<b>3rd UK-QFT Meeting</b>: <i>Non-Perturbative Quantum Field Theory and Quantum Gravity</i>

Friday 24 Jan 2014, 10:00 → 19:30 Europe/London

Shackelton Building Lecture Theatre A (44/1041) (University of Southampton)

Ismail Hamzaan Bridle (University of Southampton)

The meeting aims to bringing together Students, Postdoctoral Researchers and Senior Scientists to discuss recent trends in advanced Quantum Field Theory and Quantum Gravity.

The format of the meeting is a series of informal talks to allow for discussion and the exchange of ideas amongst participants. We plan for up to 8 slots for short presentations depending on demand and one final longer seminar given by Frank Saueressig (Mainz).

This is the third meeting of it's kind and details on the previous two can be found on the following:
1st UK-QFT Meeting: "Non-perturbative aspects in field theory" (KCL)
2nd UK-QFT Meeting: "Advances in quantum field theory and gravity" (Sussex)


 

10:00 → 10:30 Arrival and Coffee

10:30 → 11:00 Holographic Renormalisation

I will give a brief introduction to holographic renormalization and discuss recent applications.

Speaker: Kostas Skenderis (University of Southampton)

10:30 → 12:30 Morning Presentations

Convener: Mr Ismail Bridle (University of Southampton)

11:00 → 11:30 Effective Dispersion Relations in Z=2 Lifshitz QED

In studies of Lorentz-symmetry violating QFTs, phenomenological viability is often claimed from purely classical considerations with surprisingly little attention given to the effects of quantum corrections, presumably due to their supposed "smallness" and the difficulty of their calculation. In this talk I shall give a concrete example of a model in which this assumption is shown to be false- a model of QED with Lifshitz scaling (i.e. a scaling anisotropy between space and time). I shall discuss the relevant 1-loop corrections of this theory and some of the more interesting technicalities that arose in its renormalisation.

Speaker: Mr James Brister (King's College London)

11:30 → 12:00 Asymptotic safety from Ricci scalars and beyond

I plan to discuss aspects of the asymptotic safety conjecture for gravity for actions constructed from Ricci-scalar and -tensor invariants.

Speaker: Daniel Litim

12:00 → 12:30 Discrepancies of the Single Field Approximation in Asymptotic Safety

Motivated by recent studies at Southampton (Morris and Dietz, JHEP 1307:064, 2013) of the f(R) approximation in Quantum Gravity have found that, in certain formulations of the truncated RG flow, the space of relevant eigenoperators is empty. We demonstrate with the well understood model of a single component scalar field in d=3 dimensions that the Single Field Approximation (SFA) used in Quantum Gravity, where we identify the background field as the full classical field, can lead to discrepancies in the fixed point structure. In our scalar field example, use of the SFA gives us new non-trivial fixed point but we lose the expected Wilson-Fisher fixed point. As a means to remedy this we apply the modified shift Ward Identity, recovering the standard result and demonstrating a form of universality among RG flows.

Speaker: Mr Ismail Bridle (University of Southampton)

12:30 → 13:30 Lunch Break

Details TBC

13:30 → 14:00 Supergravity, the super-Higgs effect and inflation

Supergravity is a very well motivated theoretical paradigm, which, if it exists, must be broken at low energies. As such, understanding the origin of this symmetry breaking is key for making contact with known phenomenology. We detail a non-pertubative breaking mechanism for supergravity in the super-Higgs effect realised via gravitino condensation, which also provides a UV motivated, phenomenologically viable inflationary mechanism at no added cost. In practice this is achieved by direct computation of one loop corrections in relevant supergravity models, allowing the analytic form for the (quantum) condensate potential to be explicitly found. We present results consistent with known physics, and detail current research establishing contact between this scenario and the NMSSM.

Speaker: Mr Nicholas Houston (King's College London)

13:30 → 15:30 Afternoon Presentations

Convener: Mr Ismail Bridle (University of Southampton)

14:00 → 14:30 Manifest Causality and the Path Integral

We describe the calculation of manifestly-causal transition amplitudes over finite space-time domains. Specifically, we show how such amplitudes arise naturally within the path-integral representation of the Schwinger-Keldysh closed-time path formalism of non-equilibrium thermal field theory. We conclude by highlighting a difference in the resulting loop structure compared with the usual scattering-matrix case and discuss potential impacts on resummation.

Speaker: Dr Peter Millington (University of Manchester)

14:30 → 15:00 Sequestering the Standard Model Vacuum Energy

We propose a very simple reformulation of General Relativity, which completely sequesters from gravity all of the vacuum energy from a matter sector, including all loop corrections and renders all contributions from phase transitions automatically small. The idea is to make the dimensional parameters in the matter sector functionals of the 4-volume element of the universe. For them to be nonzero, the universe should be finite in spacetime. If this matter is the Standard Model of particle physics, our mechanism prevents any of its vacuum energy, classical or quantum, from sourcing the curvature of the universe. The mechanism is consistent with the large hierarchy between the Planck scale, electroweak scale and curvature scale, and early universe cosmology, including inflation. Consequences of our proposal are that the vacuum curvature of an old and large universe is not zero, but very small, that wDE≃−1 is a transient, and that the universe will collapse in the future.

Speaker: Antonio Padilla (University of Nottingham)

15:00 → 15:30 Asymptotically Safe Starobinksy inflation

I will discuss how Starobinsky inflation can be successfully embedded in a quantum gravitational context, and in particular within the scenario of Asymptotic Safety. After presenting the (non—perturbative) beta functions for Newton’s coupling G and the dimensionless R^2 coupling, I will show how an attractive, asymptotically free UV fixed point exists for the latter, while an asymptotically safe one exists for the former under the renormalisation group (RG). I will then explain how the realisation of observationally viable Starobinsky inflation is naturally ensured by the presence of the asymptotically free fixed point under the RG, for a wide range of scales. I will also discuss the corresponding RG dynamics of the action from the UV to IR, as well as how inflationary and classical observations define the renormalisation conditions for the gravitational couplings.

Speaker: Ippocratis Saltas

15:30 → 16:00 Coffee Break

16:00 → 16:15 PhD Student Session

A short lecture from Frank Saueressig, the final seminar speaker, aimed to help PhD students understand the Seminar topic. This session is for PhD students only.

Convener: Mr Ismail Bridle (University of Southampton)

16:00 PhD Student Session

Speaker: Dr Frank Saueressig (University of Mainz)

16:15 → 17:15 Final Seminar

16:15 → 17:15 Gravitational RG Flows on Foliated Spacetimes

The role of time and the possibility of spacetime carrying a foliation structure are long standing questions which lately received a lot of renewed attention from the quantum gravity community. In this talk, I will review recent progress in formulating a Wetterich-type functional renormalization group equation on foliated spacetimes and outline its potential applications. In particular, I will discuss first results concerning the RG flow of anisotropic gravity models, highlighting the possibility of dynamical Lorentz-symmetry restoration along the RG flow.

Speaker: Frank Saueressig

17:15 → 18:30 Discussion

A chance to discuss the day's events over snacks and drinks in the Physics and Astronomy Seminar room.