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Observational manifestations of gravitational waves in ground based interferometers and the Cosmic Microwave Background radiation

Baskaran, Deepak. 2006. Observational manifestations of gravitational waves in ground based interferometers and the Cosmic Microwave Background radiation. PhD Thesis, Cardiff University.

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Abstract

In this work we analyze two possible observational manifestations of gravitational waves. We consider the effects of gravitational waves on ground based laser interferometric detectors, and the imprints of relic gravitational waves on the Cosmic Microwave Background (CMB) radiation. In order to study the effect of a gravitational wave on a laser interferometer it is crucial to understand the movement of free test particles. 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. A gravitational wave bring about the relative motion of free test masses. In particular, analogous to movement of free charges in a field of an electromagnetic wave, 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. Using different methods, we demonstrate the presence and importance of the 'magnetic' component of motion of free masses. We then explicitly 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. Another promising venue for detecting gravitational waves are the anisotropics in temperature and polarization of the CMB radiation. A strong variable gravitational field of the very early Universe inevitably generates relic gravitational waves by amplifying their zero-point quantum oscillations. These relic gravitational waves leave their imprint on the anisotropics of the CMB. We explain and summarize the properties of relic gravitational waves that are needed to derive their effects on CMB temperature and polarization anisotropics. Analyzing the radiative transfer equations, we reduce them to a single integral equation of Voltairre type and solve it analytically as well as numerically. We formulate the possible correlation functions Cfx> and derive their amplitudes, shapes and oscillatory features. We show that the TE correlation at lower ts must be negative, 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 anti-correlation at t 30 and show that such an anti- correlation 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.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
ISBN: 9781303205361
Date of First Compliant Deposit: 30 March 2016
Last Modified: 09 Jan 2018 20:45
URI: http://orca.cf.ac.uk/id/eprint/56098

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