Etherington duality breaking: gravitational lensing in non-metric spacetimes versus intrinsic alignments by Eileen Sophie Giesel et al. on Tuesday 22 November

The Etherington distance duality relation is well-established for metric

theories of gravity, and confirms the duality between the luminosity distance

and the angular diameter distance through the conservation of surface

brightness. A violation of the Etherington distance duality due to lensing in a

non-metric spacetime would lead to fluctuations in surface brightness of

galaxies. Likewise, fluctuations of the surface brightness can arise in

classical astrophysics as a consequence of intrinsic tidal interaction of

galaxies with their environment. Therefore, we study these in two cases in

detail: Firstly, for intrinsic size fluctuations and the resulting changes in

surface brightness, and secondly, for an area-metric spacetime as an example of

a non-metric spacetime where the distance duality relation itself acquires

modifications. The aim of this work is to quantify whether a surface brightness

fluctuation effect due to area-metric gravity would be resolvable compared to

the similar effect caused by intrinsic alignment. We thus compare the auto- and

cross-correlations of the angular spectra in these two cases and show that the

fluctuations in intrinsic brightness can potentially be measured with a

cumulative signal-to-noise ratio $\Sigma(\ell) \geq 3$ in a Euclid-like survey.

The measurement in area-metric spacetimes, however, depends on the specific

parameter choices, which also determine the shape and amplitude of the spectra.

While lensing surveys do have sensitivity to lensing-induced surface brightness

fluctuations in area-metric spacetimes, the measurement does not seem to be

possible for natural values of the Etherington-breaking parameters.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2208.07197v2