Some Problems of Quantum Cosmology and Dark Matter Physics
Abstract
In this thesis we study the quantum cosmology of the string universe obtained by embedding the Robertson Walker metric in the nonlinear sigma model. We find that initially the universe exists in a series of metastable bound states with the scale factor taking discrete values. Then it tunnels through a barrier and comes out in an inflationary state. This tunneling (or evolution in imaginary time) also has the effect of heating up the matter field so that we have a condition of chaotic inflation. Our asymptotic solutions agree with those obtained from the classical Einstein equations. We consider quantum cosmology of a 4 dimensional universe using the effective action of superstrings. We apply both HartleHawking and Vilenkin boundary conditions to the solution of WheelerDeWitt equation. We find that under certain conditions (fermions added) the universe will tunnel through to the Lorentzian regime from the Euclidean regime and time is dynamically generated. We apply Chudnovsky and Vilenkin's idea of possible existence of cosmic strings in the Sun. Stellar evolution with cosmic strings at solar age gives us a radius and luminosity of the star which are in contradiction with observation. We study the astrophysical bound on the change of gravitational constant with time. We find that dot G/G < 10^{12 }yr^{1} is the condition that has to be satisfied in order not to cause the conflict with observation. We study the effect of axions on the steller evolution of a 10 solar mass star model. If the axion mass is larger than.1 ev the star's age is significantly different at late stages, compared to the star without axions. We argue that if cosmions (or WIMPS) solve the solar neutrino problem, then they must also play an important role in the evolution of low mass star main sequence stars; If they do so, then a simple (long mean free path) model for the interaction of cosmions with baryons leads to changes in the structure of the nuclearburning core which may in principle be observable.
 Publication:

Ph.D. Thesis
 Pub Date:
 1991
 Bibcode:
 1991PhDT........13W
 Keywords:

 EARLY UNIVERSE;
 Physics: Astronomy and Astrophysics;
 Boundary Conditions;
 Dark Matter;
 Gravitational Constant;
 Main Sequence Stars;
 Metastable State;
 Stellar Mass;
 String Theory;
 Temperature Effects;
 Astrophysics;
 Asymptotic Series;
 Cosmology;
 Einstein Equations;
 Fermions;
 Matter (Physics);
 Mean Free Path;
 Neutrinos;
 Stellar Evolution;
 Universe;
 Astrophysics