The weak commutativity group $\chi(G)$ is generated by two isomorphic groups $G$ and $G^{ \varphi }$ subject to the relations $[g,g^{ \varphi}]=1$ for all $g \in G$. The group $\chi(G)$ is an extension of $D(G) = [G,G^{ \varphi}]$ by $G \times G$. We prove that if $G$ is a finite solvable group of derived length $d$, then $\exp(D(G))$ divides $\exp(G)^{ d}$ if $|G|$ is odd and $\exp(D(G))$ divides $2^{ d-1}\cdot \exp(G)^{ d}$ if $|G|$ is even. Further, if $p$ is a prime and $G$ is a $p$-group of class $p-1$, then $\exp(D(G))$ divides $\exp(G)$. Moreover, if $G$ is a finite $p$-group of class $c\geq 2$, then $\exp(D(G))$ divides $\exp(G)^{ \lceil \log_{ p-1}(c+1)\rceil}$ ($p\geq 3$) and $\exp(D(G))$ divides $2^{ \lfloor \log_2(c)\rfloor} \cdot \exp(G)^{ \lfloor \log_2(c)\rfloor+1}$ ($p=2$).
Categories: math.GR