Breaking the conformal freedom of spacetime with supernova neutrino imaging

TL;DR

This paper demonstrates that combining supernova light cone measurements with neutrino cone observations can fully determine the spacetime metric, overcoming the conformal gauge freedom inherent in light-based measurements alone.

Contribution

The authors introduce a method to measure neutrino cones alongside light cones, enabling complete spacetime metric determination, which was previously limited by conformal gauge ambiguity.

Findings

Neutrino cone measurements remove conformal gauge ambiguity.

Ultrarelativistic neutrinos are essential for this measurement.

The method provides a more complete geometric understanding of spacetime.

Abstract

It is known that a geometric measurement of the light cones of supernovae determines the conformal class of the visible part of the spacetime. The conformal factor is physically meaningful but cannot be determined geometrically by anything with zero mass, such as the photon. We show that measuring the neutrino cones in addition to light cones completely removes this gauge freedom. We describe the physical model in great detail, including why ultrarelativistic neutrinos are the only option.