The 125 GeV Higgs and Electroweak Phase Transition Model Classes

Recently, the ATLAS and CMS detectors have discovered a bosonic particle which, to a reasonable degree of statistical uncertainty, fits the profile of the Standard Model Higgs. One obvious implication is that models which predict a significant departure from Standard Model phenomenology, such as large exotic (e.g., invisible) Higgs decay or mixing with a hidden sector scalar, are already ruled out. This observation threatens the viability of electroweak baryogenesis, which favors, for example, a lighter Higgs and a Higgs coupled to or mixed with light scalars. To assess the broad impact of these constraints, we propose a scheme for classifying models of the electroweak phase transition and impose constraints on a class-by-class basis. We find that models, such as the MSSM, which rely on thermal loop effects are severely constrained by the measurement of a 125 GeV Higgs. Models which rely on tree-level effects from a light singlet are also restricted by invisible decay and mixing constraints. Moreover, we find that the parametric region favored by electroweak baryogenesis often coincides with an enhanced symmetry point with a distinctive phenomenological character. In particular, enhancements arising through an approximate continuous symmetry are phenomenologically disfavored, in contrast with enhancements from discrete symmetries. We also comment on the excess of diphoton events observed by ATLAS and CMS. We note that although Higgs portal models can accommodate both enhanced diphoton decay and a strongly first order electroweak phase transition, the former favors a negative Higgs portal coupling whereas the latter favors a positive one, and therefore these two constraints are at tension with one another.Comment: 35 pages, 7 figure

Optimisation of Novel Elliptically-Based Web Opening Shapes of Perforated Steel Beams

A new study was carried out and presented herein, on the optimisation of novel elliptically-based web opening shapes which enhance the structural behaviour of the perforated beams as well as lead to economic design in terms of both manufacture and usage. The finite element (FE) model used in the study was validated against experimental work conducted by the authors and the results of the comprehensive study are presented in this research paper. For ease of comparison, the yield patterns and deflected shapes of the perforated beams are presented at three characteristic load level points. Finally, shear-moment interaction FEM curves are presented for six different web opening shapes to allow for easy use of the empirical design formulas that have previously been proposed by the authors in a complementary research paper. An overall study of many standard and non-standard web opening shapes, it was shown that perforated beams with vertical and inclined classic elliptical web openings (3:4 width to depth ratio) behave more effectively compared to perforated beams with conventional circular and hexagonal web openings, mainly in terms of stress distribution and local deflection. Therefore, perforated steel beams with large novel elliptically-based web openings with short critical opening length at the top and bottom tee-section as well as straight-line edges are presented for first time and examined in the current research programme