Optimal observables in galaxy surveys
  The sufficient statistics of the one-point probability density function of
the dark matter density field is worked out using cosmological perturbation
theory and tested to the Millennium simulation density field. The logarithmic
transformation is recovered for spectral index close to $-1$ as a special case
of the family of power transformations. We then discuss how these transforms
should be modified in the case of noisy tracers of the field and focus on the
case of Poisson sampling. This gives us optimal local transformations to apply
to galaxy survey data prior the extraction of the spectrum in order to capture
most efficiently the information encoded in large scale structures.
