1,051 research outputs found
Cosmic Neutrino Bound on the Dark Matter Annihilation Rate in the Late Universe
How large can the dark matter self-annihilation rate in the late universe be?
This rate depends on (rho_DM/m_chi)^2 , where rho_DM/m_chi is the
number density of dark matter, and the annihilation cross section is averaged
over the velocity distribution. Since the clustering of dark matter is known,
this amounts to asking how large the annihilation cross section can be.
Kaplinghat, Knox, and Turner proposed that a very large annihilation cross
section could turn a halo cusp into a core, improving agreement between
simulations and observations; Hui showed that unitarity prohibits this for
large dark matter masses. We show that if the annihilation products are
Standard Model particles, even just neutrinos, the consequent fluxes are ruled
out by orders of magnitude, even at small masses. Equivalently, to invoke such
large annihilation cross sections, one must now require that essentially no
Standard Model particles are produced.Comment: 4 pages, 2 figures; to appear in the proceedings of the TeV Particle
Astrophysics II Workshop, Madison, Wisconsin, 28-31 Aug 200
Searching for Dark Matter in the CMB: A Compact Parameterization of Energy Injection from New Physics
High-precision measurements of the temperature and polarization anisotropies
of the cosmic microwave background radiation have been previously employed to
set robust constraints on dark matter annihilation during recombination. In
this work we improve and generalize these constraints to apply to energy
deposition during the recombination era with arbitrary redshift dependence. Our
approach also provides more rigorous and model-independent bounds on dark
matter annihilation and decay scenarios. We employ principal component analysis
to identify a basis of weighting functions for the energy deposition. The
coefficients of these weighting functions parameterize any energy deposition
model and can be constrained directly by experiment. For generic energy
deposition histories that are currently allowed by WMAP7 data, up to 3
principal component coefficients are measurable by Planck and up to 5
coefficients are measurable by an ideal cosmic variance limited experiment. For
WIMP dark matter, our analysis demonstrates that the effect on the CMB is
described well by a single (normalization) parameter and a "universal" redshift
dependence for the energy deposition history. We give WMAP 7 constraints on
both generic energy deposition histories and the universal WIMP case.Comment: 30 pages, 24 figure
The Case for a 700+ GeV WIMP: Cosmic Ray Spectra from PAMELA, Fermi and ATIC
Multiple lines of evidence indicate an anomalous injection of high-energy e+-
in the Galactic halo. The recent fraction spectrum from the Payload for
Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) shows a
sharp rise up to 100 GeV. The Fermi Gamma-ray Space Telescope has found a
significant hardening of the e+e- cosmic ray spectrum above 100 GeV, with a
break, confirmed by HESS at around 1 TeV. The Advanced Thin Ionization
Calorimeter (ATIC) has also detected detected a similar excess, falling back to
the expected spectrum at 1 TeV and above. Excess microwaves towards the
galactic center in the WMAP data are consistent with hard synchrotron radiation
from a population of 10-100 GeV e+- (the WMAP ``Haze''). We argue that dark
matter annihilations can provide a consistent explanation of all of these data,
focusing on dominantly leptonic modes, either directly or through a new light
boson. Normalizing the signal to the highest energy evidence (Fermi and HESS),
we find that similar cross sections provide good fits to PAMELA and the Haze,
and that both the required cross section and annihilation modes are achievable
in models with Sommerfeld-enhanced annihilation. These models naturally predict
significant production of gamma rays in the galactic center via a variety of
mechanisms. Most notably, there is a robust inverse-Compton scattered (ICS)
gamma-ray signal arising from the energetic electrons and positrons, detectable
at Fermi/GLAST energies, which should provide smoking gun evidence for this
production.Comment: 28 pages; v2 plots corrected, references added; v3 included Fermi
electron data at reviewer request, references adde
On Galactic density modeling in the presence of dust extinction
Inferences about the spatial density or phase-space structure of stellar
populations in the Milky Way require a precise determination of the effective
survey volume. The volume observed by surveys such as Gaia or near-infrared
spectroscopic surveys, which have good coverage of the Galactic mid-plane
region, is highly complex because of the abundant small-scale structure in the
three-dimensional interstellar dust extinction. We introduce a novel framework
for analyzing the importance of small-scale structure in the extinction. This
formalism demonstrates that the spatially-complex effect of extinction on the
selection function of a pencil-beam or contiguous sky survey is equivalent to a
