Forthcoming events in this series


Mon, 24 Oct 2011

12:00 - 13:00
L3

Bundles over nearly-Kähler homogeneous spaces in heterotic string theory

Michael Klaput
(Oxford)
Abstract

String compactifications incorporating non-vanishing H-flux have received increased attention over the past decade for their potential relevance to the moduli stabilization problem. Their internal spaces are in general not Kähler and, therefore, not Calabi-Yau. In the heterotic string an important technical problem is to construct gauge bundles on such spaces. I will present a method of how to explicitly construct gauge bundles over homogeneous nearly-Kähler manifolds of dimension six and discuss some of the arising implications for model building.

Mon, 17 Oct 2011

12:00 - 13:00
L3

A ten-dimensional action for non-geometric fluxes

David Andriot
(LMU Munich)
Abstract

Four-dimensional (4d) supergravities with non-geometric terms in their potential are very promising models for phenomenology. Indeed, these terms, generated by so-called non-geometric fluxes, generically help to obtain de Sitter vacua, or to stabilise moduli. Unfortunately, deriving these theories from a compactified ten-dimensional (10d) supergravity has not been achieved so far. One reason is that non-geometric fluxes do not seem to match any 10d field, and another reason is the appearance of global issues in 10d non-geometric configurations.

After reviewing some background material, we present in this talk a solution to the two previous issues. Thanks to a field redefinition, we make the non-geometric Q-flux appear in a 10d action, which only differs from the NSNS action by a total derivative. In addition, this new action is globally well-defined, at least in some examples, and one can then perform the dimensional reduction to recover the 4d non-geometric potential. We also mention an application to the heterotic string.

Based on 1106.4015.

Mon, 10 Oct 2011

12:00 - 13:00
L3

Superconformal Chern-Simons Theories and The AdS/CFT Correspondence

Arthur Lipstein
(Oxford)
Abstract

The study of superconformal Chern-Simons theories has led to a deeper understanding of M-theory and a new example of the AdS/CFT correspondence. In this talk, I will give an overview of superconformal Chern-Simons theories and their gravity duals. I will also describe some recent work on scattering amplitudes in these theories.

Mon, 13 Jun 2011

12:00 - 13:00
L3

3D-partition functions on the sphere: exact evaluation and mirror symmetry

Sara Pasquetti
(QMUL)
Abstract
Recently it has been shown that path integrals of N=4 theories on the three-sphere can be  localised  to matrix integrals. I will show how to obtain exact expressions  of partition functions by an explicit evaluation of these matrix integrals.
Mon, 06 Jun 2011

12:00 - 13:00
L3

String compactifications on toric varieties

Magdalena Larfors
(LMU Munich)
Abstract
In the absence of background fluxes and sources, compactifying string theories on Calabi-Yau three-folds leads to supersymmetric solutions. Turning on fluxes, e.g. to lift the moduli of the compactification, generically forces the three-fold to break the Calabi-Yau conditions, and instead fulfill the weaker geometrical condition of having a reduced structure group. In this talk I will demonstrate that three-dimensional smooth, compact, toric varieties can have reduced structure group, and thus be suitable for flux compactifications of string theory. Since the class of three-dimensional SCTV is large, this is promising for the construction of new, phenomenologically interesting string theory vacua.
Mon, 23 May 2011

12:00 - 13:00
L3

Trivertices and SU(2)'s

Amihay Hanany
(Imperial College)
Abstract
Given a graph with lines and 3-valent vertices, one can construct, using a simple dictionary, a Lagrangian that has N=2 supersymmetry in 3+1 dimensions. This is a construction which generalizes the notion of a quiver. The vacuum moduli space of such a theory is well known to give moment map equations for a HyperKahler manifold. We will discuss the class of hyperkahler manifolds which arise due to such a construction and present their special properties. The Hilbert Series of these spaces can be computed and turns out to be a function of the number of external legs and loops in the graph but not on its detailed structure. The corresponding SCFT consequence of this property indicates a crucial universality of many Lagrangians, all of which have the same dynamics. The talk is based on http://arXiv.org/pdf/1012.2119.
Mon, 16 May 2011

12:00 - 13:30
L3

Stability conditions on local P^2

Tom Bridgeland
(Oxford)
Abstract
This talk will be about spaces of stability conditions. I will start by recalling Mike Douglas' original work on Pi-stability for D-branes, and go on to explain a couple of of the main open questions in the subject. The second half of the talk will focus on an illustrative example, namely the case of the local projective plane.
Mon, 09 May 2011
12:00
L3

CANCELLED

Sara Pasquetti
(QMUL)
Mon, 21 Feb 2011

12:00 - 13:00
L3

TBA

James Sparks
(Oxford)
Mon, 14 Feb 2011

12:00 - 13:00
L3

TBA

Volker Braun
(Dublin Institute of Advanced Studies)
Mon, 07 Feb 2011

12:00 - 13:00
L3

Could Spacetime be Causal Structure Alone?

