Reading the result dict and time-evolution output

The result dict

run_bbn() (and PRIMAT.solve()) returns a dict with these keys:

Key

Description

YPBBN

Helium-4 mass fraction (BBN convention)

YPCMB

Helium-4 mass fraction (CMB convention)

DoH

D/H

He3oH

(He3+H3)/H

Li7oH

(Li7+Be7)/H

Neff

Effective number of neutrino species

Omeganurel

Ω_ν h² × 10⁶ (relativistic)

OneOverOmeganunr

1 / (Ω_ν h² × 10⁻⁶) (non-relativistic)

The neutrino-sector keys (Neff, Omeganurel, OneOverOmeganunr) are only present if the background actually provides that information — see primat.main.PRIMAT.solve.

Monte-Carlo uncertainties

When a Monte-Carlo run is requested (--mc N on the CLI, or run_mc()/mc_uncertainty() via to_flat_dict()), every observable above also gets a matching sigma_<key> entry with its 1-sigma MC uncertainty, e.g. sigma_DoH alongside DoH. See Rate variation and Monte-Carlo uncertainty for how the underlying samples are drawn.

Time-evolution output

Set output_time_evolution=True to make the full cosmic-time evolution available via the "evolution" key of the result dict (an EvolutionResult, see primat.evolution). If output_file is also set to a path, a TSV file is written with the unified schema:

t_s, a, T_gamma_MeV, T_nue_MeV, T_numu_MeV, T_nutau_MeV, [Nheating],
Y_<nuclide> (one column per tracked species),
n_to_p_weak_rate, p_to_n_weak_rate, [nuclear rates]

  • output_file defaults to results/output_tables.tsv (relative to the current directory); set it to None to skip the disk write entirely — the time-evolution data is still accessible via result["evolution"] either way, on both backends (see primat.backend).

  • Nheating is included only for incomplete_decoupling=True (a real NEVO heating table).

  • [abundances] is one Y<species> column per nuclide of the chosen network — 8 for small/small_parthenope, ~59 for large, fewer with an amax cutoff.

  • [nuclear rates] (output_rates_time_evolution=True) is only available for small/small_parthenope — omitted (with a printed note) for network="large".

  • output_n_points (default 500) controls how many interpolated rows the file has.

primat.evolution (load_evolution, dump_evolution) and primat.plotting provide tools for loading and plotting this data — see the BBN abundance evolution notebook for a worked example.