Spontaneously Broken $(-1)$-Form U(1) Symmetries

Understand

Spontaneous breaking of symmetries leads to universal phenomena.

• We extend this notion to $(-1)$-form U(1) symmetries.
• The spontaneous breaking is diagnosed by a dependence of the vacuum energy on a constant background field $\theta$, which can be probed by the topological susceptibility.
• This leads to a reinterpretation of the Strong CP problem as arising from a spontaneously broken instantonic symmetry in QCD.