= Internal free fermions in a four-dimensional bosonic string
{title2=$4+N_f/2-26=0$}
Keeping the ordinary reparameterization <bc ghost system>, four embedding bosons require 44 additional real chiral fermions in each chirality to cancel the <worldsheet Weyl anomaly>. These are internal matter fields, not an assumed locally supersymmetric RNS construction. Their bilinear currents generate the chiral $\mathfrak{so}(44)$ current algebra, with $\binom{44}{2}=946$ currents. A full closed fermionic model also requires consistent spin-structure and modular projections; the central-charge count alone does not determine these choices.
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