low-pass filtering of the extinction-affected selection function with the
smooth density field. We find that the angular resolution of current 3D
extinction maps is sufficient for analyzing Gaia sub-samples of millions of
stars. However, the current distance resolution is inadequate and needs to be
improved by an order of magnitude, especially in the inner Galaxy. We also
present a practical and efficient method for properly taking the effect of
extinction into account in analyses of Galactic structure through an effective
selection function. We illustrate its use with the selection function of
red-clump stars in APOGEE using and comparing a variety of current 3D
extinction maps.Comment: Code available at https://github.com/jobovy/mwdust and at
https://github.com/jobovy/apogee-map
CMB Constraints on WIMP Annihilation: Energy Absorption During the Recombination Epoch
We compute in detail the rate at which energy injected by dark matter
annihilation heats and ionizes the photon-baryon plasma at z ~ 1000, and
provide accurate fitting functions over the relevant redshift range for a broad
array of annihilation channels and DM masses. The resulting perturbations to
the ionization history can be constrained by measurements of the CMB
temperature and polarization angular power spectra. We show that models which
fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays
are already close to the 95% confidence limits from WMAP. The recently launched
Planck satellite will be capable of ruling out a wide range of DM explanations
for these excesses. In models of dark matter with Sommerfeld-enhanced
annihilation, where sigma v rises with decreasing WIMP velocity until some
saturation point, the WMAP5 constraints imply that the enhancement must be
close to saturation in the neighborhood of the Earth.Comment: 17 pages, 6 figures, v2 extends discussion of constraints on
Sommerfeld-enhanced model
Pseudo-Dipole Signal Removal from WMAP Data
It is discovered in our previous work that different observational
systematics, e.g., errors of antenna pointing directions, asynchronous between
the attitude and science data, can generate pseudo-dipole signal in full-sky
maps of the cosmic microwave background (CMB) anisotropy published by The
Wilkinson Microwave Anisotropy Probe (WMAP) team. Now the antenna sidelobe
response to the Doppler signal is found to be able to produce similar effect as
well. In this work, independent to the sources, we uniformly model the
pseudo-dipole signal and remove it from published WMAP7 CMB maps by model
fitting. The result demonstrates that most of the released WMAP CMB quadrupole
is artificial.Comment: V3: using WMAP7 dat
Constraining the Cosmic Background Light with four BL Lac TeV spectra
The intrinsic BL Lac spectra above few hundreds GeV can be very different
from the observed ones due to the absorption effects by the diffuse
Extragalactic Background Light (EBL), at present poorly known. With the recent
results, there are now 4 sources with good spectral information: Mkn 421
(z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650
(z=0.047). Making simple assumptions on the shape of the intrinsic spectra
(according to the present blazar knowledge), we have considered the effects of
different EBL spectral energy distributions (SED) for the first time on all 4
objects together, deriving constraints for the EBL fluxes. These resulted
significantly lower than many direct estimates.Comment: 4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas
Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicag
Extrapolation of Galactic Dust Emission at 100 Microns to CMBR Frequencies Using FIRAS
We present predicted full-sky maps of submillimeter and microwave emission
from the diffuse interstellar dust in the Galaxy. These maps are extrapolated
from the 100 micron emission and 100/240 micron flux ratio maps that Schlegel,
Finkbeiner, & Davis (1998; SFD98) generated from IRAS and COBE/DIRBE data.
Results are presented for a number of physically plausible emissivity models.
We find that no power law emissivity function fits the FIRAS data from 200 -
2100 GHz. In this paper we provide a formalism for a multi-component model for
the dust emission. A two-component model with a mixture of silicate and
carbon-dominated grains (motivated by Pollack et al., 1994}) provides a fit to
an accuracy of about 15% to all the FIRAS data over the entire high-latitude
sky. Small systematic differences are found between the atomic and molecular
phases of the ISM.
Our predictions for the thermal (vibrational) emission from Galactic dust at
\nu < 3000 GHz are available for general use. These full-sky predictions can be
made at the DIRBE resolution of 40' or at the higher resolution of 6.1 arcmin
from the SFD98 DIRBE-corrected IRAS maps.Comment: 48 pages, AAS LaTeX, 6 figures, ApJ (accepted). Data described in the
text, as well as 4 additional figures, are available at
http://astro.berkeley.edu/dus
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