Loewy lengths of blocks with abelian defect groups

Abstract: We consider $p$-blocks with abelian defect groups and in the first part prove a relationship between its Loewy length and that for blocks of normal subgroups of index $p$. Using this, we show that if $B$ is a $2$-block of a finite group with abelian defect group $$D \cong C_{2^{a_1}} \times \cdots \times C_{2^{a_r}} \times (C_2)<sup>s$$, where $a_i &gt; 1$ for all $i$ and $r \geq 0$, then $d &lt; LL(B) \leq 2<sup>{a_1}+\cdots+2<sup>{a_r}+2s-r+1$, where $|D|=2<sup>d$. When $s=1$ the upper bound can be improved to $2<sup>{a_1}+\cdots+2<sup>{a_r}+2-r$. Together these give sharp upper bounds for every isomorphism type of $D$. A consequence is that when $D$ is an abelian $2$-group the Loewy length is bounded above by $|D|$ except when $D$ is a Klein-four group and $B$ is Morita equivalent to the principal block of $A_5$. We conjecture similar bounds for arbitrary primes and give evidence that it holds for principal $3$-blocks.