ACT DR6 parameters

Parameters and run settings for ACT DR6 using cobaya.

File Structure

All yaml files are top-level. To perform a run with cobaya, you can invoke

[python -m] cobaya run runs/<file>.yaml

Where runs/<file>.yaml is any one of the run files contained in the runs/ directory.

If you want to add new files, please consider the following style guides:

• Run files go into runs/.

• Theory code files go into theories/.

• Likelihood files go into likelihoods/.

• Parameter files go into params/. You can include priors on your parameters, but please only use physical bounds. External priors (i.e. priors from external analyses) are to be included in prior files. It is recommended to put references on parameters.

• Prior files go into priors/. These contain external priors only.

Notes on existing files

theories/camb.yaml uses the high accuracy settings for CAMB at least as accurate as in Hill et al. (2020). Note that we intend to use cosmorec instead of recfast as main recombination code - see the section Installing Cosmorec below for instructions.

theories/cosmopower.yaml uses Cosmopower as implemented in the Simons Observatory package SOLikeT. See the section Setting up CosmoPower on instructions of setting this up.

params/foregrounds.yaml uses the baseline foreground model implemented in MFLike based on the Choi et al. (2020) foreground model but with modifications for DR6. The corresponding foreground priors are found in priors/foregrounds.yaml.

params/foregrounds_Choi2020.yaml uses the foreground model implemented in MFLike based on the Choi et al. (2020) foreground model. The corresponding foreground priors are found in priors/foregrounds_Choi2020.yaml.

params/foreground_sims.yaml uses a model similar to the expected the DR6 foreground model, but allows parameters to go outside physical constraints (i.e. negative for values that are expected to be non-negative). UPDATE FEB 2024 We will loosen the restriction that the CIB spectral indices are equal (e.g. we now let beta_c and beta_p vary independently), and we add a varying spectral index for the radio sources beta_r.

params/systematics.yaml uses the systematics parameters for DR6.

params_DR4_baseline.yaml is a simple set of fixed parameters that can be used to evaluate your model at the ACT DR4+WMAP baseline parameters found in Choi et al. and Aiola et al.

Codes used

Likelihood

The current files are set to be used with the MFLike likelihood from the Simons Observatory (SO). Right now, it is set up to be coupled to the main branch release of the public git.

We are using the ACT DR6 MFLike likelihood that functions as a DR6-specific implementation for MFLike.

sroll2

For better constraints on reionization, we recommend the use of the sroll2 likelihood. It comes pre-packaged with cobaya, so you can simply invoke cobaya-install planck_2018_lowl.EE_sroll2 once to install the data.

WMAP

See this github page for the open-source python implementation of the high-ell WMAP likelihood that is used.

Theory

For cosmological observables, there are two options to be used right now. One can either use camb as it exists within cobaya, or you can use the cosmopower code that exists in SOLikeT, the likelihood and theory code library developed by the SO collaboration.

Installing CosmoRec

We use the recombination code CosmoRec for camb. By default, camb only comes with the recombination code Recfast installed, but this code is not accurate enough for our purposes. To install CosmoRec, follow these instructions:

1. Install camb (v1.5.0 or higher) for cobaya.

2. Download and untar CosmoRec via:

wget https://www.cita.utoronto.ca/~jchluba/Recombination/_Downloads_/CosmoRec.v2.0.3b.tar.gz
tar -xvf CosmoRec.v2.0.3b.tar.gz

3. In the cosmorec Makefile.in file, add the -fPIC flag to the CXXFLAGS parameter, so that line 11 now reads:

CXXFLAGS = -Wall -pedantic -O2 -fPIC

4. You can now invoke make all to compile cosmorec.

5. Now, in the location where you installed camb (this will either be a directory where you have a separate instance of camb, or a directory within your cobaya packages path), locate the fortran/Makefile_main file. Add the following two lines all the way at the top:

RECOMBINATION_FILES = recfast cosmorec
COSMOREC_PATH = <path/to/cosmorec>

Where <path/to/cosmorec> is the path where you unpacked CosmoRec in step 2.

6. Recompile the camb fortran library by invoking

python setup.py make

in the main camb directory. This should compile camb with CosmoRec enabled.

Setting up CosmoPower

If you intend to use the CosmoPower theory code, you should modify the theory_cosmopower.yaml file to make sure that the theory code can find your networks. The file is setup for use of the emulators described in Bolliet et al. (2023), and you only need to change the two lines that start with network_path to the path where you stored the emulators on your machine.

If you intend to use this code with your own emulators, check out the SOLikeT documentation on the CosmoPower wrapper for instructions.

CosmoPower: 'KeyError: _manual' bug

This bug has been fixed as of cobaya verison 3.3. Consider updating your cobaya package.

(TL;DR: see this pull request if you get this error).

If you are using Cobaya version 3.2.1 along with SOLikeT.CosmoPowerDerived, then you will likely run into a cryptic error message that ends with KeyError: _manual. This bug is caused by some internal cobaya logic. A fix for this bug can be found here. It is currently accepted into the main development branch for Cobaya, so any future releases should fix this error.