Character triples and relative defect zero characters

Given a character triple $(G,N,\theta )$, which means that $G$ is a finite group with $N⊲G$ and $\theta \in \mathrm{I}\mathrm{r}\mathrm{r}(N)$ is $G$-invariant, we introduce the notion of a $\pi$-quasi extension of $\theta$ to $G$ where $\pi$ is the set of primes dividing the order of the cohomology element $[\theta {]}_{G\mathrm{/}N}\in H^2(G\mathrm{/}N,{\mathbb{C}}^{\times })$ associated with the character triple, and then establish the uniqueness of such an extension in the normalized case. As an application, we use the $\pi$-quasi extension of $\theta$ to construct a bijection from the set of $\pi$-defect zero characters of $G\mathrm{/}N$ onto the set of relative $\pi$-defect zero characters of $G$ over $\theta$. Our results generalize the related theorems of M. Murai and of G. Navarro.