704 research outputs found
Relic gravitational waves: latest revisions and preparations for new data
The forthcoming release of data from the Planck mission, and possibly from
the next round of Wilkinson Microwave Anisotropy Probe (WMAP) observations,
make it necessary to revise the evaluations of relic gravitational waves in the
existing data and, at the same time, to refine the assumptions and data
analysis techniques in preparation for the arrival of new data. We reconsider
with the help of the commonly used CosmoMC numerical package the previously
found indications of relic gravitational waves in the 7-year (WMAP7) data. The
CosmoMC approach reduces the confidence of these indications from approximately
2 level to approximately 1 level, but the indications do not
disappear altogether. We critically analyze the assumptions that are currently
used in the Cosmic Microwave Background (CMB) data analyzes and outline the
strategy that should help avoid the oversight of relic gravitational waves in
the future CMB data. In particular, it is important to keep away from the
unwarranted assumptions about density perturbations. The prospects of confident
detection of relic gravitational waves by the Planck satellite have worsened,
but they are still good. It appears that more effort will be required in order
to mitigate the foreground contamination.Comment: 11 pages, 4 figures, 3 tables; v.3: improvements, published versio
Separating E and B types of polarization on an incomplete sky
Detection of magnetic-type (-type) polarization in the Cosmic Microwave
Background (CMB) radiation plays a crucial role in probing the relic
gravitational wave (RGW) background. In this paper, we propose a new method to
deconstruct a polarization map on an incomplete sky in real space into purely
electric and magnetic polarization type maps, and
, respectively. The main properties of our
approach are as follows: Firstly, the fields and
are constructed in real space with a minimal loss
of information. This loss of information arises due to the removal of a narrow
edge of the constructed map in order to remove various numerical errors,
including those arising from finite pixel size. Secondly, this method is fast
and can be efficiently applied to high resolution maps due to the use of the
fast spherical harmonics transformation. Thirdly, the constructed fields,
and , are scalar
fields. For this reason various techniques developed to deal with temperature
anisotropy maps can be directly applied to analyze these fields. As a concrete
example, we construct and analyze an unbiased estimator for the power spectrum
of the -mode of polarization . Basing our results on the
performance of this estimator, we discuss the RGW detection ability of two
future ground-based CMB experiments, QUIET and POLARBEAR.Comment: 43 pages, 15 figures, 1 table. The finial version, will appear in PR
Quantum Effects In Cosmology
Contents:
Introduction. The Present State of the Universe.
What Can We Expect From a Complete Cosmological Theory?
An Overview of Quantum Effects in Cosmology.
Parametric (Superadiabatic) Amplification of Classical Waves.
Graviton Creation in the Inflationary Universe.
Quantum States of a Harmonic Oscillator.
Squeezed Quantum States of Relic Gravitons and Primordial Density
Perturbations.
Quantum Cosmology, Minisuperspace Models and Inflation.
From the Space of Classical Solutions to the Space of Wave Functions.
On the Probability of Quantum Tunneling From "Nothing".
Duration of InflationComment: (43 pages, to be published in "The Origin of Structure in the
Universe", ed. P.Nardone
Components of the gravitational force in the field of a gravitational wave
Gravitational waves bring about the relative motion of free test masses. The
detailed knowledge of this motion is important conceptually and practically,
because the mirrors of laser interferometric detectors of gravitational waves
are essentially free test masses. There exists an analogy between the motion of
free masses in the field of a gravitational wave and the motion of free charges
in the field of an electromagnetic wave. In particular, a gravitational wave
drives the masses in the plane of the wave-front and also, to a smaller extent,
back and forth in the direction of the wave's propagation. To describe this
motion, we introduce the notion of `electric' and `magnetic' components of the
gravitational force. This analogy is not perfect, but it reflects some
important features of the phenomenon. Using different methods, we demonstrate
the presence and importance of what we call the `magnetic' component of motion
of free masses. It contributes to the variation of distance between a pair of
particles. We explicitely derive the full response function of a 2-arm laser
interferometer to a gravitational wave of arbitrary polarization. We give a
convenient description of the response function in terms of the spin-weighted
spherical harmonics. We show that the previously ignored `magnetic' component
may provide a correction of up to 10 %, or so, to the usual `electric'
component of the response function. The `magnetic' contribution must be taken
into account in the data analysis, if the parameters of the radiating system
are not to be mis-estimated.Comment: prints to 29 pages including 9 figures, new title, additional
explanations and references in response to referee's comments, to be
published in Class. Quant. Gra
New Primordial-Magnetic-Field Limit from The Latest LIGO S5 data
Since the energy momentum tensor of a magnetic field always contains a spin-2
component in its anisotropic stress, stochastic primordial magnetic field (PMF)
in the early universe must generate stochastic gravitational wave (GW)
background. This process will greatly affect the relic gravitational wave
(RGW), which is one of major scientific goals of the laser interferometer GW
detections. Recently, the fifth science (S5) run of laser interferometer
gravitational-wave observatory (LIGO) gave a latest upper limit
on the RGW background. Utilizing this upper
limit, we derive new PMF Limits: for a scale of galactic cluster
Mpc, the amplitude of PMF, that produced by the electroweak phase transition
(EPT), has to be weaker than Gauss; for a
scale of supercluster Mpc, the amplitude of PMF has to be weaker
than Gauss. In this manner, GW observation
has potential to make interesting contributions to the study of primordial
magnetic field.Comment: 17 pages, 3 figures, accepted for publication in PR
On the observational determination of squeezing in relic gravitational waves and primordial density perturbations
We develop a theory in which relic gravitational waves and primordial density
perturbations are generated by strong variable gravitational field of the early
Universe. The generating mechanism is the superadiabatic (parametric)
amplification of the zero-point quantum oscillations. The generated fields have
specific statistical properties of squeezed vacuum quantum states.
