Lawrence J. Hall

A natural SUSY Higgs near 125 GeV

A bstractThe naturalness of a Higgs boson with a mass near 125xa0GeV is explored in a variety of weak-scale supersymmetric models. A Higgs mass of this size strongly points towards a non-minimal implementation of supersymmetry. The Minimal Supersymmetric Standard Model now requires large A-terms to avoid multi-TeV stops. The fine-tuning is at least 1xa0% for low messenger scales, and an order of magnitude worse for high messenger scales. Naturalness is significantly improved in theories with a singlet superfield S coupled to the Higgs superfields via λSHuHd. If λ is perturbative up to unified scales, a fine-tuning of about 10xa0% is possible with a low mediation scale. Larger values of λ, implying new strong interactions below unified scales, allow for a highly natural 125xa0GeV Higgs boson over a wide range of parameters. Even for λ as large as 2, where a heavier Higgs might be expected, a light Higgs boson naturally results from singlet-doublet scalar mixing. Although the Higgs is light, naturalness allows for stops as heavy as 1.5 TeV and a gluino as heavy as 3 TeV. Non-decoupling effects among the Higgs doublets can significantly suppress the coupling of the light Higgs to b quarks in theories with a large λ, enhancing the γγ and Wxa0W signal rates at the LHC by an order one factor relative to the Standard Model Higgs.

Freeze-In Production of FIMP Dark Matter

We propose an alternate, calculable mechanism of dark matter genesis, “thermal freeze-in”, involving a Feebly Interacting Massive Particle (FIMP) interacting so feebly with the thermal bath that it never attains thermal equilibrium. As with the conventional “thermal freeze-out” production mechanism, the relic abundance reflects a combination of initial thermal distributions together with particle masses and couplings that can be measured in the laboratory or astrophysically. The freeze-in yield is IR dominated by low temperatures near the FIMP mass and is independent of unknown UV physics, such as the reheat temperature after inflation. Moduli and modulinos of string theory compactifications that receive mass from weak-scale supersymmetry breaking provide implementations of the freeze-in mechanism, as do models that employ Dirac neutrino masses or GUT-scale-suppressed interactions. Experimental signals of freeze-in and FIMPs can be spectacular, including the production of new metastable coloured or charged particles at the LHC as well as the alteration of big bang nucleosynthesis.

Spread Supersymmetry with

A bstractThe discovery of a Higgs boson near 125 GeV, together with the absence of LHC signals for supersymmetry or direct detection signals of dark matter, motivate further study of a particular theory of split supersymmetry. In arguably the theoretically simplest implementation of split, the superpartner spectrum is spread over several decades. The squarks and sleptons are heavier than the gravitino and Higgsinos by a factor MPl/M*, where M* is the mediation scale of supersymmetry breaking and is high, between unified and Planck scales. On the other hand the gaugino masses are 1-loop smaller than the gravitino and Higgsino masses, arising from both anomaly mediation and a Higgsino loop. Wino dark matter arises from three sources: gravitino production by scattering at high temperatures, gravitino production from squark decays, and thermal freeze-out. For reheating temperatures larger than the squark mass, these conspire to require that the squarks are lighter than about 104 TeV, while collider limits on gaugino masses require squarks to be heavier than about 100 TeV. Whether winos constitute all or just a fraction of the dark matter, a large fraction of the allowed parameter space has the gluino within reach of the LHC with 0.1 mm <

\widetilde{W}

ctau widetilde{{_g}}

LSP: gluino and dark matter signals

< 10 cm, leading to displaced vertices. In addition, events with cascades via

A finely-predicted Higgs boson mass from a finely-tuned weak scale

{{widetilde{W}}^{pm }}

750 GeV Diphotons: Implications for Supersymmetric Unification

lead to disappearing charged tracks with

Origins of hidden sector dark matter I: cosmology

c{tau_{{{{{widetilde{W}}}^{pm }}}}}

Minimal mirror twin Higgs

∼ 10 cm. The squarks and sleptons are predicted to be just heavy enough to solve the supersymmetric flavor and CP problems. Thus gluino decay modes may typically violate flavor and involve heavy quarks:

Grand unification and intermediate scale supersymmetry

left[ {overline{t}left( {t,c,u} right)+overline{b}left( {b,s,d} right)} right]{{widetilde{W}}^0}