Astronomy Unit PhD Student Pritha Paul has led a study, published in Physical Review Letters, showing that large scale galaxy distribution is not as symmetric as we thought.
In cosmology, it is generally expected that galaxy clustering on large scales is invariant under parity transformations. In three dimensions, a parity inversion is defined as a mirror image followed by a rotation. This parity invariance is expected at a fairly fundamental level as the key forces involved are parity invariant, and generating initial fluctuations which underly the distribution of galaxies seems to be very implausible. However intriguing recent observations of the large-scale distribution of galaxies indicate that there could be some sort of parity asymmetry on the largest scales of the cosmos. If true this could require some very fundamental changes to the laws of physics as we know them.Now new research led by PhD student Pritha Paul in the Astronomy Unit suggests that this symmetry could potentially be broken and explained simply by the existing laws of general relativity. Traditionally, researchers have relied on a Newtonian approximation to compute large-scale correlations. She has demonstrated, however, that this approximation does not capture the full picture, as relativistic corrections introduce odd-parity contributions to lower-order statistics, and are important on the scales probed in modern large-scale structure surveys. Pritha’s work extends this understanding, showing that these corrections are equally significant for the complex correlation function used in the observational analyses. Pritha says, “These relativistic contributions are really important for upcoming surveys which are probing ever larger fractions of the sky. It is now imperative we take them into account."This work has recently been published in Physical Review Letters [link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.121001] with co-authors Chris Clarkson, Head of the Astronomy Unit, and Roy Maartens, University of the Western Cape. It was selected as an Editors Suggestion due to its "particular importance, innovation, and broad appeal”. You can watch Pritha and Chris discussing this work on “Cosmology Talks" here https://youtu.be/WPlrF9GvDHM