Abstract
Minimal Dark Matter (MDM) is a theoretical framework highly appreciated for its minimality and yet its predictivity. Of the two only viable candidates singled out in the original analysis, the scalar eptaplet has been found to decay too quickly to be around today, while the fermionic quintuplet is now being probed by indirect Dark Matter (DM) searches. It is therefore timely to critically review the MDM paradigm, possibly pointing out generalizations of this framework. We propose and explore two distinct directions. One is to abandon the assumption of DM electric neutrality in favor of absolutely stable, millicharged DM candidates which are part of SU(2)L multiplets with integer isospin. Another possibility is to lower the cutoff of the model, which was originally fixed at the Planck scale, to allow for DM decays. We find new viable MDM candidates and study their phenomenology in detail.
Highlights
The presence of Dark Matter (DM) in the universe is a clear evidence for new physics beyond the Standard Model (SM)
Minimal Dark Matter (MDM) [1] is a theoretical framework highly appreciated for its minimality and yet its predictivity
Contrary to many models where DM stability is imposed by hand through a global symmetry, MDM candidates are made stable on cosmological timescales by accidental symmetries occurring through a careful selection of the DM quantum numbers
Summary
The presence of Dark Matter (DM) in the universe is a clear evidence for new physics beyond the Standard Model (SM). The argument just presented is very general and can be applied outside the MDM framework It concerns any model featuring a color and hypercharge-neutral scalar multiplet containing a DM candidate, unless ad-hoc symmetries are introduced to prevent DM from decaying. From a GUT standpoint, one may object that small values of hypercharge are difficult to accommodate in models of grand unification While this is definitely true, we note that the whole MDM framework is not GUT friendly, since its large multiplets badly modify the running of the SM gauge couplings and they supposedly require a large GUT representation to embed the X field, generating a severe doublet-triplet splitting-like problem. In the following we first review the most stringent constraints on the DM electric charge , and discuss the possible millicharged MDM candidates (1, n, ) and compute the mass of few of them
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