Extensions of group schemes of $\mu$-type by a constant group scheme
  For a number field $K$, a finite set of primes $S$ not containing a fixed prime $p$, we explain when extensions of group schemes of $\mu_p$ by $\Z/p\Z$ split over the ring of $S$-integers $O_S$ of $K$. 
Hendrik Verhoek
math.NT math.AG