Landscaping the Strong CP Problem

Understand

One often hears that the strong $CP$ problem is the one problem which cannot be solved by anthropic reasoning.

• We argue that this is not so.
• Due to nonperturbative dynamics, states with a different $CP$ violating paramenter $\theta$ acquire different vacuum energies after the QCD phase transition.
• These add to the total variation of the cosmological constant in the putative landscape of Universes.