Is natural higgsino-only dark matter excluded?

The requirement of electroweak naturalness in supersymmetric (SUSY) models of particle physics necessitates light higgsinos not too far from the weak scale characterized by m(weak)~ m(W,Z,h)~100 GeV. On the other hand, LHC Higgs mass measurements and sparticle mass limits point to a SUSY breaking scale in the multi-TeV regime. Under such conditions, the lightest SUSY particle is expected to be a mainly higgsino-like neutralino with non-negligible gaugino components (required by naturalness). The computed thermal WIMP abundance in natural SUSY models is then found to be typically a factor 5-20 below its measured value. To gain concordance with observations, either an additional DM particle (the axion is a well-motivated possibility) must be present or additional non-thermal mechanisms must augment the neutralino abundance. We compare present direct and indirect WIMP detection limits to three natural SUSY models based on gravity-, anomaly- and mirage-mediation. We show that the case of natural higgsino-only dark matter where non-thermal production mechanisms augment its relic density, is essentially excluded by a combination of direct detection constraints from PandaX-II, LUX and Xenon-1t experiments, and by bounds from Fermi-LAT/MAGIC observations of gamma rays from dwarf spheroidal galaxies.Comment: 16 pages with 6 .png figures; some added references for version

WEAK SCALE SUPERSYMMETRY FROM THE MULTIVERSE

The CERN Large Hadron Collider (LHC) has not found any experimental evidence yet for Supersymmetric (SUSY) particles. This has pushed the limits on the masses of SUSY particles in the multi-TeV region high enough to question whether nature is finetuned for SUSY to exists. However, with the introduction of the Electroweak (EW) fine tuning measure, some distinct SUSY models are found to be natural even if they involve highly massive SUSY particles. Naturalness require the superpotential mu parameter mu around 110 - 350 GeV. However, it is not straightforward to explain the origin of such low value of mu and this leads to the SUSY mu-problem. These natural SUSY models provide a higgsino-like Lightest Supersymmetric Particle (LSP) which can serves as a possible DM candidate (considering R-parity conservation) if it has no color or electric charge. Such a thermally-produced LSP alone cannot account for the entire DM content of the universe. At this point the Axion, arising in a different context, rescues the model from under-producing DM. The PQ solution to the strong CP problem, that gives rise to Axion, requires implementation of U(1)_{PQ} symmetry as the fundamental symmetry, which being a global symmetry, is incompatible with the inclusion of gravity. Hence the model suffers from a gravity-spoliation problem. Two hybrid models have been introduced here to simultaneously solve the SUSY mu problem, and the gravity-spoliation problem while still solving the strong CP problem. Since, the string landscape approach arising from multiverse argument could successfully predict the value of the Cosmological Constant, so the possibility that the magnitude of the Peccei-Quinn (PQ) scale is also set by string landscape considerations has been explored. It has also been shown how the string theory landscape affects the mirage mediated SUSY breaking framework and how it leads to a natural mixed decoupling/quasi-degeneracy solution to the SUSY flavor problem and a decoupling solution to the SUSY CP problem. A detailed phenomenological study of two important SUSY search channels in the LHC : 1. Gluino pair production and 2. Wino pair production for the natural SUSY models which has higgsino-like LSP have been done. Two other important channel for SUSY searches in LHC are top squark pair production and higgsino pair production. All of these search channels have been confronted with current LHC constraints and projected constraints from High Luminosity LHC (HL-LHC) and High Energy LHC (HE-LHC) to show what sort of upgradation is needed for LHC to discover or falsify natural supersymmetry

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

While LHC has discovered 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 or at WIMP seach experiments. For the case of weak scale supersymmetry (SUSY), 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 mu 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.Comment: 47 pages; version 2 includes typo fixes and some added discussion; version 3 contains minor re-wording on weak scale limits from Agrawal et a

Is the magnitude of the Peccei-Quinn scale set by the landscape?

Rather general considerations of the string theory landscape imply a mild statistical draw towards large soft SUSY breaking terms tempered by the requirement of proper electroweak symmetry breaking where SUSY contributions to the weak scale are not too far from m(weak)~ 100 GeV. Such a picture leads to the prediction that m_h~ 125 GeV while most sparticles are beyond current LHC reach. Here we explore the possibility that the magnitude of the Peccei-Quinn (PQ) scale f_a is also set by string landscape considerations within the framework of a compelling SUSY axion model. First, we examine the case where the PQ symmetry arises as an accidental approximate global symmetry from a more fundamental gravity-safe Z(24)^R symmetry and where the SUSY mu parameter arises from a Kim-Nilles operator. The pull towards large soft terms then also pulls the PQ scale as large as possible. Unless this is tempered by rather severe (unknown) cosmological or anthropic bounds on the density of dark matter, then we would expect a far greater abundance of dark matter than is observed. This conclusion cannot be negated by adopting a tiny axion misalignment angle theta_i because WIMPs are also overproduced at large f_a. Hence, we conclude that setting the PQ scale via anthropics is highly unlikely. Instead, requiring soft SUSY breaking terms of order the gravity-mediation scale m_{3/2}~ 10-100 TeV places the mixed axion-neutralino dark matter abundance into the intermediate scale sweet zone where f_a~ 10^{11}-10^{12} GeV. We compare our analysis to the more general case of a generic SUSY DFSZ axion model with uniform selection on theta_i but leading to the measured dark matter abundance: this approach leads to a preference for f_a~ 10^{12} GeV.Comment: 24 pages plus 10 figure