Physics
Scientific paper
Aug 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt........15s&link_type=abstract
Thesis (PhD). HELSINGIN YLIOPISTO (FINLAND), Source DAI-C 62/03, p. 447, Fall 2001, 53 pages.
Physics
Scientific paper
The production of the light elements, deuterium, helium, and lithium, during the first minutes of the big bang is well established (big bang nucleosynthesis, BBN). BBN provides at present the most accurate way of determining the baryon content of the universe. In standard big bang nucleosynthesis (SBBN) matter is assumed to be homogeneously distributed during the nucleosynthesis epoch. The objective of this thesis is to study two nonstandard big bang nucleosynthesis scenarios. In inhomogeneous big bang nucleosynthesis (ISBN) one assumes an inhomogeneous baryon density during nucleosynthesis. In antimatter big bang nucleosynthesis (ABBN) the early universe is assumed to contain regions of antimatter. Production of antimatter regions is possible in many baryogenesis models. Both scenarios studied lead to a modified light element production. IBBN may improve the consistency between the observations of helium and deuterium. We give updated limits to the baryon density based on the recent observational situation. In the case of the ABBN scenario, we give constraints on the antimatter fraction at various length scales. At small scales the limit comes from underproduction of He-4 due to annihilation of neutrons before BBN. At larger scales the limit comes from overproduction of He-3. The most important sources of He-3 are annihilation and photodisintegration of He-4. The constraints from BBN are tighter than those from distortion of the cosmic microwave background (CMB) spectrum up to scales of 1 pc. It is shown that in ABBN it is possible to accommodate a high baryon density, which is not allowed in SBBN, with observations of D and He-4. Because of the overproduction of lithium, the upper limit on the baryon density is, however, relaxed only slightly.
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