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Indirect search for dark matter with micrOMEGAs2.4
G. Belanger, F. Boudjema, P. Brun, A. Pukhov, S. Rosier-Lees, P. Salati, A. Semenov
TL;DR
Indirect dark-matter searches require accurate annihilation-signal predictions across particle-physics models and astrophysical propagation settings. The paper presents a flexible micrOMEGAs module that computes annihilation spectra and indirect fluxes, with adjustable charged-particle propagation. The module extends coverage to photon radiation and charged cosmic-ray propagation for implemented weakly interacting dark-matter models, while specific approximations and neutrino-capture effects remain scope boundaries.
Problem
Indirect-detection data require accurate dark-matter annihilation signals across multiple channels and particle-physics models.
Method
The module computes annihilation cross sections and spectra, halo-dependent photon fluxes, and charged-particle propagation with adjustable parameters.
Results
The new module provides charged-cosmic-ray propagation and full photon-radiation computation for any implemented model containing a weakly interacting particle.
Takeaways & Limitations
micrOMEGAs becomes a comprehensive code for studying weakly interacting cold-dark-matter candidates in various Standard Model extensions.
Takeaways & Limitations
The photon-radiation approximation can fail when the non-radiative cross section is symmetry-suppressed or vanishing, and diffusive reacceleration and galactic convection are not included.
Abstract
from arXiv · showhide
We present a new module of micrOMEGAs devoted to the computation of indirect signals from dark matter annihilation in any new model with a stable weakly interacting particle. The code provides the mass spectrum, cross-sections, relic density and exotic fluxes of gamma rays, positrons and antiprotons. The propagation of charged particles in the Galactic halo is handled with a new module that allows to easily modify the propagation parameters.
1 Introduction
The new micrOMEGAs indirect-detection module computes dark-matter annihilation signals across particle-physics models, including annihilation processes, halo modeling, photon fluxes, and charged-particle propagation. Its flexible propagation and solar-modulation treatment supports model-independent predictions for gamma rays, positrons, and antiprotons.
- Motivation and scope: The module targets accurate indirect-signal calculations for dark-matter annihilation across different particle-physics models.It computes signals from annihilation products including gamma rays, positrons, and antiprotons.
- Annihilation processes: It automatically provides tree-level two-body annihilation cross sections for all implemented models.The module also includes radiative photon emission, polarized gauge bosons, and MSSM loop-induced γγ and γZ0 processes.
- Astrophysical modeling: The module models dark-matter halos generally, allows dark-matter clumps, and computes line-of-sight integrals for gamma-ray signals.These features connect particle annihilation spectra to predicted observable photon fluxes.
- Charged-particle propagation: Charged-particle propagation through the Galaxy and solar modulation can be computed with adjustable propagation parameters.The module therefore supports propagation-related treatment for positron and antiproton signals.
- Generality and context: The package provides model-independent predictions of indirect-detection signals and extends the public-code landscape beyond DarkSUSY's minimal supersymmetric model restriction.DarkSUSY is described as confined to the minimal supersymmetric model, whereas micrOMEGAs includes several models and facilities for incorporating new ones.
- Scope boundary: The neutrino spectrum is computed, but incorporating the usually dominant neutrinos from dark-matter capture in the Sun or Earth is left for a later upgrade.This limits the present treatment of the neutrino signature relative to the gamma-ray, positron, and antiproton focus.
2 Fluxes from DM annihilation
The module computes dark-matter annihilation spectra and flux inputs for photons and stable antiparticles, incorporating polarized gauge bosons and photon-radiation effects. It also addresses propagation and compares enhanced spectral contributions in representative cases.
- DM annihilation produces γ, e+ and p̄ through hadronization and decay of Standard Model final states.The production rate depends on the annihilation cross section, dark-matter density, candidate mass, and per-reaction energy distribution.
- Cross sections for two-body annihilation channels are automatically calculated for every model implemented in micrOMEGAs.The calculation uses CalcHEP and defaults to relative velocity v = 0, with an option to define another value.
- Vector boson polarisation: The module includes polarized gauge-boson production and computes stable-particle spectra after polarized-boson decay and hadronization.Polarization is determined automatically from the three-body process χχ →W−e+νe, and two spectrum-generation methods were found to agree.
- Vector boson polarisation: At most a factor of 3/2 increase occurs for the most energetic charged particles when transverse W polarization is included.Transverse W bosons produce harder positron spectra, whereas the longitudinal spectrum vanishes at high energy.
- Photon radiation: Photon spectra include radiative contributions beyond factorized final-state radiation, which can be enhanced when an exchanged particle lies near resonance.For the CMSSM example, neutralinos annihilate dominantly into tau pairs and internal-line photon radiation is enhanced by the nearby stau exchange.
3 Galactic propagation of charged particles
The module models charged-particle transport through the Galactic halo using diffusion, energy losses, convection, and particle interactions, with propagation parameters constrained by cosmic-ray data. Positrons and antiprotons are treated with species-specific diffusion equations and Green-function methods.
- General framework: Charged-particle spectra are altered during Galactic-halo propagation by diffusion, energy losses, reacceleration, and convection.The framework includes dark-matter source terms and treats antiproton annihilation in the interstellar medium separately.
