A cosmic speed-trap: a gravity-independent test of cosmic acceleration using baryon acoustic oscillations

TL;DR

This paper introduces a new, gravity-independent method to test cosmic acceleration by comparing BAO measurements at different redshifts, which can strongly distinguish between accelerating and non-accelerating universe models.

Contribution

It derives a novel inequality involving BAO observables that is violated by models with recent cosmic acceleration, providing a model-independent test of acceleration.

Findings

Expected to exclude non-accelerating models at ~4σ with current data

Can reach ~7σ significance with future surveys

Test is independent of gravity theories and other cosmological observations

Abstract

We propose a new and highly model-independent test of cosmic acceleration by comparing observations of the baryon acoustic oscillation (BAO) scale at low and intermediate redshifts: we derive a new inequality relating BAO observables at two distinct redshifts, which must be satisfied for any reasonable homogeneous non-accelerating model, but is violated by models similar to LambdaCDM, due to acceleration in the recent past. This test is fully independent of the theory of gravity (GR or otherwise), the Friedmann equations, CMB and supernova observations: the test assumes only the Cosmological Principle, and that the length-scale of the BAO feature is fixed in comoving coordinates. Given realistic medium-term observations from BOSS, this test is expected to exclude all homogeneous non-accelerating models at ~ 4\sigma significance, and can reach ~ 7\sigma with next-generation surveys.