# Oeljeklaus–Toma manifolds and arithmetic invariants

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## Abstract

We consider Oeljeklaus–Toma manifolds coming from number fields with precisely one complex place. Our general theme is to relate the geometry to the arithmetic. We show that just knowing the fundamental group allows us to recover the number field. We also show that this fails if there are more complex places. The first homology turns out to be related to an interesting ideal. We compute the volume in terms of the discriminant and regulator of the number field. Is there a conceptual reason for this? We explore this and see what happens if we (entirely experimentally) regard them as “baby siblings” of hyperbolic manifolds coming from number fields.

## Mathematics Subject Classification

53C55## Notes

### Acknowledgments

I would like to express my sincere gratitude to Victor Vuletescu for teaching me a lot of things, not all of them of mathematical nature. This note is a direct result of his inspiring ideas about the interplay of geometric and arithmetic conditions in Oeljeklaus–Toma manifolds. I also thank Chris Wuthrich for introducing me to SAGE. I would also like to thank the anonymous referee for a number of helpful remarks, which have led to a much clearer presentation.

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