- General framework: The propagation equation is solved semi-analytically in a two-zone model with a thick diffusion halo, thin Galactic disk, vertical wind, and vanishing boundary densities.The transport parameters include δ, K0, L, and VC, with typical values compatible with B/C measurements.
- Positrons: Positron spectra are computed from the diffusion-loss equation using space diffusion and energy losses, then evaluated with Green functions for the density near the Sun.The positron loss rate is dominated by synchrotron radiation and inverse Compton scattering; the implementation tabulates a universal diffusion function for efficient repeated calculations.
- Positrons: Positron propagation neglects diffusive reacceleration and Galactic convection because their impact was shown to occur only below a few GeV.The calculation uses τE = 10^16 s as the typical energy-loss time.
- Antiprotons: Antiproton propagation includes diffusion, Galactic wind, dark-matter production, and a negative source term for annihilation in interstellar H and He.Secondary antiproton production is not included, and the Earth spectrum is obtained through a 3D integration with boundary-suppression treatments near the Galactic edge.
- Antiprotons: The antiproton calculation neglects energy losses and obtains the spectrum by solving a diffusion equation with symmetry and boundary conditions.The final spectrum is accelerated by interpolating a smoothly energy-dependent integral until the requested precision is reached.
4 Functions of micromegas
micrOMEGAs 2.4 exposes routines for storing, interpolating, displaying, and propagating annihilation spectra, while allowing halo and propagation parameters to be changed globally. Separate functions compute positron, antiproton, and photon fluxes from model-dependent spectra and annihilation rates.
- Module interface: The indirect-detection module adds global parameters and dedicated routines beyond the general micrOMEGAs function set.The online manual and manual4.tex describe the available functions and default parameters.
- Spectra interpolation and display: Spectra are stored in NZ=250-element arrays indexed by z_i = log(E_i/Mχ), representing particle yields or fluxes.Interpolation routines return either dN/dE or dN/dz distributions, and displaySpectrum applies user-defined energy cuts.
- Annihilation spectra: calcSpectrum computes annihilation spectra and σv for γ, e+, antiprotons, and neutrino flavors, with switches for gauge-boson polarization and photon radiation.Photon radiation is included across subprocesses for photon spectra, while the positron option includes χχ → e+e−γ.
- Propagation inputs: Halo profiles and solar-location parameters can be changed, while charged-particle propagation depends on configurable diffusion, halo, and convection parameters.Relevant global parameters include K_dif, Delta_dif, L_dif, Rsun, Rdisk, Tau_dif, and Vc_dif.
- Charged-particle fluxes: posiFluxTab and pbarFlux compute propagated positron and antiproton fluxes from annihilation spectra or differential production cross sections.Lowering the positron Emin increases computation time, and the same array may be used for spectra before and after propagation in FluxTab routines.
- Photon flux: Photon flux depends on the line-of-sight angle, detector cone angle, annihilation cross section, and photon spectrum rather than diffusion parameters.gammaFluxTab integrates along the line of sight and over the detector opening angle.
5 Examples and results
The sample output demonstrates micrOMEGAs calculations for an MSSM model, while comparisons with DarkSusy show agreement for indirect signals and expose substantial propagation uncertainty.
- 5.1 Sample output: The sample run reports a 147.7 GeV lightest neutralino with dominant annihilation contributions from W+W− and ZZ channels.The relative contributions are 60% for W+W− and 26% for ZZ.
- 5.1 Sample output: The run gives sigmav=1.83E-26 cm^3/s, a photon flux of 2.01E-14 [cm^2 s GeV]^{-1}, and positron and antiproton fluxes at 73.8 GeV.The positron flux is 8.09E-12 [cm^2 sr s GeV]^{-1}, while the antiproton flux is 1.77E-11 [cm^2 sr s GeV]^{-1}.
- 5.2 Comparison with other packages: The comparison uses two MSSM sample models generated with DarkSusy and passed to micrOMEGAs through SLHA files.Both packages compute annihilation cross-sections, branching ratios, propagation, and distributions for the comparison.
- 5.2 Comparison with other packages: The positron comparison differs by only a few percent after correcting for the initial sigmav and accounting for different diffusion-coefficient conventions.DarkSusy defines K at 4 GeV, whereas micrOMEGAs uses 1 GeV; DarkSusy also takes δ = 0 below p = 4 GeV for positrons.
- 5.2 Comparison with other packages: Good agreement is recovered for the antiproton signal, while propagation uncertainty exceeds one order of magnitude across its full energy range.For positrons, the uncertainty is mainly large at low energies because high-energy positrons are produced locally.
6 Conclusions
The new indirect-detection module makes micrOMEGAs a comprehensive tool for weakly interacting cold dark matter models, supporting charged-particle propagation and higher-order annihilation processes.
- 6 Conclusions: The module computes indirect signals for any implemented model containing a weakly interacting particle.It includes propagation of charged cosmic rays and higher-order processes in dark matter annihilation.
- 6 Conclusions: Full photon-radiation computation and MSSM loop-induced gamma-ray lines are included among the module’s new features.The MSSM-specific line calculation covers loop-induced gamma-ray signals.
- 6 Conclusions: The modular structure allows users to improve specific code components, including by adding functions for dark matter clumps.The neutrino signal from dark matter capture in the Sun or Earth is not yet included.