Open bosonic string mass spectrum
= Open bosonic string mass spectrum
{title2=$\alpha'M^2=N-a$}
The <string level operator> for a free-ended <open string> is $N=\sum_{k>0}\alpha_{-k}\cdot\alpha_k$. The quantum condition is $\alpha'M^2=N-a$, where $a$ is the <normal-ordering constant of a string>. Lorentz-consistent <bosonic string theory> has $a=1$.