Constraining dark energy fluctuations with supernova correlations

TL;DR

This paper explores how spatial fluctuations in dark energy could affect supernova observations, using covariance analysis to constrain such fluctuations and finding current data consistent with no fluctuations.

Contribution

It introduces a method to relate dark energy fluctuation spectra to supernova magnitude covariance and applies it to observational data for constraints.

Findings

No significant dark energy fluctuations detected

Current data allows for linear regime fluctuations

Method links fluctuation spectra to observable covariance

Abstract

We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state is not equal to -1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.