Fractal universe and cosmic acceleration in a Lema\^itre-Tolman-Bondi
  scenario
  In this paper we attempt to answer to the question: can cosmic acceleration
of the Universe have a fractal solution? We give an exact solution of a
Lema\^itre-Tolman-Bondi (LTB) Universe based on the assumption that such a
smooth metric is able to describe, on average, a fractal distribution of
matter. While the LTB model has a center, we speculate that, when the fractal
dimension is not very different from the space dimension, this metric applies
to any point of the fractal structure when chosen as center so that, on
average, there is not any special point or direction. We examine the observed
magnitude-redshift relation of type Ia supernovae (SNe Ia), showing that the
apparent acceleration of the cosmic expansion can be explained as a consequence
of the fractal distribution of matter when the corresponding space-time metric
is modeled as a smooth LTB one and if the fractal dimension on scales of a few
hundreds Mpc is $D=2.9 \pm 0.02$.
