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Nanopoulos, Dimitri Wang, Jin 2011-05-07T12:43:04Z 2011-05-07T12:43:04Z 10000-01-01 1991 In this thesis we study the quantum cosmology of the string universe obtained by embedding the Robertson-Walker metric in the non-linear $\sigma$ 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 Hartle-Hawking and Vilenkin boundary conditions to the solution of Wheeler-DeWitt 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 $\vert\dot G/G\vert < 10\sp{-12}yr\sp{-1}$ 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 nuclear-burning core which may in principle be observable. Made available in DSpace on 2011-05-07T12:43:04Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9211025.pdf: 3015640 bytes, checksum: 2f0fa437a67af60b67e8c514c6017906 (MD5) Previous issue date: 1991 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:44:47Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:19:45-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9211025 (UMI)AAI9211025 http://hdl.handle.net/2142/20571 eng Copyright 1991 Wang, Jin Physics, Astronomy and Astrophysics Some problems of quantum cosmology and dark matter physics text Astronomy Astronomy University of Illinois at Urbana-Champaign Dissertation Ph.D.