Abstract

We study the analogy between propagation of light rays in a stationary curved spacetime and in a toroidal (meta-)material. After introducing a novel gravitational analog of the index of refraction of a magneto-electric medium, it is argued that light rays not only feel a Lorentz-like force in a magneto-electric medium due to the non-vanishing curl of the toroidal moment, but also there exists an optical analog of Aharonov–Bohm effect for the rays traveling in a region with a curl-free toroidal moment. Experimental realization of this effect could utilize either a multiferroic material or a toroidal metamaterial.

Highlights

  • Apart from yet being the most successful theory of gravity, general relativity and the exact solutions of Einstein field equations, in recent years have turned into a very powerful tool to study linear and nonlinear phenomena in other branches of physics

  • In the present article, motivated by the gravitational Aharonov-Bohm effect, first we use the 1 + 3 formulation of spacetime decomposition to exhibit an interesting analogy between electromagnetic wave propagation in a stationary curved spcetime and in a magneto-electricmaterial, and employ this analogy to show that there should be an optical analog of this effect inmaterials with toroidal moment

  • In section five after a brief introduction of the gravitational Aharonov-Bohm effect we discuss our prediction of the optical analog of the Aharonov-Bohm effect in toroidalmaterials with any value for the toroidal moment and show that it reduces to the previous result in the limit of small toroidal moment

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Summary

INTRODUCTION

Apart from yet being the most successful theory of gravity, general relativity and the exact solutions of Einstein field equations, in recent years have turned into a very powerful tool to study linear and nonlinear phenomena in other branches of physics. Their nontrivial properties, such as negative refractive index [3], originate not from the composition of their constituents, but from the way these subwavelength macroscopic constituents are assembled Another key development was the introduction of transformation optics [4], which formulates how electromagnetic field lines and the corresponding light rays could be redirected by deforming the underlying space in which they are embedded, very much like rerouting a river by deforming its bed. For a stationary spacetime we arrive at a novel form for the spacetime index of refraction, introduced here for the first time in the literature, which enables us to interpret it as the gravitational analog of the magneto-electric index of refraction in a material with toroidal moment In section three this analogy is extended to Maxwell equations in a stationary spacetime and their corresponding constitutive equations which include magneto-electric terms. Throughout we use the (+,-,-,-) signature for spacetime metric and our convention for indices is such that the Latin indices run from 1 to 3 while the Greek ones run from 0 to 3

CURVED SPACETIME AS A MEDIUM
Summary and Discussion

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