On the global Gaussian bending measure and its applications in stationary spacetimes

TL;DR

This paper introduces a global Gaussian bending measure applicable to stationary spacetimes, providing a new geometric framework to test and distinguish modified gravity theories in strong-field regions using local experiments.

Contribution

It defines a global bending measure based on differential geometry, applicable across various gravity theories and spacetime regions, enabling new tests of gravity in strong-field environments.

Findings

Applicable to massless and massive messengers like photons and neutrinos

Describes gravitational bending in stationary spacetimes outside rotating black holes

Facilitates design of local strong-field experiments for gravity testing

Abstract

Modified gravity theories have been suggested to address the limitations of general relativity, each exhibiting differences, particularly in their strong-field limits. Nonetheless, there lacks effective means to distinguish or test these theories through local strong-field measurements. In this work, we define a global Gaussian bending measure over singular spacetime regions, establish a corresponding global theory, and demonstrate its applications in a general stationary spacetime. The global theory is based on differential geometry, rather than on specific gravity theories, allowing it to depict various physics within general relativity and beyond. For example, it can be applied to describe the gravitational bending of massless or massive messengers, such as photons, neutrinos, cosmic rays, and possibly massive gravitational waves predicted in certain theories of gravity. Besides, the global theory is applicable to any stationary spacetime regions outside a rotating black hole. As an instance of its direct applications, we investigate the highly-curved spacetime effects of the black hole in its immediate surrounding regions and design local strong-field experiments involving different shapes of singular lensing patches. New means can be therefore anticipated to be developed according to the global theory to differentiate between different gravity theories and test them in their strong-field regions.