Ghost oscillator vacuum
= Ghost oscillator vacuum
{title2=$b_{n\geq0}|0\rangle=c_{n>0}|0\rangle=0$}
For the anticommuting <bc system>, $\{b_m,c_n\}=\delta_{m+n,0}$. A useful oscillator vacuum obeys $b_n|0\rangle=c_n|0\rangle=0$ for $n>0$ and $b_0|0\rangle=0$. Its partner $c_0|0\rangle$ is nonzero. This specifies a ghost zero-mode doublet and differs from imposing annihilation by both zero modes.