Higgs Physics and Cosmology

Recently, a new framework for describing the multiverse has/nbeen proposed which is based on the principles of quantum mechanics./nThe framework allows for well-defined predictions, both regarding global/nproperties of the universe and outcomes of particular experiments,/naccording to a single probability formula. This provides complete/nunification of the eternally inflating multiverse and many worlds/nin quantum mechanics. We elucidate how cosmological/nparameters can be calculated in this framework, and study the probability/ndistribution for the value of the cosmological constant. We consider/nboth positive and negative values, and find that the observed value/nis consistent with the calculated distribution at an order of magnitude/nlevel. In particular, in contrast to the case of earlier measure/nproposals, our framework prefers a positive cosmological constant over/na negative one. These results depend only moderately on how we model/ngalaxy formation and life evolution therein./nWe explore supersymmetric theories in which the Higgs mass is boosted by the non-decoupling D-terms of an extended $U(1)_X$ gauge symmetry, defined here to be a general linear combination of hypercharge, baryon number, and lepton number. Crucially, the gauge coupling, $g_X$, is bounded from below to accommodate the Higgs mass, while the quarks and leptons are required by gauge invariance to carry non-zero charge under $U(1)_X$. This induces an irreducible rate, $\sigma$BR, for $pp \rightarrow X \rightarrow \ell\ell$ relevant to existing and future resonance searches, and gives rise to higher dimension operators that are stringently constrained by precision electroweak measurements. Combined, these bounds define a maximally allowed region in the space of observables, ($\sigma$BR, $m_X$), outside of which is excluded by naturalness and experimental limits. If natural supersymmetry utilizes non-decoupling D-terms, then the associated $X$ boson can only be observed within this window, providing a model independent `litmus test' for this broad class of scenarios at the LHC. Comparing limits, we find that current LHC results only exclude regions in parameter space which were already disfavored by precision electroweak data../nRecent LHC data, together with the electroweak naturalness/nargument, suggest that the top squarks may be significantly lighter/nthan the other sfermions. We present supersymmetric models in which/nsuch a split spectrum is obtained through ``geometries'': being/n``close to'' electroweak symmetry breaking implies being ``away from''/nsupersymmetry breaking, and vice versa. In particular, we present/nmodels in 5D warped spacetime, in which supersymmetry breaking and/nHiggs fields are located on the ultraviolet and infrared branes,/nrespectively, and the top multiplets are localized to the infrared/nbrane. The hierarchy of the Yukawa matrices can be obtained while/nkeeping near flavor degeneracy between the first two generation sfermions, avoiding stringent constraints from flavor and $CP$ violation. Through the AdS/CFT correspondence, the models can be interpreted as purely 4D theories in which the top and Higgs multiplets are composites of/nsome strongly interacting sector exhibiting nontrivial dynamics at/na low energy. Because of the compositeness of the Higgs and top/nmultiplets, Landau pole constraints for the Higgs and top couplings/napply only up to the dynamical scale, allowing for a relatively heavy/nHiggs boson, including $m_h = 125~{\rm GeV}$ as suggested by the/nrecent LHC data. We analyze electroweak symmetry breaking for/na well-motivated subset of these models, and find that fine-tuning/nin electroweak symmetry breaking is indeed ameliorated. We also/ndiscuss a flat space realization of the scenario in which supersymmetry/nis broken by boundary conditions, with the top multiplets localized/nto a brane while other matter multiplets delocalized in the bulk.

Advisor: Nomura, Yasunori