Domain Wall Constraints on Two Higgs Doublet Models with $Z_2$ Symmetry

Understand

The Two Higgs Doublet Model (2HDM) with spontaneously broken $Z_2$ symmetry predicts a production of domain walls at the electroweak scale.

• We derive cosmological constraints on model parameters for both Type-I and Type-II 2HDMs from the requirement that domain walls do not dominate the Universe by the present day.
• For Type-I 2HDMs, we deduce the lower bound on the key parameter $\tan\beta > 10^5$ for a wide range of Higgs-boson masses $\sim$ 100 GeV or greater close to the Standard Model alignment limit.
• In addition, we perform numerical simulations of the 2HDM with an approximate as well as an exact $Z_2$ symmetry but biased initial conditions.