Université de GenèveDépartement de Physique ThéoriqueCAP Genève

Limits of Quasi-Static Approximation in Modified-Gravity Cosmologies

25. March 2015
Cite as: 
E. Bellini and I. Sawicki, [arXiv:1503.06831]
Members involved: 

We investigate the limits of applicability of the quasi-static approximation in cosmologies featuring general models of dark energy or modified gravity. We show that the quasi-static approximation always breaks down outside of the sound horizon of the dark-energy, rather than the cosmological horizon as is frequently assumed. When the sound speed of dark energy is significantly below that of light, the quasi-static limit is only valid in a limited range of observable scales and this must be taken into account when computing effects on observations in such models. In particular, in the analysis of data from today's weak-lensing and peculiar-velocity surveys, dark energy can be modelled as quasi-static only if the sound speed is larger than order 1% of that of light. In upcoming surveys, such as Euclid, it should only be used when the sound speed exceeds around 10% of the speed of light.


Département de Physique Théorique
Université de Genève
24, quai Ernest Ansermet
1211 Genève 4
Directions & contact