Dark matter with $t$-channel mediator: a simple step beyond contact interaction    [PDF]

Haipeng An, Lian-Tao Wang, Hao Zhang
Effective contact operators provide the simplest parameterization for dark matter searches at the LHC. At the same time, light mediator can change the sensitivity and search strategies in important ways. Considering simple models of mediators is an important next step for collider searches. In this paper, we consider the case of a $t$-channel mediator. Its presence opens up new contributions to the monojet$+\displaystyle{\not{\text{E}}}_T$ searches and can change the reach significantly. We also study the complementarity between monojet$+\displaystyle{\not{\text{E}}}_T$ and direct pair production of the mediators. There is a large region of parameter space in which the monojet$+\displaystyle{\not{\text{E}}}_T$ channel provides the stronger limit. We combine the reaches of LHC search and direct detection, and compare it with the requirement from thermal relic abundance. We find that in the Dirac fermion dark matter case, there is no region in the parameter space that reconciles the combined constraint of monojet$+\displaystyle{\not{\text{E}}}_T$ search and direct detection with constraint from not over closing the universe; and in the Majorana fermion dark matter case, the mass of dark matter must be larger than about 200 GeV. If the relic abundance requirement are not satisfied within the simple model, discovery of dark matter at the LHC in monojet$+\displaystyle{\not{\text{E}}}_T$ and di-jet $+\displaystyle{\not{\text{E}}}_T$ channels predicts additional new physics.
View original: http://arxiv.org/abs/1308.0592