Constraints on the speed of sound in the k-essence model of dark energy

Abstract

We consider a k-essence scalar field model for the late-time cosmic acceleration in which the sound speed, parametrized as $$c_s$$ c s is constant. We compute the relevant background and perturbation quantities corresponding to the observables like cosmic microwave background, type Ia supernova, cosmic chronometers, baryon acoustic oscillations, and the $$f\sigma _8$$ f σ 8 . We put constraints on the $$c_s^2$$ c s 2 parameter from these observations along with other parameters. We find lower values of $$c_s^2$$ c s 2 which are close to zero are tightly constrained. Particularly, we find mean value of $$\log _\textrm{10} (c_s^2)$$ log 10 ( c s 2 ) to be $$-0.61$$ - 0.61 and $$c_s^2 \le 10^{-3}$$ c s 2 ≤ 10 - 3 is more than 3$$\sigma $$ σ away from this mean value. This means these observations favor a homogeneous dark energy component compared to the clustering one.