Effect of torsion on the radiation fields in curved spacetime
Susobhan Mandal (Department of Physical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur - 741 246, WB, India)
The torsion-free connection is one of the important assumptions in Einstein's General theory of Relativity which has not been verified so far from experimental observation. In this article, the effect of torsion on the on-shell action of radiation fields in curved spacetime is reported in order to show certain consequences and possible ways to probe torsion in curved spacetime. In order to describe non-vanishing torsion, we mostly use contorsion tensor in connection which can be written in the combination of torsion tensor and vice versa. We have discussed how does the field equation coming from the minimization of action with respect to torsion changes the matter part of the on-shell action of radiation through substitution of the spin tensor. We have also studied here the effect of torsion on the scalar and vector radiation field in curved spacetime. It is shown that the presence of torsion leads to extra polarizations in Gravitational waves or radiations other than the usual two polarizations already present in General Relativity. Further, it is also shown that in the presence of torsion, there exists a non-trivial vacuum configuration that is different from the trivial vacuum in the absence of coupling with torsion. It is also found that in a generic theory of vector field, the presence of torsion breaks the gauge invariance just like the presence of mass shows the violation of gauge invariance. The observational consequences of these results are also discussed.