= Type II gamma-factor mass poles
{c}
{title2=$s=4n/\alpha',\quad n=0,1,\ldots$}
At generic fixed $t$, the factor $\Gamma(-\alpha's/4)$ has simple poles at the displayed nonnegative values of $s$. Its denominator $\Gamma(1+\alpha's/4)$ is finite there. The $t,u$ factors do not generically cancel those poles under $s+t+u=0$. Factorization identifies massless and massive intermediate states at those masses. The factor has no negative-mass-squared poles; special polarization or momentum choices can suppress individual residues and cannot establish the degeneracy of an entire level.
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