Brane tensions and coupling constants from within M-theory

Reviewing the cancellation of local anomalies of M-theory on R10×S1/Z2 the Yang-Mills coupling constant on the boundaries is rederived. The result is λ2=21/3(2π)(4πκ2)2/3 corresponding to η=λ6/κ4=256π5 in the “upstairs” units used by Hořava and Witten and differs from their calculation. It is shown that these values are compatible with the standard membrane and fivebrane tensions derived from the M-theory bulk action. In view of these results it is argued that the natural units for M-theory on R10×S1/Z2 are the “downstairs” units where the brane tensions take their standard form and the Yang-Mills coupling constant is λ2=4π(4πκ2)2/3.