Particles, Fields and Extended Objects

The STFC research programme of the Theoretical High Energy Physics Group at
Cambridge University is focused on the fundamental problems of collider
phenomenology, quantum field theory, string theory and gravity, and analysing
class of strongly interacting particles called mesons.

We are analysing and interpreting Large Hadron Collider data from CERN to do
various things: looking for signs of new particles or forces, developing
search and measurement strategies for them, or making high precision
predictions of various theories. The Standard Model is the current model of
particle physics that is well accepted, verified and measured. Most of its
predictions agree well with collider data. However, it leaves many questions
unanswered: why is the Higgs boson so light (the theory predicts it should be
10^15 times heavier)? what is dark matter? how come the universe is made of
matter and not anti-matter? Models of new physics explain some or all of
these, and typically predict new particles. Finding these (or ruling them out)
is a priority in order to test such theories. The Large Hadron Collider has
just upgraded to its highest energy, 13 TeV, which means that heavier
particles may be found that haven't been seen before. There have been exciting
unexpected "bumps" in data recently: for example too many pairs of particles
of light (photons) seem to be coming out of the proton proton collisions with
an energy equivalent to 750 proton masses. If it is verified, this would be a
signal of a new particle which decays to two photons, and the question is:
where does this fit and what does it mean? We are actively working on such
questions.

Quantum field theory provides a very successful description of known particle
interactions. However, special techniques are required to get predictions when
the interactions are strong. We shall be developing various techniques to
improve these, and to provide understanding of the underlying dynamics.
String theory is an extraordinarily mathematically rich structure, that
purports to describe gravity. One variant of it may also even underlie all of
the interactions between particles that are observed in nature. The tiny loops
behave like particles unless one probes them at energies that are far too high
for us to reach in current experiments. Some of our research examines the rich
structure behind the mathematics of these theories: it turns out that
scattering two particles and scattering three particles have strict relations
between the interaction probabilities. Sometimes, truths such as these are
easier understood by mapping one string theory to another one, which has a
different coupling strength and a different number of space-time
dimensions. These "dualities" help us winkle out truths and
deep connections in string theory. We shall be investigating their role in the
relations between interaction probabilities.
We are analysing instabilities in theories of black holes, depending on the
number of dimensions and how bent the underlying space-time is.

Some particles
are strongly bound states of smaller ones, such as B-mesons.
For these, sophisticated computer programs are
built which break space and time up into a grid of points, and the quantum
fluctuations of the sub-nuclear interactions are simulated using random
numbers on this lattice. Analytic calculations must be done to match the
numbers obtained on the computer to experimental data. We shall develop these
calculations, and perform new ones so that data can be used to extract the
level 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 also
help the extraction of the difference between matter and anti-matter from
experimental data.

The research proposal is aimed at understanding matter, forces, space and
time. We cannot predict when fundamental research will translate into
new technology, however history implies that fundamental discoveries eventually
leads to no spin-offs or direct applications. One example in collider
physics (such as is done at the LHC) is proton cancer therapy. In any case,
the science that we do has an immediate impact on the integration of science
into culture. Our field inspires and attracts people, and our investigators
have a collective expertise and skill as public communicators. This already
benefits those who are stimulated by acquiring new knowledge about science.
Our blogs also influence thinking about science and society (for example in
terms of evidence-based policy). We are motivators for young people to follow
a career in science.
Part of our work is to give train students in creative and analytic thinking,
skills that are directly relevant for the UK economy for those that leave
academia and go into industry (often scientific industry) or financial
services.

We will communicate the results of our research to the general public (for
example in music and other cultural festivals) and to
school children. Our goal is to both educate and to inspire, to explain the
wonder of
the natural world, the excitement of being involved in cutting edge research
and the joy of understanding something that no one else on the planet
knows. Members of the group have media connections through radio, television,
print and the internet and we will continue to develop these.