Redshift drift as a model independent probe of dark energy
Asta Heinesen
Abstract
It is well known that a positive value of redshift drift is a signature of violation of the strong energy condition within general relativistic Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) universe models. In the Lambda Cold Dark Matter ($\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$) paradigm of cosmology, founded on the FLRW model ansatz, the violation of the strong energy condition is realized by a dark energy component with ``equation of state'' equal to minus unity. This dark energy component, which is unexplained in the standard model of particle physics, facilitates the acceleration of cosmological length scales. Such an acceleration is needed to provide a consistent fit of the general relativistic FLRW universe models to available data. It remains a possibility that dark energy, and the associated violation of the strong energy condition, is an artefact of the FLRW model ansatz imposed for the interpretation of data, rather than due to a fundamental cosmological constant of nature. Here we show---without making assumptions on the metric tensor of the Universe---that redshift drift is a promising direct probe of violation of the strong energy condition within the theory of general relativity. We discuss our results in relation to upcoming Lyman-$\ensuremath{\alpha}$ forest measurements of redshift drift.