pMSSM versus complete models and the excellent prospects for top-squark discovery at HL-LHC

TL;DR

This paper critiques the standard practice of interpreting LHC SUSY searches within the pMSSM, arguing that ignoring RG evolution and high-scale dynamics introduces biases that undermine naturalness assessments. By adopting gravity-mediation-inspired NUHM4 with decoupled first/second generation sfermions, the authors demonstrate that natural SUSY typically features light top-squarks in the ~1–2 TeV range and favorable HL-LHC discovery prospects via $\tilde{t}_1\tilde{t}_1^*$ production, alongside higgsino/wino pair channels. The work shows that RG-running heavy sfermions together with non-universal gaugino masses can yield spectra consistent with $m_h\simeq125$ GeV and natural $Δ_{EW}$, while the HL-LHC reach can largely cover the natural parameter space. Overall, the paper advocates for focusing on complete, motivated SUSY models rather than purely phenomenological weak-scale scans, highlighting top-squark discovery at HL-LHC as a highly promising pathway to SUSY detection. The analysis emphasizes decoupling of the first two generations as a natural solution to flavor/CP constraints and positions NUHM4 as a plausible LE-EFT for gravity-mediated SUSY in the LHC era.

Abstract

LHC sparticle search limits are usually performed within the context of simplified models and subsequently interpreted within the 19 parameter phenomenological MSSM (pMSSM) as to how many models avoid search limits for a particular sparticle mass, often including WIMP dark matter constraints. We provide a critical discussion of this procedure and how it can go wrong due to the introduction of new prejudices. By ameliorating these conditions, one is pushed into the more plausible four extra parameter non-universal Higgs model (NUHM4). Implementing a decoupling/quasi-degeneracy solution to the SUSY flavor and CP problems leads to first/second generation sfermions in the tens-of-TeV range. In this case, the natural solutions typically contain top-squarks in the 1-2 TeV range which are accessible to high-lumi LHC (HL-LHC) searches. This search channel, along with higgsino and wino pair production, may allow a nearly complete scan of natural/plausible parameter space by HL-LHC.

Figures (7)

• Figure 1: Plot of weak scale gaugino masses vs. mirage mediation mixing parameter $\alpha$.
• Figure 2: Plot of a) $\Delta_{EW}$ vs $m_{\tilde{g}}$ and b) $\Delta_{EW}$ vs. $m^0$ from pMSSM19 scan S with $10^6$ points.
• Figure 3: Plot of pMSSM scan points in the $m_{\tilde{q}}$ vs. $m_{\tilde{g}}$ plane for a) scan S, b) scan ${\bf S_u}$ with gaugino mass unification $M_3=3.5M_2=7M_1$, c) scan T and d) scan ${\bf T_u}$ with gaugino mass unification. In frame e), we plot results from the SUGRA9 model (scan U) and in f), we plot the scan ${\bf U_u}$ results with gaugino mass unification $M_1=M_2=M_3\equiv m_{1/2}$ at the GUT scale.
• Figure 4: Plot of pMSSM scan points in the $\mu$ vs. $\Delta m^0$ plane for a) scan S, b) scan ${\bf S_u}$ with gaugino mass unification $M_3=3.5M_2=7M_1$, c) scan T and d) scan ${\bf T_u}$ with gaugino mass unification. In frame e), we plot results from the SUGRA9 model (scan U) and in f) we plot the scan ${\bf U_u}$ results with gaugino mass unification $M_1=M_2=M_3\equiv m_{1/2}$ at the GUT scale.
• Figure 5: Plot of a) $\Delta_{EW}$ and b) $\Delta m^0\equiv m_{\tilde{\chi}_2^0}-m_{\tilde{\chi}_1^0}$ vs. $M_2=2M_1$ for a NUHM4 benchmark point with non-universal gaugino masses with $m_0(1,2,3)=5$ TeV, $M_{3}=1.2$ TeV, $A_0=-8$ TeV, $\tan\beta =10$ with $\mu =200$ GeV and $m_A=2$ TeV.