= Massless first closed-string level
{title2=$N=\widetilde N=1,\quad M^2=0$}
In the critical <bosonic string theory>, the states $\alpha_{-1}^i\widetilde\alpha_{-1}^j|0;p\rangle$ have $M^2=0$. Their coefficient matrix decomposes into a symmetric trace-free tensor, an antisymmetric tensor, and a scalar trace, representing the <graviton>, <Kalb–Ramond field>, and <dilaton>. Their transverse <particle polarization> counts add to $(D-2)^2$. The <normal-ordering constant of a string> is one.
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