# Elementary Particle Theory - The Standard Model

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.

### Standard Model Phenomenology and Precision Theory

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. Its recent discovery at the Large Hadron Collider (LHC) at CERN has redoubled the need for precision theory at high energies.

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, including the recent finding the Higgs boson. Uncovering the properties of the Higgs boson is a primary goal of the LHC as well as particle colliders currently under study for possible construction, such as the ILC, CLIC and FCC. 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 with 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 and ongoing analysis for the physics of the CERN LHC. These calculations also have immediate consequences for the ongoing studies in the final data analysis for the now closed 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 which Dr. Ward has extended to QCD for LHC applications.

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. Recent progress includes an estimate of the cosmological constant with the result ρ_{Λ} = (0.0024 eV)^{4}.

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