arXiv subjects

James Babington

Publications and source records attributed to James Babington.

15 recordsLinked to original sources

arXiv2021

Ray-Wave Duality of Electromagnetic Fields: A Feynman Path integral Approach to Classical Vectorial Imaging

We consider how vectorial aspects (polarization) of light propagation can be implemented, and its origin, within a Feynman path integral approach. A key part of this scheme is in generalising the standard optical path length integral from a scalar to a matrix quantity. Reparametrization invariance along the rays allows a covariant formulation where propagation can take place along a general curve. A general gradient index background is used to demonstrate the scheme. This affords a description of classical imaging optics when the polarization aspects may be varying rapidly and cannot be neglected.

physics.optics↗

arXiv2011

Graphene membranes and the Dirac-Born-Infeld action

We propose the use of the Dirac-Born-Infeld action in the phenomenological description of graphene sheet dynamics and interactions. Both the electronic properties of the Dirac fermions and the overall dynamics can be incorporated into this model. Classical static configurations, as well as quantum fluctuations of the membrane degrees of freedom can be studied in this framework. This makes it an interesting tool for Casimir physics and novel QED processes.

cond-mat.mes-hall↗

arXiv2011

Magneto-Electric response functions for simple atomic systems

We consider a simple atomic two-body bound state system that is overall charge neutral and placed in a static electric and magnetic field, and calculate the magneto-electric response function as a function of frequency. This is done from first principles using a two-particle Hamiltonian for both an harmonic oscillator and Coulomb binding potential. In the high frequency limit, the response function falls off as 1/ω^2 whilst at low frequencies it tends to a constant value.

quant-ph↗

arXiv2010

Casimir momentum of magneto-chiral matter

We consider a scattering formulation of radiative momentum transfer to a Magneto-Chiral system that is subjected to a constant background magnetic field. The system takes the form of a collection magnetic dipoles that exhibit the Faraday effect. It is shown that the first non-trivial contribution of the momentum transfer to the object from the radiation field occurs at fourth order in the Born series.

cond-mat.mes-hall↗

arXiv2010

Casimir Forces in Multi-Sphere Configurations

We calculate the Casimir force on an isolated dielectric sphere in an ensemble of $N$ spheres due to multiple mutual interactions of the collection of spheres. In particular we consider dielectric spheres immersed in some other background dielectric. As an example, the Casimir force between two and three spheres at zero and finite temperature is evaluated. For a very large number of spheres, we consider a large-$N$ scaling limit of the Casimir force.

quant-ph↗

arXiv2010

Universal scaling laws for dispersion interactions

We study the scaling behaviour of dispersion potentials and forces under very general conditions. We prove that a rescaling of an arbitrary geometric arrangement by a factor a changes the atom-atom and atom-body potentials in the long-distance limit by factors 1/a^7 and 1/a^4, respectively and the Casimir force per unit area by 1/a^4. In the short-distance regime, electric and magnetic bodies lead to different scaling behaviours. As applications, we present scaling functions for two atom-body potentials and display the equipotential lines of a plate-assisted two-atom potential.

quant-ph↗

arXiv2010

Casimir forces from a loop integral formulation

We reformulate the Casimir force in the presence of a non-trivial background. The force may be written in terms of loop variables, the loop being a curve around the scattering sites. A natural path ordering of exponentials take place when a particular representation of the scattering centres is given. The basic object to be evaluated is a reduced (or abbreviated) classical pseudo-action that can be operator valued.

quant-ph↗

arXiv2009

Casimir forces between spheres

We discuss the calculation of Casimir forces between a collection of $N$-dielectric spheres. This is done by evaluating directly the force on a sphere constructed from a stress tensor, rather than an interaction energy. Two and three body forces between the spheres are evaluated for setups of two and three sphere systems respectively. An approximate large-$N$ limit is also obtained for the functional dependence on the number of spheres.

quant-ph↗

arXiv2009

Casimir forces between spheres and loop integrals

A summary of recent calculations of Casimir forces between a collection of $N$-dielectric spheres is presented. This is done by evaluating directly the force on a sphere constructed from a stress tensor, rather than an interaction energy. A loop integral formulation is also discussed where we rewrite the expressions for the force in terms of loop integrals for the effective classical propagation of the electric and magnetic fields.

quant-ph↗

arXiv2005

Towards a Holographic Dual of SQCD: Holographic Anomalies and Higher Derivative Gravity

