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Thermostats without conjugate points
- Part of
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- Journal:
- Ergodic Theory and Dynamical Systems / Volume 46 / Issue 6 / June 2026
- Published online by Cambridge University Press:
- 03 March 2026, pp. 1494-1520
- Print publication:
- June 2026
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- Article
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We generalize Hopf’s theorem to thermostats: the total thermostat curvature of a thermostat without conjugate points is non-positive and vanishes only if the thermostat curvature is identically zero. We further show that, if the thermostat curvature is zero, then the flow has no conjugate points and the Green bundles collapse almost everywhere. Given a thermostat without conjugate points, we prove that the Green bundles are transverse everywhere if and only if it is projectively Anosov. Finally, we provide an example showing that Hopf’s rigidity theorem on the
$2$-torus cannot be extended to thermostats. It is also the first example of a projectively Anosov thermostat which is not Anosov.
