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    High Energy Theory Group Seminars

    Strong CP, the QCD vacuum and axions: old questions and new perspectives

    by Andreas Ringwald (DESY)

    → Europe/Rome
    Dipartimento di Fisica e Astronomia - Edificio Ricci-Curbastro (ex-Paolotti)

    Dipartimento di Fisica e Astronomia - Edificio Ricci-Curbastro (ex-Paolotti)
    Description

    The strong CP problem remains a central open question in particle physics and a primary motivation for the QCD axion. Recent proposals have challenged this picture, arguing that an appropriate treatment of the infinite-volume limit removes strong CP violation. In this seminar, I will examine these claims through the interplay between fixed topological charge, the order of limits, and QCD’s response to external sources. Low-energy effective theory and anomalous Ward identities provide complementary tests of the proposed phase alignment, while lattice results offer quantitative consistency checks. I will discuss what these arguments establish, which assumptions they require, and their implications for the strong CP problem and the motivation for axion searches.