Macroscopically, squeezing manifests itself in a non-stationary character of
variances and correlation functions of the fields, the periodic structures of
the metric power spectra, and, as a consequence, in oscillatory behavior of the
higher order multipoles C_l of the cosmic microwave background anisotropy. We
start with the gravitational wave background and then apply the theory to
primordial density perturbations. We derive an analytical formula for the
positions of peaks and dips in the angular power spectrum l(l+1)C_l as a
function of l. This formula shows that the values of l at the peak positions
are ordered in the proportion 1:3:5:..., whereas at the dips they are ordered
as 1:2:3:.... We compare the derived positions with the actually observed
features, and find them to be in reasonably good agreement. It appears that the
observed structure is better described by our analytical formula based on the
(squeezed) metric perturbations associated with the primordial density
perturbations, rather than by the acoustic peaks reflecting the existence of
plasma sound waves at the last scattering surface. We formulate a forecast for
other features in the angular power spectrum, that may be detected by the
advanced observational missions, such as MAP and PLANCK. We tentatively
conclude that the observed structure is a macroscopic manifestation of
squeezing in the primordial metric perturbations.Comment: 34 pages, 3 figures; to appear in Phys. Rev. D66, 0435XX (2002);
includes Note Added in Proofs: "The latest CBI observations (T.J.Pearson et
al., astro-ph/0205388) have detected four peaks, at l ~ 550, 800, 1150, 1500,
and four dips, at l ~ 400, 700, 1050, 1400. These positions are in a very
good agreement with the theoretical formula (6.35) of the present paper. We
interpret this data as confirmation of our conclusion that it is gravity, and
not acoustics, that is responsible for the observed structure.
Imprints of Relic Gravitational Waves in Cosmic Microwave Background Radiation
A strong variable gravitational field of the very early Universe inevitably
generates relic gravitational waves by amplifying their zero-point quantum
oscillations. We begin our discussion by contrasting the concepts of relic
gravitational waves and inflationary `tensor modes'. We explain and summarize
the properties of relic gravitational waves that are needed to derive their
effects on CMB temperature and polarization anisotropies. The radiation field
is characterized by four invariants I, V, E, B. We reduce the radiative
transfer equations to a single integral equation of Voltairre type and solve it
analytically and numerically. We formulate the correlation functions
C^{XX'}_{\ell} for X, X'= T, E, B and derive their amplitudes, shapes and
oscillatory features. Although all of our main conclusions are supported by
exact numerical calculations, we obtain them, in effect, analytically by
developing and using accurate approximations. We show that the TE correlation
at lower \ell's must be negative (i.e. an anticorrelation), if it is caused by
gravitational waves, and positive if it is caused by density perturbations.
This difference in TE correlation may be a signature more valuable
observationally than the lack or presence of the BB correlation, since the TE
signal is about 100 times stronger than the expected BB signal. We discuss the
detection by WMAP of the TE anticorrelation at \ell \approx 30 and show that
such an anticorrelation is possible only in the presence of a significant
amount of relic gravitational waves (within the framework of all other common
assumptions). We propose models containing considerable amounts of relic
gravitational waves that are consistent with the measured TT, TE and EE
correlations.Comment: 61 pages including 15 figures, v.2: additional references and
clarifications, to be published in Phys. Rev.
Best Unbiased Estimates for the Microwave Background Anisotropies
It is likely that the observed distribution of the microwave background
temperature over the sky is only one realization of the underlying random
process associated with cosmological perturbations of quantum-mechanical
origin. If so, one needs to derive the parameters of the random process, as
accurately as possible, from the data of a single map. These parameters are of
the utmost importance, since our knowledge of them would help us to reconstruct
the dynamical evolution of the very early Universe. It appears that the lack of
ergodicity of a random process on a 2-sphere does not allow us to do this with
arbitrarily high accuracy. We are left with the problem of finding the best
unbiased estimators of the participating parameters. A detailed solution to
this problem is presented in this article. The theoretical error bars for the
best unbiased estimates are derived and discussed.Comment: 26 pages, revtex; minor modifications, 8 new references, to be
published in Phys. Rev.
The Implications of the Microwave Background Anisotropies for Laser-Interferometer-Tested Gravitational Waves
The observed microwave background anisotropies in combination with the theory
of quantum mechanically generated cosmological perturbations predict a well
measurable amount of relic gravitational waves in the frequency intervals
tested by LISA and ground-based laser interferometers.Comment: revised, corrected, and slightly expanded version to be published in
Classical and Quantum Gravity; 22 pages, 1 Postscript figure, Latex; Based on
a talk presented at the First Internationsl LISA Symposium, 9 - 12 July 1996,
RAL, U
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