## BAO + BBN constraints on H0

Posts: 2
Joined: July 08 2019
Affiliation: HZDR, TU-Dresden

### BAO + BBN constraints on H0

Hi all,

I would like to reproduce Figures 3(Left) and 4 of this paper (https://arxiv.org/abs/1707.06547), using CosmoMC. For that matter I'd like to understand how to combine the two data sets of Galaxy BAO and Lya BAO like done in Figure 3. As written in the paper the D/H constraint is applied via a Omegabh^2 Gaussian prior... how do I add that?
So far I computed several chains using the different BAO data using a modified test.ini for the respective data set.. e.g.:

Code: Select all

#general settings
#Bicep-Keck-Planck 2015, varying cosmological parameters
DEFAULT(batch3/BK15.ini)

#Planck 2018
DEFAULT(batch3/lensing.ini)

#Other Likelihoods
DEFAULT(batch3/DR14_LYxQSO_BAO.ini)

#general settings
DEFAULT(batch3/common.ini)

#high for new runs
MPI_Max_R_ProposeUpdate = 30

propose_matrix= planck_covmats/base_TT_lowTEB_plik.covmat

#Folder where files (chains, checkpoints, etc.) are stored
root_dir = chains/

#Root name for files produced
file_root=test
#action= 0 runs chains, 1 importance samples, 2 minimizes
#use action=4 just to quickly test likelihoods
action = 0

#expected result for -(log like)
test_check_compare = 663.808

start_at_bestfit =F
feedback=1
use_fast_slow = T

checkpoint = T

#sampling_method=7 is a new fast-slow scheme good for Planck
sampling_method = 7
dragging_steps  = 3
propose_scale = 2

#Set >0 to make data files for importance sampling
indep_sample=10

#these are just small speedups for testing
get_sigma8=T

But I'm not sure if I'm missing something crucial...
Sorry if these things are obvious, but I'm fairly new to CosmoMC and MCMC procedure and it's not straight forward for me.

Thanks,

Antony Lewis
Posts: 1646
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: BAO + BBN constraints on H0

See batch3/baryon_density.ini for an example of how to set a parameter prior. To combine data sets you just run a chain with both (or importance sample if they are consistent).

Btw, you probably don't want BK15 if not varying r.

Posts: 2
Joined: July 08 2019
Affiliation: HZDR, TU-Dresden

### Re: BAO + BBN constraints on H0

Thank you very much for the illuminating answer!

For this run I used the following .ini:

Code: Select all

#general settings
#DES 1Yr
#DEFAULT(batch3/DES.ini)

#Other Likelihoods
DEFAULT(batch3/BAO.ini)
#general settings
DEFAULT(batch3/common.ini)
DEFAULT(batch3/DR14_LYAUTO_BAO.ini)

#e.g. to vary r in addition to standard 6:
#(for r>0 also need compute_tensors=T)
#compute_tensors = T
#param[r] = 0.03 0 2 0.04 0.04

#high for new runs
MPI_Max_R_ProposeUpdate = 30

propose_matrix= planck_covmats/base_TT_lowTEB_plik.covmat

#Folder where files (chains, checkpoints, etc.) are stored
root_dir = chains/BAOBBN2/

#Root name for files produced
file_root=test3_prior
#action= 0 runs chains, 1 importance samples, 2 minimizes
#use action=4 just to quickly test likelihoods
action = 0
samples = 10000

#expected result for -(log like)

#if you want to get theory cl for test point
#test_output_root = output_cl_root

start_at_bestfit =F
feedback=1
use_fast_slow = T

checkpoint = T

#sampling_method=7 is a new fast-slow scheme good for Planck
sampling_method = 1
dragging_steps  = 3
propose_scale = 2

#Set >0 to make data files for importance sampling
indep_sample=10

#these are just small speedups for testing
get_sigma8=T
include_fixed_parameter_priors = T
prior[omegabh2] = 0.0222 0.0005

#Uncomment this if you don't want one 0.06eV neutrino by default
#num_massive_neutrinos=
#to vary parameters set param[name]= center, min, max, start width, propose width
#param[mnu] = 0 0 0 0 0

#for PICO install from https://pypi.python.org/pypi/pypico and download data file
#cosmology_calculator=PICO
#pico_datafile = pico3_tailmonty_v34.dat
#pico_verbose=F

Resulting in the attached plot, which is roughly the one from the paper :-). I think the rough outlines are due to my sample size of 10000 reaching only R-1=0.1.
I have still some open questions:
1st) Is the part

Code: Select all

include_fixed_parameter_priors = T
prior[omegabh2] = 0.0222 0.0005

the correct implementation of the prior, when some range for omegabh2 in the params_CMB_defaults.ini is set? Because if I would leave out the boundaries in the params_CMB_defaults.ini file, the code would not start.
2nd) Is there a way of speeding up the run by using some default .covmat or building my own one?
Thanks!
Attachments
Omega_mH0.png (76.17 KiB) Viewed 9114 times

Antony Lewis
Posts: 1646
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: BAO + BBN constraints on H0

Looks OK. You should certainly set a propose_matrix (lots supplied for Planck in planck_covmats).