Physical Review D 69,6 (2004) 062001;
The unification of quantum field theory and general relativity is a fundamental goal of modern physics. In many cases, theoretical efforts to achieve this goal introduce auxiliary gravitational fields, ones in addition to the familiar symmetric second-rank tensor potential of general relativity, and lead to nonmetric theories because of direct couplings between these auxiliary fields and matter. Here, we consider an example of a metric-affine gauge theory of gravity in which torsion couples nonminimally to the electromagnetic field. This coupling causes a phase difference to accumulate between different polarization states of light as they propagate through the metric-affine gravitational field. Solar spectropolarimetric observations are reported and used to set strong constraints on the relevant coupling constant k:k(2)< (2.5 km)(2).
gregory-coude telescope;; spectral-lines;; instrumental polarization;; equivalence principle;; nonsymmetric theories;; magnetic fluxtubes;; field;; birefringence;; invariance;; particle
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