The pregalactic cosmic gravitational wave background

An outline is given that estimates the expected gravitational wave background, based on plausible pregalactic sources. Some cosmologically significant limits can be put on incoherent gravitational wave background arising from pregalactic cosmic evolution. The spectral region of cosmically generated and cosmically limited radiation is, at long periods, P greater than 1 year, in contrast to more recent cosmological sources, which have P approx. 10 to 10(exp -3)

Gravitational Radiation and the Equivalence Principle by the Technique of Virtual Quanta

After reviewing the Weizsächer-Williams technique of virtual quanta for calculation of electromagnetic radiation in bremsstrahlung encounters, we extend the method to the domain of gravitational encounters and set up a correlation between collision problems and the corresponding problem of the generation of gravitational radiation. In the local rest frame of a relativistic test particle the gravitational field of a large mass consists predominantly of a pulse of plane—fronted gravitational waves. We Fourier—analyse this equivalent pulse and consider the scattering of the individual frequency components, virtual quanta, by the test body. The scattering occurs because of the long—range Newtonian field which gives a Rutherford—like cross section. The escape of this radiation to infinity, suitably transformed, gives us the radiative loss of gravitational energy by a rapidly moving particle. The radiation spectrum and total energy radiated are computed as an example. We then turn to the case where one or both of the masses possess an electric charge, and calculate the total electromagnetic and gravitational energy radiated in such encounters. We consider both the case in which the deflection is principally electromagnetic in nature, and the case in which the deflection is principally gravitational. The results are interpreted by considering the predictions of the equivalence principle, for the behavior of the test particle, and for the behavior of the virtual quanta. As expected from the equivalence principle, the total radiation produced is larger for electromagnetic deflection than for gravitational deflection through the same angle

Light Propagation in inhomogeneous Universes

Using a multi-plane lensing method that we have developed, we follow the evolution of light beams as they propagate through inhomogeneous universes. We use a P3M code to simulate the formation and evolution of large-scale structure. The resolution of the simulations is increased to sub-Megaparsec scales by using a Monte Carlo method to locate galaxies inside the computational volume according to the underlying particle distribution. The galaxies are approximated by isothermal spheres, with each morphological type having its own distribution of masses and core radii. The morphological types are chosen in order to reproduce the observed morphology-density relation. This algorithm has an effective resolution of 9 orders of magnitudes in length, from the size of superclusters down to the core radii of the smallest galaxies. We consider cold dark matter models normalized to COBE, and perform a large parameter survey by varying the cosmological parameters Omega_0, lambda_0, H_0, and n (the tilt of the primordial power spectrum). The values of n are chosen by imposing particular values or sigma_8, the rms mass fluctuation at a scale of 8/h Mpc. We use the power spectrum given by Bunn & White. This is the largest parameter survey ever done is this field.Comment: 3 pages, gzip'ed tar file, including TeX source (not Latex). To be published in a periodical of the Yukawa Institute for Theoretical Physics (1998