25,267 research outputs found
Multipole invariants and non-Gaussianity
We propose a framework for separating the information contained in the CMB
multipoles, , into its algebraically independent components. Thus
we cleanly separate information pertaining to the power spectrum,
non-Gaussianity and preferred axis effects. The formalism builds upon the
recently proposed multipole vectors (Copi, Huterer & Starkman 2003; Schwarz &
al 2004; Katz & Weeks 2004), and we elucidate a few features regarding these
vectors, namely their lack of statistical independence for a Gaussian random
process. In a few cases we explicitly relate our proposed invariants to
components of the -point correlation function (power spectrum, bispectrum).
We find the invariants' distributions using a mixture of analytical and
numerical methods. We also evaluate them for the co-added WMAP first year map
The Multipole Vectors of WMAP, and their frames and invariants
We investigate the Statistical Isotropy and Gaussianity of the CMB
fluctuations, using a set of multipole vector functions capable of separating
these two issues. In general a multipole is broken into a frame and
ordered invariants. The multipole frame is found to be suitably sensitive to
galactic cuts. We then apply our method to real WMAP datasets; a coadded masked
map, the Internal Linear Combinations map, and Wiener filtered and cleaned
maps. Taken as a whole, multipoles in the range or show
consistency with statistical isotropy, as proved by the Kolmogorov test applied
to the frame's Euler angles. This result in {\it not} inconsistent with
previous claims for a preferred direction in the sky for . The
multipole invariants also show overall consistency with Gaussianity apart from
a few anomalies of limited significance (98%), listed at the end of this paper.Comment: 9 pages. Submitted to MNRA
Template fitting and the large-angle CMB anomalies
We investigate two possible explanations for the large-angle anomalies in the
Cosmic Microwave Background (CMB): an intrinsically anisotropic model and an
inhomogeneous model. We take as an example of the former a Bianchi model (which
leaves a spiral pattern in the sky) and of the latter a background model that
already contains a non-linear long-wavelength plane wave (leaving a stripy
pattern in the sky). We make use of an adaptation of the ``template''
formalism, previously designed to detect galactic foregrounds, to recognize
these patterns and produce confidence levels for their detection. The
``corrected'' maps, from which these patterns have been removed, are free of
anomalies, in particular their quadrupole and octupole are not planar and their
intensities not low. We stress that although the ``template'' detections are
not found to be statistically significant they do correct statistically
significant anomalies.Comment: 8 pages. MNRAS submitte
Effects of weak self-interactions in a relativistic plasma on cosmological perturbations
The exact solutions for linear cosmological perturbations which have been
obtained for collisionless relativistic matter within thermal field theory are
extended to a self-interacting case. The two-loop contributions of scalar
theory to the thermal graviton self-energy are evaluated, which
give the corrections in the perturbation equations. The changes
are found to be perturbative on scales comparable to or larger than the Hubble
horizon, but the determination of the large-time damping behavior of subhorizon
perturbations requires a resummation of thermally induced masses.Comment: 11 pages, REVTEX, 4 postscript figures included by epsf.sty -
expanded version (more details on the resummation of thermal masses which is
required for the late-time damping behaviour
Stochastic Inflation and Replica Field Theory
We adopt methods from statistical field theory to stochastic inflation. For
the example of a free test field in de Sitter and power-law inflation, the
power spectrum of long-wavelength fluctuations is computed. We study its
dependence on the shape of the filter that separates long from short wavelength
modes. While for filters with infinite support the phenomenon of dimensional
reductions is found on large super-horizon scales, filters with compact support
return a scale-invariant power spectrum in the infra-red. Features of the power
spectrum, induced by the filter, decay within a few e-foldings. Thus the
late-time power spectrum is independent of the filter details.Comment: 15 pages, 14 figure
Reconnections of Vortex Loops in the Superfluid Turbulent HeII. Rates of the Breakdown and Fusion processes
Kinetics of merging and breaking down vortex loops is the important part of
the whole vortex tangle dynamics. Another part is the motion of individual
lines, which obeys the Biot-Savart law in presence of friction force and of
applied external velocity fields if any. In the present work we evaluate the
coefficients of the reconnection rates and
. Quantity is a number (per unit of time and per unit of
volume) of events, when two loops with lengths and collide and
form the single loop of length . Quantity
describes the rate of events, when the single loop of the length breaks
down into two the daughter loops of lengths and . These
quantities ave evaluated as the averaged numbers of zeroes of vector
connecting two points on the loops of
and at moment of time . Statistics of the individual
loops is taken from the Gaussian model of vortex tangle. PACS-number 67.40Comment: 9 pages, 5 figures, To be submitted to JLT
Fabrication of alignment structures for a fiber resonator by use of deep-ultraviolet lithography
We present a novel method to mount and align an optical-fiber-based resonator
on the flat surface of an atom chip with ultrahigh precision. The structures
for mounting a pair of fibers, which constitute the fiber resonator, are
produced by a spin-coated SU-8 photoresist technique by use of deep-UV
lithography. The design and production of the SU-8 structures are discussed.
From the measured finesses we calculate the coupling loss of the SU-8
structures acting as a kind of fiber splice to be smaller than 0.013 dB.Comment: 4 pages, 3 figure
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