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Jan Heisig, University of Viginia, Title of talk: From coannihilation to conversion-driven freeze-out: Dark matter genesis beyond the WIMP paradigm

Abstract:
The nature of dark matter poses one of the most pressing questions in fundamental physics today. Thermal freeze-out of a weakly interacting massive particle (WIMP) has proved to be a successful framework for explaining the measured dark matter abundance in the Universe. However, the sizeable couplings of dark matter to the Standard Model particles required in its simplest realizations have been put under severe pressure by experimental null-results at colliders, direct and indirect detection experiments. Hence, fulfilling the relic density constraint often requires the exploration of ‘exceptional’ regions, e.g. the region where coannihilation effects increase the effective annihilation rate. In this talk, we revisit the assumptions commonly made within the coannihilation scenario and discuss a new variant of dark matter freeze-out, dubbed conversion-driven freeze-out (or coscattering). In this scenario, the relic abundance is set by the freeze-out of conversion processes requiring significantly smaller couplings of dark matter to the standard model. While this parameter region is largely immune to direct detection constraints, it predicts an interesting signature of disappearing tracks or displaced vertices at the LHC. We will also discuss the effect of bound state formation of the coannihilating particle which considerably enhance the valid parameter space into the multi-TeV region, making it a prime target for upcoming long-lived particle searches at the LHC.

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