Elementary Particle Theory

Supersymmetry postulates that every particle has a massive "shadow" partner. One of these-neutralino-might make up dark matter.
Feynman diagrams involving Higgs boson, top quark, and squark in supersymmetric extension of the Standard Model.
Gluon-gluon fusion into Higgs boson expected to occur in LHC: Lowest order and next leading order Feynman diagrams.
The Grand Unified Theory of strong, weak, and electromagnetic interactions predicts new force carriers that lead to proton decay

The ultimate goal of elementary particle physics is to understand the basic constituents of matter and their interactions in terms of an economical set of principles. This hope for unified understanding of natural laws, cherished by our early pioneers such as Newton, Maxwell, and Einstein, appears to have come very close to fulfillment during the past two decades with the discovery of unified gauge theories of fundamental interactions.

Theoretical particle physics attempts to develop the models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments. An elementary particle theorists typically studies and does research in one or a few of the following categories:

General Theorists:

  • General Theorists have an interest in exploring the deeper physical meaning of the theory itself, typically exploiting various mathematical techniques to gain insight into its physical nature. This type of particle physicist is often found producing general theorems or equations that others may use to simplify their calculations.

Model Building:

  • A Model Builder attempts to construct an extension (at higher energies or smaller distances) of the Standard Model of Particle Physics in such a way as to either fix a problem inherent in this theory (or one of its extensions), or to explain some phenomenon that the experimentalists have detected. This work is often motivated by the hierarchy problem and is constrained by existing experimental data. It may involve work on supersymmetry, alternatives to the Higgs mechanism, extra spatial dimensions, Preon theory, combinations of these, or other ideas.

Phenomenology:

  •  A Phenomenologist is usually occupied with explaining some experimental phenomenon by doing an actual calculation of an experimental process using a particular model. The end result is an actual number that can be compared with current experimental data or relayed to experimentalists so that they may design an experiment to test the validity of the predicted value.

String Theory:

  • String theorists attempt to construct a unified description of quantum mechanics and general relativity by building a theory based on small strings, and branes rather than particles.  The fundamental building blocks of nature in the view of String Theory are extended objects (having at least one length dimension), instead of, like in traditional particle physicists, point particles (objects of zero size). String Theory is still young and consequently not enough is known about it: in fact, it remains a major goal of String Theorists to demonstrate that the theory describes nature. On the other hand, if the theory is successful, it may be considered a "Theory of Everything".

Other Areas:

Particle physicists internationally agree on the most important goals of particle physics research in the near and intermediate future. The overarching goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the Standard Model. There are several powerful experimental reasons to expect new physics, including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at accessible energy scales. Most importantly, though, there may be unexpected and unpredicted surprises which will give us the most opportunity to learn about nature.

Theory & Computation: 
Selected Publications: 

S. M. Barr, New type of seesaw mechanism for neutrino masses, Phys. Rev. Lett. 92, 101601 (2004). [PDF]

N. Fortson, P. Sandars, and S. M. Barr, The search for a permanent electric dipole moment, Phys. Today 56(6), 33 (2003). [PDF]