Study of dark matter and QCD-charged mediators in the quasidegenerate regime

Abstract

We study a scenario in which the only light new particles are a Majorana fermion dark matter candidate and one or more QCD-charged scalars, which couple to light quarks. This scenario has several interesting phenomenological features if the new particles are nearly degenerate in mass. In particular, LHC searches for the light scalars have reduced sensitivity, since the visible and invisible products tend to be softer. Moreover, dark matter-scalar co-annihilation can allow even relatively heavy dark matter candidates to be consistent thermal relics. Finally, the dark matter nucleon scattering cross section is enhanced in the quasi-degenerate limit, allowing direct detection experiments to use both spin-independent and spin-dependent scattering to probe regions of parameter space beyond those probed by the LHC. Although this scenario has broad application, we phrase this study in terms of the MSSM, in the limit where the only light sparticles are a binolike dark matter candidate and light-flavored squarks. arXiv:1707.02460v2 [hep-ph] 1 Dec 2017 * L,R ) QA µ −

Cornering colored coannihilation

“…In particular, our results are directly applicable to SUSY models where the gluino and/or the different squark flavors coannihilate with the neutralino. Note that, for squark-neutralino coannihilation, since flavor constraints strongly limit the annihilation rates between different sfermion species, the existence of multiple degenerate squark or slepton flavors can lead to particularly tight relic density bounds [27][28][29]. Another major class of models with multiple coannihilation partners is Kaluza-Klein theories where the dark matter is the lightest Kaluza-Klein particle and can coannihilate with higher modes that are nearly degenerate with each other [30].…”

Simplified dark matter models with charged mediators

“…Several more detailed equations are discussed in Appendix A, while complete descriptions of the Incredible Bulk and co-annihilation scenarios can be be found in Refs. [1] and [2,3], respectively.…”

“…For complete and self-contained discussions of dipole moments, collider searches, direct detection and indirect detection in the context of charged mediator models, please see previous work in respective Refs. [7,1], [13,8,9], [5,6,2,3] and [4,14].…”

“…In the near-degenerate limit, the kinematics of non-relativistic scattering causes the mediator propagator to go nearly on-shell. As a result, next generation direct detection experiments may be sensitive to models well above the mass reach of the LHC in the neardegenerate limit [2].…”

“…• If the mass splitting between the the dark matter and the lightest charged mediator is small, then the charged mediator may also be abundant at the time of dark matter thermal freeze out. In this case, co-annihilation can sufficiently deplete the dark matter density [2,3].…”