1. The Search for a Stochastic Background of Gravitational Radiation Part I Rosa M. Luna, D. Auzmus, M. Casquette, C.W. Torres, M.C. Diaz, J.D. Romano, and J.T. Whelan Research Partially Supported by: NASA-JPL #961298 and NSF PHY_9981795 (University of Texas of Brownsville)

2. Are a prediction of Einstein’s theory of General Relativity in 1915. Are ripples in the fabric of space time. Are similar to electromagnetic waves. –They both carry energy and momentum. –They both propagate at the speed of light. –They both are polarized. Unlike electromagnetic waves, propagate essentially unchanged from their sources, unaffected by scattering or absorption due to intervening matter. Gravitational Waves

3. Picture courtesy of: A. Rodriguez GW Polarization

4. Coalescing binary system - two neutron stars and/or black holes in orbit about one another Pulsars - rotating neutron stars Supernovae - exploding stars Stochastic background - random signal of gravitational radiation Sources of Gravitational Waves

5. Locations of Laser Interferometer Detectors

6. A laser beam is bounced off mirrors mounted at the ends of each L (4 km arm) of the detector. A photo-detector measures a shift in the interference pattern of the laser light indicating a change in distance between the masses,  L. The two U.S. sites have a sensitivity ratio  L/L of 10 -21. Picture courtesy of Dr. W. Anderson Laser Interferometry

7. Stochastic Background of Gravitational Radiation Stochastic background is a random signal produced by many independent and uncorrelated events. Stochastic background of gravitational radiation is similar to the stochastic background of electromagnetic radiation. -They are both formed by processes that occurred very early during the formation of the universe. -They both can give us a picture of the early universe. Unlike electromagnetic radiation, which decoupled from matter 100,000 years after the Big Bang, stochastic radiation decoupled from matter fractions of a second after the Big Bang.

8. The output of the two detectors will consist in general of both a signal and detector noise: d 1 [j] = s 1 [j] + n 1 [j] d 2 [j] = s 2 [j] + n 2 [j] The statistic used to analyze the detector output for the presence of a signal is: = s 1 s 2 + s 1 n 2 + n 1 s 2 + n 1 n 2 X is a random variable that has a mean value and variance:  := =  2 := - 2  Since the mean value, , depends only on the gravity-wave signals, the signal can be extracted from the noise in this way. For non-coincident and non-coaligned detectors, the optimal filter function needs to be added: Q contains information about the noise in the detectors, and the separation/orientation of the detectors. CROSS CORRELATION