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Quantum Field Theory Seminar (past)

Tue, 23/04
12:00 		Philip Stamp (Vancouver) Quantum Field Theory Seminar Add to calendar L3
The search for Intrinsic Decoherence
              Conventional decoherence (usually called 'Environmental Decoherence') is supposed to be a result of correlations established between some quantum system and the environment. 'Intrinsic decoherence' is hypothesized as being an essential feature of Nature - its existence would entail a breakdown of quantum mechanics. A specific mechanism of some interest is 'gravitational decoherence', whereby gravity causes intrinsic decoherence. I will begin by discussing what is now known about the mechanisms of environmental decoherence, noting in particular that they can and do involve decoherence without dissipation (ie., pure phase decoherence). I will then briefly review the fundamental conflict between Quantum Mechanics and General Relativity, and several arguments that suggest how this might be resolved by the existence of some sort of 'gravitational decoherence'.  I then outline a theory of gravitational decoherence (the 'GR-Psi' theory) which attempts to give a quantitative discussion of gravitational decoherence, and which makes predictions for experiments. The weak field regime of this theory (relevant to experimental predictions) is discussed in detail, along with a more speculative discussion of the strong field regime.
Tue, 05/03
12:00 		Francis Brown (Paris, visiting Newton Institute) Quantum Field Theory Seminar Add to calendar L3
Modular forms in quantum field theory
Tue, 15/01
12:00 		Mir Faizal Quantum Field Theory Seminar Add to calendar L3
Supersymmetric loop space
We will first review the construction of N =1 supersymmetric Yang-Mills theory in three dimensions. Then we will construct a superloop space formulation for this super-Yang-Mills theory in three dimensions.Thus, we will obtain expressions for loop connection and loop curvature in this superloop space. We will also show that curvature will vanish, unless there is a monopole in the spacetime. We will also construct a quantity which will give the monopole charge in this formalism. Finally, we will show how these results hold even in case of deformed superspace.
Tue, 30/10/2012
12:00 		Alastair Kay Quantum Field Theory Seminar Add to calendar L3
Protecting Topological Encodings Against Local Perturbations

Topological quantum error correcting codes, such as the Toric code, are
ideal candidates for protecting a logical quantum bit against local noise.
How are we to get the best performance from these codes when an unknown
local perturbation is applied? This talk will discuss how knowledge, or lack
thereof, about the error affects the error correcting threshold, and how
thresholds can be improved by introducing randomness to the system. These
studies are directed at trying to understand how quantum information can be
encoded and passively protected in order to maximise the span of time between successive rounds of error correction, and what properties are
required of a topological system to induce a survival time that grows
sufficiently rapidly with system size. The talk is based on the following
papers: arXiv:1208.4924 and Phys. Rev. Lett. 107, 270502 (2011).
Tue, 16/10/2012
12:00 		Simon Gindikin (Rutgers) Quantum Field Theory Seminar Add to calendar L3
Penrose transform and Cauchy-Fantappie formula
Tue, 22/05/2012
12:00 		Tony Padilla (Nottingham) Quantum Field Theory Seminar Add to calendar L3
From classical duals to cleaning Lambda
Tue, 15/05/2012
12:00 		Elizabeth Gasparim (UNICAMP-Brazil) Quantum Field Theory Seminar Add to calendar L3
BPS state counting on singular varieties
This is a report of joint work with T. Koppe, P. Majumdar, and K.  Ray. I will define new partition functions for theories with targets on toric singularities via products of old partition functions on  crepant resolutions. I will present explicit examples  and show that the  new partition functions turn out to be homogeneous on MacMahon factors.
Tue, 24/04/2012
12:00 		Simon Brain (Luxembourg) Quantum Field Theory Seminar Add to calendar L3
Gauge Theory on Noncommutative Manifolds
Tue, 14/02/2012
12:00 		Stefan Pokorski (Warsaw) Quantum Field Theory Seminar Add to calendar L3
With or without a Higgs
Tue, 07/02/2012
12:00 		Yang-Hui He (City Uni/ Nankai Uni/ Merton College) Quantum Field Theory Seminar Add to calendar L3
N=2 Gauge Theories: Congruence Subgroups, Coset Graphs and Modular Surfaces
Tue, 31/01/2012
12:00 		Malcolm Fairbairn (KCL) Quantum Field Theory Seminar Add to calendar L3
An Update on Dark Matter
We still don't know what dark matter is but a class of leading candidates are weakly interacting massive particles or WIMPs. These WIMP models are falsifiable, which is why we like them. However, the epoch of their falsifiability is upon us and a slew of data from different directions is placing models for WIMPs under pressure. I will try and present an updated overview of the different pieces of evidence, false (?) alarms and controversies that are making this such an active area of research at the moment.
Tue, 29/11/2011
12:00 		Nazim Bouatta (DAMTP) Quantum Field Theory Seminar Add to calendar L3
Quantum Field Theory: Where do we come from? What are we? Where are we going?
In recent decades, quantum field theory (QFT) has become the framework for several basic and outstandingly successful physical theories. Indeed, it has become the lingua franca of entire branches of physics and even mathematics. The universal scope of QFT opens fascinating opportunities for philosophy. Accordingly, although the philosophy of physics has been dominated by the analysis of quantum mechanics, relativity and thermo-statistical physics, several philosophers have recently undertaken conceptual analyses of QFT. One common feature of these analyses is the emphasis on rigorous approaches, such as algebraic and constructive QFT; as against the more heuristic and physical formulations of QFT in terms of functional (also knows as: path) integrals. However, I will follow the example of some recent mathematicians such as Atiyah, Connes and Kontsevich, who have adopted a remarkable pragmatism and opportunism with regard to heuristic QFT, not corseted by rigor (as Connes remarks). I will conceptually discuss the advances that have marked heuristic QFT, by analysing some of the key ideas that accompanied its development.  I will also discuss the interactions between these concepts in the various relevant fields, such as particle physics, statistical mechanics, gravity and geometry. 
Tue, 15/11/2011
12:00 		Jean Alexandre (KCL) Quantum Field Theory Seminar Add to calendar L3
Review on Lifshitz type quantum field theories in Particle Physics
Attractive features of Lifshitz type theories are described with different examples, as the improvement of graphs convergence, the introduction of new renormalizable interactions, dynamical mass generation, asymptotic freedom, and other features related to more specific models. On the other hand, problems with the expected emergence of Lorentz symmetry in the IR are discussed, related to the different effective light cones seen by different particles when they interact.

For any corrections/updates to these listings, please contact seminars [-at-] maths [dot] ox [dot] ac [dot] uk.

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