Bayesian analysis of sneutrino dark matter in the NMSSM with a type-I seesaw mechanism

Abstract

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with extra heavy neutrino superfields, neutrino may acquire its mass via a seesaw mechanism and sneutrino may act as a viable dark matter (DM) candidate. Given the strong tension between the naturalness for Z boson mass and the DM direct detection experiments for customary neutralino DM candidate, we augment the NMSSM with Type-I seesaw mechanism, which is the simplest extension of the theory to predict neutrino mass, and study the scenarios of sneutrino DM. We construct likelihood function with LHC Higgs data, B-physics measurements, DM relic density and its direct and indirect search limits, and perform a comprehensive scan over the parameter space of the theory by Nested Sampling method. We adopt both Bayesian and frequentist statistical quantities to illustrate the favored parameter space of the scenarios, the DM annihilation mechanism as well as the features of DMnucleon scattering. We find that the scenarios are viable over broad parameter regions, especially the Higgsino mass µ can be below about 250GeV for a significant part of the region, which predicts Z boson mass in a natural way. We also find that the DM usually co-annihilated with the Higgsinos to get the measured relic density, and consequently the DM-nucleon scattering rate is naturally suppressed to coincide with the recent XENON-1T results even for light Higgsinos. Other issues, such as the LHC search for the Higgsinos, are also addressed.1 Numerically speaking, the mixing angle should satisfy sin θν ∼ 0.02 for mν = 100GeV to predict the right DM relic density by the Z boson mediated annihilation, which corresponds to the scattering rate at the order of 10 −45 cm −2 [34]. Such a rate has been excluded by the latest XENON-1T experiment, which, on the other side, limits sin θν < 0.01 by the recent calculation in [35]. Moreover, we find that the correlation between the relic density and the scattering rate is underestimated in FIG.1 of [36].

Suppressing the scattering of WIMP dark matter and nucleons in supersymmetric theories

“…We set the soft breaking masses for the first two generation sneutrino fields at 2 TeV, and use some statistic quantities such as confidence interval (CI) and best point to show our results. A brief introduction of these quantities is presented in [24,88]…”

“…Besides, the singlet Higgs field can also mediate the transition of the sneutrino pair into a Higgsino pair and vice versa in the thermal bath of the early universe. If the sneutrino and the Higgsino are approximately degenerated in mass, the annihilation of the Higgsinos in the freeze-out stage can affect the DM density significantly, which makes the relic density consistent with its experimental measurements [24] (in literature this phenomenon is called co-annihilation [29,30]). Similar to the secluded DM case,ν 1 couples very weakly with the SM particles due to its singlet nature and consequently its scattering with nucleon is suppressed.…”

“…The ENNS contains only the fields of the NMSSM with its parameter space satisfying automatically the constraints from DM physics and its potentially large collider signals self contained in the framework. This scenario is motivated by following observations • From the discussion in previous sections and also from our Bayesian analysis of the Type-I NMSSM in [24], the co-annihilation of the sneutrino DM with the lightest neutralino is the most important mechanism to get the measured DM density 8 .…”

96 GeV diphoton excess in seesaw extensions of the natural NMSSM

“…A great advantage of the former candidate over the latter one is that, regardless the value of the Higgsino mass, the couplings of the sneutrino pair with SM particles are always weak due to its singlet nature. This causes its scattering with nucleon suppressed greatly, and thus alleviates the constraints of the DM DD experiments on the theory [44]. In the following, we only discuss the case with a sneutrino DM since it has much broader parameter space allowed by experiments.…”

“…Since the latest XENON-1T results have improved the previous sensitivity by a factor of about 5, we checked that the space becomes experimentally disfavored [35]. Given the great theoretical advantages of the NMSSM and unfortunately the strong experimental constraints on its most natural parameter space, we were motivated to augment the NMSSM with different seesaw mechanisms to generate neutrino mass and also to enable the lightest sneutrinoν 1 as a viable DM candidate [43][44][45]. The general feature of such extensions is that the singlet Higgs field plays extra roles [43,44]: apart from being responsible for heavy neutrino mass via the interactionŜνν in superpotential (Ŝ andν denote the superfields of the singlet Higgs and the heavy neutrino respectively), it contributes to the annihilation ofν 1 and consequently makes the property ofν 1 compatible with various measurements in a natural way.…”