I'm attempting to recreate some plots of individual particle chemical potentials from S. Reddy et. al.'s paper on neutrino interactions in hot and dense matter (of the same title). The specifics aren't, I think, terribly important. In particular, I'd like to recreate the plot in Figure 2.
Consider an absorption reaction $\nu_e + B_2 \to e^- + B_4$ (where $B_2$ and $B_4$ are baryons — for instance, $\nu_e + n \to e^- + p$) in thermal equilibrium (hence $\mu_n + \mu_p = \mu_e + \mu_{\nu_e}$).
The paper plots $\mu_e, \mu_{\nu_e}$, and uses the values $\mu_{B_2}$, $\mu_{B_4}$, as a function of $u = n_B/n_0$ (where $n_0$ is the empirical nuclear equilibrium density, and $n_B$ the baryon density) for particular values of $Y_L$ (where $Y_i = n_i/n_B$ for $i=n,p,e^-,\nu_e$, and where $Y_L = Y_{\nu_e} + Y_{e^-}$).
I'd like to determine numerical values for $\mu_{e^-}, \mu_{\nu_e}, \mu_{B_2}$ and $\mu_{B_4}$ for use in further calculations.Here's what I've tried:
I know that the distribution functions for leptons and baryons can both be written as:
$$f_\pm(p) = \frac{1}{e^{(E(p)-\mu)/T} \pm 1}$$
In some notes from a statistical mechanics class (unfortunately, I cannot find an more authoritative reference) I find that:
$$\mu_i = T\textrm{ln}\bigg(\frac{n_i}{n_{max,i}}\bigg)$$
We have that $u = n_B/n_0$, hence $n_B = u \times n_0$. We have also that $Y_i = n_i/n_B$, hence $n_i = Y_i \times n_B = Y_i \times (u \times n_0)$. Consequently:
$$\mu_i = T\textrm{ln}\bigg(\frac{Y_i\times u \times n_0}{n_{max,i}}\bigg)$$
It isn't clear to me, however, how I might go about determining $n_{max,i}$. Moreover, if I simply plug in the values of $T,Y_i$ and $n_0$ used in the paper, it seems as though I cannot find $n_{max,i}$ such that the plot of this function fits that given in the paper.
How do I find numerical values for the chemical potentials, as a function of potential energy $u$ and for given $Y_i$?
Edit: A related paper ("Neutrino Opacity in High Density Nuclear Matter", S. Santos et. al) gives:
The chemical potential for particle $i$ is given by:
$$\mu_i^* = \mu_i - \chi_{\omega i}\frac{g_\omega^2}{m_\omega^2}\rho_B -\chi_{\rho i}I_{3,i}\frac{g_\rho^2}{m_\rho^2}\rho_3$$ ---where $\rho_e,\rho_\nu$, and $\rho_B$ are the electron, neutron, and baryon densities, respectively, and the lepton fraction is defined as the ratio $Y_L = (\rho_e + \rho_\nu)/\rho_B$.
Unfortunately, it does not define $I_{3,i}$, $\chi_{\omega i}$, $\chi_{\rho i}$, $g_\omega$, or $g_\rho$ (I think the latter are degeneracies?).