Midi-review: Status of weak scale supersymmetry after LHC Run 2 and ton-scale noble liquid WIMP searches

Abstract

After completion of LHC Run 2, the Atlas and CMS experiments had collected of order 139 fb −1 of data at √ s = 13 TeV. While discovering a very Standard Model-like Higgs boson of mass m h 125 GeV, no solid signal for physics beyond the Standard Model has emerged so far at LHC. In addition, no WIMP signals have emerged so far at ton-scale noble liquid WIMP search experiments. For the case of weak scale supersymmetry (SUSY), which is touted as a simple and elegant solution to the gauge hierarchy problem and likely low energy limit of compactified string theory, LHC has found rather generally that gluinos are beyond about 2.2 TeV whilst top squark must lie beyond 1.1 TeV. These limits contradict older simplistic notions of naturalness that emerged in the 1980s-1990s, leading to the rather pessimistic view that SUSY is now excluded except for perhaps some remaining narrow corners of parameter space. Yet, this picture ignores several important developments in SUSY/string theory that emerged in the 21st century: 1. the emergence of the string theory landscape and its solution to the cosmological constant problem, 2. a more nuanced view of naturalness including the notion of "stringy naturalness", 3. the emergence of anomaly-free discrete R-symmetries and their connection to R-parity, Peccei-Quinn symmetry, the SUSY µ problem and proton decay and 4. the importance of including a solution to the strong CP problem. Rather general considerations from the string theory landscape favor large values of soft terms, subject to the vacuum selection criteria that electroweak symmetry is properly broken (no CCB minima) and the resulting magnitude of the weak scale is not too far from our measured value. Then stringy naturalness predicts a Higgs mass m h ∼ 125 GeV whilst sparticle masses are typically lifted beyond present LHC bounds. In light of these refinements in theory perspective confronted by LHC and dark matter search results, we review the most likely LHC, ILC and dark matter signatures that are expected to arise from weak scale SUSY as we understand it today.

Moduli Stabilisation and the Statistics of SUSY Breaking in the Landscape

“…The p i are the fundamental parameters of the theory, while m Z denotes the mass of the Z boson. Taking the parameters to be the various soft terms and µ parameter from the mSUGRA/CMSSM model and requiring 10% fine-tuning, one obtains upper limits of m g ∼ 400 GeV [1]. Most other superpartners are also close to the weak scale (defined as m weak m W,Z,h ∼ 100 GeV).…”

“…9 The atomic principle [83] comes closest in relevance in this context. It can be incorporated within the fine-tuning measure introduced in [84], whose starting point is the expression for the mass of the Z boson in supersymmetry: m 2 Z /2 −m 2 Hu − µ 2 − Σ u u ( t1,2 ) (for details and exact expressions, we refer to the original paper and [1]). Here, Σ u u contains the various radiative corrections [85].…”

“…Furthermore, the theory is supported by several sets of data via radiative corrections: gauge coupling unification, the value of the top mass, and the value of the Higgs mass which falls within the window allowed by the Minimal Supersymmetric Standard Model (MSSM). For a detailed discussion of the recent status of supersymmetric phenomenology, see [1] and references therein. From a more formal point of view, supersymmetry plays a key rôle in making string theory a consistent theory of quantum gravity.…”

“…This dependence gives rise to a large number of vacua with low-energy supersymmetry and reproduces in detail previous expectations following an intuition based on dynamical supersymmetry breaking [34][35][36][37] (although a significant difference is that [34,35] found a logarithmic distribution even in the case of KKLT, which we do not find). 1 LVS models are particularly interesting also because they provide examples where a crucial assumption formulated in [10] can be explicitly shown to hold. This is the assumption that the distribution of the supersymmetry breaking scale is decoupled from the one of the cosmological constant.…”

A dark matter WIMP that can be detected and definitively identified with currently planned experiments

“…Following many brilliant innovations during the past third of a century, current dark matter experiments have achieved amazing sensitivities , imposing stringent constraints on any theoretical dark matter candidate [25][26][27][28][29][30][31][32][33]. In particular, the most simplistic models with supersymmetry (susy) and weakly interacting massive particles (WIMPs) have been disconfirmed by experiment, and this has led some to increasing pessimism about their existence [34][35][36].…”