Other
Scientific paper
Jul 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.......106a&link_type=abstract
Thesis (PhD). HELSINGIN YLIOPISTO (FINLAND), Source DAI-C 59/03, p. 711, Fall 1998, 104 pages.
Other
Scientific paper
The field equations of the electromagnetic field, combined with models of the early universe, make it possible to study electromagnetic phenomena at the early stages of the universe. Electromagnetic fields provide us with a tool to estimate electrical conductivity and transport coefficients (heat conductivity and viscosity) in the primordial plasma of the hot early universe. Electrical conductivity plays an important role, for example, in the dissipation of the axion field (a weakly interacting dark matter candidate) and in the creation and dissipation of the primordial magnetic field. On the other hand, heat conductivity and shear viscosity are important, for example, in connection with primordial density perturbations, i.e., galaxy formation, early phase transitions, and primordial magnetic fields. First, in paper I, we derived the equations of motion for the axion field coupled with an electromagnetic field. It was found that energy from the axion field can be transferred to the electromagnetic field. Therefore the damping of the axion field depends on electrical conductivity but that the electromagnetic dissipation cannot, however, significantly damp the axion field. In paper II we developed the tools with which to estimate electrical conductivity in the primordial plasma. We used the Boltzmann collision equation to study how a beam of charged particles will be scattered in the early hot universe. We integrated the collision integral numerically by a simple Monte Carlo integration routine. We discovered that the charged leptons give the largest contribution to the electrical conductivity; the quark contribution was found to be negligible. In Paper III, we estimated with an Abelian Higgs model what kind of a primordial magnetic field can be created in first order phase transition bubble collisions. Assuming that the Abelian model reflects the properties of the full electroweak case, we found that the seed field created is of the right order of magnitude in order to explain the intergalactic magnetic fields observed today. We also found that the strength of the magnetic field created is depending on the electrical conductivity of the surrounding primordial plasma and on the velocity of the bubble walls. Finally, we continued to develop further the tools of paper II in paper IV. There we have studied more carefully the proper introduction of screening thermal mass terms into the otherwise divergent u- and t-channel propagators. This helped us to make more accurate estimates for electrical conductivity. We also calculated heat conductivity and shear viscosity in the primordial plasma. Reliable knowledge about the transport coefficients is important when trying to understand the seeding of galaxies, observed galactic magnetic fields and early phase transitions.
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