Model breaking measure for cosmological surveys

Recent observations have led to the establishment of the concordance ΛCDM model for cosmology. A number of experiments are being planned to shed light on dark energy, dark matter, inflation and gravity, which are the key components of the model. To optimize and compare the reach of these surveys, several figures of merit have been proposed. They are based on either the forecasted precision on the ΛCDM model and its expansion or on the expected ability to distinguish two models. We propose here another figure of merit that quantifies the capacity of future surveys to rule out the ΛCDM model. It is based on a measure of the difference in volume of observable space that the future surveys will constrain with and without imposing the model. This model breaking figure of merit is easy to compute and can lead to different survey optimizations than other metrics. We illustrate its impact using a simple combination of supernovae and baryon acoustic oscillation mock observations and compare the respective merit of these probes to challenge ΛCDM. We discuss how this approach would impact the design of future cosmological experiments.