17 research outputs found
Relic gravitational waves in the light of 7-year Wilkinson Microwave Anisotropy Probe data and improved prospects for the Planck mission
The new release of data from Wilkinson Microwave Anisotropy Probe improves
the observational status of relic gravitational waves. The 7-year results
enhance the indications of relic gravitational waves in the existing data and
change to the better the prospects of confident detection of relic
gravitational waves by the currently operating Planck satellite. We apply to
WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D.
Baskaran, and L.P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data.
We also revised by the same methods our previous analysis of WMAP3 data. It
follows from the examination of consecutive WMAP data releases that the maximum
likelihood value of the quadrupole ratio , which characterizes the amount of
relic gravitational waves, increases up to , and the interval
separating this value from the point (the hypothesis of no gravitational
waves) increases up to a level. The primordial spectra of density
perturbations and gravitational waves remain blue in the relevant interval of
wavelengths, but the spectral indices increase up to and
. Assuming that the maximum likelihood estimates of the perturbation
parameters that we found from WMAP7 data are the true values of the parameters,
we find that the signal-to-noise ratio for the detection of relic
gravitational waves by the Planck experiment increases up to , even
under pessimistic assumptions with regard to residual foreground contamination
and instrumental noises. We comment on theoretical frameworks that, in the case
of success, will be accepted or decisively rejected by the Planck observations.Comment: 27 pages, 12 (colour) figures. Published in Phys. Rev. D. V.3:
modifications made to reflect the 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
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
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.
The surfing effect in the interaction of electromagnetic and gravitational waves. Limits on the speed of gravitational waves
In the current work we investigate the propagation of electromagnetic waves
in the field of gravitational waves. Starting with simple case of an
electromagnetic wave travelling in the field of a plane monochromatic
gravitational wave we introduce the concept of surfing effect and analyze its
physical consequences. We then generalize these results to an arbitrary
gravitational wave field. We show that, due to the transverse nature of
gravitational waves, the surfing effect leads to significant observable
consequences only if the velocity of gravitational waves deviates from speed of
light. This fact can help to place an upper limit on the deviation of
gravitational wave velocity from speed of light. The micro-arcsecond resolution
promised by the upcoming precision interferometry experiments allow to place
stringent upper limits on as a function of the energy
density parameter for gravitational waves . For this limit amounts to
On the road to discovery of relic gravitational waves: The TE and BB Correlations in the cosmic microwave background radiation
The detection of primordial gravitational waves is one of the biggest
challenges of the present time. The existing (Wilkinson Microwave Anisotropy
Probe) observations are helpful on the road to this goal, and the forthcoming
experiments (Planck) are likely to complete this mission. We show that the
5-year Wilkinson Microwave Anisotropy Probe data contains a hint of the
presence of gravitational wave contribution. In terms of the parameter ,
which gives the ratio of contributions from gravitational waves and density
perturbations to the temperature quadrupole, the best-fit model produced
. Because of large residual noises, the uncertainty of this
determination is still large, and it easily includes the R=0 hypothesis.
However, the uncertainty will be strongly reduced in the forthcoming
observations which are more sensitive. We numerically simulated the Planck data
and concluded that the relic gravitational waves with will be present
at a better than 3 level in the observational channel, and at a
better than 2 level in the `realistic' channel. The balloon-borne
and ground-based observations may provide a healthy competition to Planck in
some parts of the lower- spectrum.Comment: 39 pages, including 23 figures. Modifications and clarifications in
response to referees' comments have been added. Includes the final
corrections made at proof reading stage. Published in PR
Limits on the speed of gravitational waves from pulsar timing
In this work, analyzing the propagation of electromagnetic waves in the field
of gravitational waves, we show the presence and significance of the so called
surfing effect for pulsar timing measurements. It is shown that, due to the
transverse nature of gravitational waves, the surfing effect leads to enormous
pulsar timing residuals if the speed of gravitational waves is smaller than
speed of light. This fact allows to place significant constraints on parameter
, which characterizes the relative deviation of the speed of
gravitational waves from the speed of light. We show that the existing
constraints from pulsar timing measurements already place stringent limits on
and consequently on the mass of graviton . These limits on
are three orders of magnitude stronger than the current constraints from
Solar System tests. The current constraints also allow to rule out massive
gravitons as possible candidates for cold dark matter in galactic halo. In the
near future, the gravitational wave background from extragalactic super massive
black hole binaries, along with the expected sub-microsecond pulsar timing
accuracy, will allow to achieve constrains of and
possibly stronger
Is it possible to detect gravitational waves with atom interferometers?
We investigate the possibility to use atom interferometers to detect
gravitational waves. We discuss the interaction of gravitational waves with an
atom interferometer and analyze possible schemes