribution of clusters
is also
demonstrated to be sensitive to the underlying mass function. A
semi-quantitative assessment is given of its impact on the
concentration
parameter and the temperature of intracluster gas.
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.
On the influence of the global cosmological expansion on the
local dynamics in the Solar System
Authors: Matteo
Carrera, Domenico
Giulini
Comments: 37 pages, 2 figures
Report-no: Freiburg THEP-06/03
In this expository paper we address the question of
whether, and to
what
extent, the cosmological expansion influences the dynamics on small
scales (as
compared to cosmological ones), particularly in our Solar System. We
distinguish between dynamical and kinematical effects and critically
review the
status of both as presented in the current literature.
Reduction of Cosmological Data for the Detection of
Time-varying Dark Energy Density
Authors: Jason
Dick, Lloyd
Knox, Mike
Chu
Comments: 10 pages, 9 figures
We present a method for reducing cosmological data to
constraints on
the
amplitudes of modes of the dark energy density as a function of
redshift. The
modes are chosen so that 1) one of them has constant density and 2) the
others
are non-zero only if there is time-variation in the dark energy density
and 3)
the amplitude errors for the time-varying modes are uncorrelated with
each
other. We apply our method to various combinations of CMB data, baryon
acoustic
oscillation data Eisenstein et. al. (2005), the Riess et. al. (2004)
'Gold'
supernova data set, and the Supernova Legacy Survey data set Astier et.
al.
(2005). We find no significant evidence for a time-varying dark energy
density
or for non-zero mean curvature.
Parametrizations of the Dark Energy Density and Scalar
Potentials
Authors: Zong-Kuan
Guo, Nobuyoshi
Ohta, Yuan-Zhong
Zhang
Comments: 4 pages, 2 figures, RevTeX
We develop a theoretical method of constructing the
scalar
(quintessence or
phantom) potential directly from the dimensionless dark energy function
X(z),
the dark energy density in units of its present value. We apply our
method to
two parametrizations of the dark energy density, the quiessence-Lambda
ansatz
and the generalized Chaplygin gas model, and discuss some features of
the
constructed potentials.
New Regions for a Chameleon to Hide
Authors: Baruch
Feldman, Ann
Nelson
Comments: 17 pages, 1 figure
We show that inclusion of an extremely small quartic
coupling constant
in the
potential for a nearly massless scalar field greatly increases the
experimentally allowed region for the mass term and the coupling of the
field
to matter.
Impact of dark matter decays and annihilations on reionzation
Authors: M.
Mapelli (1), A.
Ferrara (1), E.
Pierpaoli (2), ((1) SISSA, (2) Caltech)
Comments: 6 pages, 5 figures, submitted to MNRAS
One of the possible methods to distinguish among
various dark matter
candidates is to study the effects of dark matter decays. We consider
four
different dark matter candidates (light dark matter, gravitinos,
neutralinos
and sterile neutrinos), for each of them deriving the
decaying/annihilation
rate, the influence on reionization, matter temperature and CMB
spectra. We
find that light dark matter particles (1-10 MeV) and sterile neutrinos
(2-7
keV) can be sources of partial early reionization (z<~100). However,
their
integrated contribution to Thomson optical depth is small (<~0.01).
Finally,
they can significantly affect the behavior of matter temperature. On
the
contrary, effects of heavy dark matter candidates (gravitinos and
neutralinos)
on reionization and heating are minimal. All the considered dark matter
particles have completely negligible effects on the CMB spectra.
A New Definition of Substructure in Dark Matter Halos
Authors: L.
Shaw, J.
Weller, J.P.
Ostriker, P.
Bode
Comments: 12 pages, 11 figures, submitted to ApJ
We present a new definition of subhalos in
dissipationless dark matter
N-body
simulations, based on the coherent identification of their dynamically
bound
constituents. Whereas previous methods of determining the energetically
bound
components of a subhalo ignored the contribution of all the remaining
particles
in the halo (those not geometrically or dynamically associated with the
subhalo), our method allows for all the forces, both internal and
external,
exerted on the subhalo. We compare our new method to previously adopted
means
of identifying subhalos by applying each to a sample of 1838 virialized
halos
extracted from a high resolution cosmological simulation. We find that
the
subhalo distributions are similar in each case, and that the increase
in the
binding energy of a subhalo from including all the particles located
within it
is almost entirely balanced by the losses due to the external forces;
the net
increase in the mass fraction of subhalos is roughly 10%, and the extra
substructures tending to reside in the inner parts of the system.
Finally, we
compare the subhalo populations of halos to the sub-subhalo populations
of
subhalos, finding the two distributions to be similar. This is a new
and
interesting result, suggesting a self-similarity within the
hierarchical
structures of cluster mass halos, with the 2nd generation of subhalos
distributed within the 1st generation in the same manner as the latter
are
distributed within the cluster as a whole.
