Nontrival Cosmological Constant in Brane Worlds with Unorthodox
  Lagrangians
  In self-tuning brane-world models with extra dimensions, large contributions
to the cosmological constant are absorbed into the curvature of extra
dimensions and consistent with flat 4d geometry. In models with conventional
Lagrangians fine-tuning is needed nevertheless to ensure a finite effective
Planck mass. Here, we consider a class of models with non conventional
Lagrangian in which known problems can be avoided. Unfortunately these models
are found to suffer from tachyonic instabilities. An attempt to cure these
instabilities leads to the prediction of a positive cosmological constant,
which in turn needs a fine-tuning to be consistent with observations.
