Cosmology and legacy settings¶

Density conventions and precedence¶

Parameters named omega_* are physical densities \(\omega=\Omega h^2\); parameters named Omega_* are fractional densities. Where both are present, the current parser checks omega_* first.

Component	Accepted settings, in precedence order	Default
Hubble parameter	`h`	`0.67556`
CDM	`omega_cdm`, `Omega_cdm`	`Omega_cdm = 1`
Baryons	`omega_b`, `Omega_b`	`Omega_b = 0`
Photons	`T_cmb`, `omega_g`, `Omega_g`	`Omega_g = 0`
Ultra-relativistic species	`N_ur`, `N_eff`, `omega_ur`, `Omega_ur`	Standard `N_ur = 3.046` times the photon density
Additional fluid	`omega_fld`, `Omega_fld`	`0`
Scalar modified gravity	`Omega_smg`	`0`

T_cmb is in Kelvin and is converted using Planck's law. N_ur and N_eff use the standard neutrino relation

\[ \Omega_\mathrm{ur} = N_\mathrm{ur}\frac{7}{8}\left(\frac{4}{11}\right)^{4/3}\Omega_\gamma. \]

Unless baryon treatment = sample, baryons are not a separate particle ensemble and their mass is combined with the cold particle species.

The parser requires total matter density in (0, 1] and non-negative total radiation density no larger than the remaining density budget. It then sets

\[ \Omega_\Lambda = 1-\Omega_\mathrm{m}-\Omega_\mathrm{rad}-\Omega_\mathrm{fld}. \]

Omega_k and the v1.3 LTB/non-flat workflow are not parsed by the current GPU path. Do not carry them into a v2.0 settings file expecting equivalent behaviour. Omega_smg is a placeholder input in the current branch and is passed to the CLASS interface for a future integration with hi_CLASS. It is not subtracted in the gevolution parser's Omega_Lambda expression and is not a replacement for the removed v1.3 curvature workflow. It should not be treated as a supported feature of the current branch.

Non-CDM species¶

Parameter	Default	Behaviour
`m_ncdm`	none	Fundamental masses in eV. The number of entries is used to infer `N_ncdm` when omitted.
`N_ncdm`	inferred	Number of active non-CDM species; cannot exceed the number of supplied masses.
`deg_ncdm`	`1` per species	Degeneracy factors.
`T_ncdm`	`0.71611` per species	Temperature relative to photons, used by the initial phase-space distribution.

Each density follows

\[ \omega_{\mathrm{ncdm},i} = \frac{m_{\mathrm{ncdm},i}\,\mathrm{deg}_{\mathrm{ncdm},i}} {93.14\ \mathrm{eV}}. \]

A non-CDM species remains part of the cosmological background even when its tiling factor is zero.

Additional fluid and primordial spectrum¶

The additional fluid uses

\[ w(a)=w0_\mathrm{fld}+wa_\mathrm{fld}(1-a). \]

Parameter	Default	Behaviour
`w0_fld`	`-1`	Present-day equation of state.
`wa_fld`	`0`	Time-dependent part.
`cs2_fld`	`1`	Effective sound speed squared for CLASS perturbations.
`A_s`	`2.215e-9`	Primordial curvature-spectrum amplitude.
`n_s`	`0.9619`	Scalar spectral index.
`k_pivot`	`0.05` 1/Mpc	Primordial pivot scale.

The current parser treats positive Omega_fld with exactly w0_fld = -1 as singular and resets Omega_fld to zero with a warning. Use the derived cosmological constant for a true \(w=-1\) component.

Disk/restart-style metadata¶

For IC generator = read from disk, the parser accepts:

restart redshift;
cycle, tau, and dtau;
up to three metric file entries;
gevolution version.

These values can restore selected counters, timing information, metric fields, and light-cone bookkeeping when compatible files are available. They do not constitute a supported GPU checkpoint contract.

With restart-style cycle metadata, GR metric files use the legacy order \(\phi\), \(\chi\), \(B\); Newtonian restart-style input uses its first metric entry for \(B\). These files must be mutually compatible with the particle inputs and settings.

The parser also accepts hibernation path, hibernation file base, hibernation redshifts, and hibernation wallclock limit.

Hibernation is rejected

The GPU executable does not write hibernation checkpoints. A non-empty hibernation redshifts schedule or positive hibernation wallclock limit is therefore a validation error. This prevents a run from stopping after falsely claiming that a restart point was written.

v1.3 compatibility status¶

v1.3 feature or setting	v2.0 GPU status
Most CLASS-compatible cosmology names	Retained
Basic generator and disk input	Retained, with GPU-reader limitations
Hibernation and restart files	Legacy parser/reader support remains; checkpoint writes disabled
`Omega_k` and LTB generator/settings	Removed from the GPU path
prevolution	Rejected
FalconIC	Rejected
RELIC/second-order workflow	Compile-time optional; not production-supported by default
LATfield2 external I/O server	Not ported; defining `EXTERNAL_IO` is a compile-time error