In two Higgs doublet models (2HDMs) shaped by some unbroken symmetry, imposing perturbativity requirements on the quartic couplings can imply that the allowed masses of all the fundamental scalars are bounded from above. This important property is analyzed in detail for the only two realistic 2HDMs with an exact symmetry, the case with Z2 symmetry and the case with CP symmetry. It is also noticeable that one exception arises in each case: when the vacuum is assumed to respect the imposed symmetry, a decoupling regime can nevertheless appear without violating perturbativity requirements. In both models with an exact symmetry and no decoupling regime, soft symmetry breaking terms can however lead to a decoupling regime: the possibility that this regime might be unnatural, since it requires some fine-tuning, is also analyzed.

中文翻译：

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两个希格斯双峰模型中的有界质量、自发 CP 破坏和 Z2 对称性

在由一些完整的对称性塑造的两个 Higgs 双峰模型 (2HDM) 中，对四次耦合施加扰动要求可能意味着所有基本标量的允许质量从上方有界。对于仅有的两个具有精确对称性的实际 2HDM，即具有 Z2 对称性的情况和具有 CP 对称性的情况，详细分析了这一重要特性。还值得注意的是，在每种情况下都会出现一个例外：当假设真空尊重强加的对称性时，仍然可以在不违反微扰性要求的情况下出现去耦机制。然而，在具有精确对称性和无解耦机制的两种模型中，软对称破坏项可能导致解耦机制：还分析了该机制可能不自然的可能性，因为它需要一些微调。