ETD Collection

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Subject: search.filters.subject.Holography

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Now showing 1 - 4 of 4
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    Towards the resolution of divergences in the holographic computation of extremal correlators
    (2017) Rajaobelina Iarilala, Elie Danien
    The main goal of this dissertation is to construct a better understanding of the subtleties that arise in the holographic computation of extremal correlators. It is well known that these computations, in the gravitational description, su er from divergences, but the interpretation and origin of these divergences is unclear. The study starts with detailed computations of two- and three-point functions of a scalar eld minimally coupled to gravity on Euclidean AdSd space, three-point functions of two giant gravitons and one light graviton, and three-point functions of the Kaluza-Klein gravitons, using supergravity theory. Further, we also give the computation of these same correlators in the dual CFT. These involve novel techniques in the matrix model, including methods that employ Schur polynomials in the dual gauge theory analysis. By employing the usual AdS=CFT dictionary, we argue that extremal correlators are naturally related to collinear particles. There are divergences that arise in collinear amplitudes as a consequence of the fact that the particles momenta are parallel. We therefore reach the suggestive idea that the divergences in extremal correlator computations are linked to collinear divergences. Much remains to be done to really establish this connection.
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    Holographic descriptions of CFT scattering
    (2017) Shrif, Esra Mohammed Shrif Mohammed Salih Mohammed
    The holographic computation of extremal correlators is often frustrated by divergences. The interpretation of these divergences is incomplete. The primary goal of this study is to develop a better understanding of these divergences. Towards this end, working within the AdS/CFT correspondence we review the computation of correlators. In the field theory we review well known matrix model techniques useful to study the planar limit, as well as methods exploiting group representation theory that are useful for the computation of correlators in large N but non-planar limits. On the gravity side of the correspondence, we describe in detail the computation of two- and three point functions of a scalar field coupled to gravity on the Euclidian AdSd+1 space, three-point functions of two giant gravitons and one pointlike graviton as well as correlators of Kaluza-Klein gravitons. A key observation of this study is that extremal correlators are mapped to scattering amplitudes of particles with parallel momenta. These are naturally accompanied by involve collinear divergences. Therefore, we suggest that the divergences in the computation of extremal correlators are linked to collinear divergences. A lot more work is needed to establish this connection.
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    Investigation of higher spin theory through holography and mathematical methods in free conformal field theory
    (2017) Rabe, Randle
    In this dissertation, we will develop novel methods for determining the spectrum of primary operators in a free conformal eld theory (vector model) and to construct some of these primaries. To count the spectrum of primaries, we use group theoretic techniques to obtain character formulas for any number of elds as representations of SO(4; 2). More precisely, we will construct generating functions that can be expanded to any order in the conformal scaling dimension to yield the complete spectrum of primaries constructed out of n scalar elds. We also develop e cient methods to construct these primaries by using a polynomial description. Finally, these primary operators, which are higher spin currents in the free conformal vector model, correspond to higher spin gauge elds in Vasiliev higher spin theory through the holographic duality.
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    Holographic measurement of the 26m HartRAO telescope
    (2009-05-08T10:08:02Z) Klein, Benjamin
    Microwave holography is a well established method of using the Fourier relationship between an antenna’s current distribution and its complex beam-pattern to produce surface maps of large parabolic antennas. As the final part of a surface upgrade, a holographic map of the HartRAO 26 m telescope was produced. This showed that the surface has an RMS error of 0.45 mm. The measurement used a small reference dish to correlate against and retrieve amplitude and phase values. Due to system phase instabilities, this dish had to be attached to the measured antenna in order to enable sharing a high frequency local oscillator (LO). The movement was modelled and corrected for. However, a slight distortion remained. It is recommended that, either the LO distribution system is stabilised by using multiple PLLs or amplifiers and low loss cables are used to enable moving the reference antenna to a stationary position.