Sentence:  Similarly, \hat A(M) is represented by the closed differential form / ::: \hat A(M) = \sqrt{\operatorname{det\left (\frac{R/2}{\sinh(R/2)} \right ) / where R is the <WSD>Riemannian</WSD> curvature of the metric g, regarded as an \textstyle\operatorname{End}(TM)-valued two form, and \sqrt{\operatorname{det is the Pfaffian, which is an invariant polynomial defined on the Lie algebra of skew symmetric matrices in even dimensions. 
Meaning of the word marked with <WSD> tags:  Of or relating to the work, or theory developed from the work, of German mathematician (Bernhard Riemann), especially to Riemannian manifolds and Riemannian geometry.