# Orthogonality relations for characters of VOAs?

If $$G$$ is a finite group, the characters of its irreps satisfy $$\langle \chi_1,\chi_2\rangle := \frac{1}{|G|}\sum_{g\in G} \chi_1(g)\; \overline{\chi_2(g)} = \delta_{\chi_1,\chi_2}.$$

Alexei Latyntsev asked me the following question.

Instead of a group $$G$$, let us consider a vertex algebra $$V$$ (let's say a rational unitary VOA).

Is there an analog of the above orthogonality relations which applies to the characters of irreducible $$V$$-modules? (Or maybe genus one 1-point functions?)

• It is reminiscent of the statement that if you take the twice-punctured P^1 and insert two different modules, you will get zero.. – Theo Johnson-Freyd Apr 2 at 14:26
• @Theo Johnson-Freyd. Absolutely correct! And if you take your twice-punctured P^1, and label the points by the same module (or maybe the module and its dual), you get a one-dimensional space of conformal blocks. Also, in the above situation, you can "sew the two points to each other" and get a genus one curve... So it all looks very suggestive. But does this translate into something like orthogonality relations??? – André Henriques Apr 3 at 12:24
• I don't see it that way cause that's just the fact of not having pairings between non-isomorphic irreps which is akin to Schur's Lemma more than the asked orthogonality. On the other hand. What you ask seems more about Hermitian structures on bundles on $P^1$ when viewed as the moduli space of elliptic curves. Let $V$ be a rational $C_2$ cofinite vertex algebra. Then characters are flat sections of a local system on $P^1$ with a singularity at infinity. It seems to me that you're asking if the corresponding vector bundle has a natural hermitian metric making the sections an orthonormal basis. – Reimundo Heluani Apr 3 at 13:55
• ... Using that any such bundle decomposes as a sum of $\mathcal{O}(n)$ you may try to prove that there exists a unique such hermitian metric. – Reimundo Heluani Apr 3 at 13:56