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

TL;DR

micrOMEGAs provides a public, self-contained tool to compute the relic density $\Omega h^2$ of the LSP in the MSSM by including all tree-level annihilation and coannihilation channels (over 2800 processes) with exact cross-sections from CompHEP. It follows the Gondolo–Gelmini formalism for the Boltzmann-equation evolution of the yield $Y$, incorporating relativistic thermal averaging, pole/threshold handling, and two numerical modes (fast and accurate) for efficient scans of large parameter spaces. The package supports both weak-scale MSSM inputs and SUGRA models via ISASUGRA, uses loop-corrected Higgs masses/widths from FeynHiggsFast and HDECAY, and implements constraints such as $(g-2)_\mu$ and $b\to s\gamma$. Validation against DarkSUSY shows good agreement when the same channels are used, while highlighting the impact of additional coannihilations and Higgs-width treatments on the final relic density. This tool enables precise exploration of MSSM parameter space under cosmological relic-density constraints and collider phenomenology, with future updates planned for loop corrections to neutralino masses and additional loop processes.

Abstract

We present a code that calculates the relic density of the LSP in the MSSM. 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 and bsgamma are also included.

Figures (1)

• Figure 1: $\Omega h^2$ in the $m_0-m_{1/2}$ plane in a SUGRA model with $\tan\beta=10$, $\mu>0$ and $m_{top}=175$GeV. The dark (blue) region corresponds to $.1< \Omega h^2< .3$ and the light (pink) region to $\Omega h^2< .1$. In the white region at large $m_0-m_{1/2}$, the relic density is above the present limit $\Omega>.3$ and in the region at small $m_0$, the $\tilde{\tau}$ is the LSP. The yellow (light grey) region correspond to the region excluded by $b\rightarrow s\gamma$. The LEP limit on $m_h=113$GeV is also displayed.