Theoretical Particle Physics

Particle physics addresses the fundamental laws of nature which are revealed at short distances or high energies. Great progress has recently been made in this field, both by large-scale, high-precision experiments and by theoretical research. Our current knowledge is encoded in the "Standard Model", a theory based on the mathematical concepts of gauge invariance and the Higgs mechanism (which predicts the Higgs boson whose probable discovery has recently been announced).

There are strong reasons, including hints from cosmology and the anomalous magnetic moment of the muon, to believe that the Standard Model is not the ultimate description of nature even at energies accessible in the near future. Furthermore a new mathematical framework, for which string theory is the leading candidate, appears to be required for a consistent description of gravity and the other fundamental forces studied in particle physics. The challenge of discovering the ultimate description of particle physics can be addressed from two sides: by performing high-precision analyses of the wealth of data being produced by the Large Hadron Collider (LHC) and other particle physics experiments, in order to seek the imprint of such an underlying theory; and by showing how string theory naturally leads to the Standard Model. Our group is in the vanguard of both these approaches.

String theory requires, for its mathematical consistency, the microscopic existence of more than the three macroscopic dimensions of space. Therefore a main challenge is to understand how the so-called compactification of these extra dimensions can lead to a theory of the form of the SM, possibly accompanied by additional predictions at LHC energies, and cosmological implications. An intermediate stage in this process is usually a supersymmetric version of the Standard Model, which we expect would reveal itself at high energies, Beyond the Standard Model (BSM)--but perhaps accessible at LHC. Supersymmetry postulates that the particles which constitute matter (fermions) and transmit forces (bosons) are related; the main attraction of the concept is that it explains the minute masses possessed by fundamental particles. Another important topic in string theory, also addressed by our group, is the description of black holes. This places in sharp relief the challenges of reconciling gravity and quantum physics.

QFTs such as the Standard Model and its possible extensions (e.g. supersymmetry) are so complicated that they cannot be solved exactly. For scattering processes at colliders such as the LHC, the only known method is by successive approximations called perturbation theory, where the predictions of the theory are expanded in terms of a small parameter. Members of our group play an internationally leading role in such calculations, which are not only indispensable for the correct interpretation of the experimental results, but also for gaining structural insights which will guide further research.

Although the interactions in a collider are between fundamental particles such as quarks, individual quarks are never observed as reaction products; they are only seen combined as hadrons consisting of 2 or 3 quarks, bound together by the "strong interactions"--a phenomenon called quark confinement. It thus becomes vital to understand confinement and the strong interactions, in order to reconstruct the interactions in colliders from the reaction fragments. This requires novel techniques as most particle physics computations are based on the interactions being weak (as described above). The most effective such technique is the simulation of spacetime by a lattice of discrete points. Our group is involved in the use of high performance computing for this purpose and is especially interested in lattice simulations of hadrons. We are also interested in theoretical mechanisms for confinement.

Particle physics addresses some of the most fundamental questions in science. Experimental and observational facilities and research results on these topics have proved of great public interest. While most theoretical physics research is neither `front page news', nor directly relevant to industry, it is nevertheless an indispensable part of fundamental science. Interpreting LHC results or cosmological observations in terms of fundamental concepts is impossible without theoretical research; and highly popular topics such as quarks, Black Holes, the Higgs particle, strings and Dark Energy were first introduced as theoretical concepts.

Many young people are motivated to study mathematics or physics by these fundamental topics. Thus the presence of leading research groups in fundamental science and their outreach programmes is important, especially to widen participation in structurally weak regions such as NW England.

Since 2006 our group has been organizing the Barkla lectures, a series with one well-publicized open lecture each year by an eminent scientist -- previous speakers include the Nobel laureates Wilczek, Veltman and 't Hooft. The funding of this successful series was originally provided by the university, but now requires new sources. Our group also participates in Cafe Sci (www.juniorcafesci.org.uk), an organisation which brings scientists into schools to lead a discussion about the topic of their research. The normal format is a brief introduction (10-15 minutes) by the scientist followed by 30-40 minutes discussion. For example, Mohaupt visited Sts Peter and Paul School, Widnes, in 2009 to lead a session on Black Holes; and Tatar led a session on String Theory in Jan 2013 in a central Liverpool hotel. Teubner visited Bolingbroke Academy in Runcorn (Sep 2011) and West Kirby Grammar School (Jan 2012) as part of the STEMNET ambassador scheme. Mohaupt has given a talk at Euroscience Open Forum in Dublin.

The Outreach Team of the Department of Mathematical Sciences, together with their colleagues in the other two departments (physics and chemistry) of the School of Physical Sciences at Liverpool, run a vigorous outreach programme. During the academic year 2011-2012, the Outreach Team interacted with 11,000 pupils on 70 school visits. 67% of the schools were in areas having young peoples' Higher-Education participation rates within HEFCE's two lowest classification bands. There is evidence that this programme substantially contributes to attracting pupils to our university. As part of a series of Year-12 masterclasses, the Outreach team are developing a workshop studying the maths involved in finding the Higgs. In particular, it will use simulations to develop a mathematical understanding of the behaviour of subatomic particles, and facilitate the students gaining an understanding of confidence intervals and their role in finding the Higgs.

Two of our recent PhD graduates are continuing in academia; one with a postdoc at IPT, CEA-Saclay, and one supported by an STFC STEP award. However most of our PhD students leave academia after obtaining their degree. Taking part in our cutting-edge research, including international teamwork and conferences, provides them with much improved skills which are then transferred to their new area of work. These improvements include, e.g., the ability to solve non-routine problems independently, time and project management, communication and presentation skills and ability to work when required as part of a team; all of which are highly valued by employers outside academia.

Destinations of our recent (and upcoming) PhD graduates include

* Software Development, Dorset Software
* Postdoctoral research, carbon capture and storage, Newcastle Uni
* Pension actuary, KPMG
* Forecaster, Met Office

Furthermore two of our recent graduates entered teaching via the Graduate Teacher Programme, and will thus contribute indirectly to long-term science and innovation in the UK.