Mini-Split

TL;DR

The paper argues that the lack of new physics near the weak scale points to a tuned electroweak sector and motivates Split/Split-like scenarios where scalar sparticles are heavy ($m_0$ up to $10^5$ TeV) but gauginos and higgsinos remain accessible at colliders. It analyzes how different mediation mechanisms—Anomaly Mediation, U(1)' mediation, gauge mediation, and triplet mediation—generate characteristic mass hierarchies between scalars and fermions, and how RG running can induce tachyonic scalars affecting EWSB. It identifies two main EWSB patterns tied to $m_{H_u}^2$ and $\mu/B_\mu$ tuning, and discusses the phenomenology of light EWinos, Higgsino LSP scenarios, and possible displaced gluino signatures, along with implications for Higgs couplings such as $h\to\gamma\gamma$. The work emphasizes that collider tests—especially of gaugino/higgsino sectors and potential linear-collider measurements—can illuminate the SUSY-breaking scale and the unification structure even when scalars are heavy.

Abstract

The lack of evidence for new physics beyond the standard model at the LHC points to a paucity of new particles near the weak scale. This suggests that the weak scale is tuned and that supersymmetry, if present at all, is realized at higher energies. The measured Higgs mass constrains the scalar sparticles to be below 10^5 TeV, while gauge coupling unification favors Higgsinos below 100 TeV. Nevertheless, in many models gaugino masses are suppressed and remain within reach of the LHC. Tuning the weak scale and the renormalization group evolution of the scalar masses constrain Split model building. Due to the small gaugino masses, either the squarks or the up-higgs often run tachyonic; in the latter case, successful electroweak breaking requires heavy higgsinos near the scalar sparticles. We discuss the consequences of tuning the weak scale and the phenomenology of several models of Split supersymmetry including anomaly mediation, U(1)_(B-L) mediation, and Split gauge mediation.

Figures (12)

• Figure 1: Natural ratios of gluino, stop, and up-Higgs soft masses as a function of the one-loop RG running between the soft scale $m$ and the messenger scale $\Lambda$, assuming the scalar soft masses are generated radiatively from the gluino mass.
• Figure 2: The fine-tuning in the gluino--lightest stop ($\tilde{t}_1$) mass plane for various values of $\Lambda$ and the LSP mass. The green and yellow shaded areas correspond to the excluded regions from direct gluino and stop production searches at the LHC naturalsusybounds, respectively.
• Figure 3: The Higgs mass prediction as a function of the scalar mass scale in Split and High-Scale Supersymmetry for different values of $\tan \beta$, taken from strumia.
• Figure 4: The scalar mass scale in Split Supersymmetry as a function of $\tan \beta$ for a Higgs mass fixed at 125.5 GeV for no and maximal stop mixing. The 1$\sigma$ error bands coming from the top mass measurement (which dominate over other uncertainties) are also shown.
• Figure 5: The Higgs mass (here chosen to be 125.5 GeV) constrains the scalar and fermion masses to be in the shaded region, for varying $\tan \beta$. The green bands are the 1$\sigma$ error from the top mass measurement for the given value of $\tan \beta$. Gauge coupling unification constrains the parameters to be to the left of the solid bordeaux (1$\sigma$) or dashed bordeaux (2$\sigma$) lines as described in the text. This plot was generated using the results of strumia.