Dual gravitons in AdS <inf>4</inf>/CFT <inf>3</inf> and the holographic Cotton tensor

We argue that gravity theories in AdS4 are holographically dual to either of two three-dimensional CFT's: the usual Dirichlet CFT1 where the fixed graviton acts as a source for the stress-energy tensor, and a dual CFT2 with a fixed dual graviton which acts as a source for a dual stress-energy tensor. The dual stress-energy tensor is shown to be the Cotton tensor of the Dirichlet CFT. The two CFT's are related by a Legendre transformation generated by a gravitational Chern-Simons coupling. This duality is a gravitational version of electric-magnetic duality valid at any radius r, where the renormalized stress-energy tensor is the electric field and the Cotton tensor is the magnetic field. Generic Robin boundary conditions lead to CFT's coupled to Cotton gravity or topologically massive gravity. Interaction terms with CFT1 lead to a non-zero vev of the stress-energy tensor in CFT2 coupled to gravity even after the source is removed. We point out that the dual graviton also exists beyond the linearized approximation, and spell out some of the details of the non-linear construction

Chern-Simons theory, 2d Yang-Mills, and Lie algebra wanderers

We work out the relation between Chern-Simons, 2d Yang-Mills on the cylinder, and Brownian motion. We show that for the unitary, orthogonal and symplectic groups, various observables in Chern-Simons theory on S^3 and lens spaces are exactly given by counting the number of paths of a Brownian particle wandering in the fundamental Weyl chamber of the corresponding Lie algebra. We construct a fermionic formulation of Chern-Simons on $S^3$ which allows us to identify the Brownian particles as B-model branes moving on a non-commutative two-sphere, and construct 1- and 2-matrix models to compute Brownian motion ensemble averages

S-matrices for Planckian scattering

String theory seems to ive a unitary description of physics in the nei hbourhood of certain black holes.A nice example of this is the AdS/CFT conjecture,where processes in the near-horizon region of sev- eral black branes are described by a conformal field theory which is unitary.However,it is hard to understand from the CFT where exactly Hawkin sarument oeswron. An alternative but related pro ram for understanding these issues was started by t Hooft,who considered the near-horizon region of the Schwarzschild black hole,namely flat space.The interactions between outgoin Hawkin radiation and ingoin particles,which near the black hole are boosted to the speed of light,can then be simulated by the gravitational interactions between massless particles.An S -matrix for their scatterin can then readily be computed.For a review on the S -matrix Ansatz we further refer to [1 ]. In this note we discuss the quantum mechanical properties of this model,and its possible relation to the AdS/CFT conjecture

Non-commutative black-hole algebra and string theory from gravity

We generalize the action found by 't Hooft, which describes the gravitational interaction between ingoing and outgoing particles in the neighbourhood of a black hole. The effect of this back-reaction is that of a shock wave, and it provides a mechanism for recovering information about the momentum of the incoming particles. The new action also describes particles with transverse momenta and takes into account the transverse curvature of the hole, and has the form of a string theory action. Apart from the Polyakov term found by 't Hooft, we also find an antisymmetric tensor, which is here related to the momentum of the particles. At the quantum level, the identification between position and momentum operators leads to four non-commuting coordinates. A certain relation to M(atrix) theory is proposed

Chern-Simons Theory in Lens Spaces from 2d Yang-Mills on the Cylinder

We use the relation between 2d Yang-Mills and Brownian motion to show that 2d Yang-Mills on the cylinder is related to Chern-Simons theory in a class of lens spaces. Alternatively, this can be regarded as 2dYM computing certain correlators in conformal field theory. We find that the partition function of 2dYM reduces to an operator of the type U=ST^pS in Chern-Simons theory for specific values of the YM coupling but finite k and N. U is the operator from which one obtains the partition function of Chern-Simons on S^3/Z_p, as well as expectation values of Wilson loops. The correspondence involves the imaginary part of the Yang-Mills coupling being a rational number and can be seen as a generalization of the relation between Chern-Simons/WZW theories and topological 2dYM of Witten, and Blau ant Thompson. The present reformulation makes a number of properties of 2dYM on the cylinder explicit. In particular, we show that the modular transformation properties of the partition function are intimately connected with those of affine characters

A note on knot invariants and q-deformed 2d Yang-Mills

We compute expectation values of Wilson loops in q-deformed 2d Yang-Mills on a Riemann surface and show that they give invariants of knots in 3-manifolds which are circle bundles over the Riemann surface. The areas of the loops play an essential role in encoding topological information about the extra dimension, and they are quantized to integer or half integer values

The Invisibility of Diffeomorphisms

I examine the relationship between $(d+1)$-dimensional Poincar\'e metrics and $d$-dimensional conformal manifolds, from both mathematical and physical perspectives. The results have a bearing on several conceptual issues relating to asymptotic symmetries, in general relativity and in gauge-gravity duality, as follows: (1: Ambient Construction) I draw from the remarkable work by Fefferman and Graham (1985, 2012) on conformal geometry, in order to prove two propositions and a theorem that characterise the classes of diffeomorphisms that qualify as gravity-invisible. I define natural notions of gravity-invisibility (strong, weak, and simpliciter) which apply to the diffeomorphisms of Poincar\'e metrics in any dimension. (2: Dualities) I apply the notions of invisibility to gauge-gravity dualities: which, roughly, relate Poincar\'e metrics in $d+1$ dimensions to QFTs in $d$ dimensions. I contrast QFT-visible vs. QFT-invisible diffeomorphisms: those gravity diffeomorphisms that can, respectively cannot, be seen from the QFT. The QFT-invisible diffeomorphisms are the ones which are relevant to the hole argument in Einstein spaces. The results on dualities are surprising, because the class of QFT-visible diffeomorphisms is larger than expected, and the class of QFT-invisible ones is smaller than expected, or usually believed, i.e. larger than the PBH diffeomorphisms in Imbimbo et al. (2000). I also give a general derivation of the asymptotic conformal Killing equation, which has not appeared in the literature before