Imprint of non-linear effects on HI intensity mapping on large scales
  Intensity mapping of the HI brightness temperature provides a unique way of
tracing large-scale structures of the Universe up to the largest possible
scales. This is achieved by using a low angular resolution radio telescopes to
detect emission line from cosmic neutral Hydrogen in the post-reionization
Universe. We use general relativistic perturbation theory techniques to derive
for the first time the full expression for the HI brightness temperature up to
third order in perturbation theory without making any plane-parallel
approximation. We use this result and the renormalization prescription for
biased tracers to study the impact of nonlinear effects on the power spectrum
of HI brightness temperature both in real and redshift space. We show how mode
coupling at nonlinear order due to nonlinear bias parameters and redshift space
distortion terms modulate the power spectrum on large scales. The large scale
modulation may be understood to be due to the effective bias parameter and
effective shot noise.
