  We study the relation between the causality and the positivity of energy
bounds in Gauss-Bonnet gravity in AdS_7 background and find a precise
agreement. Requiring the group velocity of metastable states to be bounded by
the speed of light places a bound on the value of Gauss-Bonnet coupling. To
find the positivity of energy constraints we compute the parameters which
determine the angular distribution of the energy flux in terms of three
independent coefficients specifying the three-point function of the
stress-energy tensor. We then relate the latter to the Weyl anomaly of the
six-dimensional CFT and compute the anomaly holographically. The resulting
upper bound on the Gauss-Bonnet coupling coincides with that from causality and
results in a new bound on viscosity/entropy ratio.
