Investigations of particles, quantum fields and extended objects

点击翻译按钮获取中文摘要

We are interested in what is happening to the smallest bits of matter, howthey interact with each other, what a force really is, and how all of thisfits into what we observe around us in the universe. We have a very goodtheory that describes all this for many of the particles and interactions(quantum field theory). By and large, themeasurements line up with the predictions and this is a significant scientificachievement. However, there are large holes in our knowledge and this leavesoppurtunity for work by our research group.For instance, in the centre of atoms lies the nucleus. The nucleus is stronglybound, which means that we don't know how to calculate anything analytically(with a pen and paper) using the standard techniques. Our research has found a clever way of mathematically modelling the nucleususing analytic techniques: the Skyrme model. Now, we can describe all nucleifrom atomic number 1 to 108 using this model. We shall be exploring themathematics behind this in more detail: it has a connection to gravitationaltheories and string theories (mathematical theories that model particles astiny quantum loops). There are also other particles other than nuclei whichare strongly bound, such as B-mesons. For these, sophisticated computer programs must bebuilt which break space and time up into a grid of points, and the quantumfluctuations of the sub-nuclear interactions are simulated using randomnumbers on this lattice. Analytic calculations must be done to match thenumbers obtained on the computer to experimental data. We shall develop thesecalculations, and perform new ones so that data can be used to extract thelevel to which various quarks (for example, the up quark and the b-quark)mix. This helps provide an accurate description of an unexplained phenomenon:how the funny pattern of quark mixing comes about. These calculations alsohelp the extraction of the difference between matter and anti-matter fromexperimental data. String theory is an extraordinarily mathematically rich structure, thatpurports to describe gravity. One variant of it may also even underlie all ofthe interactions between particles that are observed in nature. The tiny loopsbehave like particles unless one probes them at energies that are far too highfor us to reach in current experiments. Some of our research examines the richstructure behind the mathematics of these theories: it turns out thatscattering two particles and scattering three particles have strict relationsbetween the interaction probabilities. Sometimes, truths such as these areeasier understood by mapping one string theory to another one, which has adifferent coupling strength and a different number of space-timedimensions. These "dualities" help us winkle out truths anddeep connections in string theory. We shall be investigating their role in therelations between interaction probabilities. The LHC will start up again after the shut-down around 2015 with double theenergy that it had in 2012. This means that if supersymmetry keeps the higgslight (this is the main motivation for the kind of supersymmetry that the LHCcan discover), the LHC should discover supersymmetric particles in the firstyear of running. Even if this idea of supersymmetry is not present in nature,some other particles or interactions should be responsible for cancelling thequantum fluctuations (a seething random mass of particles popping in and outof existence) which tend to make the Higgs mass some 10^15 times heavier thanhas just been observed at the LHC. These particles should also be discoveredsoon. We shall be interpreting the data, and discriminating various models bycomparing their predictions to any signals that the LHC sees. We should beable to work out which theories are ruled out, and which are favoured.