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

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

Revisiting the SUSY μ problem and its solutions in the LHC era

© 2019 authors. Published by the American Physical Society.The supersymmetry (SUSY)-preserving μ parameter in SUSY theories is naively expected to be of order the Planck scale while phenomenology requires it to be of order the weak scale. This is the famous SUSY μ problem. Its solution involves two steps: first forbid μ, perhaps via some symmetry, and then regenerate it of order the scale of soft SUSY-breaking terms. However, present LHC limits suggest the soft breaking scale msoft lies in the multi-TeV regime while naturalness requires μ∼mW,Z,h∼100 GeV so that a little hierarchy (LH) appears with μ msoft. We review 20 previously devised solutions to the SUSY μ problem and reevaluate them in light of whether they are apt to support the LH. We organize the 20 solutions as follows: (1) solutions from supergravity/superstring constructions, (2) extended minimal supersymmetric Standard Model solutions, (3) solutions from an extra local U(1)′ and (4) solutions involving Peccei-Quinn symmetry and axions. Early solutions invoked a global Peccei-Quinn symmetry to forbid the μ term while relating the μ solution to solving the strong CP problem via the axion. We discuss the gravity-safety issue pertaining to global symmetries and the movement instead toward local gauge symmetries or R symmetries, either continuous or discrete. At present, discrete R symmetries of order M (ZMR) which emerge as remnants of the Lorentz symmetry of compact dimensions seem favored. Even so, a wide variety of regenerative mechanisms are possible, some of which relate to other issues such as the strong CP problem or the generation of neutrino masses. We also discuss the issue of the experimental verification or falsifiability of various solutions to the μ problem. Almost all solutions seem able to accommodate the LH11Nsciescopu