221 research outputs found

### The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological parameters

The angular power spectrum of the SZ effect, C_l, is a powerful probe of
cosmology. It is easier to detect than individual clusters in the field, is
insensitive to observational selection effects and does not require a
calibration between cluster mass and flux, reducing the systematic errors which
dominate the cluster-counting constraints. It receives a dominant contribution
from cluster region between 20-40% of the virial radius and is thus insensitive
to the poorly known gas physics in the cluster centre, such as cooling or
(pre)heating. In this paper we derive a refined analytic prediction for C_l
using the universal gas-density and temperature profile and the dark-matter
halo mass function. The predicted C_l has no free parameters and fits all of
the published hydrodynamic simulation results to better than a factor of two
around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and
is almost independent of all of the other cosmological parameters. This differs
from the local cluster abundance studies, which give a relation between sigma_8
and Omega_m. We also compute the covariance matrix of C_l using the halo model
and find a good agreement relative to the simulations. We estimate how well we
can determine sigma_8 with sampling-variance-limited observations and find that
for a several-square-degree survey with 1-2 arcminute resolution one should be
able to determine sigma_8 to within a few percent, with the remaining
uncertainty dominated by theoretical modelling. If the recent excess of the CMB
power on small scales reported by the CBI experiment is due to the SZ effect,
then we find sigma_8(Omega_b h/0.029)^0.3 = 1.04 +- 0.12 at the 95% confidence
level (statistical) and with a residual 10% systematic (theoretical)
uncertainty.Comment: 17 pages, 14 figures, 1 table, sigma8 constraint including CBI and
BIMA, matches the accepted version in MNRA

### Constraints on the annihilation cross section of dark matter particles from anisotropies in the diffuse gamma-ray background measured with Fermi-LAT

Annihilation of dark matter particles in cosmological halos (including a halo
of the Milky Way) contributes to the diffuse gamma-ray background (DGRB). As
this contribution will appear anisotropic in the sky, one can use the angular
power spectrum of anisotropies in DGRB to constrain properties of dark matter
particles. By comparing the updated analytic model of the angular power
spectrum of DGRB from dark matter annihilation with the power spectrum recently
measured from the 22-month data of Fermi Large Area Telescope (LAT), we place
upper limits on the annihilation cross section of dark matter particles as a
function of dark matter masses. We find that the current data exclude <\sigma
v> >~ 10^{-25} cm^3 s^{-1} for annihilation into b\bar{b} at the dark matter
mass of 10 GeV, which is a factor of three times larger than the canonical
cross section. The limits are weaker for larger dark matter masses. The limits
can be improved further with more Fermi-LAT data as well as by using the power
spectrum at lower multipoles (l <~ 150), which are currently not used due to a
potential Galactic foreground contamination.Comment: 13 pages, 18 figures, comments welcom

### AKARI near-infrared background fluctuations arise from normal galaxy populations

We show that measurements of the fluctuations in the near-infrared background
(NIRB) from the AKARI satellite can be explained by faint galaxy populations at
low redshifts. We demonstrate this using reconstructed images from deep galaxy
catalogs (HUGS/S-CANDELS) and two independent galaxy population models. In all
cases, we find that the NIRB fluctuations measured by AKARI are consistent with
faint galaxies and there is no need for a contribution from unknown
populations. We find no evidence for a steep Rayleigh-Jeans spectrum for the
underlying sources as previously reported. The apparent Rayleigh-Jeans spectrum
at large angular scales is likely a consequence of galaxies being removed
systematically to deeper levels in the longer wavelength channels.Comment: Submitted to MNRAS Letter

### Limits on anisotropic inflation from the Planck data

Temperature anisotropy of the cosmic microwave background offers a test of
the fundamental symmetry of spacetime during cosmic inflation. Violation of
rotational symmetry yields a distinct signature in the power spectrum of
primordial fluctuations as $P({\mathbf k})=P_0(k)[1+g_*(\hat{\mathbf
k}\cdot\hat{\mathbf E}_{\rm cl})^2]$, where $\hat{\mathbf E}_{\rm cl}$ is a
preferred direction in space and $g_*$ is an amplitude. Using the
\textit{Planck} 2013 temperature maps, we find no evidence for violation of
rotational symmetry, $g_*=0.002\pm 0.016$ (68% CL), once the known effects of
asymmetry of the \textit{Planck} beams and Galactic foreground emission are
removed.Comment: 5 pages, 2 figures. (v2) References added. A typo fixed. (v3) Various
confidence levels included, Journal reference added (v4) error of a
duplicated pdf file fixe

### Constraints on primordial magnetic fields from the optical depth of the cosmic microwave background

Damping of magnetic fields via ambipolar diffusion and decay of
magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the
intergalactic medium (IGM). Delayed recombination of hydrogen atoms in the IGM
yields an optical depth to scattering of the cosmic microwave background (CMB).
The optical depth generated at $z\gg 10$ does not affect the "reionization
bump" of the CMB polarization power spectrum at low multipoles, but affects the
temperature and polarization power spectra at high multipoles. Writing the
present-day energy density of fields smoothed over the damping scale at the
decoupling epoch as $\rho_{B,0}=B_{0}^2/2$, we constrain $B_0$ as a function of
the spectral index, $n_B$. Using the Planck 2013 likelihood code that uses the
Planck temperature and lensing data together with the WMAP 9-year polarization
data, we find the 95% upper bounds of $B_0<0.63$, 0.39, and 0.18~nG for
$n_B=-2.9$, $-2.5$, and $-1.5$, respectively. For these spectral indices, the
optical depth is dominated by dissipation of the decaying MHD turbulence that
occurs shortly after the decoupling epoch. Our limits are stronger than the
previous limits ignoring the effects of the fields on ionization history.
Inverse Compton scattering of CMB photons off electrons in the heated IGM
distorts the thermal spectrum of CMB. Our limits on $B_0$ imply that the
$y$-type distortion from dissipation of fields in the post decoupling era
should be smaller than $10^{-9}$, $4\times10^{-9}$, and $10^{-9}$,
respectively.Comment: 14 pages, 30 figures, calculations revised and updated, accepted for
publication in JCA

### Results from the Wilkinson Microwave Anisotropy Probe

The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of
temperature and polarization over the entire sky in five microwave frequency
bands. These full-sky maps were used to obtain measurements of temperature and
polarization anisotropy of the cosmic microwave background with the
unprecedented accuracy and precision. The analysis of two-point correlation
functions of temperature and polarization data gives determinations of the
fundamental cosmological parameters such as the age and composition of the
universe, as well as the key parameters describing the physics of inflation,
which is further constrained by three-point correlation functions. WMAP
observations alone reduced the flat $\Lambda$ cold dark matter ($\Lambda$CDM)
cosmological model (six) parameter volume by a factor of >68,000 compared with
pre-WMAP measurements. The WMAP observations (sometimes in combination with
other astrophysical probes) convincingly show the existence of non-baryonic
dark matter, the cosmic neutrino background, flatness of spatial geometry of
the universe, a deviation from a scale-invariant spectrum of initial scalar
fluctuations, and that the current universe is undergoing an accelerated
expansion. The WMAP observations provide the strongest ever support for
inflation; namely, the structures we see in the universe originate from quantum
fluctuations generated during inflation.Comment: 26 pages, 9 figures, invited review for Special Section "CMB
Cosmology" of Progress of Theoretical and Experimental Physics (PTEP). (v2)
New ns-r figure added. Accepted for publicatio

- …