Observed galaxy number counts on the lightcone up to second order: I.   Main result
  We present the galaxy number overdensity up to second order in redshift space on cosmological scales for a concordance model. The result contains all general relativistic effects up to second order that arise from observing on the past light cone, including all redshift effects, lensing distortions from convergence and shear, and contributions from velocities, Sachs-Wolfe, integrated SW and time-delay terms. This result will be important for accurate calculation of the bias on estimates of non-Gaussianity and on precision parameter estimates, introduced by nonlinear projection effects. 
Daniele Bertacca (Western Cape), Roy Maartens (Western Cape,   Portsmouth), Chris Clarkson (Cape Town)
astro-ph.CO