"Natural SUSY vs. the LHC"

 

We derive the latest constraints on various simplified models of natural SUSY with light higgsinos, stops and gluinos, using a detailed and comprehensive reinterpretation of the most recent 13 TeV ATLAS and CMS searches with $\sim 15$~fb$^{-1}$ of data. We discuss the implications of these constraints for fine-tuning of the electroweak scale. A key aspect of this work is an improved calculation of the tuning measure (including two-loop effects, a proper treatment of UV vs.~IR masses, and threshold effects), which significantly relaxes the naturalness bounds on the stop and gluino masses. Despite this, natural SUSY is under pressure from the LHC.

 

While the most "vanilla" version of SUSY (the MSSM with R-parity and flavor-degenerate sfermions) with 10\% fine-tuning is ruled out by the current constraints, models with decoupled valence squarks or reduced missing energy can still be fully natural. However, in all of these models, the mediation scale must be extremely low ($<100$~TeV). We conclude by considering the prospects for the high-luminosity LHC era and discussing further model-building directions for natural SUSY that are motivated by this work.