Volume-coupling relation for M-theory on K3
= Volume-coupling relation for M-theory on K3
{title2=$g_{H,7}^2\propto(V/\ell_p^4)^{3/2}$}
A wrapped <M5-brane> fixes the heterotic <string tension> proportional to $V/\ell_p^6$. Reduction of the gravitational coupling gives $G_7\propto\ell_p^9/V$. Therefore $G_7/\ell_{s,H}^5\propto(V/\ell_p^4)^{3/2}$, yielding the displayed dimensionless coupling relation. This derivation separates the K3 volume modulus from its shape <Narain moduli space>.