(Location: Charles Carter Building, A19)
Everybody is welcome to attend the meeting.
For further information please contact Robin Hillier.
11:00 - 12:00 Chris Fewster (York)
12:00 - 13:30 Lunch
13:30 - 14:00 Markus Froeb (Leipzig)
14:00 - 14:30 Jacob Thompson (Sheffield)
14:30 - 15:00 Coffee break
15:00 - 16:00 Elizabeth Winstanley (Sheffield)
16:00 - 17:00 Informal discussions and open end
Chris Fewster: Asymptotic measurement schemes for all observables of a QFT
I will review some of the problems that have long been identified as fundamental problems in the measurement of relativistic quantum fields and describe a recently developed framework that solves many of them, by providing a covariant, causal and consistent account of measurement schemes for local observables and associated state update rules. I will also describe very recent work that shows that the framework is also comprehensive, by showing that all observables of a scalar field theory can be measured, to arbitrary approximation, using these methods.
Based on Commun. Math. Phys. 378 (2020) 851-889 (with Rainer Verch), Phys. Rev. D 103 (2021) 025017 (with Henning Bostelmann and Maximilian Ruep) and arXiv:2203.09529 (with Ian Jubb and Maximilian Ruep; Published online Annales Henri Poincaré.)
Markus B. Fröb: Local composite operators in the Sine-Gordon model
The Sine-Gordon model is a widely studied two-dimensional quantum field theory, which depending on the value of the coupling β is finite (for β² < 4π), super-renormalizable (4π ≤ β² < 8π) or just renormalizable (β² = 8π). However, local composite operators have not been studied in the theory, apart from a few simple examples. We show that even in the finite range β² < 4π composite operators such as ∂μϕ∂νϕ and the stress tensor Tμν need additional renormalization beyond the free-field normal-ordering at each order in perturbation theory. We then prove convergence of the renormalized perturbative series for these operators.
Based on work with D. Cadamuro: arXiv:2205.09223
Jacob Thompson: Quantum energy inequalities and stationary worldlines
Quantum energy inequalities (QEIs) are lower bounds on the averaged energy density of a quantum field. They have been proved in various different field theories and spacetimes, although explicit examples are few and far between. The purpose of this talk is to give a brief flavour of QEIs and how they are constructed, before giving specific examples in the case of a massless minimally coupled scalar field in four dimensional Minkowski spacetime along stationary worldlines.
This talk is based on joint work with Professor C.J. Fewster, see arXiv:2301.01698.
Elizabeth Winstanley: On the equivalence of adiabatic and Hadamard renormalization
In order to obtain physically meaningful results, any two renormalization prescriptions should yield consistent answers for the expectation values of field operators such as the stress-energy tensor. In this talk we focus on three approaches to renormalization: Hadamard, deWitt-Schwinger and adiabatic. The latter is particularly useful for computations on flat cosmological space-times. Working in two and three dimensions, and considering a charged scalar field, we demonstrate by explicit construction that the divergent parts of the Green's function are identical in all three frameworks. In all three approaches there are finite terms which are also to be subtracted from the Green's function. We describe the relationship between the finite terms in the above three renormalization schemes, paying particular attention to those arising in adiabatic renormalization in three dimensions.
This talk is based on joint work with Silvia Pla, arXiv:2209.01079, Phys. Rev. D 107, 025004 (2023)
Some general info https://www.lancaster.ac.uk/about-us/maps-and-travel/#
The talks will take place at the Charles Carter Building, indicated on the map below.