= No-ghost theorem below the critical bosonic dimension
{title2=$2\le d\le26,\quad a=1$}
For integer target dimension $2\le d\le26$, intercept $a=1$ and ordinary nonzero momentum, the <old covariant string quantization> conditions leave a positive-semidefinite physical inner product. Quotienting its physical <null string states> removes gauge degeneracy. A <DDF operator> basis displays $d-2$ positive transverse oscillators; below dimension 26 the remaining physical longitudinal sector can be organized as a unitary <Virasoro algebra> sector with central charge $26-d$ and highest weight zero. At $d=26$ this extra sector becomes null and the quotient reduces to the 24 transverse oscillators. The result concerns negative-norm states, not the removal of the bosonic <tachyon>, and it does not itself cancel the <worldsheet Weyl anomaly> of a subcritical matter theory.
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