We consider the holographic dual of SQCD in the conformal phase. It is based on a higher derivative gravity theory, which ensures the correct field theory anomalies. This is then related to a six dimensional gravity theory via S^1 compactification. Some speculations are then made about the correspondence, Seiberg duality, and the nature of confinement from a holographic perspective.

hep-th↗

arXiv2005

Space-time dependent couplings in N=1 SUSY gauge theories: Anomalies and Central Functions

We consider N=1 supersymmetric gauge theories in which the couplings are allowed to be space-time dependent functions. Both the gauge and the superpotential couplings become chiral superfields. As has recently been shown, a new topological anomaly appears in models with space-time dependent gauge coupling. Here we show how this anomaly may be used to derive the NSVZ beta function in a particular, well-determined renormalisation scheme, both without and with chiral matter. Moreover we extend the topological anomaly analysis to theories coupled to a classical curved superspace background, and use it to derive an all-order expression for the central charge c, the coefficient of the Weyl tensor squared contribution to the conformal anomaly. We also comment on the implications of our results for the central charge a expected to be of relevance for a four-dimensional C-theorem.

hep-th↗

arXiv2003

A Non-supersymmetric Deformation of the AdS/CFT Correspondence

We deform the AdS/CFT Correspondence by the inclusion of a non-supersymmetric scalar mass operator. We discuss the behaviour of the dual 5 dimensional supergravity field then lift the full solution to 10 dimensions. Brane probing the resulting background reveals a potential consistent with the operator we wished to insert.

hep-th↗

arXiv2003

A Stable Supergravity Dual of Non-supersymmetric Glue

We study non-supersymmetric fermion mass and condensate deformations of the AdS/CFT Correspondence. The 5 dimensional supergravity flows are lifted to a complete and remarkably simple 10 dimensional background. A brane probe analysis shows that when all the fermions have an equal mass a positive mass is generated for all six scalar fields leaving non-supersymmetric Yang Mills theory in the deep infra-red. We numerically determine the potential, produced by the background, in the Schroedinger equation relevant to the study of O^++ glueballs. The potential is a bounded well, providing evidence of stability and for a discrete, confined spectrum. The geometry can also describe the supergravity background around an (unstable) fuzzy 5-brane.

hep-th↗

arXiv2001

Field Theory Operator Encoding in N=2 Geometries

We investigate supergravity solutions describing D5 branes wrapped on a two cycle which are dual to N=2 super Yang Mills theory. Brane probing these solutions allows the moduli space of the field theory to be identified. There are a unique set of coordinates in which the field theory on the probe takes an N=2 form and in these coordinates the running coupling of the gauge theory may be identified. We show that the geometry, when restricted to the moduli space, takes a very simple form involving only two functions. One is the running gauge coupling whilst the other parametrizes the scalar operators of the field theory. The D5 brane distributions, for the full set of solutions in the literature,can be determined by assuming the field theory's form for the running coupling as a function of scalar vevs. We show that the resulting distributions also correctly reproduce the scalar operators parametrized elsewhere providing the first non-trivial consistency check on the duality.

hep-th↗

arXiv2001

Secrets of the Metric In N=4 and N=2* Geometries

The metric of the gravity dual of a field theory should contain precisely the same information as the field theory. We discuss this connection in the N=4 theory where a scalar vev may be introducedat the level of 5d supergravity and the solutions lifted to 10d. We stress the role of brane probing in finding the coordinates appropriate to the field theory. In these coordinates the metric parametrizes the gauge invariant operators of the field theory and either side of the duality is uniquely determined by the other. We follow this same chain of computations for the 10d lift of the N=2* geometry of Pilch and Warner. The brane probe of the metric reveals the 2d moduli space and the functional form of the gauge coupling. In the coordinates appropriate to the field theory the metric on moduli space takes a very simple form and one can read off the gravity predictions for operators in the field theory. Surprisingly there is logarithmic renormalization even in the far UV where the field theory reverts to N=4 super Yang-Mills. We extend the analysis of Buchel et al to find the D3 brane source distribution that generates the supergravity prediction for the gauge coupling for the whole class of solutions corresponding to different points on moduli space. This distribution does not account for the logarithmic behaviour in the rest of the metric though. We discuss possible resolutions of the discrepancy.

hep-th↗