= BRST physical-state constraints of an open string
{c}
{title2=$(L_0-1)|\Psi\rangle=L_{m>0}|\Psi\rangle=0$}
For a matter state tensored with the <ghost oscillator vacuum>, the <BRST charge> produces the independent ghost states $c_0|0\rangle$ and $c_{-m}|0\rangle$ with coefficients $(L_0-1)|\Psi\rangle$ and $L_m|\Psi\rangle$. Thus BRST closure is equivalent to $(L_0-1)|\Psi\rangle=0$ and $L_{m>0}|\Psi\rangle=0$ in this sector. It reproduces <old covariant string quantization> and the <open bosonic string mass spectrum>.
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