SHEP Research

Particle physics is the study of the most elementary constituents of matter, the basic forces of nature by which they interact, and their role in the early Universe. The study of particle physics relies on experiments ranging from huge particle accelerators, to deep underground laboratories, to orbiting satellites, to particle simulations using the most powerful computers.

The next generation of such experiments is poised to unlock some of the deepest questions such as why is the Universe so large, and how did it begin and how will it end? What is the nature of dark matter and structure in the Universe? What is the origin of particle masses? Can the forces of nature be unified? Are there extra space dimensions? Why are there three families of matter particles? Can the equations describing the strong interaction be cracked?

With the aid of the new data the theoretical physics group at Southampton aims to shed light on such fundamental questions. We have experts who are currently involved in trying to answer all of these questions, using the latest ideas in lattice theory, quantum field theory, string theory, supersymmetry, and cosmology.

For background information on high energy physics, look at Big Bang Science from the Particle Physics Department at the Rutherford Appleton Laboratory, or Fermilab's Inquiring Minds exhibit.

The following list reflects the current major interests of members of the group.

Lattice Quantum Chromodynamics (QCD)

We work with the UKQCD collaboration of seven British universities and with the US-based Riken-Brookhaven-Columbia (RBC) Collaboration, exploiting our custom-designed 10 Tflop/s QCDOC supercomputer. We have a strong interest in kaon physics and heavy quark (b and charm) physics, calculating quantities needed to test the Standard Model picture of quark flavour-mixing and CP violation as well as to check our understanding of QCD itself. Research on related theoretical techniques complements numerical work.

B-Physics Phenomenology

Results from BaBar and Belle, ongoing work at Fermilab and the imminent startup of the LHC drive our interest in b-quark phenomenology, especially CP-violation and the CKM matrix. Our work includes developing and exploiting our factorisation formalism for two-body hadronic decays such as B -> pi pi and B -> pi K, and extracting the CKM matrix element V_ub from combined experimental and theoretical results for exclusive semileptonic B -> pi decays. We have active links with the LHCb group at RAL.

MHV Methods

New techniques for computing multi-parton scattering related to twistor-theory have been developed in the past few years following Witten's seminal paper on twistor-strings in 2003. As well as their intrinsic interest, these methods look very promising for making manageable the computation of important but complicated processes at the LHC. Here at Southampton we are developing a deeper understanding of these methods via changes of field variables. This has already resolved certain puzzles (so-called missing amplitudes) with these methods. It also points the way to their more general application within the Standard Model and it is this aspect that we are presently researching.

Weak Interaction Corrections

Weak interaction corrections to processes dominated by strong forces are becoming increasingly relevant as present and future accelerators (RHIC, Tevatron, LHC and a LC) probe higher energies with greater precision. Calculations of these effects within the Standard Model are currently being carried out within our group. For example, large weak interaction effects have been identified in jet, Z boson and photon production. This project has already attracted Royal Society, British Council and INFN research grants as well as financial support from the European Science Foundation (ESF) in the form of funding for an ESF Exploratory Workshop.

Collider Phenomenology

We are also engaged in phenomenological studies of the physics potential of present and future high energy particle accelerators in performing tests of the Higgs sector of the Standard Model and of its minimal and non-minimal Supersymmetric extensions, by using numeric calculational methods including full event simulation through Monte Carlo techniques, as implemented in the HERWIG program. Such MC programs are crucial tools needed to analyse present and future collider data, bringing the Southampton group in direct contact with the experiments at BNL, FNAL and CERN. The collider phenomenology program is benefiting from Royal Society, NATO, British Council, Leverhulme and FP6 financial support. These activities are carried out in the framework of the NExT Institute.

Beyond the Standard Model

This area of our research is concerned with addressing the following unresolved puzzles of the Standard Model: The origin of mass (the origin of the weak scale, its stability under radiative corrections, and the solution to the hierarchy problem); The problem of flavour (the problem of the undetermined fermion masses and mixing angles (including neutrino masses and mixing angles); The question of unification (the question of whether the three known forces of the standard model may be related into a grand unified theory, and whether such a theory could also include a unification with gravity). The approaches we develop are based on Supersymmetric Grand Unified Theories (SUSY GUTs) with extra Family Symmetries or String-Inspired models involving D-branes embedded in Extra Dimensions. We are interested in the experimental consequences of these theories at experiments such as the forthcoming Large Hadron Collider or the many Neutrino Experiments.

Particle Physics and Cosmology

This area of our research is concerned with addressing the following unresolved puzzles of the Cosmological Standard Model: The origin of dark matter and dark energy (the embarrassing fact that 20 per cent of the matter and 75 per cent of the energy of the Universe are in a form that is presently unknown); The problem of matter-antimatter asymmetry (the problem of why there is a tiny excess of matter over antimatter in the Universe, at a level of one part in a billion, without which there would be no stars, planets or life); The question of the size, age, flatness and smoothness of the Universe (the question of why the Universe is much larger and older than the Planck size and time, and why it has a globally flat geometry with a very smooth cosmic microwave background radiation). The approaches we develop are based on ideas of Inflationary Cosmology and Leptogenesis which are related to the latest ideas of physics Beyond the Standard Model (see above).

High Temperature and Density QCD

RHIC (Brookhaven) and ALICE (CERN) have renewed interest in QCD at high temperature and density, where the quark gluon plasma shows signs of being a perfect fluid. There is also interest in the idea that cool and dense QCD (as in neutron stars) may be a colour superconductor. We study these phases using thermal models and through weakly coupled string theory duals to strongly coupled gauge theories. The latter, using anti-de-Sitter black holes and their quasi-normal modes, allow the computation of transport coefficients in the plasma as well as computing properties of mesons melting in the background thermal bath.

Strings and Branes

We work on dualities between supersymmetric gauge theories and string theories. Recently we have used the AdS/CFT correspondence and its deformations to understand new descriptions of confinement and chiral symmetry breaking. We are involved in work to realise new dualities of this type. We are also interested in applying these techniques to phenomenological aspects of strongly coupled theories including QCD -- we are currently working on AdS/QCD models of mesons and their application to hadronization in colliders.

If you are interested in a PhD degree with us, there is more information about our PhD programme (and how to apply), plus more general information about physics research at Southampton.