Behaviour of the Brascamp--Lieb constant
  Recent progress in multilinear harmonic analysis naturally raises questions about the local behaviour of the best constant (or bound) in the general Brascamp--Lieb inequality as a function of the underlying linear transformations. In this paper we prove that this constant is continuous, but is not in general differentiable. 
Jonathan Bennett, Neal Bez, Michael G. Cowling, and Taryn C. Flock
math.CA