I am a high energy particle physicist with strong interests in cosmology. My early research involved the introduction of supersymmetry and supergravity into particle physics theories. Some of my key contributions were the introduction of Wilson lines in string vacua to break gauge symmetry to the standard model, a five-dimensional superspace called heterotic M-theory that serves as a string vacuum for realistic models of particle physics and the development of algebraic geometric methods necessary for the construction of gauge connections and explicit evaluation of the low energy spectrum. Within this context, I constructed heterotic vacua with exactly the particle spectrum of the minimal supersymmetric standard model with right-handed neutrinos. These theories were applied to cosmology, where a new theory of the early universe– ekpyrotic cosmology –was introduced based on colliding branes. More recently, I have given detailed renormlization group analyses of realistic superstring particle theories, studying phase transitions in the gauge group and explored their low energy predictions for the LHC. Within this context I has also consider aspects of late-time cosmology, including gauge domain walls, dark matter and baryogenesis. ➤ |

My research interest lies in a variety of problems of elementary particle physics ranging from the study of basic interactions to experimental tests of fundamental theories. My background is in basic theory (effective Lagrangian of superstring and M-theory, supergravity, and general relativity) as well as in phenomenology (implications of extended gauge structures and phenomenological implications of string theories), and I tend to pursue research that bridges the gap between basic theory and the experimental consequences of these theories. My main research contributions have been along the following directions: (a) Constructions of four-dimensional solutions of superstring theory and derivations of their phenomenological implication, (b) Nonperturbative gravitational physics in fundamental theory, (c) Supersymmetric black holes in string theory, and (d) Consistent non-linear Kaluza-Klein compactifications of string and M-theory and studies of M-theory dynamics on spaces with special holonomy. ➤ |

I work on basic questions concerning the nature of space and time and on foundational issues in field theory and string theory. Some of my work has addressed the origin of gravitational thermodynamics and the emergence of spacetime as the effective description of underlying quantum degrees of freedom. My work has also made basic contributions to our understanding of field theory, partly via the AdS/CFT correspondence relating quantum field theories to theories of gravity. Finally, I have has developed new approaches to model building in the complex landscape of string vacua. ➤ |

My research interests lie at the interface of particle physics and cosmology. A central theme of my research program is the possibility that the dark sector includes new light degrees of freedom that couple not only to dark matter but also to baryonic matter. Part of my research efforts over the last few years have focused on the development of screening mechanisms, such as chameleon and symmetron, to explain why such scalars, if light, have escaped detection from laboratory/solar system tests of gravity. The manifestation of these scalar fields therefore depends sensitively on their environment, which in turn leads to striking experimental signatures. Another central theme of my research program is the development of novel theories of the very early universe that can address the traditional problems of standard big bang cosmology and generate density perturbations consistent with observations. Part of my research efforts focus on alternatives to the inflationary paradigm,such as the Ekpyrotic Universe, in which the seeds of structure formation are generated in a long phase of slow contraction before the big bang.➤ |

I study models that may shed light on the fundamental physics of the nature of dark matter, the origin of the baryon asymmetry, and the fundamental origin of inflation or other physics of the early universe. The goal is to use the clues contained in cosmological data to guide the construction of models of new physics. I am also interested in the role that cosmological data can play in constraining models of particle physics beyond the standard model. Such constraints can often provide complementary information about fundamental physics to that provided through terrestrial experiments such as those performed at colliders. My work within these areas has been broad, spanning approaches to dark energy and dark matter; extra dimensional models of particle physics and cosmology; the baryon asymmetry of the universe; inflation and its problems and alternatives; topological defects in cosmology; and the BPS structure of intersecting branes in supersymmetric theories. Specifically, my work has mapped out the space of viable models of the accelerating universe. This has included investigating the microphysical implications of exotic dark energy models, and proposing one of the most-studied approaches to the idea that a modification of general relativity may explain cosmic acceleration. ➤ |

I am a postdoctoral fellow in the high energy group and in the Center for Particle Cosmology. I am interested in gravitational physics, cosmology, quantum and classical field theory, and particle physics. I have worked on the (weak field) n body problem in General Relativity using field theory based methods; this may be of increasing importance as we push our tests of gravity to ever higher levels of sensitivity. Currently I am looking at modifications to the n body gravitational dynamics arising from a class of scalar field theories known as Galileons. I am also actively trying to understand -- from first principles -- how light propagates over cosmological distances. This is crucial, in this data driven era of the discipline, to ensuring that we are interpreting cosmological observations accurately. In particular, light in the perturbed spatially flat FLRW universe we live in does not solely travel on null geodesics, but also travel at all speeds less than unity. To my knowledge, this latter "off-the-null-cone" piece of light has never been examined before in the literature. Other pursuits I am involved in include: (with Tanmay Vachaspati) the calculation of the rate of quantum scattering of cosmic microwave background photons and neutrinos off cosmic strings in motion, i.e. the cosmic 'gravitational Aharonov-Bohm effect'. ➤ |

is a postdoctoral fellow in string theory. She has worked on problems in the AdS/CFT correspondence and has proposed a new Kerr/CFT correspondence between conformal field theories and the geometry in the vicinity of extreme Kerr black holes. |

I am interested in aspects of effective four-dimensional theories arising from string compactifications and their connecting dualities. In this context, the examination of geometrical properties of the compactification geometry is often crucial for the understanding of the physics of the four-dimensional effective theories. My early research covered the study of heterotic orbifold compactifications and their smooth blow-up Calabi-Yau threefolds. Then I moved on to the study of D-branes in Type II and F-theory compactifications. In these theories the exact calculation of holomorphic coupling functions, most notably the superpotential, in the N=1 supersymmetric effective theory is possible. For this calculation I explicitly determined the D5-brane effective action, which relates the effective superpotential to geometric quantities, the periods and certain chain-integrals on the Calabi-Yau threefold. In subsequent works, methods from string dualities like mirror symmetry for Calabi-Yau threefolds and open strings as well as for Calabi-Yau fourfolds relevant for F-theory compactifications were used to calculate these geometrical objects explicitly. Further connections to heterotic compactifications could be drawn exploiting heterotic/F-theory duality for heterotic five-branes. Finally a novel type of duality was proposed relating a compactification with D5- or M5-branes to a dual flux compactification with SU(3)-structure. My current work is focused on an application and extension of the geometrical and String-duality related methods to improve the understanding of non-perturbative string effects in compactifications with N=1 supersymmetry. ➤ |

is a postdoctoral fellow in the high energy group and in the Center for Particle Cosmology. His recent work has involved the modified gravity and early universe cosmology. |