Long live the Higgs portal!

Abstract

In Higgs portal models of fermion dark matter, scalar couplings are unavoidably suppressed by strong bounds from direct detection experiments. As a consequence, thermal dark matter relics must coexist with mediators in a compressed spectrum of dark particles. Small couplings and small mass splittings lead to slow mediator decays, leaving signatures with displaced vertices or disappearing tracks at colliders. We perform a comprehensive analysis of long-lived mediators at the LHC in the context of a minimal dark matter model with a naturally small Higgs portal, also known as the wino-bino scenario in supersymmetry. Existing searches for disappearing charged tracks and displaced hard leptons already exclude tiny portal couplings that cannot be probed by current direct and indirect detection experiments. For larger portal couplings, we predict new signatures with displaced soft leptons, which are accessible with run-II data. Searches for displaced particles are sensitive to weakly coupling mediators with masses up to the TeV scale, well beyond the reach of prompt signals. Contents

Coscattering in next-to-minimal dark matter and split supersymmetry

“…The possible collider signatures for singlet-triplet models have been analyzed in detail e.g. in [10,16,20,[29][30][31][32][33]. Therefore, here we will only briefly review the state of the most important LHC search for the model in the coscattering phase, which is the search for disappearing charged tracks.…”

Inert sextuplet scalar dark matter at the LHC and future colliders

“…Here we define six signal regions by requiring m ∈ [1,10], [1,20], [1,40], [1,50], [1,60], and [1,70], dubbed SR-10, SR-20, SR-40, SR-50, SR-60, and SR-70, respectively. Table 5 also lists the visible cross sections and the signal significances of the four BMPs in the signal regions SR-60, SR-40, and SR-20.…”

Soft displaced leptons at the LHC

“…[7]). The decay length of the dark partner can vary between zero and a few centimeters for co-annihilation and up to a meter for coscattering [5,6,[8][9][10][11][12], depending on the model. For even smaller dark matter couplings, dark matter is never in thermal equilibrium and the relic abundance can be produced through freeze-in [13] or the decay of thermal dark states [14], which results in even larger decay lengths at colliders [11,[15][16][17].…”