Natural SUSY Predicts: Higgs Couplings

TL;DR

This work presents a predictive framework for Higgs couplings in natural SUSY with an extended Higgs sector, anchored by the existence of a $125$ GeV Higgs and an approximately type-II 2HDM at the weak scale. Higgs observables are shown to depend on four parameters: two capturing loop effects from MSSM states (notably stops and charginos) and two describing Higgs mixing, with the rest of the MSSM contributions either subdominant or constrained by naturalness and experimental data. The authors derive concrete, testable relations among the modified couplings, find that diphoton rates can be enhanced by $\sim4$–$6\times$ the SM value, and establish correlations such as $\mu_{\gamma\gamma}/\mu_{WW,ZZ} \lesssim 1.4$ and $\mu_{bb;AP} \lesssim 1.5$ in viable natural SUSY scenarios. They further explore non-decoupling D-term and F-term extensions, showing that these can shift the bottom Yukawa coupling $y_b$ in characteristic directions, thereby producing distinctive experimental signatures in Higgs decay channels and production modes. Overall, the paper provides a falsifiable, four-parameter framework that connects collider Higgs measurements to underlying natural SUSY dynamics and guides future experimental tests.

Abstract

We study Higgs production and decays in the context of natural SUSY, allowing for an extended Higgs sector to account for a 125 GeV lightest Higgs boson. Under broad assumptions, Higgs observables at the LHC depend on at most four free parameters with restricted numerical ranges. Two parameters suffice to describe MSSM particle loops. The MSSM loop contribution to the diphoton rate is constrained from above by direct stop and chargino searches and by electroweak precision tests. Naturalness, in particular in demanding that rare B decays remain consistent with experiment without fine-tuned cancellations, provides a lower (upper) bound to the stop contribution to the Higgs-gluon coupling (Higgs mass). Two parameters suffice to describe Higgs mixing, even in the presence of loop induced non-holomorphic Yukawa couplings. Generic classes of MSSM extensions, that address the fine-tuning problem, predict sizable modifications to the effective bottom Yukawa, yb. Non-decoupling gauge extensions enhance yb, while a heavy SM singlet reduces yb. A factor of 4-6 enhancement in the diphoton rate at the LHC, compared to the SM prediction, can be accommodated. The ratio of the enhancements in the diphoton vs. the WW and ZZ channels cannot exceed 1.4. The h to bbbar rate in associated production cannot exceed the SM rate by more than 50%.

Figures (11)

• Figure 1:
• Figure 2: Natural range in $r_G$ as a function of $\tan\beta$ (details in Sec. \ref{['sec: stopsummary']}). Solid curves correspond to total fine-tuning, defined in Eq. (\ref{['eq:tot']}), while dashed curves correspond to tuning with respect to the $Z$ boson mass alone, defined in Eq. (\ref{['eq:Dz']}). Note that the stop contribution to $r_G$ is inversely related to $r_\gamma$, see Eq. (\ref{['eq:gamG']}).
• Figure 3: Upper limit on $m_h$ in the MSSM, as function of $\tan\beta$. The solid line corresponds to scenarios with up to 10% total fine-tuning (defined in Eq. (\ref{['eq:tot']})), while the dashed line corresponds to $Z$ boson mass tuning alone (Eq. (\ref{['eq:Dz']})).
• Figure 4: Contours of the Higgs mass, the total fine tuning and $r_G^2$ in the $(m_{Q_3}, X_t)$ plane. We set $\mu = 150$ GeV, $m_{Q_3} = m_{u_3}$ and $X_t=A_t-\mu/\tan\beta$.
• Figure 5: $(r_t-1)$ as a function of $m_A$ for $\tan\beta = 3$ (left) and $\tan\beta = 10$ (right). In addition to the stop-higgsino loop with parameters $A_t$ and $\mu$ as shown, a sbottom-gluino contribution is also included with $m_{D3}=300$ GeV, $M_{\tilde{g}}=800$ GeV. The solid curves are derived by using the value of $r_b$, extracted from FeynHiggs, in our formula Eq. (\ref{['eq:parr']}). The dashed curves are derived using FeynHiggs. Similar results are found for $r_V$.