micrOMEGAs: A program for calculating the relic density in the MSSM

We present a code that calculates the relic density of the lightest supersymmetric particle (LSP) in the minimal supersymmetric standard model. All tree-level processes for the annihilation of the LSP are included as well as all possible coannihilation processes with neutralinos, charginos, sleptons, squarks and gluinos. In all we have included over 2800 processes not counting charged conjugate states. The cross-sections extracted from CompHEP are calculated exactly. Relativistic formulae for the thermal average are used and care is taken to handle poles and thresholds by adopting specific integration routines. The input parameters can be either the soft SUSY parameters in a general MSSM or the five parameters of a SUGRA model. A link with ISASUGRA/ISAJET allows to calculate the parameters of the MSSM at the weak scale for an input at the GUT scale. The Higgs masses are calculated with FeynHiggsFast. Routines calculating (g − 2)μ and b → sγ are also included. LAPTH-881/01 Dec. 2001