E11 must be a symmetry of strings and branes

We construct the non-linear realisation of the semi-direct product of E11 and its vector representation in five and eleven dimensions and find the dynamical equations it predicts at low levels. Restricting these results to contain only the usual fields of supergravity and the generalised space-time to be the usual space-time we find the equations of motion of the five and eleven dimensional maximal supergravity theories. Since this non-linear realisation contains effects that are beyond the supergravity approximation and are thought to be present in an underlying theory we conclude that the low energy effective action of string and branes must possess an E11 symmetry.Comment: 17 pages, The eleven dimensional results are given in more detail and are shown to be uniquely determined. Typographical and transcription errors are also correcte

Generalised vielbeins and non-linear realisations

We briefly review why the non-linear realisation of the semi-direct product of a group with one of its representations leads to a field theory defined on a generalised space-time equipped with a generalised vielbein. We give formulae, which only involve matrix multiplication, for the generalised vielbein, the Cartan forms and their transformations. We consider the generalised space-time introduced in 2003 in the context of the non-linear realisation of the semi-direct product of E(11) and its first fundamental representation. For this latter theory we give explicit expressions for the generalised vielbein up to and including the levels associated with the dual graviton in four, five and eleven dimensions and for the IIB theory in ten dimensions. We also compute the generalised vielbein, up to the analogous level, for the non-linear realisation of the semi-direct product of very extended SL(2) with its first fundamental representation, which is a theory associated with gravity in four dimensions.Comment: 42 page

The X-ray eclipse of OY Car resolved with XMM-Newton: X-ray emission from the polar regions of the white dwarf

We present the XMM-Newton X-ray eclipse lightcurve of the dwarf nova OY Car. The eclipse ingress and egress are well resolved for the first time in any dwarf nova placing strong constraints on the size and location of the X-ray emitting region. We find good fits to a simple linear eclipse model, giving ingress/egress durations of 30+/-3 sec. Remarkably this is shorter than the ingress/egress duration of the sharp eclipse in the optical as measured by Wood et al. (1989) and ascribed to the white dwarf (43+/-2 sec). We also find that the X-ray eclipse is narrower than the optical eclipse by 14+/-2 sec, which is precisely the difference required to align the second and third contact points of the X-ray and optical eclipses. We discuss these results and conclude that X-ray emission in OY Car most likely arises from the polar regions of the white dwarf. Our data were originally reported by Ramsay et al (2001), but they did not make a quantitative measurement of eclipse parameters. We have also corrected important timing anomalies present in the data available at that time.Comment: 6 pages, 5 figures; accepted for publication in MNRA

Geophysical and television logging trials in horizontal boreholes for probing ahead of tunnels

Imperial Users onl

Chiral Green's Functions in Superconformal Field Theory

By solving the Ward identities in a superconformal field theory we find the unique three-point Green's functions composed of chiral superfields for N = 1,2,3,4 supersymmetry. We show that the N=1 four-point function with R-charge equal to one is uniquely determined by the Ward identities up to the specification of four constants. We discuss why chiral Green's functions above three-points, with total R-charge greater than N, are not uniquely determined.Comment: 32 pages, no figures, LaTeX2e forma

Policy Recognition in the Abstract Hidden Markov Model

In this paper, we present a method for recognising an agent's behaviour in dynamic, noisy, uncertain domains, and across multiple levels of abstraction. We term this problem on-line plan recognition under uncertainty and view it generally as probabilistic inference on the stochastic process representing the execution of the agent's plan. Our contributions in this paper are twofold. In terms of probabilistic inference, we introduce the Abstract Hidden Markov Model (AHMM), a novel type of stochastic processes, provide its dynamic Bayesian network (DBN) structure and analyse the properties of this network. We then describe an application of the Rao-Blackwellised Particle Filter to the AHMM which allows us to construct an efficient, hybrid inference method for this model. In terms of plan recognition, we propose a novel plan recognition framework based on the AHMM as the plan execution model. The Rao-Blackwellised hybrid inference for AHMM can take advantage of the independence properties inherent in a model of plan execution, leading to an algorithm for online probabilistic plan recognition that scales well with the number of levels in the plan hierarchy. This illustrates that while stochastic models for plan execution can be complex, they exhibit special structures which, if exploited, can lead to efficient plan recognition algorithms. We demonstrate the usefulness of the AHMM framework via a behaviour recognition system in a complex spatial environment using distributed video surveillance data