Enumeration
NumCosmoMathPowspecAnalyticShape
Description [src]
Shape of the transfer function $T(k)$ in $P(k,z) = A k^{n_s} T(k)^2 B(k) D(z)^2$.
NCM_POWSPEC_ANALYTIC_SHAPE_POWER_LAW has no scale of its own and is the
case that isolates everything else.
NCM_POWSPEC_ANALYTIC_SHAPE_BBKS is the default and the one that resembles a
real matter power spectrum, with $q = k/k_\mathrm{eq}$,
\begin{equation}
T(q) = \frac{\ln(1 + 2.34q)}{2.34q}
\Big[1 + 3.89q + (16.1q)^2 + (5.46q)^3 + (6.71q)^4\Big]^{-1/4} .
\end{equation}
It carries both features a $k$-quadrature benchmark cares about: a turnover,
and a $k^{n_s-4}\ln^2 k$ tail rather than a pure power law.
NCM_POWSPEC_ANALYTIC_SHAPE_RATIONAL is a deliberate contrast: it has a
turnover but a clean, log-free $k^{n_s-4}$ tail. It is not a good
imitation of a matter power spectrum — fitted against one it is off by a
factor of five across $k \in [10^{-5}, 10]\,\mathrm{Mpc}^{-1}$ — and exists
so that the effect of the tail’s slope can be measured rather than assumed.