Forthcoming events in this series
The non-compact exceptional simple group G_2* turns out to be the symmetry group of quantized twistor theory. Certain implications of this remarkable fact will be explored in this talk.
This is a joint GR-QFT seminar, to celebrate in advance the 90th birthday of Roger Penrose later in the summer, comprising 9 talks on conformal cyclic cosmology. The provisional schedule is as follows:
11:00 Roger Penrose (Oxford, UK) : The Initial Driving Forces Behind CCC
11:10 Paul Tod (Oxford, UK) : Questions for CCC
11:20 Vahe Gurzadyan (Yerevan, Armenia): CCC predictions and CMB
11:30 Krzysztof Meissner (Warsaw, Poland): Perfect fluids in CCC
11:40 Daniel An (SUNY, USA) : Finding information in the Cosmic Microwave Background data
11:50 Jörg Frauendiener (Otago, New Zealand) : Impulsive waves in de Sitter space and their impact on the present aeon
12:00 Pawel Nurowski (Warsaw, Poland and Guangdong Technion, China): Poincare-Einstein expansion and CCC
12:10 Luis Campusano (FCFM, Chile) : (Very) Large Quasar Groups
12:20 Roger Penrose (Oxford, UK) : What has CCC achieved; where can it go from here?
Dark matter is known to exist, but no-one knows what it is or where it came
from. We describe a new production mechanism of particle dark matter, which
hinges on a first-order cosmological phase transition. We then show that
this mechanism can be slightly modified to produce primordial black holes.
While solar mass and supermassive black holes are now known to exist,
primordial black holes have not yet been seen but could solve a number of
problems in cosmology. Finally, we demonstrate that if an evaporating
primordial black hole is observed, it will provide a unique window onto
Beyond the Standard Model physics.
I will be first introducing the Polyakov loop space formalism to
gauge theories. I will also discuss how the Polyakov loop space is modified
by Planck scale corrections. The gauge theory will be deformed by the
Planck length as the minimum measurable length in the background spacetime.
This deformation will in turn deform the Polyakov loops space. It will be
observed that this deformation can have important consequences for
non-abelian monopoles in gauge theories.
The conformal bootstrap program for CFTs in d>2 dimensions is
based on well-defined rules and in principle it could be easily included
into rigorous mathematical physics. I will explain some interesting
conjectures which emerged from the program, but which so far lack rigorous
proof. No prior knowledge of CFTs or conformal bootstrap will be assumed.
How to evaluate meromorphic germs at their poles while preserving a
locality principle reminiscent of locality in QFT is a question that
lies at the heart of pQFT. It further arises in other disguises in
number theory, the combinatorics on cones and toric geometry. We
introduce an abstract notion of locality and a related notion of
mutually independent meromorphic germs in several variables. Much in the
spirit of Speer's generalised evaluators in the framework of analytic
renormalisation, the question then amounts to extending the ordinary
evaluation at a point to certain algebras of meromorphic germs, in
such a way that the extension factorises on mutually independent
germs. In the talk, we shall describe a family of such extended
evaluators and show that modulo a Galois type transformation, they
amount to a minimal subtraction scheme in several variables.
This talk is based on ongoing joint work with Li Guo and Bin Zhang.
I take the “collapse of the wave-function” to be an objective physical process—OR (the Objective Reduction of the quantum state)—which I argue to be intimately related to a basic conflict between the principles of equivalence and quantum linear superposition, which leads us to a fairly specific formula (in agreement with one found earlier by Diósi) for the timescale for OR to take place. Moreover, we find that for consistency with relativity, OR needs to be “instantaneous” but with curious retro-active features. By extending an argument due to Donadi, for EPR situations, we find a fundamental conflict with “gradualist” models such as CSL, in which OR is taken to be the result of a (stochastic) evolution of quantum amplitudes.
In this talk I will explain how theories with local symmetries are treated in perturbative Algebraic Quantum Field Theory (pAQFT). The main mathematical tool used here is the Batalin Vilkovisky (BV) formalism. I will show how the perturbative Master Ward Identity can be applied in this formalism to make sense of the renormalised Quantum Master Equation. I will also comment on perspectives for a non-perturbative formulation.
Subfactors and K-theory are useful mechanisms for understanding modular tensor categories and conformal field theories. As part of this programme, one issue to try and construct or reconstruct a conformal field theory as the representation theory of a conformal net of algebras, or as a vertex operator algebra from a given abstractly presented modular tensor category. Orbifold models play an important role and orbifolds of Tambara-Yamagami systems are relevant to understanding the double of the Haagerup as a conformal field theory. This is joint work with Andreas Aaserud, Terry Gannon and Ulrich Pennig.
