Ph.D : 1978, University of Chicago
Thesis Advisors: Benjamin Lee, Yoichiro Nambu
Thesis: An Sp(4) x U(1) Theory of the Weak and Electromagnetic Interactions
Research Associate: 1978-1980, Brandeis University
Member: 1980-1983, The Institute for Advanced Study
Assistant Professor: 1983-1985, The Rockefeller University
Associate Professor: 1985-1990, University of Pennsylvania
Full Professor: 1990- present, University of Pennsylvania
Adjunct Professor: 1988-1990, The Rockefeller University
Scientific Associate:1992-1993, CERN, Geneva
Member: 1996-1997, The Institute for Advanced Study
Visiting Member: 1997-2000, The Institute for Advanced Study
Humboldt Professor: 1998-2000, Humboldt University, Berlin and the Ludwig Maximillian University, Munich
My primary research interests are on the following three areas.
Superstrings and M-Theory:
I have been doing research in this subject since the first "superstring revolution" in the early 1980's. My principal contributions are the following. In Phys. Lett. B158, 1985, I was one of the people to introduce the concept of Wilson lines into heterotic string theory. Wilson lines were used to break the E6 group to smaller, phenomenologically relevant gauge groups. With my student, Gabriel Cardoso, I calculated the non-holomorphic threshold corrections in superstring theory, showing that these corrections are associated with non-perturbative superpotentials. This work appeared in Nuc. Phys. B369, 1992. In hep-th/9710208, my collaborators and I computed the four-dimensional effective action of the strongly coupled heterotic superstring. Important recent research was the construction the "bane world" scenario from M-theory. This work, which appeared in hep-th/9803235 and hep-th/9806051, is a paradigm for phenomenological brane physics derived from fundamental theory, and is now called heterotic M-theory. In hep-th/9912208 it was shown that heterotic M-theory allows vacuum states containing standard-like models of particle physics.
Cosmology:
I have a long standing interest in applying new ideas in particle physics to issues of early universe cosmology. With Paul Steinhardt, I was among the first to introduce supergravity into the theory of inflation. This work appeared in Phys. Lett. B133, 1983. With several collaborators, I presented a theory for the large scale structure of matter based on non-equilibrium phase transitions and percolation theory. This work was published in Nuc.Phys. B434, 1995. In hep-th/9812052 and hep-th/9902071 I explored basic concepts of cosmological expansion and inflation within the context of the strongly coupled heterotic superstring and M-theory brane universes. It has become clear that all the properties of cosmology, including the flatness, horizon and monopole problems, can be addressed using brane collisions in string and M-theory, and do not require a period of inflation. This alternative to inflation, called the Ekpyrotic Universe, was presented in hep-th/0103239, hep-th/0105199 and hep-th/0108187
Geometry of Superstrings:
Much of my research work in both superstrings, M-theory and in cosmology requires new mathematical methods in topology and geometry, particularly algebraic geometry. I have a strong interest in applying this new mathematics to questions of particle physics. In hep-th/9811168 and hep-th/9901009, I showed how grand unified theories can occur on branes by constructing generalized G-instantons on Calabi-Yau threefolds. This work was extended to produce the standard model on a brane world by constructing specialized holomorphic vector bundles. This very technical mathematical physics was presented in hep-th/0008008, math.AG/0008010 and math.AG/0008011. An important mathematical ingredient of Ekpyrotic cosmology is the "small" instanton phase transition, which was presented for brane collisions in hep-th/0001133.