Averaged Lema\^itre-Tolman-Bondi dynamics
  We consider cosmological backreaction effects in Buchert's averaging
formalism on the basis of an explicit solution of the Lema\^itre-Tolman-Bondi
(LTB) dynamics which is linear in the LTB curvature parameter and has an
inhomogeneous bang time. The volume Hubble rate is found in terms of the volume
scale factor which represents a derivation of the simplest phenomenological
solution of Buchert's equations in which the fractional densities corresponding
to average curvature and kinematic backreaction are explicitly determined by
the parameters of the underlying LTB solution at the boundary of the averaging
volume. This configuration represents an exactly solvable toy model but it does
not adequately describe our "real" Universe.
