Non-Riemannian metric emergent from scalar quantum field theory

Abstract

We show that the two-point function \sigma(x,x')=\sqrt{<[\phi(x)-\phi(x')]^{2}>} of a scalar quantum field theory is a metric (i.e., a symmetric positive function satisfying the triangle inequality) on space-time (with imaginary time). It is very different from the Euclidean metric |x-x'| at large distances, yet agrees with it at short distances. For example, space-time has finite diameter which is not universal. The Lipschitz equivalence class of the metric is independent of the cutoff. \sigma(x,x') is not the length of the geodesic in any Riemannian metric. Nevertheless, it is possible to embed space-time in a higher dimensional space so that \sigma(x,x') is the length of the geodesic in the ambient space. \sigma(x,x') should be useful in constructing the continuum limit of quantum field theory with fundamental scalar particles.