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A theta relation in genus 4. (English) Zbl 0987.11035
The $$2^g$$ theta constants of second kind generate a ring of dimension $$g(g+1)/2+1$$. In the case $$g\leq 2$$ they are algebraically independent. In the case $$g=3$$ there is a relation in degree 16, which is related to the so-called Schottky relation. In this paper, the authors investigate the case $$g=4$$ and find a relation whose degree is 24. The relation has two remarkable properties. Namely, it is invariant under the full Siegel modular group, and it is mapped to a nontrivial relation under Siegel’s $$\Phi$$-operator. The proof is based on the theory of codes. The relation is obtained as a linear combination of code polynomials of the 9 self-dual doubly-even codes of length 24.

##### MSC:
 11F46 Siegel modular groups; Siegel and Hilbert-Siegel modular and automorphic forms 11F27 Theta series; Weil representation; theta correspondences 94B05 Linear codes (general theory)
##### Keywords:
Siegel modular forms; codes; theta series
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##### References:
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