Detecting the relativistic bispectrum in 21cm intensity maps

Understand

We investigate the detectability of leading-order relativistic effects in the bispectrum of future 21cm intensity mapping surveys.

• The relativistic signal arises from Doppler and other line-of-sight effects in redshift space.
• In the power spectrum of a single tracer, these effects are suppressed by a factor $\cH^2/k^2$.
• By contrast, in the bispectrum the relativistic signal couples to short-scale modes, leading to an imaginary contribution that scales as $\cH/k$, thus increasing the possibility of detection.