Elliptic genus, anomaly cancellation and heterotic M-theory

We derive global consistency condition for strongly coupled heterotic string in the presence of M5-branes. Its elliptic genus is interpretable as generating functional of anomaly polynomials and so, on anomaly-free vacua, the genus is both holomorphic and modular invariant. In the holomorphic basis, we identify the modular properties by calculating the phase. By interpreting the refinement parameters as background curvature of tangent and vector bundles, we show that the extended Bianchi identity for Kalb-Ramond field of heterotic M-theory is satisfied in the presence of arbitrary numbers of M5-branes.