Seminarium "Teoria cząstek elementarnych i kosmologia"

The resonance region is still a viable part of the parameter space in many simple and otherwise highly-constrained dark matter (DM) models. A dark matter annihilation near the resonance is usually described in the standard Breit-Wigner approximation. However, if a mediator is coupled more strongly to the DM than to the annihilation products, the DM contribution can dominate the mediator width. In this case near threshold effects become important and one is forced to employ Dyson-resummed propagator with full self-energy instead of the fixed width in the Breit-Wigner formula. Moreover, if the vector bosons are present in the theory the gauge-invariance and proper high-energy behaviour of the amplitudes are not given in a straightforward way. In this talk I will present the calculation of the resonant annihilation cross-section using pinch technique methods that satisfies the necessary physical conditions. The consequences for the determination of dark matter relic abundance will be illustrated within the Abelian vector dark matter model taking into account the thermal corrections coming from the early kinetic decoupling.