Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8k&link_type=abstract
Ph.D. Thesis Brown Univ., Providence, RI.
Other
Cosmology, Flux Density, Gravitational Waves, Mathematical Models, String Theory, Universe, Neutrinos, Plane Waves, Wave Excitation
Scientific paper
Few selected topics in the inflationary universe models and the cosmic string theories are studied. After the advent of inflationary universe models, questions were raised about the initial conditions of the scalar field which is necessary to give rise to inflation. At present, there are two viable inflationary models: New Inflation, and Linde's Chaotic Inflation. The time evolutions of single plane wave initial excitations of a real singlet scalar field with the potential V(phi) = lambda(phi)/2(phi2 - sigma2)2 was studied. The initial value of the scalar field energy density was bounded by the planck energy density. It is shown that even within this regime there are regions of the phase space for which the universe will enter into chaotic inflation and new inflation. The issue of the stability of chaotic inflation was also studied. Specifically, the possible interference effects of initially exciting another generic plane wave mode was investigated in addition to the mode which when evolved alone is known to give rise to chaotic inflation. The properties of the spectrum of gravitational radiation that was generated by a network of cosmic strings, which decayed by gravitational radiation in an expanding universe were studied. The network of cosmic strings that were used is an improvement of the network that was used in the literature. The conclusion is that the bounds on the gravitational energy density from the nucleosynthesis, the microwave anisotropy, and the pulsar timings arguments can not yet rule out cosmic string theories with Gmu approximately 10-6. The clustering of hot massive neutrinos by a cosmic string loop as a non-adiabatic perturbation is studied using Zel'dovich approximation in conjunction with the neutrino Jeans length. First, the results for a non-decaying loop using the Zel'dovich approximation are shown to exactly reproduce previous results using the Gilbert equation. Second, the analysis is extended to clustering by a decaying loop. It is shown that the effect of loop decay is to increase the radius and mass of the smallest structures that can be seeded by cosmic strings. In conclusion, with decaying loops, the smallest structures that can form by the present time via direct accretion onto loops have a mass of about M = 2.4 x 108 solar mass (gamma/50)3/4(Gmu/10-6)3/2(veq/0.04)3/4(h-5/2) with a turn around radius of about r = 29Kpc(gamma/50)1/4(Gm u/10-6)1/2(veq/0.04)(1/4)(h-3/2), which is to be compared to the present neutrino jeans mass of M = 2.8 x 104 solar mass(veq/0.04)3(h-7) and its Jeans length of r = 2.9Kpc(veq/0.04)h-3.
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