Implications of a 125 GeV Higgs for supersymmetric models (1112.3028v3)

Abstract: Preliminary results of the search for a Standard Model like Higgs boson at the LHC with 5 fb-1 data have just been presented by the ATLAS and CMS collaborations and an excess of events at a mass of ~125 GeV has been reported. If this excess of events is confirmed by further searches with more data, it will have extremely important consequences in the context of supersymmetric extensions of the Standard Model and, in particular the minimal one, the MSSM. We show that for a standard-like Higgs boson with a mass 123 < M_h < 127 GeV, several unconstrained or constrained (i.e. with soft supersymmetry-breaking parameters unified at the high scale) MSSM scenarios would be excluded, while the parameters of some other scenarios would be severely restricted. Examples of constrained MSSM scenarios which would be disfavoured as they predict a too light Higgs particle are the minimal anomaly and gauge mediated supersymmetry breaking models. The gravity mediated constrained MSSM would still be viable, provided the scalar top quarks are heavy and their trilinear coupling large. Significant areas of the parameter space of models with heavy supersymmetric particles, such as split or high-scale supersymmetry, could also be excluded as, in turn, they generally predict a too heavy Higgs particle.

• The paper demonstrates that a 125 GeV Higgs imposes stringent constraints on MSSM and related supersymmetric frameworks.
• It shows that no-mixing scenarios require extremely high SUSY-breaking scales while maximal mixing demands large tanβ and heavy top squarks.
• The research informs experimental strategies by clarifying viable SUSY parameter spaces aligned with current LHC observations.

Implications of a 125 GeV Higgs for Supersymmetric Models

The paper "Implications of a 125 GeV Higgs for Supersymmetric Models" explores the ramifications of a Standard Model (SM)-like Higgs boson, specifically with a mass of approximately 125 GeV, as suggested by initial results from the ATLAS and CMS collaborations at the LHC. Such a finding, while preliminary, if substantiated, could significantly impact supersymmetric models, particularly the Minimal Supersymmetric Standard Model (MSSM).

Overview

The discovery of a Higgs boson with a mass of ~125 GeV aligns well with the SM predictions of a light Higgs boson, reinforcing high-precision electroweak data suggesting $M_H < 160$ GeV at the 95\% confidence level. For supersymmetric models, the value of 125 GeV for the Higgs mass imposes stringent constraints. Supersymmetry (SUSY), especially the MSSM and its variants, naturally protects the Higgs mass from large radiative corrections and stabilizes the hierarchy between the electroweak and Planck scales. Moreover, SUSY models allow for gauge coupling unification and offer dark matter candidates via the lightest SUSY particle (LSP).

Phenomenological and Constrained MSSM Scenarios

In the phenomenological MSSM or pMSSM, which allows soft SUSY-breaking parameters to vary freely, the authors demonstrate that for the Higgs mass constraint $123 < M_h < 127$ GeV, substantial restrictions emerge. The no-mixing scenario is wholly excluded unless the SUSY-breaking scale $M_S$ is exceedingly large. Conversely, the maximal mixing scenario necessitates large $M_S$ and $\tan\beta$ values.

For constrained MSSM scenarios, such as mSUGRA, gauge mediated (GMSB), and anomaly mediated (AMSB) SUSY breaking models, the implications are more profound. Minimal AMSB and GMSB predict too light a Higgs mass, positioning themselves as less favorable under the indicated Higgs mass range. In contrast, the gravity-mediated mSUGRA can still accommodate the Higgs mass if heavy scalar top quarks and a substantial trilinear coupling are considered.

Split and High-Scale SUSY Models

The paper further discusses split SUSY, where scalar particles (barring one Higgs doublet) gain large masses at the high scale $M_S$, and high-scale SUSY, which even decouples gauginos and higgsinos, resulting in a sparse low-energy SUSY spectrum. Both these models typically predict too heavy a Higgs and thus face constraints similarly. The requirement for $M_h \approx 125$ GeV predicates split SUSY scenarios on relatively lower energy scales compared to the unification scale and disfavors very high $M_S$ values.

Implications and Future Prospects

The findings depicted illustrate that the MSSM and its extensions face notable constraints and exclusions based on the approximately 125 GeV Higgs, suggesting a necessity for substantial parameter space revisions or alternative SUSY breaking schemes. These constraints propel further exploration in refining and potentially extending supersymmetric models, considering the new empirical data constraints, and underscore the nuanced interplay between theoretical predictions and experimental discoveries.

In theoretical terms, the results imply a potentially reduced desert between the weak scale and higher energy scales, facilitating a renewed focus on characterizing SUSY particles accessible at the LHC. Practically, this aligns well with current LHC operations, guiding both search strategies for SUSY particles and informing refined parameter space scopes in focused experimental hunts.

In conclusion, the paper underscores a critical juncture for SUSY models in light of emerging Higgs observations, blending rigorous constraints with pathways to explore the remnant parameter spaces within MSSM frameworks and beyond. This emphasizes ongoing experimental collaborations to further validate and potentially unlock new insights into fundamental interactions at the interface of current physics paradigms.