The revised reference models we propose here rely on different assumptions on the microphysics of CR transport instead of different values of parameters within the same configuration. This change in philosophy stems from the fact that with increasing precision in the (multiwavelength and multimessenger) observational data and improvements on the theory side, we expect to arrive soon to a much better understanding and description of the CR microphysics itself than it was possible two decades ago [@MarcowithEtAl2016; @AmatoEtAl2018].

Transport description {#ssec:transport}
---------------------

### Transport equation {#sssec:prop_eq}

The general formalism that provides a powerful description of the transport of CRs in the Milky Way derives from the seminal textbook by Ginzburg and Syrovatskii [@GinzburgEtAl1964] (see also [@BerezinskiiEtAl1990; @Schlickeiser2002]), and relies on the following diffusion-advection equation for a CR species of index $\alpha$, here in the steady-state approximation and in energy space (rather than rigidity or momentum space):

\[eq:prop\] & - \_[**x**]{} { K(E)\_[**x**]{}\_- \_[c]{} \_} + { b\_[tot]{}(E)\_- \^2 K\_[pp]{} } + \_v\_ n\_[ism]{} \_+ \_\_\
& = q\_+\_ { \_v\_n\_[ism]{}+\_ }\_.

This equation describes the spatial and energy evolution of the differential interstellar CR density per unit energy $\psi_\alpha\equiv dn_\alpha/dE$, assuming a net primary injection rate of $q_\alpha$, and a 