# Research

## Research Topics and Staff

### Cosmology

The principal objective in this subtheme is to discover ways of testing innovative particle physics and quantum gravity theories against hard astrophysical data. A particular strength of the Group is the leading expertise in both theoretical cosmological models and the extraction of phenomenology from the data. We have made significant contributions to the inflationary theory of cosmological perturbations, using both analytical and lattice techniques. One focus is on the physics arising at the end of inflation, particularly in relation to defect production. Alternatives to inflation are also investigated including cyclic universe models and varying speed of light theories. Modified theories of gravity obviating the need for dark matter are another focus. The cosmology group has been pioneering the extraction of phenomenology from quantum gravity in several guises and testing it against data. On the more observational side, we continue to work on the development and application of methods of CMB data analysis, including involvement in a number of experimental efforts such as Planck and Spider.

#### Staff

- Carlo Contaldi

The early universe, cosmological perturbation theory, theory of Inflation, theory and observation of the Cosmic Microwave Background (CMB) and Large Scale Structure (LSS), lensing, dark energy - Joao Magueijo

Early universe cosmology. Phenomenology of quantum gravity. Varying constant theories.

### Quantum Field Theory

Our research in quantum field theory covers a wide range of applications from particle physics and cosmology to effective theories of condensed matter systems and quantum gravity, and it even has connections with the theory of complex networks. We are particularly interested in topological defects and other non-perturbative aspects of field theories both in and out of equilibrium.

#### Staff

- Tim Evans

Nonequilibrium physics, emergence, complexity, networks. - Hugh Jones Non-perturbative methods in quantum mechanics and quantum field theory, non-Hermitian but
*PT*-symmetric Hamiltonians in quantum mechanics, applications to classical optics. - Arttu Rajantie Theoretical particle cosmology, quantum field theory, lattice field theory, topological solitons, magnetic monopoles, MoEDAL experiment, cosmological inflation, preheating, phase transitions.
- Tom Kibble

Quantum field theory and cosmology, especially spontaneous symmetry breaking and topological defect formation. - Ray Rivers

Phase transitions in quantum field theory of condensed matter systems; superconductors, cold Fermi gases; defects. Complex systems and social network analysis; maximum entropy and stochastic cost-benefit analysis of archaeological data.

### String Theory and M-theory

Within this subtheme we work on the physical and mathematical structure of string/M-theory as a proposed framework for unifying the Standard Model of Particle Physics with General Relativity. In addition, string/M-theory provides deep insights into the non-perturbative structure of quantum field theory.

The AdS/CFT correspondence, which relates strongly coupled quantum field theory to weakly coupled gravitational descriptions in higher spacetime dimensions, is one of the most profound discoveries in string/M-theory and is a major focus of the group. Our activities of the Group in this area are supported by two ERC Advanced Grants. One is focussed on exploring integrability structures present in particular systems. The second Is focussed on trying to apply the AdS/CFT correspondence to poorly understood strongly coupled systems that arise in condensed matter physics, such as the high temperature superconductors. The properties of black holes play a central role in this work, as they do in other areas of research in this subtheme. The Group also actively investigates the very rich mathematical structure of string/M-theory. This line of research could lead to a precise mathematical definition of what string/M-theory is. It is also important in connecting string theory with particle phenomenology and in obtaining exact non-perturbative results in quantum field theory. This area is supported by an EPSRC Programme Grant.

#### Staff

- Mike Duff

Unified theories of the elementary particles, quantum gravity, supergravity, Kaluza-Klein theory, superstrings, supermembranes, M-theory and quantum information theory. - Jerome Gauntlett

String and M-theory, quantum field theory, black holes, geometry, gauge-gravity duality and applications to study exotic states of matter that arise in condensed matter physics - Amihay Hanany

Branes and gauge theory dynamics in various dimensions and supersymmetries, Brane Tilings and Quiver Gauge Theories, Moduli spaces and Hilbert series of supersymmetric gauge theories. - Chris Hull

String, M-theory, quantum field theory, duality, geometry, non-geometric configurations, double field theory. - Kelly Stelle

Supergravity, string and M-theory; brane and black-hole solutions; duality symmetry orbits; ultraviolet divergences and counterterm structures; consequences of higher derivatives in effective actions. - Arkady Tseytlin

String theory, gauge theory - string theory relations, AdS/CFT duality and higher spin theory. - Dan Waldram

String and M-theory, quantum field theory, gauge-gravity duality and the geometry underlying string symmetries and backgrounds. - Toby Wiseman

Gravity, black holes, extra dimensions, string theory and gauge-gravity duality. In particular, numerical approaches to solving the Einstein equations in exotic settings and for solving gauge theories relevant for the gauge-gravity duality.

### Quantum Gravity and Foundations of Quantum Mechanics

The Group also works on other approaches to quantum gravity including causal set theory, which posits that spacetime is fundamentally discrete. The foundations of quantum mechanics, including the emergence of classicality, are investigated both in connection to low energy phenomenology and to provide insights into the structure of quantum gravity.

#### Staff

- Fay Dowker

The causal set approach to quantum gravity, quantum gravity phenomenology, quantum cosmology, topological geons, topology change in quantum gravity, foundations of quantum mechanics, the path integral (histories) approach to quantum foundations. - Jonathan Halliwell

Foundations of quantum mechanics, the decoherent histories approach to quantum theory, emergent classicality, time in quantum mechanics, the quantum Zeno effect, quantum cosmology and quantum gravity. - Chris Isham

Quantum foundations, topos theory, quantum gravity.