Non-linear spherical collapse in tachyon models and a comparison of collapse in tachyon and quintessence models of dark energy

Abstract

We study evolution of perturbations in dark matter and dark energy for spherical collapse using a completely self consistent, relativistic approach. We study tachyon models of dark energy using the approach outlined in Rajvanshi and Bagla (2018). We work with models that are allowed by current observations. We find that as with quintessence models allowed by observations, dark energy perturbations do not affect evolution of perturbations in dark matter in a significant manner. Perturbations in dark energy remain small for such models. We then take two different Lagrangians for dark energy: tachyon and quintessence models, reconstruct potentials to have same expansion history and then compare if two can be distinguished in the nonlinear regime. Any variations we find are only due to a different Lagrangian density, and allow a comparison of different classes of models in a fair manner. We find that dark matter perturbations carry no imprint of the class of dark energy models for the same expansion history: this is significant in that we can work with any convenient model to study clustering of dark matter. We find that the evolution of dark energy perturbations carries an imprint of the class of models and dark energy perturbations grow differently in tachyon models and quintessence models for the same expansion history. However, the difference between these diminishes for (1 + w) ≪ 1 and hence prospects for differentiating between models using characteristics of perturbations are limited in our Universe.

Spherical collapse of non-top-hat profiles in the presence of dark energy with arbitrary sound speed

“…Our method shows very good agreement with linear solution in EdS model and with the top-hat SC collapse model for the cases with c s = 1 and c s = 0. We have confirmed that DE fluctuations with c s = 1 remain very small compared to matter fluctuations, even in the nonlinear regime, as expected in Quintessence and Tachyon models [18,28]. We also verified that, for c s < 10 −5 , DE fluctuations behave as dust and can become nonlinear, also depending on w. In this case, the evolution of matter fluctuations is strongly impacted.…”

“…If c s 1, DE fluctuations are much smaller than matter fluctuations on small scales and essentially do not modify the growth of nonlinear structures. The nonlinear evolution of Quintessence and Tachyon models were studied in [28]. For Quintessence, c s = 1, and its perturbation remains very small even when matter perturbations become nonlinear.…”

Large-scale structure with superhorizon isocurvature dark energy

“…[46] investigated the effect of nonlinear-clustering of matter with quintessence dark energy, following which Refs. [47,48] showed the comparison of matter clustering with quintessence dark energy against tachyonic dark energy in the linear and nonlinear regime.…”