I discuss a ``running vacuum cosmological model'' of a string-inspired
Universe, in which gravitational anomalies play an important role, in
inducing, through condensates of primordial gravitational waves, an early de
Sitter inflationary phase, during which constant (in cosmic time)
backgrounds of the antisymmetric (Kalb-Ramond (KR)) tensor field of the
massless bosonic string multiplet remain undiluted until the exit from
inflation and well into the subsequent radiation era. During the radiation
phase, such backgrounds, which violate spontaneously Lorentz and CPT
symmetry, induce lepton asymmetry (Leptogenesis) in models involving
right-handed neutrinos. Chiral matter is generated in the model at the exit
phase of inflation, and this leads to the cancellation of gravitational
anomalies in the post inflationary universe. During the radiation era, non
perturbative effects can also be held responsible for the generation of a
potential for the gravitational axion, associated in (3+1)-dimensions with
the field strength of the KR field, which can thus play the role of a Dark
Matter component. In the talk, I discuss the underlying formalism and argue
in favour of the consistency of a theory with gravitational anomalies in the
early Universe. I connect the energy density of such a universe with that of
the so called ``running-vacuum model'' in which the vacuum energy density is
expressed in terms of even powers of the Hubble parameter, which in general
depends on cosmic time. The gravitational-wave condensate induces a term in
the energy density proportional to the fourth-power of the Hubble parameter
H^4 , which is responsible for the early de Sitter phase, during which the
Hubble parameter is approximately a constant. I also discuss briefly a
connection of this string inspired model with the Swampland and weak gravity
conjectures and explain how consistency with such conjectures is achieved,
despite the fact that the model is compatible with slow-roll inflationary
phenomenology.
We consider an analogue of Kontsevich's matrix Airy function where the cubic potential $\mathrm{Tr}(\Phi^3)$ is replaced by a quartic term $\mathrm{Tr}(\Phi^4)$. By methods from quantum field theory we show that also the quartic case is exactly solvable. All cumulants can be expressed as composition of elementary functions with the inverse of another elementary function. For infinite matrices the inversion gives rise to hyperlogarithms and zeta values as familiar from quantum field theory. For finite matrices the elementary functions are rational and should be viewed as branched covers of Riemann surfaces, in striking analogy with the topological recursion of the Kontsevich model. This rationality is strong support for the conjecture that the quartic analogue of the Kontsevich model is integrable.
Measurement outcomes in quantum theory are randomly distributed, and local measurements of the energy density of a QFT exhibit nontrivial fluctuations even in a vacuum state. This talk will present recent progress in determining the probability distribution for such measurements. In the specific case of 1+1 dimensional CFT, there are two methods (one based on Ward identities, the other on "conformal welding") which can lead to explicit closed-form results in some cases. The analogous problem for the free field in 1+3 dimensions will also be discussed.
In this talk I will explain (a) what observations speak for the
hypothesis of dark matter, (b) what observations speak for
the hypothesis of modified gravity, and (c) why it is a mistake
to insist that either hypothesis on its own must
explain all the available data. The right explanation, I will argue,
is instead a suitable combination of dark matter and modified
gravity, which can be realized by the idea that dark matter
has a superfluid phase.
I will review some of the major research themes in Quantum Chaos over the past 50 years, and some of the questions currently attracting attention in the mathematics and physics literatures.
Magnetic skyrmions are topological solitons which occur in a large class
of ferromagnetic materials and which are currently attracting much
attention in the condensed matter community because of their possible
use in future magnetic information storage technology. The talk is
about an integrable model for magnetic skyrmions, introduced in a recent
paper (arxiv 1812.07268) and generalised in (arxiv 1905.06285). The
model can be solved by interpreting it as a gauged nonlinear sigma
model. In the talk will explain the model and the geometry behind its
integrability, and discuss some of the solutions and their physical
interpretation.
The renormalized expectation value of the stress energy tensor (RSET) is an object of central importance in quantum field theory in curved space-time, but calculating this on black hole space-times is far from trivial. The vacuum polarization (VP) of a quantum scalar field is computationally simpler and shares some features with the RSET. In this talk we consider the properties of the VP for a massless, conformally coupled scalar field on asymptotically anti-de Sitter black holes with spherical, flat and hyperbolic horizons. We focus on the effect of the different horizon curvature on the VP, and the role played by the boundary conditions far from the black hole.
String compactifications are essential for connecting string theory to low energy particle physics and cosmology. Moduli stabilisation gives rise to effective Lagrangians that capture the low-energy degrees of freedom. Much recent interest has been on swampland consistency conditions on such effective
field theories - which low energy Lagrangians can arise from quantum gravity? Furthermore, given that moduli stabilisation scenarios often exist in AdS space, we can also ask: what do swampland conditions mean in the context of AdS/CFT? I describe work on developing a holographic understanding of moduli stabilisation and swampland consistency conditions. I focus in particular on the Large Volume Scenario, which is especially appealing from a holographic perspective as in the large volume limit all its interactions can be expressed solely in terms of the AdS radius, with no free dimensionless parameters.