Galaxy clusters are the most efficient convertors of axion-like particles to photons in the universe. I discuss the physics and phenomenology of ALPs, and describe their astrophysical implications, with particular reference to the recently observed 3.5 keV X-ray line that is a candidate for a dark matter decay line.

F-theory paints a beautiful picture that relates gauge theories to purely geometric information, whereby the Dynkin diagrams of gauge groups come to life as 2-cycles of internal spaces. The caveat is that, such spaces are necessarily singular, and treating them sensibly requires resolving or deforming the singularities. Recently, my collaborator R. Savelli and I have proposed a new strategy that allows one to deal with singular spaces directly. It is based on Eisenbud’s so-called matrix factorisations. This remarkably simple concept has very deep connections to the mathematics of singularities. In this talk, I will review the basic notions needed to formulate the issues, assuming only standard knowledge of string theory. Then, after introducing our proposal, I will show examples of its applications, such as computations of chiral spectra for bound states of 7-branes.

Light-like polygonal super-Wilson loops are dual to scattering amplitudes in planar N=4 super-Yang-Mills and enjoy an infinite-dimensional Yangian symmetry which extends the superconformal symmetry.  However, this symmetry is anomalous.  In this talk we will describe a super-Wilson loop on a smooth contour, which is free of UV divergences and on which the superconformal symmetry operators are not anomalous.  We also study the action of level one Yangian generators on the one-loop expectation value of this super-Wilson loop. [This is work in progress with N.Beisert, D.Muller and J.Plefka]

CFTs at large central charge display some universal features which can be inferred from holography. Using these as a guide one can obtain some necessary conditions for a given CFT to admit a classical gravity dual. I will describe attempts to construct a large class of CFTs satisfying these conditions exploiting some technology of permutation orbifolds. Time permitting I will also outline some tests for the sufficiency of these conditions.

The algebras of higher spin symmetries in conformal field theories in four and six dimensions are not unique and have a richer structure due to the existence of infinite short multiplets besides the usual scalar and spinor. We will focus on recent results that show there exists a one parameter family (continuous of d=4 and discrete for d=6) of higher spin algebras and superalgebras, and give an explicit unitary representation for these algebras using quasiconformal methods. We will also discuss the implications of these results for the AdS5/CFT4 and AdS7/CFT6 higher spin holography.

I will explain how to compute the Hilbert series that counts chiral operators parametrising the Coulomb branch of the moduli space of vacua of three-dimensional N=4 supersymmetric gauge theories. The formula has applications to Physics, such as to the study of infrared dualities in three dimensions and of string backgrounds with eight supercharges, as well as to Mathematics, where it provides a new way to characterise HyperKaehler cones as algebraic varieties.  I will then show how the Coulomb branch of certain 3d N=4 generalised quiver gauge theories can be used to compute the Hilbert series of the moduli space of k G-instantons, for any simple Lie group G. The construction is alternative to the ADHM construction that is only available for classical groups G.

TBA

Workshop information and registration http://www.mth.kcl.ac.uk/~ss299/MOST/

Workshop homepage for information and registration http://www.mth.kcl.ac.uk/~ss299/MOST/

I will discuss basic features of a formulation of higher-spin field theory in which conventional space-time gets extended to a hyperspace with a number of extra dimensions that effectively describe the spin degrees of freedom of the fields in the ordinary space-time. In this formulation an infinite number of higher spin fields are packed into a single scalar and spinor field propagating in the hyperspace. The dynamics of higher spin fields is encoded in equations of motion of the scalar and spinor hyperfields. The hyperfield equatons on flat and AdS-like hyperspaces are related to each other by a generalized conformal transformation, which also relates two-, three- and four-point functions in the AdS-like hyperspace to the corresponding correlators in the flat hyperspace.

This is a one-day meeting on localisation and gauge gravity duality. More information at http://kings-meeting.wikidot.com/

South East Mathematical Physics Seminar: For details see http://www.mth.kcl.ac.uk/SEMPS/ Speakers: Leron Borsten,Paul Sutcliffe, Vidas Regelskis, Abera Muhamed, Craig Lawrie

Student Triangle Seminar! http://www.mth.kcl.ac.uk/studenttriangle.html

Recently a powerful approach to the computation of one-point functions in the quantum XXZ spin 1/2 chain has been proposed by Boos, Jimbo, Miwa and Smirnov; this framework relies on the existence of a particular basis in the state space of the theory: the fermionic basis. I will present the construction of these fermions for the scaling limit of inhomogeneous XXZ spin 1/2 chain, the sine-Gordon model, and for its twin, the sinh-Gordon model. If time allows it, I will briefly present a possible interpretation of the fermionic basis and one-point functions in terms of the action of a modified version of the sinh-Gordon model.

Unstable string states in curved spacetime is not well-understood compared to those in the flat spacetime. We consider potentially tachyonic open string states in AdS_5xS^5 which should correspond to a determinant-like operator in N=4 super Yang-Mills by the AdS/CFT correspondence. Its conformal dimension is studied using integrability and perturbative methods in N=4 SYM. By proposing and solving the boundary thermodynamic Bethe ansatz (BTBA) equations, we find an indication that states of N=4 SYM turn into tachyonic at finite coupling where the total energy of the corresponding string becomes zero.

In this talk I will discuss the localisation of supersymmetric gauge theories on Riemannian three-manifolds with the topology of a three-sphere. The three-manifold is always equipped with an almost contact structure and an associated Reeb vector field. The partition function depends only on this vector field and has an explicit expression in terms of the double sine function. In addition, I will discuss the possibility of generalising this work to five dimensions.

There has been phenomenal recent progress in computing CFT entanglement and Renyi entropies, holographically and otherwise. We extend these investigations to the higher spin regime -- where sensible notions of geometry are sorely lacking -- by computing ground state Renyi entropies in certain classes of holographic CFTs with higher spin symmetry. Our calculations are performed at both classical and one-loop level, from gravity and CFT. Along the way, we establish some new general results about Renyi entropy in any CFT, higher spin symmetry aside.

The positivity of energy in quantum field theory is traditionally but not altogether clearly encoded in the possibility of ‘Wick rotation’ – the analytic continuation of various observable quantities to ‘imaginary time’. My talk, an account of joint work with Maxim Kontsevich, will describe a somewhat different point of view on this. I shall motivate the definition of a specific infinite-dimensional domain of complex-valued metrics on a smooth manifold which is a complexification of the usual space of real Riemannian metrics, but has the Lorentzian metrics on its boundary. The positivity of energy is then encoded in the fact that the theory is the boundary value of a holomorphic theory defined for space-time manifolds with complex metrics belonging to the domain. Questions of the unitarity of field theory in a curved space-time are thereby related to familiar phenomena in representation theory.

Using the fermionic basis we conjecture explicit formulae for the one-point functions in the sinh-Gordon model on a cylinder at finite temperature). The conjecture is checked against known results.

Exceptional generalised geometry (or exceptional field theory) is an extension of generalised complex geometry (or double field theory) "geometrising" all degrees of freedom of 11d or type II supergravity. Concentrating on the case in which the 11d tangent space is split into four and seven dimensional spaces, we will discuss the geometry and gauge structure of these exceptional theories. We will show how closure of the "exceptional Lie algebra" requires adding a tower of four-dimensional p-form fields, known in the 4d gauged supergravity language as the tensor hierarchy. This indicates the existence of an underlying structure compatible with the E_{11} construction.