Cosmic shear bispectrum from second-order perturbations in General
  Relativity
  Future lensing surveys will be nearly full-sky and reach an unprecedented
depth, probing scales closer and closer to the Hubble radius. This motivates
the study of the cosmic shear beyond the small-angle approximation and
including general relativistic corrections that are usually suppressed on
sub-Hubble scales. The complete expression of the reduced cosmic shear at
second order including all relativistic effects was derived in [1]. In the
present paper we compute the resulting cosmic shear bispectrum when all these
effects are properly taken into account and we compare it to primordial
non-Gaussianity of the local type. The new general relativistic effects are
generically smaller than the standard non-linear couplings. However, their
relative importance increases at small multipoles and for small redshifts of
the sources. The dominant effect among these non standard corrections is due to
the inhomogeneity of the source redshift. In the squeezed limit, its amplitude
can become of the order of the standard couplings when the redshift of the
sources is below 0.5. Moreover, while the standard non-linear couplings depend
on the angle between the short and long mode, the relativistic corrections do
not and overlap almost totally with local type non-Gaussianity. We find that
they can contaminate the search for a primordial local signal by f_NL>10.
