We study the feasibility of strong first-order electroweak phase transition (EWPT) in a degenerate-scalar scenario of a complex singlet extension of the Standard Model, in which a mass of an additional scalar is nearly degenerate with that of the Higgs boson, 125 GeV. This scenario is known to provide an exquisite solution for circumventing constraints from dark matter direct detection experiments due to cancellations between two scattering amplitudes mediated by two scalars. In the analysis of EWPT, we employ two gauge-invariant calculation schemes on the scalar potential and two familiar resummation methods in evaluating one-loop (gauge dependent) effective potential. We point out that one of the conditions for the strong first-order EWPT is incompatible with the known suppression mechanism of a dark matter cross-section scattering off the nucleons. Nevertheless, we find that strong first-order EWPT is still possible in the degenerate-scalar scenario by dodging dark matter constraints differently.

我们研究了在标准模型的复杂单线态扩展的简并标量场景中强一​​阶电弱相变 (EWPT) 的可行性，其中附加标量的质量几乎与希格斯玻色子的质量一致，125伏特。众所周知，由于两个标量介导的两个散射幅度之间的抵消，这种情况提供了一种巧妙的解决方案，用于规避暗物质直接检测实验的限制。在 EWPT 的分析中，我们在标量势上采用了两种规范不变的计算方案和两种熟悉的求和方法来评估单环（规范相关）有效势。我们指出，强一阶 EWPT 的条件之一与已知的暗物质截面散射核子的抑制机制不相容。尽管如此，我们发现通过以不同方式躲避暗物质约束，在简并标量场景中仍然可以实现强一阶 EWPT。