Search

The standard model and its extensions predict multiple phase transitions in the early universe. In addition to the electroweak phase transition, one or several of these could occur at energies close to the weak scale. Such phase transitions can leave their imprint on the relic abundance of TeV-scale dark matter. In this paper, we enumerate several physical features of a generic phase transition and parametrize the effect of each on the relic abundance. In particular, we include among these effects the presence of the scalar field vacuum energy and the cosmological constant, which is sensitive to UV physics. Within the context of the standard model Higgs sector, we find that the relic abundance of generic TeV-scale dark matter is affected by the vacuum energy at the order of a fraction of a percent. For scalar field sectors with strong first-order phase transitions, an order 1% apparent tuning of coupling constants may allow corrections induced by the vacuum energy to be of order unity. [ABSTRACT FROM AUTHOR]

Monojet searches are a powerful way to place model-independent constraints on effective operators coupling dark matter to the standard model. For operators generated by the exchange of a scalar mediator, however, couplings to light quarks are suppressed and the prospect of probing such interactions through the inclusive monojet channel at the LHC is limited. We propose dedicated searches, focusing on bottom and top quark final states, to constrain this class of operators. We show that a search in mono b-jets can significantly improve current limits. The mono-b signal arises partly from direct production of b quarks in association with dark matter, but the dominant component is from top quark pair production in the kinematic regime where one top is boosted. A search for tops plus missing energy can strengthen the bounds even more; in this case signal and background have very different missing energy distributions. We find an overall improvement by several orders of magnitude in the bound on the direct detection cross section for scalar or pseudoscalar couplings. [ABSTRACT FROM AUTHOR]