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arXiv · 2402.17518

Strong CP problem in the quantum rotor

David Albandea·Guilherme Catumba·Alberto Ramos
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Abstract

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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David Albandea, Guilherme Catumba, Alberto Ramos. 2024-02-27. Strong CP problem in the quantum rotor. https://doi.org/10.1103/physrevd.110.094512

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