Particle Physics

The warped geometry present in Randall-Sundrum (RS) models provides an elegant means by which to generate stable scale hierarchies. Given the famous hierarchy problem of the Standard Model, and the relatively small number of known mechanisms which may solve it, the RS model has deservedly received a lot of attention. However the construction of a completely realistic RS model remains difficult and requires a number of modifications beyond the minimal framework. In this talk I will give an overview of the RS model, the difficulties encountered in realistic implementations and the types of modifications necessary to address them.

As LHC era is coming close, all sorts of ideas about physics beyond the standard model are being explored. It remains possible that a strong-coupling chiral theory could appear at TeV scale. When it comes to strongly coupled theories, lattice is still the most reliable and straightforward regularization method. But defining a chiral gauge theory on the lattice is formidable on its own. In this talk, I will present some most recent theoretical developments in attempt to tackle this problem, and explain some general theorems we proved for generic chiral gauge theories on lattice. These results should be useful in future studies in the field. I will also present some numerical results suggesting that the idea of constructing a chiral gauge theory by decoupling the mirror fermions using a high scale strong- coupling gauge symmetric phase suffers from severe constraints. I will end my talk by a brief outlook on how one may hope to reach a conclusive prove on the feasibility of this idea in general.

One of the most challenging problems in theoretical physics today is the so called cosmological constant problem. While current observations are consistent with the prediction of GR with an unexplainable tiny cosmological constant, it remains possible that it\'s the deviation of the law of gravity at large distance from Einstein\'s theory that resolves the puzzle. In this talk, I will briefly review some of the theoretical attempts we made along this line, in particular, the so called \'classically constrained gravity\' and its implications in quantum cosmology. I will also present some most recent study on massive spin-2 particles in De Sitter space, and describe a model, initially motivated by DGP theory, which allows one to explore the Higuchi forbidden mass range of the graviton on the De Sitter background.

Extension of the minimal supersymmetric standard model (MSSM) that include a U(1)\' gauge symmetry are motivated by top-down constructions and offer an elegant solution to the MSSM mu problem. In this talk I will describe some of the opportunities that such models offer, such as a new mechanism for mediation of supersymmetry breaking, as well as some of the challenges in constructing viable supersymmetric U(1)\' models.

I will discuss a simple two-dimensional theory, whose unparticle sector is a modification of the Schwinger model, that gives new insights into the qualitative features of unparticle physics. I will analyze the transition between the short-distance perturbative physics and large-distance unparticle behavior. Then I will show how to compute processes that involve unparticle self-interactions, for which nontrivial higher n-point functions of the conformal theory are essential.

Recent experimental results seem to require a dramatic change in our view of the dark matter sector. In this talk I will describe the reasons for this change and the ingredients required to describe the new data. I will present possible field theories that give rise to such phenomena and delineate the resulting collider signatures.

Recent PAMELA and ATIC results may represent a breakthrough in dark matter searches beyond its gravitational imprint. After briefly reviewing the possible (classes of) explanations for the observed excesses in positron and electron cosmic ray fluxes I will focus on a two component dark matter model that may provide an explanation for large boost factors needed in the dark matter annihilation interpretation of the signals.

The interpretation of virtual gluons as ghosts in the non-linear gluonic structure of QCD permits the formulation and realization of a manifestly gauge-invariant and Lorentz covariant theory of interacting quarks/antiquarks, for all values of coupling. The simplest example of quark/antiquark scattering in a high-energy, quenched, eikonal model at large coupling is shown to be expressable as a set of finite, local integrals which may be evaluated numerically; and before evaluation, it is clear that the result will be dependent only on, and damped by increasing momentum transfer, while displaying physically-reasonable color dependence in a manner underlying the MIT Bag Model and an effective, asymptotic freedom. These results are compatible with an earlier, instanton, field-strength analysis of Reinhardt, et.al.