Mathematics – Logic
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt.........4k&link_type=abstract
Thesis (PH.D.)--STANFORD UNIVERSITY, 1996.Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6795.
Mathematics
Logic
Nucleosynthesis, Cosmology
Scientific paper
Based on the cosmological evolution of the single -field scalar-tensor theories, we use the nucleosynthesis constraint, together with the present limits on the Post -Newtonian parameters gamma and beta, to discuss the empirical bounds on the coefficients of the Taylor series expansion (about today) of the only free function a(phi), which specifies the scalar field coupling to matter since the nucleosynthesis era. If the function a(phi) has a minimum, nucleosynthesis typically places stronger limits on 1-gamma than solar system tests. This latter property, however, depends on the total density of the universe in a way which enables us to draw the surprising conclusion that within this class of scalar-tensor theories a measurement of a nonzero 1 -gamma in our solar system will indicate an upper limit on the amount of dark matter in the universe. Deviations due to scalar-tensor theories, if detected, may also have ramifications regarding the presence of extra dimensions to spacetime, the latter being abundantly employed in Grand Unification attempts such as Superstrings, SuperGravity, and Kaluza-Klein theories. However, the possible existence of extra dimensions to spacetime can also be tested astrophysically by extending Einstein's general relativity to higher than four dimensions. In the simplest version of the theory, there is a standard class of five-dimensional one-body problem solutions that are analogous to the four-dimensional Schwarzschild solution. However, even a small departure of the extra dimension from flatness affects the first or dominant part of the metric, making it possible to test for the existence of an extra dimension. We find the predicted changes for the classical tests to allow for gamma>1, which can be used as a leading indicator for the presence of extra dimensions, although to test for their presence better we also need to examine other astrophysical systems, and eventually devise a "super-PPN" framework which will encompass (4 + N)-gravity.
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