Spin 1 mode particle production in models of expanding universe

The standard quantization of spin 1 field in flat Robertson-Walker (RW) space-time is considered to evaluate the number of particles created in an expanding universe. The study is based on an improved form of the normal modes, previously determined, of the spin 1 field equation in flat RW space-time. A second system of normal modes is considered that is the time translated of the given one. The corresponding Bogolubov coefficients are calculated and the expectation value of the number of created particles calculated. The results are obtained for a general evolution of the cosmological background. They are ex- emplified for the linear, the exponential and the radiation dominated Standard Cosmology expansion laws. In all cases particle production is non zero. A detailed study is done in all cases for large time. In case of the exponential expansion the number of the created particle remains very small for long time. The creation of particle is possible if the mass of the particle of the field and the Hubble constant satisfy 2m_0 > H, a condition widely satisfied by the experimental data.