Toward a theory of curvature-scaling gravity

TL;DR

This paper introduces a novel approach to gravity where local curvature determines physical scales, leading to a curvature-dependent spacetime structure that extends Einstein's theory and has implications for cosmology and black holes.

Contribution

It proposes a curvature-scaling gravity framework where local Ricci scalar sets physical scales, resulting in a modified manifold and gravity theory extending Einstein's principles.

Findings

In vacuo, the theory reduces to R^2 gravity with new solutions.

One solution relates to galactic rotation curves similar to Mannheim's theory.

Another solution predicts new properties for Schwarzschild black holes.

Abstract

A salient feature of Horava gravity is the anisotropic time variable. We propose an alternative construction of the spacetime manifold which naturally enables time anisotropy. We promote the role of curvature: the Ricci scalar R at a given point sets the length scales for physical processes - including gravity - in the local inertial frames enclosing that point. The manifold is a patchwork of local regions; each region is Lorentz invariant and adopts a local scale a_R defined as a_R = 1/sqrt|R|. In each local patch, the length scales of physical processes are measured relatively to a_R, and only their dimensionless ratios partake in the dynamics of physical processes. Time anisotropy arises by requiring that the form - but not necessarily the parameters - of physical laws be unchanged under variations of the local a_R as one moves on the manifold. The time scaling is found to be dt ~ a_R^(3/2) whereas the spatial part scales as dx ~ a_R. We show how to conjoin the local patches of the manifold in a way which respects causality and special relativity, as well as the equivalence and general covariance principles. All of Einstein's insights are preserved but the parameters of physical laws are only valid locally and become functions of the prevailing Ricci scalar. This alternative construction of the manifold permits a unique choice for the Lagrangian of gravity coupled with matter. Curvature is actively involved in the dynamics of physical processes by setting the scale for them. In vacuo our theory takes the form of R^2 gravity and adopts a larger set of solutions superseding those of Einstein-Hilbert action R. We provide two solutions: one solution connects our work to Mannheim's theory of galactic rotation curves; the other leads to novel properties for Schwarzschild black holes. We apply the theory to address problems in cosmology and discuss its implications in quantum gravity.