Naturalness versus stringy naturalness with implications for collider and dark matter searches

Shadman Salam,Vernon Barger,Howard Baer

doi:10.1103/physrevresearch.1.023001

Shadman Salam, Vernon Barger + Show 1 more

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https://doi.org/10.1103/physrevresearch.1.023001

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Abstract

The notion of stringy naturalness-- that an observable O_2 is more natural than O_1 if more (phenomenologically acceptable) vacua solutions lead to O_2 rather than O_1-- is examined within the context of the Standard Model (SM) and various SUSY extensions: CMSSM/mSUGRA, high-scale SUSY and radiatively-driven natural SUSY (RNS). Rather general arguments from string theory suggest a (possibly mild) statistical draw towards vacua with large soft SUSY breaking terms. These vacua must be tempered by an anthropic veto of non-standard vacua or vacua with too large a value of the weak scale m(weak). We argue that the SM, the CMSSM and the various high-scale SUSY models are all expected to be relatively rare occurances within the string theory landscape of vacua. In contrast, models with TeV-scale soft terms but with m(weak)~100 GeV and consequent light higgsinos (SUSY with radiatively-driven naturalness) should be much more common on the landscape. These latter models have a statistical preference for m_h~ 125 GeV and strongly interacting sparticles beyond current LHC reach. Thus, while conventional naturalness favors sparticles close to the weak scale, stringy naturalness favors sparticles so heavy that electroweak symmetry is barely broken and one is living dangerously close to vacua with charge-or-color breaking minima, no electroweak breaking or pocket universe weak scale values too far from our measured value. Expectations for how landscape SUSY would manifest itself at collider and dark matter search experiments are then modified compared to usual notions.

Highlights

Supersymmetric models (SUSY) with weak-scale soft SUSY breaking terms provide an elegant solution to the gauge hierarchy problem (GHP) [2,3] but so far weak-scale sparticles have failed to appear at the CERN Large Hadron Collider (LHC) and WIMPs have failed to appear in direct detection experiments [4]
IV, we argue that the paradigm Constrained minimal supersymmetric standard model (CMSSM) SUSY model should be relatively rare on the landscape
To gain some insight on how frequent models with large values of EW might occur in the landscape, we take the limit of Eq (6), wherein the radiative corrections are small so that mZ2 −2mH2 u − 2μ2 and consider SUSY models where mH2 u is driven to large negative values at the weak scale

Summary

INTRODUCTION

Our central conclusion from stringy naturalness is: the soft SUSY breaking terms should be as large as possible subject to the constraint that the value of the weak scale in various pocket universes—with the MSSM as the low-energy effective theory—not deviate by more than a factor of a few from its measured value. II, we present details of how to implement the notion of stringy naturalness including Douglas’ notion of a prior distribution of power-law probability increase in soft term values This is to be combined with a selection criteria enforcing that the value of the weak scale in various pocket universes not deviate from our measured value by a factor of a few. The statistical draw to large soft terms coupled with a weak scale not too far from its measured value, is exactly what is needed for SUSY with radiatively driven naturalness.

PRIOR DISTRIBUTIONS AND SELECTION CRITERIA FOR LANDSCAPE SUSY

WHY THE SM IS LIKELY A RARE OCCURRENCE IN THE LANDSCAPE

RADIATIVE NATURAL SUSY FROM STRINGY NATURALNESS

Living dangerously

Naturalness versus stringy naturalness

WHY HIGH-SCALE SUSY IS LIKELY A RARE

IMPLICATIONS OF STRINGY NATURALNESS FOR

VIII. CONCLUSIONS