Sigma_8 and n_s Cosmological Parameters

[SteveDC]

Hi, I'm doing a project on galaxy clustering and in a lot of papers where they list the cosmological parameters they've used, they list σ₈ and n_s. Can anyone quickly tell me what these parameters are referring to?

Thanks

 

[bapowell]

$n_s$ is the spectral index of the scalar power spectrum ($P(k) \sim k^{n_s -1}$). $\sigma_8$ is the amplitude of the power spectrum on the scale of 8 Mpc/h.

 

[Chalnoth]

$n_s$ is the spectral index of the scalar power spectrum ($P(k) \sim k^{n_s -1}$). $\sigma_8$ is the amplitude of the power spectrum on the scale of 8 Mpc/h.

$\sigma_8$ is the current amplitude of the matter power spectrum on that scale (as inferred by linear cosmological evolution). This parameter basically encodes information about how much large-scale structure has formed.