Astrophysical Tests of Modified Gravity: Constraints from Distance Indicators in the Nearby Universe

TL;DR

This study uses nearby distance measurements from cepheids, TRGB stars, and water masers to test modified gravity theories, setting new constraints that surpass previous astrophysical limits and challenging certain f(R) models.

Contribution

It introduces a novel method of testing scalar-tensor gravity theories using multiple distance indicators in the local universe, providing the most stringent astrophysical constraints to date.

Findings

No evidence for expected force enhancements in tested theories.

Constraints rule out f(R) models with fR0 above 5e-7 at 95% confidence.

Demonstrates the effectiveness of local universe measurements for gravity tests.

Abstract

We use distance measurements in the nearby universe to carry out new tests of gravity, surpassing other astrophysical tests by over two orders of magnitude for chameleon theories. The three nearby distance indicators -- cepheids, tip of the red giant branch (TRGB) stars, and water masers -- operate in gravitational fields of widely different strengths. This enables tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars are altered (in opposite directions) over a range of chameleon gravity theory parameters well below the sensitivity of cosmological probes. Using published data we have compared cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. As a control sample we use a comparable set of screened galaxies. We find no evidence for the order unity force enhancements expected in these theories. Using a two-parameter description of the models (the coupling strength and background field value) we obtain constraints on chameleon and symmetron screening scenarios. In particular we show that f(R) models with background field values fR0 above 5e-7 are ruled out at the 95% confidence level. We also compare TRGB and maser distances to the galaxy NGC 4258 as a second test for larger field values. While there are several approximations and caveats in our study, our analysis demonstrates the power of gravity tests in the local universe. We discuss the prospects for additional, improved tests with future observations.