$m_1=0$, and giving the other a large, negative mass $(m_2<-\mu<0)$. More generally, we may interpolate between the two theories by continually varying $m_1=m$ between $0$ (Dirac) and $\infty$ (HLR), subject to $0<m<\mu<|m_2|$.

We caution that Eq. (\[eq:Lf\]) can only hope to capture the structure of low-energy excitations close to the composite Fermi surface of $\psi_{a,1}$, since excitations at this energies will involve non-universal short-distance physics outside the purview of the effective field theory of the composite (marginal) Fermi-liquid state. Hence, one should not consider the detailed high energy structure, such as linearity or curvature of the CF dispersion far from $\mu$, to be physically meaningful.

Linear response from parton theory \[app:PartonResponse\]
=========================================================

We now turn to a computation of the (linear) electric current response to (small) applied voltages and thermal gradients.

Preliminaries
-------------

The proper computation of such transport coefficients faces several subtleties. Chiefly, one must properly distinguish between “free" or “transport" currents that can pass freely between conducting leads and the sample, and circulating (i.e. have zero divergence) magnetization currents that are bound to the sample. While Kubo formulae typically yield expressions for the total (transport plus magnetization) current, in a transport measurement, only the former are observable and 