Fay Dowker
(Imperial College)
Abstract
Abstract: In the continuum the answer to the title question is "no". But if spacetime is atomic then the answer is yes. And it so happens that there is rather compelling circumstantial evidence that spacetime is actually discrete at the Planck scale. So now the question becomes, why if spacetime is discrete should it take the form of a discrete causal structure or *order*? The answer is that if you don't put causal order in fundamentally you don't get it out -- at least that's what known models of "emergent spacetime" indicate. If we want to make life easy for ourselves in quantum gravity, then, we should plump for discrete causal order (a "causal set") as the inner basis for spacetime. That, however raises the spectre of wild nonlocality. I will describe recent progress that shows that this wildness can be tamed. In particular we now have an approximately local action for causal sets and I'll explain what that means.
Mon, 31 Jan 2011

12:00 - 13:00
L3

Branes, Boxes and Black Holes

Toby Wiseman
(Imperial College)
Abstract
Abstract: I will begin by reviewing the use of Ricci flow and the associated Ricci soliton equation to provide constructive numerical algorithms to find static vacuum black holes. I will then describe recent progress to generalize these methods to stationary black holes. I will present new results found using these methods, firstly on stationary black holes in spherical boxes, and secondly, black holes localized on a Randall-Sundrum brane. The latter case hopefully resolves the validity of a phenomenologically striking and important conjecture, and also has relevance to AdS-CFT.
Mon, 24 Jan 2011

12:00 - 13:00
L3

Scattering Amplitudes and Holomorphic Linking in Twistor Space

Mathew Bullimore
(Oxford)
Abstract
Recently, there has been exciting progress in scattering amplitudes in supersymmetric gauge theories, one aspect of which is the remarkable duality between amplitudes and Wilson loops. I will explain how the complete planar S-matrix of N=4 super Yang-Mills theory is encoded in the complex analogue of a Wilson loop in holomorphic Chern-Simons theory on twistor space. The dynamics of the theory are encoded in loop equations, which describe deformations of the Wilson Loop and provide new insight into the nature of the amplitude-Wilson loop duality. The loop equations themselves yield powerful recursive methods for scattering amplitudes which are revealed as holomorphic skein relations by interpreting the Wilson loop as the complex analogue of a knot invariant. The talk will be based on the preprint arXiv:1101.1329.
Mon, 17 Jan 2011

12:00 - 13:30
L3

Generalised Geometry and M-theory

David Berman
(Queen Mary University of London)
Abstract
Abstract: We reformulate M-theory in terms of a generalised metric that combines the usual metric and the three form potential. The U-duality group is then a manifest symmetry.
Mon, 29 Nov 2010

12:00 - 13:00
L3

Generalized Geometry in AdS/CFT and Volume Minimization

Maxime Gabella
(Oxford)
Abstract
Motivated by the study of general supersymmetric AdS_5 solutions of type IIB supergravity with fluxes, I will define a notion of "generalized Sasaki-Einstein geometry," characterized by a differential system for a triple of symplectic forms in 4d. I will then show that the minimization of the contact volume over a space of generalized Sasakian structures determines the Reeb vector field for such a solution. This is the geometric counterpart of a-maximization in superconformal field theory. This variational procedure will be put to good use by computing BPS quantities for a predicted infinite family of solutions dual to mass-deformed generalized conifolds.
Mon, 22 Nov 2010

12:00 - 13:00
L3

Constraining F-theory GUTs

Sakura Schafer-Nameki
(Kings College London)
Abstract
String theory phenomenology generically suffers from either too much flexibility (and lack of predictability) or from the a high specialization to case by case studies. I will discuss how F-theory GUT model building manages to get around these pitfalls, in particular, I will explain, how to systematically include global string consistency conditions, which are independent of the specific compactification, and which come with the benefit of highly constraining the class of GUT models that can arise from F-theory.
Mon, 15 Nov 2010

12:00 - 13:00
L3

The Large Hadron Collider – the story so far

Alan Barr
(Oxford)
Abstract
String theory has a vested interest in a particular S1xS1 object found just outside Geneva. The machine in question has been colliding protons at high energy since March this year, and by now the ATLAS and CMS experiments have clocked up more than 10^12 high-energy events. In this seminar I present the status of the accelerator and detectors, highlight the major physics results obtained so far, and discuss the extent to which information from the LHC can inform us about TeV-scale theory.
Mon, 08 Nov 2010

12:00 - 13:00
L3

Generalised Space-Time and Duality

Peter West
(Kings College London)
Abstract
I will review the conjectured E_{11} symmetry of strings and branes. I will explain how it is natural in the context of this symmetry to introduce a generalised space-time with a corresponding generalised geometry.
Mon, 01 Nov 2010

12:00 - 13:00
L3

New three-generation models from the heterotic standard embedding

Rhys Davies
(Oxford)
Abstract

Recently, two new Calabi-Yau threefolds have been discovered which have small Hodge numbers, and give rise to three chiral generations of fermions via the so-called 'standard embedding' compactification of the heterotic string.
In this talk I will describe how to deform the standard embedding on these manifolds in order to achieve the correct gauge group.  I will also describe how to calculate the resulting spectrum and interactions, which is still work in progress.

Mon, 25 Oct 2010

12:00 - 13:00
L3

On the gravity duals of N=2 superconformal field theories

Ron Reid-Edwards
(Oxford)
Abstract
In 2009 Gaiotto and Maldacena demonstrated that the challenge of finding gravitational descriptions of N=2 superconformal field theories could, under certain circumstances, be reduced to a simple two-dimensional electrostatics problem. In this talk I will review their work and discuss recent progress in finding and interpreting such solutions in string and M-theory.