Unscreening Modified Gravity in the Matter Power Spectrum

TL;DR

This paper proposes a method to enhance the detection of modified gravity effects in the matter power spectrum by suppressing high-density regions, enabling more stringent cosmological constraints than traditional tests.

Contribution

It introduces a novel approach to differentiate modified gravity models from standard cosmology by focusing on unscreened low-density regions in the matter power spectrum using N-body simulations.

Findings

Percent-level measurement of clipped power constrains chameleon models more tightly than Solar System tests.

Method effective for both chameleon and Vainshtein screening mechanisms.

Density threshold variation helps address degeneracies with other effects.

Abstract

Viable modifications of gravity that may produce cosmic acceleration need to be screened in high-density regions such as the Solar System, where general relativity is well tested. Screening mechanisms also prevent strong anomalies in the large-scale structure and limit the constraints that can be inferred on these gravity models from cosmology. We find that by suppressing the contribution of the screened high-density regions in the matter power spectrum, allowing a greater contribution of unscreened low densities, modified gravity models can be more readily discriminated from the concordance cosmology. Moreover, by variation of density thresholds, degeneracies with other effects may be dealt with more adequately. Specializing to chameleon gravity as a worked example for screening in modified gravity, employing N-body simulations of f(R) models and the halo model of chameleon theories, we demonstrate the effectiveness of this method. We find that a percent-level measurement of the clipped power at k < 0.3 h/Mpc can yield constraints on chameleon models that are more stringent than what is inferred from Solar System tests or distance indicators in unscreened dwarf galaxies. Finally, we verify that our method is also applicable to the Vainshtein mechanism.