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Strong CP problem in the quantum rotor

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arxiv 2402.17518 v2 pith:SA4A2MUU submitted 2024-02-27 hep-lat hep-ph

Strong CP problem in the quantum rotor

classification hep-lat hep-ph
keywords problemlatticestrongthetatopologicalorderquantumrotor
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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Recent studies have claimed that the strong $CP$ problem does not occur in QCD, proposing a new order of limits in volume and topological sectors when studying observables on the lattice. In order to shed light on this issue, we study the effect of the topological $\theta$-term on a simple quantum mechanical rotor that allows a lattice description. The topological susceptibility and the $\theta$-dependence of the energy spectrum are both computed using local lattice correlation functions. The sign problem is overcome by considering Taylor expansions in $\theta$ exploiting automatic differentiation methods for Monte Carlo processes. Our findings confirm the conventional wisdom on the strong $CP$ problem.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. A particle on a ring or: how I learned to stop worrying and love $\theta$-vacua

    hep-ph 2026-01 accept novelty 6.0

    The ACGT order-of-limits prescription fails to reproduce the correct θ-dependent energy spectrum in the quantum rotor and quantum pendulum.

  2. Scaling flow-based approaches for topology sampling in $\mathrm{SU}(3)$ gauge theory

    hep-lat 2025-10 unverdicted novelty 6.0

    Out-of-equilibrium simulations with open-to-periodic boundary switching plus a tailored stochastic normalizing flow enable efficient topology sampling in the continuum limit of four-dimensional SU(3) Yang-Mills theory.