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Scientific paper
Feb 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.......181b&link_type=abstract
Thesis (PhD). BOSTON UNIVERSITY, Source DAI-B 59/08, p. 4203, Feb 1999, 84 pages.
Other
Scientific paper
I study baryon number (B) violation in the Standard Model (SM) of elementary particles. The SM has an infinite number of physically equivalent, degenerate vacua, separated by potential barriers. Whenever the system changes vacuum sector, B also changes. Under most experimental conditions, such transitions can only occur by quantum tunneling, at a negligible rate, and for this reason the phenomenon is usually ignored. However, B- violation can be observed when (a) the initial state has an energy at least comparable to the potential barrier and overlaps appreciably with a configuration interpolating between two vacua, or (b) the initial state has such a high energy that it overcomes any small- overlap suppression. I discuss both possibilities. In the first part of the thesis I study option a), which is realized in thermal systems at sufficiently high temperatures (T~ 200/ GeV or higher). Although these temperatures are not be reached in present laboratories, they did occur in the early universe; it is therefore possible that SM B-violating processes that took place during the Electroweak Phase Transition are responsible for the observed matter-antimatter asymmetry of the universe. I review the current status of the 'Electroweak Baryogenesis' scenario, and present a method to compute the quark-Higgs plasma transport properties, an essential element in any realistic baryogenesis calculation. As an example, I discuss the two-doublet Higgs model. The remaining chapters are devoted to the second option, the observation of B-violation during a high-energy scattering process. Computing the rate of such processes is a theoretical challenge, since the phenomenon is inherently non-perturbative, and therefore not amenable to standard analytical tools. I discuss a semiclassical method that has been suggested to overcome this difficulty, and whose potential range of applicability extends beyond the specific problem to other non- perturbative, low-coupling processes. In this approximation, rates are dominated by generalized instanton configurations. I show that in a toy model this technique provides very accurate results. Finally, I apply the method to the problem of B-violation, and compute a particularly important class of configurations, the 'periodic instantons'.
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