  We establish the existence of loop type subcontinua of nonnegative solutions
for a class of concave-convex type elliptic equations with indefinite weights,
under Dirichlet and Neumann boundary conditions. Our approach depends on local
and global bifurcation analysis from the zero solution in a non-regular
setting, since the nonlinearities considered are not differentiable at zero, so
that the standard bifurcation theory does not apply. To overcome this
difficulty, we combine a regularization scheme with a priori bounds, and
Whyburn's topological method. Furthermore, via a continuity argument we prove a
positivity property for subcontinua of nonnegative solutions. These results are
based on a positivity theorem for the associated concave problem proved in
[15], and extend previous results established in the powerlike case.
