Topological gauge dynamics of Standard Model $\theta$ vacua

by Pier Giuseppe Catinari

Thursday Jun 18, 2026, 12:00 PM → 1:30 PM Europe/Madrid

IFAE Seminar Room (In-Person)

In this talk I will discuss the infrared signatures of topological terms in the Standard Model action, focusing on their role in the strong CP problem and in non-perturbative B+L violation in the electroweak sector.

I will first revisit the massive Schwinger model as a theoretical laboratory, highlighting its structural parallels with QCD in the large—$N_c$ limit and emphasizing the role of the $\eta'$ meson in the vanishing of the topological susceptibility of QCD in the chiral limit. I will then critically examine recent claims in the literature (https://arxiv.org/abs/2408.07535) according to which the vanishing of the electroweak topological susceptibility, in the absence of B+L violations, proceeds in strict analogy with QCD in the chiral limit. Such arguments would require the presence of a new pseudoscalar state in the spectrum — an electroweak $\eta'$ — mimicking the role of the $\eta'$ meson in QCD.