sigma8_rescale module

Rescale structure measures to use a specified sigma_8

Name: sigma8_rescale

File: cosmosis-standard-library/utility/sample_sigma8/sigma8_rescale.py

Version: 1.0

Author(s):

• Susana Fernandez
• Jack Elvin-Poole

URL:

Cite:

Rules:

Assumptions:

• Spectra scale quadratically with sigma_8

Explanation

Boltzmann codes like CAMB and CLASS typically take a primordial power spectrum
amplitude A_s as an input parameter defining the amplitude of cosmic structure
fluctutations.

Late-time data sets more naturally measure a late-time amplitude, and the measure
sigma_8 is usually instead for these data. If all other cosmological parameters
are fixed A_s ~ sigma_8^2, but when other parameters can vary they are not
perfectly equivalent.

This module enables you to sample over sigma_8 while still passing A_s into a
Boltzmann code. It does this by using an input value sigma8_input, which can
be sampled over, and a fixed fiducial A_s value. After the Boltzmann code is run
and sigma_8 for the fiducial amplitude calculated, the CMB and matter power spectra
are scaled by (sigma8_input2)/(sigma8_boltzmann2), and sigma_8 is overwritten.

##Parameters

These parameters can be set in the module's section in the ini parameter file.
If no default is specified then the parameter is required.

##Inputs

These parameters and data are inputs to the module, either supplied as parameters by the sampler or computed by some previous module. They are loaded from the data block.

##Outputs

These parameters and data are computed as outputs from the module