Nonthermal particle production in Einstein-Cartan gravity with modified Holst term and nonminimal couplings

Nonthermal fermionic particle production is investigated in Einstein-Cartan modified gravity with a modified Holst term and nonminimal couplings between the spin connection and a fermion. By using the auxiliary field method, the theory is rewritten into a pseudoscalar-tensor theory with Einstein-Hilbert action and canonical kinetic and potential terms for a pseudoscalar field. The introduced field is called Einstein-Cartan pseudoscalaron. If the potential energy of the Einstein-Cartan pseudoscalaron dominates the energy density of the early universe, it causes inflationary expansion. After the end of inflation, the pseudoscalaron develops a large value and the nonminimal couplings destabilize the vacuum. Evaluating the nonthermal fermionic particle production process, we obtain the mass and the helicity dependences of the produced particle number density. We show the model parameters to enhance the preheating and reheating processes.