Nonequilibrium Fermion Production in Quantum Field Theory.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2010)
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|Item Type:||Ph.D. Thesis|
|Title:||Nonequilibrium Fermion Production in Quantum Field Theory|
The creation of matter in the early universe or in relativistic heavy-ion collisions is inevitable connected to nonequilibrium physics. One of the key challenges is the explanation of the corresponding thermalization process following nonequilibrium instabilities. The role of fermionic quantum fields in such scenarios is discussed in the literature by using approximations of field theories which neglect important quantum corrections. This thesis goes beyond such approximations. A quantum field theory where scalar bosons interact with Dirac fermions via a Yukawa coupling is analyzed in the 2PI effective action formalism. The chosen approximation allows for a correct description of the dynamics including nonequilibrium instabilities. In particular, fermion-boson loop corrections allow to study the interaction of fermions with large boson fluctuations. The applied initial conditions generate nonequilibrium instabilities like parametric resonance or spinodal instabilities. The equations of motion for correlation functions are solved numerically and major characteristics of the fermion dynamics are described by analytical solutions. New mechanisms for the production of fermions are found. Simulations in the case of spinodal instability show that unstable boson fluctuations induce exponentially growing fermion modes with approximately the same growth rate. If the unstable regime lasts long enough a thermalization of the infrared part of the fermion occupation number occurs on time scales much shorter than the time scale on which bosonic quantum fields thermalize. Fermions acquire an excess of occupation in the ultraviolet regime compared to a Fermi-Dirac statistic characterized by a power-law with exponent two. The fermion production mechanism via parametric resonance is found to be most efficient after the instability ends. Quantum corrections then provide a very efficient particle creation mechanism which is interpreted as an amplification of decay processes. The ratio of the Yukawa coupling squared to the boson self-coupling is in both mechanism of great importance. The boson dynamics is qualitatively the same for both kinds of instabilities. An initially unstable evolution shows well-known characteristics with an ensuing quasi-stationary regime. The latter exhibits infrared and/or ultraviolet power-law behaviors in the occupation number which prevent a fast thermalization. Furthermore, for not too large Yukawa couplings the impact of fermions on the dynamics of highly occupied bosons is weak. An acceleration of the evolution of the whole system towards thermal equilibrium is not observed.
|Place of Publication:||Darmstadt|
|Uncontrolled Keywords:||Nonequilibrium Quantum Field Theorie; Fermions|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 530 Physik|
|Divisions:||05 Department of Physics|
|Date Deposited:||25 Jun 2010 08:57|
|Last Modified:||07 Dec 2012 11:57|
|Referees:||Berges, Prof. Dr. Jürgen and Fischer, Prof. Dr. Christian|
|Refereed:||16 June 2010|