A Nonsymmetric Correlation Inequality for Gaussian Measure

Let?be a Gaussian measure (say, onRn) and letK,L?Rnbe such thatKis convex,Lis a “layer” (i.e.,L={x:a??x,u??b} for somea,b?Randu?Rn), and the centers of mass (with respect to?) ofKandLcoincide. Then?(K?L)??(K)·?(L). This is motivated by the well-known “positive correlation conjecture” for symmetric sets and a related inequality of Sidak concerning confidence regions for means of multivariate normal distributions. The proof uses the estimate?(x)> 1?((8/?)1/2/(3x+(x2+8)1/2))e?x2/2,x>?1, for the (standard) Gaussian cumulative distribution function, which is sharper than the classical inequality of Komatsu.