Particle Physics

The Hamiltonian for the quantized gravitational and matter fields contains both positive and negative energy particle contributions, which leads through a positive and negative energy symmetry of the vacuum to a cancellation of the zero-point vacuum energy and a vanishing cosmological constant in the presence of a gravitational field. The positive and negative energy particles interact only weakly through gravity. As in the case of antimatter, the negative energy matter is not found naturally on Earth or in galaxies in the universe. We introduce a graviton momentum cutoff ΛG ≤ 2 x10-3 eV that leads to a gravitational stability of the Minkowski spacetime vacuum with a lifetime greater than the age of the universe. A positive energy spectrum and a consistent unitary field theory for a pseudo- Hermitian Hamiltonian is obtained by demanding that the pseudo-Hermitian Hamiltonian is PT symmetric. The quadratic divergences in the two-point vacuum fluctuations and the self- energy of a scalar field are removed. By adopting a Higgsless model of electroweak theory, we remove the fine-tuning associated with a spontaneous symmetry breaking vacuum density. We also postulate that there are no phase transitions associated with QCD and at higher particle physics energy scales, removing all theorized quark-gluon vacuum density condensates and their fine-tuned vacuum densities and cosmological constant contributions.

Theories of gravity having connection as an independent dynamical variable can have a massive spin -2 particle together with the massless graviton in their spectrum. We study the potentiality of such models as a consistent infrared modification of gravity. It will be shown that these models are free from ghost like Boulware-Deser mode in the background of arbitrary torsionless Einstein manifolds. At least for weak for weak enough curvature the dangerous spin zero mode has a healthy kinetic energy in our backgrounds. vDVZ singularity seems to be a generic feature which may be cured by Vainshtein mechanism as in other infrared modified theories of gravity.

We consider a codimension-2 brane inflation scenario in a warped flux compactification of 6D gauged supergravity. The volume modulus of the model is stabilized by means of potentials localized on the regularized background branes. We discuss the cosmological evolution of the world-volume of a probe codimension-2 brane when it moves along the radial direction of the internal space. In order to have slow-roll inflation, we find that the warping of the internal space is required to be weak, in contrast to the string inflation constructions with strong warping. We discuss the parameter range that the inflation is in agreement with the observationally inferred parameters and which furthermore is consistent with the probe brane approximation. We argue that from a multi-brane solution, the backreaction of the probe brane on the weak warp factor is ignorable

Models with two supersymmetric large extra dimensions (SLED) may provide a way to approach both the cosmological constant problem and dark energy. After reviewing these ideas, I shall discuss warped brane world solutions in 6D supergravity, as a laboratory in which to explore SLED and codimension two branes in general. Solving the linearized perturbations for all the bosonic fields, and some of the fermions, we can observe how the corresponding physics compares with 5D models and standard Kaluza-Klein compactifications. These results should help to better our understanding of the cancellations in the 4D effective vacuum energy with SLED.

It is well known that new physics at the electroweak scale could solve important puzzles in cosmology, such as the nature of dark matter and the origin of the cosmic baryon asymmetry. In this talk, I discuss some of the simplest, non-supersymmetric possibilities, their collider signatures, and the prospects for their discovery and identification at the LHC.

A modified version of PQCD considered in previous works is further investigated in the case of a vanishing gluon condensate, by retaining only the quark one. In this case the Green functions generating functional is expressed in a simple form in which Dirac’s delta functions are now absent from the free propagators. The new expansion implements the dimensional transmutation effect through a single interaction vertex in addition to the standard ones in mass less QCD. The results of an ongoing two loop evaluation of the vacuum energy will be presented. The potential is parameterized as a function of the quark mass (defined by the pole of the first corrections to the quark propagator), the assumed finite zero momentum limit of the coupling constant g and the dimensional regularization parameter. The first condensate dependent corrections to the gluon and quark self-energies and propagators are evaluated. Assuming the possibility of fixing a minimum of the potential at the experimental value of the top quark mass =173 GeV, we evaluate the pole of the simplest correction to the propagator of the composite operator describing the quark condensate. Then, alter adopting the idea from the former top condensate models, in which the Higgs field corresponds to the quark condensate, the obtained pole gave a first rough estimate for the Higgs mass =168.2 GeV. Although being inside of the recently experimentally excluded region: 160-170 GeV, this mass value has the chance of being modified by a better approximation being currently considered for the gluon propagator entering its evaluation.

Particle physics, cosmology, and the study of a wide variety of theoretical models – most notably ones involving extra dimensions of space. Randall works on several of the competing models of string theory in the quest to explain the fabric of the universe.

s-channel resonances are predicted by many models of Physics Beyond the Standard Model and it is quite possible that such an object will be discovered in the early years of the LHC program. If this occurs, the task will be to understand its origins. A brief survey of models that predict s-channel resonances will be given, concentrating mainly on extra neutral gauge bosons (Z' 's) arising from extended gauge theories. This will be followed by a description of how to search for a Z' and the resulting Z' discovery reach of the LHC. I will describe various diagnostic measurements to study Z' 's and describe some new observables we have proposed that can distinguish between models that take advantage of the ability to tag 3rd generation fermions.