Tautological algebra of the moduli stack of semi stable bundles of rank two on a general curve.

Our aim in this paper is to determine the tautological algebra generated by the cohomology classes of the Brill Noether loci in the rational cohomology of the moduli stack $\mathcal{U}_C(n,d)$ of semistable bundles of rank $n$ and degree $d$. When $C$ is a general smooth projective curve of genus $g\geq 2$, $n=2$, $d=2g-2$, the tautological algebra of $ \mathcal{U}_C(2,2g-2)$ (resp. $\mathcal{SU}_C(2,L)$, $deg(L)=2g-2)$) is generated by the divisor classes (resp. the Theta divisor $\Theta$).