Inverse seesaw in NMSSM and 126 GeV Higgs boson
Introduction
The ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) have independently reported the discovery [1], [2] of a particle with production and decay modes that appear more or less consistent with the Standard Model (SM) Higgs boson of mass . In addition to the Higgs discovery, both experiments reported an excess in Higgs production and decay in the diphoton channel, around times larger than the SM expectations. The statistical significance of this apparent deviation from the SM prediction is at present not sufficiently strong to draw a definite conclusion, but if confirmed in the future, it will be clear indication of new physics around the electroweak scale. These results nevertheless serve as strong motivation to investigate possible extensions of the SM where a possible signal in the diphoton channel could be enhanced compared to the SM.
The minimal supersymmetric standard model (MSSM) [3] can accommodate values of , but this requires either a very large, , stop quark mass [4], or a large soft supersymmetry breaking (SSB) trilinear A-term, with a stop quark mass of around a TeV [5]. Such a heavy stop quark leads to the so-called “little hierarchy” problem [6] because, in implementing radiative electroweak symmetry breaking, TeV scale quantities must conspire to yield the electroweak mass scale.
On the other hand, in the next-to-minimal supersymmetric standard model (NMSSM), the Higgs mass can be raised significantly through a tree level contribution to the Higgs potential [7]. Therefore, the NMSSM can alleviate the little hierarchy problem, and a 126 GeV Higgs mass can be realized with less fine-tuning. In Ref. [8] it was shown that in order to accommodate a 126 GeV Higgs mass with only a few percent fine-tuning, the NMSSM is pushed to the edge of its parameter space, with and . Here tan β is the ratio of the vacuum expectation values (VEVs) of the up () and down () MSSM Higgs doublets. The parameter λ is the dimensionless coupling associated with the interaction , where S is a MSSM gauge singlet field. Note that assuming non-universal gaugino masses at the GUT scale, one can also alleviate the little hierarchy problem [9], but we will not discuss this possibility in this Letter.
Furthermore, in the framework of the NMSSM, Higgs production and decay in the diphoton channel can be enhanced with respect to the SM prediction due to the doublet-singlet mixing in the Higgs sector [8], [10]. It has been shown that to comply with the ATLAS and CMS results, a large stop mass still cannot be avoided. Besides, the couplings (λ, κ, ) are all of at the GUT scale, which are close to the Landau pole.1 Here κ is the dimensionless coupling corresponding to the interaction and is the top Yukawa coupling.
Inspired by recent studies on the NMSSM and the results from ATLAS and CMS, we consider an extension of the NMSSM which has previously been used to explain the origin of neutrino masses. In Ref. [12], in particular, it was shown that in the NMSSM the observed neutrino masses and mixings can be described in terms of dimension six, rather than dimension five, operators. All such operators respect the discrete symmetries of the model. The new particles associated with the inverse seesaw mechanism [13] can have sizable couplings to the Higgs boson, even with the seesaw scale of around a TeV. This, as we will show, enables the Higgs boson mass to be 126 GeV, without invoking sizable contributions from the stop quark as well as keeping the λ and κ couplings relatively small. With relatively light stop quarks in the spectrum one can enhance the diphoton production relative to the SM prediction [14], [15], [16].
The layout of this Letter is as follows. In Section 2, we briefly summarize the NMSSM and the upper bound on the lightest CP-even Higgs boson mass. In Section 3.1 we present the NMSSM with inverse seesaw mechanism for the neutrinos. In this section a SM gauge singlet field is introduced to generate dimension six (and seven) operators for the neutrinos. We discuss how the inverse seesaw mechanism affects the upper bound on the lightest CP-even Higgs boson mass. In Section 3.2, the inverse seesaw mechanism is generated through an triplet field and its impact on the Higgs mass is also considered. Our conclusions are summarized in Section 4.
Section snippets
Higgs boson mass in MSSM and NMSSM
The NMSSM is obtained by adding to the MSSM a gauge singlet chiral superfield S (with even matter parity) and including the following superpotential terms: where λ and κ are dimensionless constants, and , denote the MSSM Higgs doublets. A discrete symmetry under which S carries a unit charge is introduced in order to eliminate terms from the superpotential that are linear and quadratic in S, as well as the MSSM μ term. We also need the symmetry to forbid
NMSSM + gauge singlet field
As shown in Ref. [12], one can incorporate the observed solar and atmospheric neutrino oscillations in the NMSSM by introducing an effective dimension six operator for neutrino masses and mixings. The simplest way to generate this operator is to introduce the gauge singlet chiral superfields in the NMSSM with charges listed in Table 2. This charge assignment corresponds to the so-called case I in Table 1. It is straightforward to find the charge assignments for for other
Conclusion
Following Ref. [12], we consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are generated through TeV scale inverse seesaw mechanism. We have shown that the new particles associated with the inverse seesaw mechanism can have sizable couplings to the lightest CP-even Higgs field which can yield a large contribution to its mass. This new contribution makes it possible to have a 126 GeV Higgs with order of 200 GeV stop quarks mass and a
Acknowledgements
We thank M. Adeel Ajaib, Aleksandr Azatov and Mansoor Ur Rehman for valuable discussions. This work is supported in part by the DOE Grant No. DE-FG02-12ER41808. We also thank the Bartol Research Institute for partial support.
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