Level-two scalar in covariant string quantization
= Level-two scalar in covariant string quantization
{title2=$\langle S|S\rangle=\frac{2}{25}(D-1)(26-D)$}
At $a=1$, let $k=\sqrt{2\alpha'}p$, $k^2=-2$. The physical scalar $[\alpha_{-1}\cdot\alpha_{-1}+(D+4)(k\cdot\alpha_{-1})^2/10+(D-1)k\cdot\alpha_{-2}/5]|p\rangle$ has norm $2(D-1)(26-D)/25$. It is positive below 26, null at 26, and a <string ghost state> above 26. Matching the ordinary transverse spectrum removes this extra scalar at 26.