Positive radial ground states for nonlinear biharmonic equations: maximum principles and expanding-domain approximation

We prove the existence of nonnegative radial ground states for a class of nonlinear biharmonic equations in $\mathbb R^N$, covering subcritical and critical nonlinearities. The solutions are obtained as limits of clamped ground states on expanding balls. The Cassani-Tarsia homogeneous maximum princi