Beyond standard model cosmologies
- Authors:
Shikhar Mittal and Prakhar Bansal
- Paper:
Interacting dark matter model
ECHO21 can be used to study a special class of interacting dark matter model: Coulomb-like DM. We assume that all DM particles are Coulomb-like and that they can interact with all baryons. The interaction cross-section for such a system is given by \(\sigma(v_{\mathrm{b}\chi}) = \sigma_0(v_{\mathrm{b}\chi}/c)^{-4}\), where \(v_{\mathrm{b}\chi}\) is the baryon-DM relative velocity. In addition to cooling, IDM leads to a suppression and delay in star formation. We follow the strategy outlined by Mittal et al (2026).
IDM requires two additional parameters, namely \(m_{\chi}\) (mass of Coulomb-like DM) and \(\sigma_{45}\) (dimensionless cross-section, expressed as \(\sigma_0/10^{-45}\,\mathrm{m^2}\)). If you want work with IDM, supply both these parameters in your cosmo dictionary. Note that \(m_{\chi}\) should be provided in units of GeV. The cosmo dictionary now looks like
cosmo = {'Ho':67.4,'Om_m':0.315,'Om_b':0.049,'sig8':0.811,'ns':0.965,'Tcmbo':2.725,'Yp':0.245, 'mx_gev':1.0,'sigm45':1.0}
For the SFRD, you can work either with physically-motivated or semi-empirical model. The arguments 'hmf' and 'mdef' in the dictionary will be ignored since in the current version we work with only 'tinker08' HMF. Further, IDM can be run only for some specific values of \(m_{\chi}\) and \(\sigma_{45}\). These are 15 numbers starting from \(10^{-4}\) to \(10^{3}\) separated by 0.5 dex for both, \(m_{\chi}\) and \(\sigma_{45}\). For any other number, the code will run for the nearest number. For example, if you provide \(m_{\chi}=15\), then the code will actually compute for \(m_{\chi}=10\).