6 research outputs found
Full-sky correlations of peaks in the microwave background
We compute precise predictions for the two-point correlation function of
local maxima (or minima) in the temperature of the microwave background, under
the assumption that it is a random gaussian field. For a given power spectrum
and peak threshold there are no adjustable parameters, and since this analysis
does not make the small-angle approximation of Heavens & Sheth (1999), it is
essentially complete. We find oscillatory features which are absent in the
temperature autocorrelation function, and we also find that the small-angle
approximation to the peak-peak correlation function is accurate to better than
0.01 on all scales. These high-precision predictions can form the basis of a
sensitive test of the gaussian hypothesis with upcoming all-sky microwave
background experiments MAP and Planck, affording a thorough test of the
inflationary theory of the early Universe. To illustrate the effectiveness of
the technique, we apply it to simulated maps of the microwave sky arising from
the cosmic string model of structure formation, and compare with the bispectrum
as a non-gaussian discriminant. We also show how peak statistics can be a
valuable tool in assessing and statistically removing contamination of the map
by foreground point sources.Comment: submitted to MNRA
Cosmology with Self-Adjusting Vacuum Energy Density from a Renormalization Group Fixed Point
Cosmologies with a time dependent Newton constant and cosmological constant
are investigated. The scale dependence of and is governed by a
set of renormalization group equations which is coupled to Einstein's equation
in a consistent way. The existence of an infrared attractive renormalization
group fixed point is postulated, and the cosmological implications of this
assumption are explored. It turns out that in the late Universe the vacuum
energy density is automatically adjusted so as to equal precisely the matter
energy density, and that the deceleration parameter approaches . This
scenario might explain the data from recent observations of high redshift type
Ia Supernovae and the cosmic microwave background radiation without introducing
a quintessence field.Comment: v2: published version, two references update
Fast Parameter Estimation from the CMB Power Spectrum
The statistical properties of a map of the primary fluctuations in the cosmic
microwave background (CMB) may be specified to high accuracy by a few thousand
power spectra measurements, provided the fluctuations are gaussian, yet the
number of parameters relevant for the CMB is probably no more than about 10-20.
There is consequently a large degree of redundancy in the power spectrum data.
In this paper, we show that the MOPED data compression technique can reduce the
CMB power spectrum measurements to about 10-20 numbers (one for each
parameter), from which the cosmological parameters can be estimated virtually
as accurately as from the complete power spectrum. This offers opportunities
for very fast parameter estimation from real and simulated CMB skies, with
accurate likelihood calculations at Planck resolution being speeded up by a
factor of around five hundred million.Comment: version to appear in MNRA
Leptogenesis and Neutrino Oscillations Within A Predictive G(224)/SO(10)-Framework
A framework based on an effective symmetry that is either G(224)= SU(2)_L x
SU(2)_R xSU(4)^c or SO(10) has been proposed (a few years ago) that
successfully describes the masses and mixings of all fermions including
neutrinos, with seven predictions, in good accord with the data. Baryogenesis
via leptogenesis is considered within this framework by allowing for natural
phases (~ 1/20-1/2) in the entries of the Dirac and Majorana mass-matrices. It
is shown that the framework leads quite naturally, for both thermal as well as
non-thermal leptogenesis, to the desired magnitude for the baryon asymmetry.
This result is obtained in full accord with the observed features of the
atmospheric and solar neutrino oscillations, as well as with those of the quark
and charged lepton masses and mixings, and the gravitino-constraint. Hereby one
obtains a unified description of fermion masses, neutrino oscillations and
baryogenesis (via leptogenesis) within a single predictive framework.Comment: Efficiency factor updated, some clarifications and new references
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