The Large Hadron Collider will soon unravel the mystery of electroweak symmetry breaking (EWSB). The PI's propose to study new models of EWSB using the AdS/CFT correspondence as an essential tool. Three types of models will be considered: D-brane models, new 5D models that are motivated by D-brane constructions, and 5D models in AdS space. Models of the first type are D-brane constructions that are known to break chiral symmetries dynamically. Models of the second type have a topology that is motivated by these D-brane systems, but are five-dimensional and otherwise phenomenologically inspired. Models of the third type take a well-known holographic model of QCD in 5D AdS space as a template for a dynamical EWSB sector. The PI's will study a range of phenomenological issues including precision electroweak constraints, unitarity, naturalness, and electroweak baryogenesis. The Pi's also propose to study the phenomenology of the Lee-Wick Standard Model. This is an extension of the Standard Model that is free of quadratic divergences and which involves new particles at the TeV scale that participate in the cancellation of divergences. A simple holographic model of QCD defined on a slice of five-dimensional AdS space has proved to be remarkably successful in describing the masses and couplings of the pseudoscalar, vector and axial-vector mesons. Motivated by the observation that baryons appear naturally in stringy holographic models as topological solitons, the PI's propose to investigate whether baryons can also be described as stable solitonic objects in 5D holographic models of QCD that are formulated in AdS space. The broader impact of the proposed work is that it will stimulate interdisciplinary collaborations, further the education of undergraduate and PhD research students, involve members of under-represented groups, and promote high-energy particle physics in the southeastern part of the United States. The PI's participate in several REU activities at William and Mary and have supervise seven undergraduate theses.
The Principal Investigators and their students developed and analyzed a variety of models of particle physics relevant to current collider and astrophysics experiments. As new data has become available from these experiments, the PIs and their students explored the consequences for the Standard Model of particle physics and its various extensions. Recently, several astrophysics experiments have observed an excess of positrons and gamma rays in our galaxy. The PIs and their students have studied a number models in which this excess can be naturally explained. In several papers, the PIs have considered the possibility that dark matter in the galaxy might be decaying into the observed positrons and gamma rays. Some of the proposed models made additional predictions that can be tested in future astrophysics and collider experiments. The PIs also studied models of electroweak symmetry breaking that might be discovered at the Large Hadron Collider (LHC). Several papers focused on one of the simplest extensions of the Standard Model, the two-Higgs doublet model, and how it might emerge at the LHC. Implications of the recent evidence of a Higgs boson at 125 GeV were taken into account in this work. Other papers written by the PIs explored extensions of the Standard Model with additional generations of matter, supersymmetry, extra spatial dimensions, and unusual neutrino properties. The PIs have investigated how these and other possibilities for new physics might be discovered at the LHC. The PIs have also used techniques motivated by string theory to study aspects of the strong interactions, including unusual states of dense nuclear matter. In summary, the results of the PI’s funded research have helped to develop and constrain the landscape of possibilities for the spectrum of fundamental particles and their interactions. The PIs have worked closely with both graduate students and undergraduates on this project. Several papers were written with undergraduates who are now physics graduate students. One of the undergraduates and one of the graduate students were female, contributing to the diversity of the field. The PIs have given numerous "public interest" talks on topics ranging from the Physics of Chocolate to the Higgs boson.