Early supersymmetric cold dark matter substructure
Authors: Juerg
Diemand, Michael
Kuhlen, Piero
Madau (UC Santa Cruz)
Comments: 12 pages, 10 figures, submitted to ApJ. A version with
high-resolution figures is available at this http URL
Earth-mass dark matter microhalos may be the first
objects to collapse
and
virialize in the early universe. Their ability to survive the
hierarchical
clustering process as substructure in the larger halos that form
subsequently
has implications for direct and indirect dark matter detection
experiments. We
present here the large N-body simulation of early substructure in a
supersymmetric cold dark matter (SUSY-CDM) scenario characterized by an
exponential cutoff in the matter power spectrum at M_c=10^{-6} Msun.
The
simulation resolves a 0.014 Msun parent SUSY halo at z=75 with 12
million
particles within its virial radius. On these scales the effective index
of the
power spectrum approaches -3, a range of mass scales collapse almost
simultaneously, and the formation history of the early SUSY host
appears very
different from that of a low-redshift massive halo. Compared to a z=0
galaxy
cluster with similar concentration parameter, substructure within our
SUSY host
is less evident both in phase-space and in physical space, and it is
less
resistant against tidal stripping and disruption. As the scale factor
of the
universe increases by a factor of 1.3, we find that between 20 and 40
percent
of well-resolved SUSY substructure is destroyed, compared to only about
1
percent in the low-redshift cluster. Despite the lower contrast and
higher
disruption probability, SUSY substructure is just as abundant as in z=0
galaxy
clusters, i.e. the substructure normalized mass and circular velocity
functions
are very similar. The dark matter self-annihilation gamma-ray signal
from
resolved sub-microhalos is comparable to the spherically-averaged SUSY
host
signal, and should be included in estimates of the cosmological
extragalactic
gamma-ray background.(ABRIDGED)
Extra-Dimensions and Dark Matter
Authors: Francesco
Fucito, Andrea
Lionetto, Maurizio
Prisco
Comments: 37 pages, 17 figures, uses feynmf.sty
Report-no: ROM2F/2006/07
In this paper we study the general scenario of an
effective theory
coming
from the compactification of a higher dimensional theory in a string
inspired
setting. This leads to gauge coupling unification at an intermediate
mass
scale. After having computed all the threshold corrections (due to
Kaluza-Klein
modes) to the running of the couplings of the MSSM we embark in a
detailed
phenomenological analysis of the model, based on the numerical package
DarkSUSY, to find constraints on the scenario from Dark Matter data.
The mass
spectrum of the theory does not have tachyons. Moreover we find that
the
neutralino is still the LSP with a relic density compatible with the
most
recent experimental data. With respect to the standard mSUGRA scenario
we find
that the neutralino is higgsino like in most of the parameter space.
Our
modifications to the DarkSUSY package will be shortly available upon
request.
Spontaneous Lorentz Breaking at High Energies
Authors: Hsin-Chia
Cheng, Markus
A. Luty, Shinji
Mukohyama, Jesse
Thaler
Comments: 59 pages; 6 figures
Report-no: HUTP-06/A0006, UTAP-551
Theories that spontaneously break Lorentz invariance
also violate
diffeomorphism symmetries, implying the existence of extra degrees of
freedom
and modifications of gravity. In the minimal model (``ghost
condensation'')
with only a single extra degree of freedom at low energies, the scale
of
Lorentz violation cannot be larger than about M ~ 100GeV due to an
infrared
instability in the gravity sector. We show that Lorentz symmetry can be
broken
at much higher scales in a non-minimal theory with additional degrees
of
freedom, in particular if Lorentz symmetry is broken by the vacuum
expectation
value of a vector field. This theory can be constructed by gauging
ghost
condensation, giving a systematic effective field theory description
that
allows us to estimate the size of all physical effects. We show that
nonlinear
effects become important for gravitational fields with strength
\sqrt{\Phi} >
g, where g is the gauge coupling, and we argue that the nonlinear
dynamics is
free from singularities. We then analyze the phenomenology of the
model,
including nonlinear dynamics and velocity-dependent effects. The
strongest
bounds on the gravitational sector come from either black hole
accretion or
direction-dependent gravitational forces, and imply that the scale of
spontaneous Lorentz breaking is M < Min(10^{12}GeV, g^2 10^{15}GeV).
If the
Lorentz breaking sector couples directly to matter, there is a
spin-dependent
inverse-square law force, which has a different angular dependence from
the
force mediated by the ghost condensate, providing a distinctive
signature for
this class of models.
The Relic Neutrino Backround from the First Stars
Authors: Keith
A. Olive, Pearl
Sandick
Comments: 19 pages, 15 figures, Summary of talk given at the IIIrd
International Workshop on: NO-VE "Neutrino Oscillations in Venice",
Venice Italy, February 2006
Report-no: UMN-TH-2436/06, FTPI-MINN-06/08
We consider the relic neutrino background produced by
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 ~ 10-20. We consider both a
burst and
non-burst model for Population III star formation. We find that
although the
high redshift burst of Population III stars does lead to an appreciable
flux of
neutrinos at relatively low energy (E_\nu \approx 1 MeV), the
observable
neutrino flux is dominated by the normal mode of star formation. We
also find
that predicted fluxes are at the present level of the SuperK limit. As
a
consequence, the supernova relic neutrino background has a direct
impact on
models of chemical evolution and/or supernova dynamics.
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