Dodging the cosmic curvature to probe the constancy of the speed of light

TL;DR

This paper introduces a model-independent method using Gaussian processes to test the constancy of the speed of light, effectively removing cosmic curvature degeneracy, and demonstrates its potential with simulated future data.

Contribution

The authors develop a novel, model-independent approach to probe the speed of light's constancy, eliminating cosmic curvature degeneracy and enhancing future observational constraints.

Findings

No deviation from the current speed of light detected.

Dark Energy Survey can detect 1-2% variations in c with current data.

Future experiments could detect 0.1% variations if errors are reduced.

Abstract

We develop a new model-independent method to probe the constancy of the speed of light $c$. In our method, the degeneracy between the cosmic curvature and the speed of light can be eliminated, which makes the test more natural and general. Combining the independent observations of Hubble parameter $H(z)$ and luminosity distance $d_L(z)$, we use the model-independent smoothing technique, Gaussian processes, to reconstruct them and then detect variation of the speed of light. We find no signal of deviation from the present value of the speed of light $c_0$. Moreover, to demonstrate the improvement in probing the constancy of the speed of light from future experiments, we produce a series of simulated data. The Dark Energy Survey will be able to detect $\Delta c /c_0 \sim 1\%$ at $\sim 1.5\sigma$ confidence level and $\Delta c /c_0 \sim 2\%$ at $\sim 3\sigma$ confidence level. If the errors are reduced to one-tenth of the expected DES ones, it can detect a $\Delta c /c_0 \sim 0.1\%$ variation at $\sim 2\sigma$ confidence level.