Higgs Physics and Cosmology

by Alex Roberts

Institution: University of California – Berkeley
Year: 2016
Keywords: Physics; Astrophysics; Theoretical physics; Cosmology; D-terms; Higgs; Multiverse; Supersymmetry
Posted: 02/05/2017
Record ID: 2130930
Full text PDF: http://www.escholarship.org/uc/item/5j51p89g


Recently, a new framework for describing the multiverse has been proposed which is based on the principles of quantum mechanics. The framework allows for well-defined predictions, both regarding global properties of the universe and outcomes of particular experiments, according to a single probability formula. This provides complete unification of the eternally inflating multiverse and many worlds in quantum mechanics. We elucidate how cosmological parameters can be calculated in this framework, and study the probability distribution for the value of the cosmological constant. We consider both positive and negative values, and find that the observed value is consistent with the calculated distribution at an order of magnitude level. In particular, in contrast to the case of earlier measure proposals, our framework prefers a positive cosmological constant over a negative one. These results depend only moderately on how we model galaxy formation and life evolution therein.We 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, gX, 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, σBR, for pp  →  X  →  ℓℓ 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, (σBR, mX), 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..Recent LHC data, together with the electroweak naturalness argument, suggest that the top squarks may be significantly lighter than the other sfermions. We present supersymmetric models in which such a split spectrum is obtained through ``geometries'': being ``close to'' electroweak symmetry breaking implies being ``away from'' supersymmetry breaking, and vice versa. In particular, we present models in 5D warped spacetime, in which supersymmetry breaking and Higgs fields are located on the ultraviolet and infrared branes, respectively, and the top multiplets are localized to the infrared brane. The hierarchy of the Yukawa matrices can be obtained while keeping near flavor degeneracy between the first two generation sfermions, avoiding stringent constraints from flavor and CP violation. Through the…