Research Statement

In the last 50 years, there has been a tremendous advance in our understanding of the elementary particles and their interactions. We now have a mathematically consistent theory of the strong, electromagnetic, and weak interactions-the standard model-most aspects of which have been successfully tested in detail at colliders, accelerators, and non-accelerator experiments. It also provides a successful framework and has been strongly constrained by many observations in cosmology and astrophysics. The standard model is almost certainly an approximately correct description of Nature down to a distance scale 1/1000^th the size of the atomic nucleus. However, nobody believes that the standard model is the ultimate theory-it is too complicated and arbitrary and leaves too many questions unanswered. Therefore, most current activity is directed towards discovering the new physics which must underly the standard model. One approach, exemplified by superstring theories, is to try to develop a "theory of everything". However, promising ideas involve incredibly short distance scales, and it is challenging to make contact with accessible energies at present. Another direction is to build larger accelerators to directly search for new particles and interactions, and much attention is focussed on the Large Hadron Collider (LHC), which is currently starting up. An important complementary approach is to subject the standard model to diverse high-precision tests to determine how good it is and where it might break down. Finally, there are probes from the important overlaps of particle physics with cosmology and astrophysics. All of these approaches are likely to be essential in understanding what underlies the standard model. It is my hope that within the coming decades we will be able to combine progress in these directions to develop and test the essential aspects of a new standard model of everything, which incorporates the microscopic interactions, quantum gravity, and the origin of the Universe, and describes Nature down to the Planck scale,  ∼ 10⁻³³ cm. My research has been directed towards the theoretical interpretation of the various experimental and observational probes, and the phenomenological implications of fundamental theories-i.e., in connecting theory and experiment. For over three decades much of my effort has involved the interpretation of high-precision tests of the standard model, and has exploited the fact that the global analysis of many experiments often yields more information than the individual experiments alone. Such global analyses involve collecting the data, deriving uniform and accurate theoretical formulas to interpret it, developing expressions for the possible effects of new physics, and fitting the data to search for or set limits on new physics. A related effort has been a study of the existing constraints, physics and cosmological implications, and the discovery/diagnostic potential at present and future colliders for classes of extensions of the standard model and its minimal supersymmetric extension, especially those types that frequently occur as theory-motivated remnants of specific superstring constructions. These include additional possible gauge bosons (especially heavy Z' s), extended Higgs/neutralino sectors, and exotic fermions (with non-standard weak interactions). Other recent work has involved possibilities for studying CP violation at the LHC and new methods for mediating supersymmetry breaking between the ordinary and a quasi-hidden sector. Other phenomenological areas in which I worked extensively in the past include chiral symmetry breaking and its consequences, and theoretical models for neutrino mass and their laboratory, astrophysical, and cosmological implications. In terms of more fundamental theory, I have had a long standing interest in grand unified theories and their consequences. More recently, I have become interested in the phenomenological consequences of semi-realistic superstring compactifications. My collaborators and I have examined classes of string constructions and specific models, with emphasis on their consequences for the masses of the quarks and charged leptons, standard and non-standard mechanisms for generating small neutrino masses, and the most likely types of observable new physics at the TeV scale. I have written an advanced textbook, The Standard Model and Beyond (CRC press, December 2009), a second edition (June, 2017), and a colloquium-level monograph Can the Laws of Physics be Unified? (Princeton University Press, March 2017).