Natural dark matter and light bosons with an alternative left-right symmetry

Abstract

We perform a consistent analysis of the alternative left-right symmetric model emerging from E 6 grand unification. We include a large set of theoretical and experimental constraints, with a particular emphasis on dark matter observables and collider signals. We show that the exotic neutrino inherent to this class of models, the scotino, is a viable candidate for dark matter satisfying relic density and direct detection constraints. This has strong implications on the scotino mass restricting it to lie in a narrow window, as well as on the spectrum of Higgs bosons, rendering it predictable, with a few light scalar, pseudoscalar and charged states. Moreover, we also show that the extra charged W gauge boson can be light, and investigate the most promising signals at the future high-luminosity upgrade of the LHC. Our findings show that the most optimistic cosmologically-favoured scenarios should be observable at 5σ, whilst others could leave visible hints provided the background is under good control at the systematical level. SU (2) L × SU (2) H × U (1) X group that embeds the SU (2) L × U (1) Y electroweak symmetry. In the so-called left-right symmetric model (LRSM), that naturally accounts for non-vanishing neutrino masses [20][21][22][23], SU (2) H is identified with SU (2) R and U (1) X with U (1) B−L . In such a configuration, the right-handed SM fermions and the right-handed neutrino ν R are collected into SU (2) R doublets. The structure of the Higgs sector could however lead to non-acceptable tree-level flavour-violating interactions that would conflict with the observed properties of kaon and B-meson systems. Consequently, the SU (2) R × U (1) B−L symmetry has to be broken at a very high energy scale to mass-suppress any potential flavour-violating effect. This additionally pushes the masses of the extra Higgs and gauge bosons of the model to the high scale, making them unlikely to detect at the LHC. Furthermore, in its minimal incarnation, the LRSM lacks any viable DM candidate [24].It is nevertheless possible to associate the SU (2) H symmetry with a different SU (2) R group in which the assignments of the SM fermions into doublets are different [25,26]. This model is called the alternative left-right symmetric model (ALRSM) [27,28]. In this case, the SU (2) R partner of the right-handed up-quark u R is an exotic down-type quark d R (instead of the SM right-handed down-type quark d R ), and the SU (2) R partner of the right-handed charged lepton e R is a new neutral lepton, the scotino n R (instead of the more standard right-handed neutrino ν R ). The righthanded neutrino ν R and down-type quark d R therefore remain singlets under both the SU (2) L and SU (2) R groups. In addition, the model field content also includes SU (2) L singlet counterparts to the new states, i.e. an n L scotino and a d L down-type quark. Consequently, one generation of quarks is described by one SU (2) Similarly, one generation of leptons is described by one SU (2) L doublet L L = (ν L , e L ), one SU (2) R doublet L R = (n R ,...

Cross-fertilising extra gauge boson searches at the LHC

“…To perform our numerical analysis, we have implemented the models presented in section 2 into FeynRules (version 2.3.35) [51] and converted them into leading-order UFO libraries [52,53]. Our new implementations are based on already publicly available ones [18,29,34,54,55], that we have harmonised with each other in the context of simplified versions of the various models (that are sufficient for our purpose). Hard-scattering partonlevel events have then been generated with MG5aMC (version 3.0.3) [56], and have been analysed with MadAnalysis 5 [57][58][59] (version 1.8.58).…”

Exploring 0νββ and leptogenesis in the alternative left-right model

“…For this, an additional S-symmetry is imposed, under which the lepton number is either L ¼ S − T 3R , in the dark left-right model (DLRM) [29], or L ¼ S þ T 3R , in the dark left-right model 2 (DLRM2) with a global Uð1Þ S [30], duly extended to a local Uð1Þ S in [31]. Finally, it was shown that the partner of the right-handed electron, the scotino, is a viable DM candidate, consistent with all constraints, within suitable parameter space region [26], and the model implications at colliders was explored. In this work, we shall work within the DLRM2, with global S charge assignments as in [27,28,32].…”

“…We have explored the ALRM, an alternate way of extending the SM gauge group with a relatively low energy SUð2Þ R but without any additional symmetry with the left handed sector, either in gauge couplings or in the matter content. As has been shown in earlier studies [21] this opens a way to achieve grand unification within E 6 , while providing a rather unusual model for dark matter and an unusual phenomenology also for the vector bosons at the LHC [26]. Indeed, the scotino [22], the partner of the electron in the right-handed doublet in this model can be a viable dark matter candidate and has been studied in several variants of the model [27,29,30,69].…”

“…We refer to Refs. [26][27][28] for details and explicit expressions of the mixing matrices U A 3×3 and U H 3×3 , for the CPodd and CP-even scalars. Pertinent for our further discussion are the charged scalar bosons and their interaction with the quarks and the leptons.…”

“…II we discuss the ALRM with its origins in E 6 and the existing constraints on the relevant couplings and masses. For a more complete description of the model one may refer to [26][27][28]. In Sec.…”