Parity-odd galaxy bispectrum

The galaxy bispectrum contains a wealth of information about the early universe, gravity, as well as astrophysics such as galaxy bias. Here, we study the parity-odd imaginary part of the galaxy bispectrum which is hitherto largely unexplored. In the standard cosmological model, the odd-parity bispectrum is generated by galaxy velocities through redshift-space distortions, yielding a guaranteed signal which provides a useful consistency test of measurements of galaxy clustering. While small in the case of general relativity coupled with smooth dark energy, the signal could be larger in modified gravity scenarios. Thus, the odd bispectrum offers a clean way for searching for new physics.