Camb

CAMB (Code for Anisotropies in the Microwave Background) is a cosmology Boltzmann code used to compute theoretical predictions for the cosmic microwave background (CMB) anisotropy spectra and the linear matter power spectrum. It solves the Einstein-Boltzmann equations for linear perturbations in the early universe to produce CMB temperature and polarization power spectra and related quantities for a given set of cosmological parameters. The code was originally authored by Antony Lewis and Sarah Bridle and is maintained by the cosmology community as an open-source project.

CAMB supports a range of cosmological models (flat or curved, ΛCDM and extensions such as wCDM, varying neutrino masses, etc.). It implements line-of-sight integration, supports multiple gauges (synchronous and conformal Newtonian), and includes physical processes such as reionization, gravitational lensing of the CMB, and massive neutrinos. It can output lensed and unlensed spectra, C_l^TT, C_l^EE, C_l^TE, C_l^BB, the lensing potential power spectrum, and the matter power spectrum P(k) at various redshifts. For non-linear corrections, CAMB can interface with HALOFIT to approximate non-linear evolution on small scales.

Usage and interoperability: It is released as Fortran 90 code and is commonly used as a standalone tool or in conjunction with parameter-estimation packages such as CosmoMC; it reads input parameter files, computes spectra, and writes outputs suitable for comparison with observational data (e.g., Planck).

Impact and availability: CAMB is widely used in CMB analyses, cosmological parameter estimation, and forecasting; it is open-source and hosted on public repositories with documentation and examples.