LAUSR

By using the effective field theory approach, we investigate the role of initial conditions for the dark energy or modified gravity models. In detail, we consider the constant and linear parametrization of the effective Newton constant models. First, under the adiabatic assumption, the correction from the extra scalar degree of freedom in the beyond Lambda CDM model is found to be negligible. The dominant ingredient in this setup is the primordial curvature perturbation originated from the inflation mechanism, and the energy budget of the matter components is not very crucial. Second, the isocurvature perturbation sourced by the extra scalar field is studied. For the constant and linear models of the effective Newton constant, no such kind of scalar mode exists. For the quadratic model, there is a nontrivial one. However, the amplitude of the scalar field is damped away very fast on all scales. Consequently, it could not support a reasonable structure formation. Finally, we study the importance of the setup of the scalar field starting time. By setting different turn-on times, namely, a = 10(-2) and a = 10(-7), we compare the cosmic microwave background radiation temperature, lensing deflection angle autocorrelation function, and the matter power spectrum in the constant and linear models. We find there is an order of O(1%) thorn difference in the observable spectra for constant model, while for the linear model, it is smaller than O(0.1%).