COSMICS: Cosmological Initial Conditions and Microwave Anisotropy Codes

TL;DR

COSMICS delivers a portable, end-to-end toolkit for linear cosmological perturbation theory and initial-condition generation. It combines a high-precision linear perturbation solver (LINGER) in two gauges, a fast photon transfer-function calculator (DELTAT) for the CMB spectrum, and a Gaussian random-field initializer (GRAFIC) capable of constrained realizations via the Hoffman–Ribak method and displacement fields through the Zel'dovich approximation. The package supports isentropic and multiple isocurvature initial conditions, various input-transfer-function modes (linger-based, analytic, or scale-free), and provides outputs including transfer functions, $C_\ell$, and lattice-scale density/velocity fields ready for nonlinear evolution codes. With careful treatment of recombination physics, Thomson scattering, and relativistic species, COSMICS enables accurate, gauge-consistent links from primordial fluctuations to observable CMB signatures and to the initial conditions used in large-scale structure simulations, while remaining portable across standard platforms and preparing for parallel extensions.

Abstract

COSMICS is a package of fortran programs useful for computing transfer functions and microwave background anisotropy for cosmological models, and for generating gaussian random initial conditions for nonlinear structure formation simulations of such models. Four programs are provided: {\bf linger\_con} and {\bf linger\_syn} integrate the linearized equations of general relativity, matter, and radiation in conformal Newtonian and synchronous gauge, respectively; {\bf deltat} integrates the photon transfer functions computed by the linger codes to produce photon anisotropy power spectra; and {\bf grafic} tabulates normalized matter power spectra and produces constrained or unconstrained samples of the matter density field. Version 1.0 of COSMICS is available at http://arcturus.mit.edu/cosmics/ . The current release gives fortran-77 programs that run on workstations and vectorized supercomputers. Unix makefiles are included that make it simple to build and test the package. A future release will include portable parallel versions of the linger codes using standard message-passing libraries.