Elementary Particle Theory

The goal of theoretical elementary particle physics is to understand the most fundamental laws which govern our universe, and to understand the structure and nature of the universe at the deepest level. Theorists at Baylor are approaching these questions from a variety of perspectives.

Lattice QCD

Quantum Chromodynamics (QCD) is the most widely accepted theory of the strong interaction, the force responsible for binding together protons and neutrons in nuclei. The theory postulates that quarks come in three generations (i.e. up/down, charm/strange, and top/bottom), and that each quark carries a three-valued charge called "color" (red, green or blue), which technically means that the quarks fit into a triplet representation of a gauge group SU(3). Each quark has a corresponding anti-quark, which carries "anti-color". The gluons also interact with each other, and the color force becomes very strong at low energies, or when the quarks are far apart. The unique properties and strong coupling make QCD a notoriously difficult theory from a computational point of view.

One fruitful approach to QCD is to introduce a lattice of points and to calculate the interactions on the discretized lattice using advanced computer techniques. This numerical technique is called lattice QCD. Dr. Walter Wilcox is currently collaborating with Dr. Ron Morgan (Baylor Department of Mathematics) in this field at the intersection of computer science algorithms and particle phenomenology. Some of the topics under investigation are: the electric form factor of the neutron, the nature of pion polarizability on the lattice, disconnected quark amplitudes, and chiral perturbation theory. See Dr. Wilcox's home page and the Deflating Eigenvalues website for more information.

If you are interested in joining the research efforts on lattice QCD, you may contact Dr. Wilcox.

Standard Model Phenomenology

The interactions of all known subatomic particles can be described by a single theoretical framework known as the "Standard Model". This model describes matter in terms of leptons (including electrons, neutrinos, ...) and quarks, together with their interactions via force-carriers called "gauge bosons", which include the photon, W and Z bosons, and gluons. The theory is modeled by a gauge group SU(2)_L x U(1) x SU(3)_c which encompasses all known forces except gravity, which is too weak on small scales to have been observed in any particle physics experiments. An important constituent of the standard model is the Higgs boson, which is associated with a Higgs field which causes most of the particles in the standard model to acquire a mass.

Large high-energy physics laboratories such as the ones at FermiLab, SLAC, and CERN, have been very successful in verifying the predictions of the standard model, with the exception of finding the Higgs boson. Discovering and uncovering the properties of the Higgs boson is the primary goal of particle colliders currently under construction, including the Large Hadron Collider (LHC) at CERN. Interpreting the results of high-energy collisions in terms of the standard model requires high precision calculations of the various processes and backgrounds which are to be observed. The theoretical high energy physics phenomenology group at Baylor focuses on rigorous quantum field theoretic investigations an emphasis on the theory of higher order radiative corrections to the SU(2)_L x U(1) x SU(3)_c model of elementary particle interactions. Dr. Ward is engaged in constructing computer realizations of the quantum field theory calculations required for high-precision tests of the Standard Model.

Collision properties are calculated in the context of realistic detector simulations using "Monte Carlo" event generators, which randomly generate scattering events based on the predictions of quantum field theory. The Monte Carlo realization of the radiative corrections has played an essential role in precision Standard Model tests and new physics probes in the LEPII final data analysis, and in the preparation of the physics for the CERN LHC. These calculations also have immediate consequences for the ongoing studies at the lower-energy FNAL Tevatron and for precision Standard Model tests at the B-Factories and at the Φ-Factory. High precision is achieved via resummation methods based on the theory of Yennie, Frautschi and Suura.

The methods developed by Yennie, Frautschi and Suura for resumming the infrared terms in quantum field theory can also be applied to perturbative quantum gravity. Dr. Ward has been investigating this, and in the process has found a new way to analyze classes of quantum gravity graphs which may otherwise have been expected to produce divergences. This may provide a fruitful new approach to the long-standing problem of quantizing gravity.

If you are interested in studying the role of higher-order radiative corrections in particle physics phenomenology, you may contact Dr. Ward.

Superstrings and M-Theory

The Standard Model has done an excellent job of explaining all elementary particle interactions discovered so far, but it is widely believed that there is much physics yet to be discovered beyond the Standard Model. In particular, there are hints that a new symmetry called "supersymmetry" may play an important role in fundamental physics. Also, there is evidence that all of the forces are unified into a single force at higher energies, described by a Grand Unified Theory (GUT). Beyond that, gravity remains to be unified with the other forces, in a Theory of Everything at the "Planck scale". While such investigations are well beyond the reach of experiments, they are important for our conceptual understanding of the fabric of the universe, as well as its origin and ultimate fate. Superstring theory provides a mathematically consistent framework for unifying all of the forces, including gravity, into a single quantum theory describing interacting, vibrating strings. String theory actually comes in a number of apparently different varieties, which are however related by symmetries suggesting a deeper underlying theory which has been called M-Theory.

Dr. Gerald Cleaver has been investigating possible (near)-minimal supersymmetric standard models and supersymmetric grand unified models which may be constructed from superstring theories. Since string theory contains gravity, it provides a means of studying both particle physics and cosmology, and Dr. Cleaver is also active in the Early Universe Cosmology and Strings Group of CASPER. More information can be found at Dr. Cleaver's home page.

If you are interested in investigating the phenomena associated with superstring theory, you may contact Dr. Cleaver.