A Non Standard Model Higgs at the LHC as a Sign of Naturalness

TL;DR

The work analyzes how naturalness in supersymmetry shapes Higgs phenomenology at the LHC, focusing on light stops, stop mixing $A_t$, and Higgs mixing angle $\alpha$ as the primary levers altering gluon-fusion production and $h\to\gamma\gamma$ decay. It compares the MSSM with two extensions—DMSSM (extra D-terms) and NMSSM (singlet)—and examines large Higgs mixing scenarios, mapping how $m_A$, $\tan\beta$, and stop-sector parameters influence Higgs rates $\sigma\times\mathrm{BR}$ across different decay channels. The study highlights that natural SUSY typically yields deviations from SM predictions, with possible enhancements up to ~50% in some channels when stops are light and $A_t$ is small, while heavy stops and large mixing tend to suppress signals or hide the Higgs. It emphasizes that measuring ratios of Higgs signal strengths can achieve percent-level precision, enabling precision Higgs coupling tests at the LHC and potentially revealing the scale of new light degrees of freedom. If a ~125 GeV Higgs persists, the MSSM prefers heavier stops and larger tuning, whereas DMSSM/NMSSM can accommodate this mass with lighter stops and enhanced production, offering a tangible path to naturalness at the LHC.

Abstract

Light states associated with the hierarchy problem affect the Higgs LHC production and decays. We illustrate this within the MSSM and two simple extensions applying the latest bounds from LHC Higgs searches. Large deviations in the Higgs properties are expected in a natural SUSY spectrum. The discovery of a non-Standard-Model Higgs may signal the presence of light stops accessible at the LHC. Conversely, the more the Higgs is Standard-Model-like, the more tuned the theory becomes. Taking the ratio of different Higgs decay channels at the LHC cancels the leading QCD uncertainties and potentially improves the accuracy in Higgs coupling measurements to the percent level. This may lead to the possibility of doing precision Higgs physics at the LHC. Finally, we entertain the possibility that the ATLAS excess around 125 GeV persists with a Higgs production cross-section that is enhanced compared to the SM. This increase can only be accommodated in extensions of the MSSM and it may suggest that stops lie below 400 GeV, likely within reach of next year's LHC run.

Figures (11)

• Figure 1: CMS bounds to $m_A$ as a function of $\tan\beta$ from mAbounds.
• Figure 2: $BR(\bar{B}\to X_s\gamma)$$vs$$\tan\beta$ plot. The green-yellow band correspond to the 1$\sigma$-2$\sigma$ experimental bound. All the SUSY particles have been decoupled except 1) $m_A=250$ GeV for the red line, 2) $\mu=m_{\tilde{t}_L}=m_{\tilde{t}_R}=200$ GeV, $A_t=0$ for the dashed blue line, 3) $\mu=m_{\tilde{t}_L}=m_{\tilde{t}_R}=A_t=200$ GeV for the dot-dashed blue line.
• Figure 3: We present Higgs production contours relative to the SM in the MSSM scenario for $m_A=800$ GeV. We block out the region where the Higgs is below the LEP bound. We also draw the contours of $1\%$ (dotted-dashed)and $3\%$ (dotted) tuning. The region allowed by $b\rightarrow s \gamma$ at 95% CL lies above the solid (dashed) line when squarks are at 600 GeV (10 TeV). The shaded region is instead excluded by the LHC.
• Figure 4: Same as Fig. \ref{['MSSMhighmA']}, but with $m_A=250$ GeV.
• Figure 5: Higgs production relative to the SM as a function of the $m_A$ and the lightest stop mass when $A_t=3 m_{\tilde{t}_2}$ in the MSSM case. We also present the same Higgs mass, fine-tuning and $b \rightarrow s \gamma$ contours as in Fig. \ref{['MSSMhighmA']}.