Podcasts about quantum field theories

Michael Stöltzner (South Carolina) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Best Possible Worlds and Random Walks: The Principle of Least Action as a Thought Experiment". Abstract: Over the centuries, no other principle of classical physics has to a larger extent nourished exalted hopes of a universal theory, has constantly been plagued by mathematical counterexamples, and has ignited metaphysical controversies than has the principle of least action (PLA). The aim of this paper is first to survey a series of modern approaches, among them the structural realist readings of Planck and Hilbert, a neo-Kantian relativized a priori principle, and more recent discussions about modality within the context of analytic metaphysics. But these considerations seem outrun by the broad applicability of the PLA beyond classical physics. In the case of Feynman’s path integral, the PLA does no longer amount to the distinction of the actual dynamics among the possible ones, but to the definition of a stochastic process to which all possibilities contribute with a certain probability. To reach a unified philosophical picture of all the various applications of the PLA and its kin, I suggest to consider them as a thought experiment about the applicability of mathematics to a physical problems.

Members of the Rudolf Peierls Centre for Theoretical Physics hosted the 6th morning of Theoretical Physics covering the ways in which ideas from theoretical particle physics guide the high energy accelerator program at CERN

Members of the Rudolf Peierls Centre for Theoretical Physics hosted the 6th morning of Theoretical Physics covering the ways in which ideas from theoretical particle physics guide the high energy accelerator program at CERN

Members of the Rudolf Peierls Centre for Theoretical Physics hosted the 6th morning of Theoretical Physics covering the ways in which ideas from theoretical particle physics guide the high energy accelerator program at CERN

Karim Thebault (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "A New Prescription for the Quantization of Refoliation Invariant Field Theories". Abstract: Imagine a loaf of bread that we can irregularly cut up into a sequence of slices. The loaf is spacetime and the slices are instantaneous spatial surfaces. A foliation is a parameterization of a spacetime by a time ordered sequence of spatial slices. In a field theory such a parametrization can be local in the sense that it is defined for every point on every spatial slice. Diffeomorphism invariance implies that spacetimes described by general relativity that are related by refoliations are physically equivalent. Classically the symmetry is therefore directly connectable to the idea that only the coordinate-free information contained in a spacetime geometry has a physical basis. The implications of this symmetry for quantization are notoriously problematic. Here we offer a new prescription for the canonical quantization of gravity that side-steps the issues with refoliations via the adoption of the 'shape dynamics’ reformulation. We then offer our thoughts as to whether this is a satisfactory resolution for the problem for understanding refoliation symmetry in the context of a quantum field theory of gravity.

Ben Feintzeig (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Unitary Inequivalence in Classical Systems". Abstract: I provide an algebraic formulation of classical field theories and use this to probe our interpretation of algebraic theories more generally. I show that the problem of unitarily inequivalent representations, as discussed in Ruetsche (2011), arises in classical theories just as in quantum theories, and I argue that this gives reason to not be a Hilbert Space Conservative when interpreting algebraic theories.

Brian Padden (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Relativistic Quantum Particles the Feynman Way". Abstract: It is often believed, especially in light of theorems by Malament and others, that there is no relativistic theory of localizable quantum particles. However, an example of exactly such a theory seems to exist, and in fact occupies an important place in the storied history of quantum field theory: Feynman’s path integral approach to quantum electrodynamics. We introduce Feynman’s theory and show that, up to a few minor issues, it is satisfactory. Then, we turn to the theorems stating that such a theory is impossible and discuss which premises are violated by the Feynman theory.

Samuel Fletcher (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Classical Field Theory and Intertheoretic Reduction". Abstract: In 1986, Ehlers set out a program on how to understanding the approximative relationships between different physical theories. However, he essentially only investigated the case of classical and relativistic spacetime theories, which have a number of special features that distinguish them from broader classes of physical theories. To what extent, then, can the Ehlers program be successful? I outline some of the challenges facing the program's generalization and argue that they can largely be overcome for classical field theories.

Sarita Rosenstock (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "On Fiber Bundle and Holonomy Interpretations of Yang-Mills Theories". Abstract: In the philosophy of Yang-Mills theories, there is an ongoing debate between rival interpretations that can be grouped into two rough categories: “holonomy interpretations” (supported by, e.g., Healey, Belot, and Lyre) and “fiber bundle interpretations” (supported by, e.g., Arntzenius, Maudlin, and Leeds). I present a theorem that I interpret as providing a precise sense in which these interpretations are equivalent.

James Weatherall (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December) titled "Fiber Bundles, Yang-Mills Theory, and General Relativity". Abstract: I articulate and discuss a geometrical interpretation of Yang-Mills theory. Analogies and disanalogies between Yang-Mills theory and general relativity are also considered.

This dissertation is devoted to the investigation of the interplay of supersymmetric Yang-Mills theories (SYM) and supergravity (SUGRA). The topic is studied from two points of view: Firstly from the point of view of AdS/CFT correspondence, which realises the coupling of four dimensional superconformal N=4 SYM theory and ten dimensional type IIB SUGRA in a holographic way. In order to arrive at theories that resemble quantum chromodynamics (QCD) more closely, fundamental fields are introduced using probe D7-branes and non-trivial background configuration are considered. In particular supergravity solutions that are only asymptotically anti-de Sitter and break supersymmetry are used. This allows the description of spontaneous chiral symmetry breaking. The meson spectrum is calculated and the existence of an associated Goldstone mode is demonstrated. Moreover it is shown that highly radially excited mesons are not degenerate. Additionally instanton configurations on the D7-branes are investigated, which lead to a holographic description of the dual field theory's Higgs branch. Finally a holographic description of heavy-light mesons is developed, which are mesons consisting of quarks with a large mass difference, such that a treatment of B mesons can be achieved. The second approach to the topic of this thesis is the technique of so-called space-time dependent couplings ("local couplings"), where coupling constants are promoted to external sources. This allows to explore the conformal anomaly of quantum field theories coupled to a classical gravity background. The technique is extended to the superfield description of N=1 supergravity, a complete basis for the anomaly is given and the consistency conditions that arise from a cohomological treatment are calculated. Possible implications for an extension of Zamolodchikov's c-theorem to four dimensional supersymmetric quantum field theories are discussed.