Emergence of spacetime discreteness in Wightman function from polymer quantization of scalar field

Abstract: The Wightman function i.e. vacuum two-point function, for a massless free scalar field in Fock quantization is inversely proportional to the invariant distance squared between the corresponding spacetime points. Naturally it diverges when these two points are taken to be infinitesimally close to each other. Using a combination of analytical and numerical methods, we show that the Wightman function is bounded from above in polymer quantization of scalar field. The bounded value of the Wightman function is governed by the polymer scale and its bounded nature can be viewed as if the spacetime has a zero-point length. This emergence of effective discreteness in spacetime appears from polymer quantization of matter field alone as the geometry is treated classically. It also demonstrates that the polymer quantization of matter field itself can capture certain aspects of the effective discrete geometry. We discuss the implications of the result on the response function of a Unruh-DeWitt detector that depends on the properties of the Wightman function.