S-numbers of elementary operators on C*-algebras

We study the s-numbers of elementary operators acting on C*-algebras. The main results are the following: If $\tau$ is any tensor norm and $a,b\in B(H)$ are such that the sequences $s(a),s(b)$ of their singular numbers belong to a stable Calkin space $J$ then the sequence of approximation numbers of $a{\otimes }_{\tau }b$ belongs to $J$. If $A$ is a C*-algebra, $J$ is a stable Calkin space, $s$ is an s-number function, and $a_i,b_i\in A,$ $i=1,\mathrm{.}\mathrm{.}\mathrm{.},m$ are such that $s(\pi (a_i)),s(\pi (b_i))\in J$, $i=1,\mathrm{.}\mathrm{.}\mathrm{.},m$ for some faithful representation $\pi$ of $A$ then $s({\sum }_{i=1}^m{M}_{a_i,b_i})\in J$. The converse implication holds if and only if the ideal of compact elements of $A$ has finite spectrum. We also prove a quantitative version of a result of Ylinen.