Asta Heinesen and Hayley Macpherson tell us about their recent papers developing a formalism for measuring local parameters without assuming local isotropy (and homogeneity) and predicting what we should expect for the parameters in this formalism when we go beyond the isotropic approximation of FRW.

Asta talks about her paper from last year which developed the formalism, and how a finite number of terms can capture all the expected behaviour in the anisotropic luminosity distance, at each order of redshift.

Hayley then talks about how, together, they applied Asta’s formalism to Hayley’s fully relativistic simulations of cosmology.

They show the results for the generalised Hubble, “deceleration” and jerk parameters. It turns out that when you remove the assumption of isotropy these parameters do indeed depend, sometimes very significantly, on which direction you look on the sky.

How much this is impacting our measurements depends, among other things, on how full your sky coverage is.

Asta: https://inspirehep.net/authors/1726735
Hayley: https://hayleyjm.github.io/

Asta’s paper: https://arxiv.org/abs/2010.06534
Asta and Hayley’s paper: https://arxiv.org/abs/2103.11918

The paper Hayley mentions where she went as non-linear as possible with full general relativity: https://arxiv.org/abs/1807.01711
The paper Asta mentions that has measured a dipole in observed quasars that is slightly different to the CMB dipole: https://arxiv.org/abs/2009.14826