314 research outputs found
Polarized CMB power spectrum estimation using the pure pseudo-cross-spectrum approach
We extend the pure pseudo-power-spectrum formalism proposed recently in the
context of the Cosmic Microwave Background polarized power spectra estimation
by Smith (2006) to incorporate cross-spectra computed for multiple maps of the
same sky area. We present an implementation of such a technique, paying
particular attention to a calculation of the relevant window functions and
mixing (mode-coupling) matrices. We discuss the relevance and treatment of the
residual leakage for a number of considered sky apodizations as well as
compromises and assumptions involved in an optimization of the resulting power
spectrum uncertainty. In particular, we investigate the importance of a
pixelization scheme, patch geometry, and sky signal priors used in apodization
optimization procedures. In addition, we also present results derived for more
realistic sky scans as motivated by the proposed balloon borne experiment EBEX.
We conclude that the presented formalism thanks to its speed and efficiency can
provide an interesting alternative to the CMB polarized power spectra
estimators based on the optimal methods at least on angular scales smaller than
~10 degrees. In this regime, we find that it is capable of suppressing the
total variance of the estimated -mode spectrum to within a factor of ~2 of
the variance due to only the sampling and noise uncertainty of the B-modes
alone, as derived from the Fisher matrix approach.Comment: 31 pages, 24 figures, typos corrected on Eq. 32, Appendix C
clarified, published in Physical Review
Consistency of holonomy-corrected scalar, vector and tensor perturbations in Loop Quantum Cosmology
Loop Quantum Cosmology yields two kinds of quantum corrections to the
effective equations of motion for cosmological perturbations. Here we focus on
the holonomy kind and we study the problem of the closure of the resulting
algebra of constraints. Up to now, tensor, vector and scalar perturbations were
studied independently, leading to different algebras of constraints. The
structures of the related algebras were imposed by the requirement of anomaly
freedom. In this article we show that the algebra can be modified by a very
simple quantum correction, holding for all types of perturbations. This
demonstrates the consistency of the theory and shows that lessons from the
study of scalar perturbations should be taken into account when studying tensor
modes. The Mukhanov-Sasaki equations of motion are similarly modified by a
simple term.Comment: 5 page
CMB EB and TB cross-spectrum estimation via pseudo-spectrum techniques
We discuss methods for estimating EB and TB spectra of the Cosmic Microwave
Background anisotropy maps covering limited sky area. Such odd-parity
correlations are expected to vanish whenever parity is not broken. As this is
indeed the case in the standard cosmologies, any evidence to the contrary would
have a profound impact on our theories of the early Universe. Such correlations
could also become a sensitive diagnostic of some particularly insidious
instrumental systematics. In this work we introduce three different unbiased
estimators based on the so-called standard and pure pseudo-spectrum techniques
and later assess their performance by means of extensive Monte Carlo
simulations performed for different experimental configurations. We find that a
hybrid approach combining a pure estimate of B-mode multipoles with a standard
one for E-mode (or T) multipoles, leads to the smallest error bars for both EB
(or TB respectively) spectra as well as for the three other
polarization-related angular power spectra i.e. EE, BB and TE$. However, if
both E and B multipoles are estimated using the pure technique the loss of
precision for the EB spectrum is not larger than ~30%. Moreover, for the
experimental configurations considered here, the statistical uncertainties --
due to sampling variance and instrumental noise -- of the pseudo-spectrum
estimates is at most a factor ~1.4 for TT, EE and TE spectra and a factor ~2
for BB, TB and EB spectra, higher than the most optimistic Fisher estimate of
the variance.Comment: 23 pages, 10 figures, submitted for publication to Physical Review
Instability of the massive Klein-Gordon field on the Kerr spacetime
We investigate the instability of the massive scalar field in the vicinity of
a rotating black hole. The instability arises from amplification caused by the
classical superradiance effect. The instability affects bound states: solutions
to the massive Klein-Gordon equation which tend to zero at infinity. We
calculate the spectrum of bound state frequencies on the Kerr background using
a continued fraction method, adapted from studies of quasinormal modes. We
demonstrate that the instability is most significant for the ,
state, for . For a fast rotating hole () we find
a maximum growth rate of ,
at . The physical implications are discussed.Comment: Added references. 27 pages, 7 figure
Maximum likelihood, parametric component separation and CMB B-mode detection in suborbital experiments
We investigate the performance of the parametric Maximum Likelihood component
separation method in the context of the CMB B-mode signal detection and its
characterization by small-scale CMB suborbital experiments. We consider
high-resolution (FWHM=8') balloon-borne and ground-based observatories mapping
low dust-contrast sky areas of 400 and 1000 square degrees, in three frequency
channels, 150, 250, 410 GHz, and 90, 150, 220 GHz, with sensitivity of order 1
to 10 micro-K per beam-size pixel. These are chosen to be representative of
some of the proposed, next-generation, bolometric experiments. We study the
residual foreground contributions left in the recovered CMB maps in the pixel
and harmonic domain and discuss their impact on a determination of the
tensor-to-scalar ratio, r. In particular, we find that the residuals derived
