Electroweak baryogenesis and dark matter in a minimal extension of the MSSM

Abstract

We examine the possibility of electroweak baryogenesis and dark matter in the nMSSM, a minimal extension of the MSSM with a singlet field. This extension avoids the usual domain wall problem of the NMSSM, and also appears as the low energy theory in models of dynamical electroweak symmetry breaking with a so-called fat-Higgs boson. We demonstrate that a strong, first order electroweak phase transition, necessary for electroweak baryogenesis, may arise in regions of parameter space where the lightest neutralino provides an acceptable dark matter candidate. We investigate the parameter space in which these two properties are fulfilled and discuss the resulting phenomenology. In particular, we show that there are always two light CPeven and one light CP-odd Higgs bosons with masses smaller than about 250 GeV. Moreover, in order to obtain a realistic relic density, the lightest neutralino mass tends to be smaller than M Z /2, in which case the lightest Higgs boson decays predominantly into neutralinos.

Collider signatures of singlet extended Higgs sectors

“…In the MSSM, NMSSM, and UMSSM the invisible decay is usually kinematically inaccessible [10] in our parameter scan, which has a lower limit on m χ 0 1 of 53 GeV (half the chargino mass bound 7 ), but the invisible decay is potentially relevant for M H > 106 GeV. Invisible decays are often dominant in the n/sMSSM where the lightest neutralino mass is typically lighter than 50 GeV [5,10,15,23]. Therefore, using traditional searches the discovery of the H 1 is unlikely in the n/sMSSM.…”

“…However, if the CP-odd Higgs is very light (M A 10 GeV), the Higgs may not be directly observable [12]. 5 Many points with Higgs masses below the SM Higgs 114 GeV LEP limit are often suppressed below a significance of 0.1 due to the dominant singlet fraction. In the cases where the lightest Higgs is decoupled and light (typically in the n/sMSSM), the second Higgs state, H 2 , has a mass in the range of the lightest Higgs in the MSSM and a large significance.…”

“…The models we focus on include the Next-to-Minimal Supersymmetric SM (NMSSM) [2], the Nearly-Minimal Supersymmetric SM (nMSSM) [3,4,5], and the U(1) ′ -extended MSSM (UMSSM) [6], as detailed in Table I with the respective symmetries 1 . A Secluded U(1) ′ -extended MSSM (sMSSM) [8,9] contains three singlets in addition to the standard UMSSM Higgs singlet; this model is equivalent to the nMSSM in the limit that the additional singlet vevs are large, and the trilinear singlet coupling, λ s , is small [10].…”

The effective theory of the light stop scenario

“…Moreover beyond the MSSM there are plenty of other possibilities. The simplest one is introducing singlets in the MSSM light spectrum (the so-called NMSSM [8] or nMSSM [9]), or even adding an extra Z ′ gauge boson [10], which easily triggers a strong first order phase transition.…”

Baryogenesis from an earlier phase transition

“…While this renders the SM itself unable to produce the asymmetry, it illustrates the fact that experiments at the TeV scale are able to directly probe EWBG. Extensions of the SM which include new physics at the EW scale 1 can in fact re-open the possibility of EW baryogenesis by introducing additional bosonic fields [12,13,14,15,16] as in the Minimal Supersymmetric Standard Model (MSSM) [17,18,19,20,21,22,23,24] or fermions strongly coupled to the Higgs [31,32]. Eventually, future colliders such as the Large Hardron Collider (LHC) and possibly International Linear Collider (ILC) will unravel the nature of EWSB, and should provide a better understanding as to the nature of the electroweak phase transition (EWPT).…”