The discovery of new physics at hadron colliders such as the Large Hadron Collider that will soon begin operation at CERN is not simple, and often requires some knowledge about the exact nature of the new physics. Two questions stand out as being of critical importance. What are the best candidate theories for physics beyond the Standard Model that address the hierarchy problem? Secondly , how well can the LHC experiment test each of these theories? The research to be performed by the PI is aimed at addressing precisely these two questions. He has proposed two new classes of theories, twin Higgs theories and folded supersymmetric theories, that address the hierarchy problem up to the highest energy scales accessible to the LHC. He plans to study these theories in greater detail, with particular emphasis on their collider signatures. He also proposes to work on ultra-violet completions of these theories that extend their validity to higher energies, with particular attention to their predictions for weak scale physics. He further plans to investigate new models of electroweak symmetry breaking based on these ideas. The broader implications of the research project relate to the PI acting as a bridge between experimentalists and Theorists at the University of Maryland and at Johns Hopkins University. The PI will also participate in the training of undergraduate and graduate students as well as Postdoctoral Fellows. He will help coordinate joint seminars between the University of Maryland and Johns Hopkins University.
The focus of this project was on theories of physics beyond the Standard Model of particle physics. Although the Standard Model is in excellent agreement with experimental data, there are strong reasons to believe that this will not continue, and that current and upcoming experiments will find evidence for new physics. In particular, astronomical observations indicate that the familiar protons, electrons and neutrons of which we are all made comprise only about 20% of the matter in the universe. The remainder is made up of `dark matter' , non-luminous particles whose general properties are completely unknown, and which are not contained in the Standard Model. The Standard Model also does not explain why there is more matter than anti-matter in the universe, or why gravity is so much weaker than the other forces. In this project, new theories were proposed that addressed these questions, and the implications for experiment of these and other theories were studied. Some of the highlights are explained below. My collaborators and I proposed a theory where the observed asymmety between matter and anti-matter is generated at energies accessible to current collider experiments. We showed how signals at these experiments could validate this theory and directly probe the origin of the asymmetry. In other work, my collaboraotors and I have been involved in analyzing data obtained by gamma ray telescopes to search for signals of dark matter in the light coming to us from the center of the Milky Way, and from beyond our galaxy. Although dark matter particles are stable and do not decay, they collide with each other in dense regions of the universe such as the centers of galaxies. In this process they sometimes annihilate, emitting visible matter and light, which can potentially be observed. Scientists are particularly interested in the annihilation rate, since this determines how much of the dark matter present at the time of the Big Bang survives today. Although our analysis of the telescope data did not reveal a dark matter signal, this work has lead to some of the tightest constraints on the rate of dark matter annihilation on the universe. A theorem in relativistic quantum mechanics states that corresponding to every particle in nature there is an associated anti-particle, which has exactly equal and opposite electric charge. For a charged particle like the electron, the corresponding anti-particle has a different charge than the particle, and the two are therefore necessarily distinct. However, because dark matter is electrically neutral, an important open question is whether dark matter particles are distinct from their anti-particles or not. My collaborators and I studied this, and showed how current experiments can potentially resolve this question. We found that in most simple theories, if dark matter primarily interacts with visible matter through the spins of nuclei rather than through their charges, then dark matter particles are identical to their anti-particles. In the course of this project, several graduate students and post-doctoral scientists obtained valuable research experience. Many have obtained higher level positions in academia or industry, and are a valuable addition to the trained scientific workforce.