from the simulated data of the considered balloon-borne observatories are
sufficiently low not to be relevant for the B-mode science. However, the
ground-based observatories are in need of some external information to permit
satisfactory cleaning. We find that if such information is indeed available in
the latter case, both the ground-based and balloon-borne experiments can detect
the values of r as low as ~0.04 at 95% confidence level. The contribution of
the foreground residuals to these limits is found to be then subdominant and
these are driven by the statistical uncertainty due to CMB, including E-to-B
leakage, and noise. We emphasize that reaching such levels will require a
sufficient control of the level of systematic effects present in the data.Comment: 18 pages, 12 figures, 6 table
Bulk and Brane Decay of a (4+n)-Dimensional Schwarzschild-De-Sitter Black Hole: Scalar Radiation
In this paper, we extend the idea that the spectrum of Hawking radiation can
reveal valuable information on a number of parameters that characterize a
particular black hole background - such as the dimensionality of spacetime and
the value of coupling constants - to gain information on another important
aspect: the curvature of spacetime. We investigate the emission of Hawking
radiation from a D-dimensional Schwarzschild-de-Sitter black hole emitted in
the form of scalar fields, and employ both analytical and numerical techniques
to calculate greybody factors and differential energy emission rates on the
brane and in the bulk. The energy emission rate of the black hole is
significantly enhanced in the high-energy regime with the number of spacelike
dimensions. On the other hand, in the low-energy part of the spectrum, it is
the cosmological constant that leaves a clear footprint, through a
characteristic, constant emission rate of ultrasoft quanta determined by the
values of black hole and cosmological horizons. Our results are applicable to
"small" black holes arising in theories with an arbitrary number and size of
extra dimensions, as well as to pure 4-dimensional primordial black holes,
embedded in a de Sitter spacetime.Comment: 31 pages, latex file, data files available at
http://lpsc.in2p3.fr/ams/greybody/ some clarifying comments and references
added, typos corrected, version to appear in Phys. Rev.
Kerr-Gauss-Bonnet Black Holes: An Analytical Approximation
Gauss-Bonnet gravity provides one of the most promising frameworks to study
curvature corrections to the Einstein action in supersymmetric string theories,
while avoiding ghosts and keeping second order field equations. Although
Schwarzschild-type solutions for Gauss-Bonnet black holes have been known for
long, the Kerr-Gauss-Bonnet metric is missing. In this paper, a five
dimensional Gauss-Bonnet approximation is analytically derived for spinning
black holes and the related thermodynamical properties are briefly outlined.Comment: 5 pages, 1 figur
Probing Loop Quantum Gravity with Evaporating Black Holes
This letter aims at showing that the observation of evaporating black holes
should allow distinguishing between the usual Hawking behavior and Loop Quantum
Gravity (LQG) expectations. We present a full Monte-Carlo simulation of the
evaporation in LQG and statistical tests that discriminate between competing
models. We conclude that contrarily to what was commonly thought, the
discreteness of the area in LQG leads to characteristic features that qualify
evaporating black holes as objects that could reveal quantum gravity
footprints.Comment: 5 pages, 3 figures. Version accpeted by Phys. Rev. Let
Spherically symmetric Einstein-Maxwell theory and loop quantum gravity corrections
Effects of inverse triad corrections and (point) holonomy corrections,
occuring in loop quantum gravity, are considered on the properties of
Reissner-Nordstr\"om black holes. The version of inverse triad corrections with
unmodified constraint algebra reveals the possibility of occurrence of three
horizons (over a finite range of mass) and also shows a mass threshold beyond
which the inner horizon disappears. For the version with modified constraint
algebra, coordinate transformations are no longer a good symmetry. The
covariance property of spacetime is regained by using a \emph{quantum} notion
of mapping from phase space to spacetime. The resulting quantum effects in both
versions of these corrections can be associated with renormalization of either
mass, charge or wave function. In neither of the versions, Newton's constant is
renormalized. (Point) Holonomy corrections are shown to preclude the undeformed
version of constraint algebra as also a static solution, though
time-independent solutions exist. A possible reason for difficulty in
constructing a covariant metric for these corrections is highlighted.
Furthermore, the deformed algebra with holonomy corrections is shown to imply
signature change.Comment: 38 pages, 9 figures, matches published versio
TeV-Scale Black Hole Lifetimes in Extra-Dimensional Lovelock Gravity
We examine the mass loss rates and lifetimes of TeV-scale extra dimensional
black holes (BH) in ADD-like models with Lovelock higher-curvature terms
present in the action. In particular we focus on the predicted differences
between the canonical and microcanonical ensemble statistical mechanics
descriptions of the Hawking radiation that results in the decay of these BH. In
even numbers of extra dimensions the employment of the microcanonical approach
is shown to generally lead to a significant increase in the BH lifetime as in
case of the Einstein-Hilbert action. For odd numbers of extra dimensions,
stable BH remnants occur when employing either description provided the highest
order allowed Lovelock invariant is present. However, in this case, the time
dependence of the mass loss rates obtained employing the two approaches will be
different. These effects are in principle measurable at future colliders.Comment: 27 pages, 9 figs; Refs. and discussion adde
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