rescale_distances_rdh

Rescale computed distances to be consistent with a given value of R_d * h

File	utility/rescale_distances_rdh/rescale_distances_rdh.py
Attribution	CosmoSIS Team
URL

BAO people sometimes sample using the best-constrained BAO parameter r_d * h, where r_d is the sound horizon at the drag epoch (last scattering). This module takes a set of distances and rescales them to be consistent with a given value of r_d * h. This is useful for replicating, for example, the DESI BAO-only analysis.

For that reason this module is limited to rescale distances, and not, for example. k values in a power spectrum.

In general I’d discourage people from sampling in whatever is the best-constrained parameter for their particular analysis - it doesn’t correspond to particularly sensible priors in any other parametrization. But it can make sampling more efficient, depending on the sampler.

Specifically, this module reads a value of rd_prime computed from a (fixed) value of H0, e.g. by camb, and a sampled rdh_sample value, from which it computes rd_sample = rdh_sample / h_fid. It then sets f = rd_prime / rd_sample, and muliplies all the distance metrics by f. H(z) is also rescaled by 1/f, and mu(z) adjust accordingly too.

This module is not intended to be used in a general way, but only in the context of the specific BAO analysis described above.

Assumptions

FLRW

Setup Parameters

None

Input values

Section	Name	Type	Description
cosmological_parameters	h0	real	Fiducial value of H0 in km/s/Mpc/100. Should be fixed
	rdh	real	Sample value of R_d * h in km/s.
distances	rs_zdrag	real	Sound horizon at drag epoch computing using fiducial h0, in Mpc

Output values

Output values
Section	Name	Type	Description
cosmological_parameters	h0	real	Updated h0
distances	D_L	real 1d	Updated luminosity distance in Mpc
	D_A	real 1d	Updated angular diameter distance in Mpc
	D_V	real 1d	Updated BAO average distance in Mpc
	D_M	real 1d	Updated line of sight comoving distance in Mpc
	D_C	real 1d	Updated transverse comoving distance in Mpc
	H	real 1d	Updated Hubble parameter in km/s/Mpc
	mu	real 1d	Updated distance modulus
	rs_zsrag	real	Sound horizon at drag epoch computing using updated h0, in Mpc
	h0rd	real	Final value of h0 r_d, using updated h0