标题： 自发对称性破缺：从有效作用量到标准模型及之外的宇宙相变 显示英文标题

标题： Spontaneous Symmetry Breaking: From the Effective Action to Cosmological Phase Transitions in the Standard Model and Beyond

摘要： 本文的主要目标是研究早期宇宙中的宇宙学相变，重点研究标准模型及其扩展中的电弱相变。 在标准模型中，零温度下自发破缺的电弱对称性由于有限温度效应在早期宇宙中被恢复。 这一现象通过有限温度的有效势进行研究，该有效势决定了理论的真实真空态。 高温下的对称性恢复也通过有限温度场论进行研究，该理论用于引入虚时形式推导有限温度下的费曼规则。 此外，我们介绍了宇宙学相变的理论，重点讨论了热隧穿和气泡成核的概念。 我们还讨论了观测到的宇宙重子不对称性，以制定重子生成的条件并描述电弱重子生成。 因此，详细推导了标准模型在有限温度下的单环有效势，包括环修正，以进一步研究电弱重子生成。 我们的结果表明，电弱相变不够强烈，无法解释观测到的宇宙重子不对称性。 另一方面，标准模型的真实单态扩展描述了一个足够强烈的电弱相变，并能解释观测到的宇宙重子不对称性。 这些扩展还包括一个六维算符，该算符来源于有效场论。 特别是，对该单态扩展的参数空间进行了广泛研究，但受到许多现象学约束的限制，例如不可见的希格斯衰变宽度。 显示英文摘要

摘要： The primary objective of this work is to investigate the cosmological phase transitions in the early Universe, with a focus on the electroweak phase transition in the Standard Model and its extensions. In the Standard Model, the spontaneously broken electroweak symmetry at zero temperature is restored in the early Universe due to finite-temperature effects. This phenomenon is studied using the effective potential at finite temperatures, which determines the true vacuum state of the theory. Symmetry restoration at high temperatures is also studied by the finite-temperature field theory introduced to derive the Feynman rules at finite temperatures using the imaginary-time formalism. Furthermore, we present the theory of cosmological phase transitions, focusing on the concepts of thermal tunneling and bubble nucleation. We additionally discuss the observed baryon asymmetry of the Universe to formulate the conditions for baryogenesis and describe electroweak baryogenesis. Therefore, the one-loop effective potential in the Standard Model at finite temperatures is derived in detail including the ring corrections to study further the electroweak baryogenesis. Our results indicate that the electroweak phase transition is not strong enough to explain the observed baryon asymmetry of the Universe. On the other hand, the real singlet extensions of the Standard Model describe a strong enough electroweak phase transition and the observed baryon asymmetry of the Universe. These extensions are also discussed including a dimension-six operator, which originates from an effective field theory. In particular, the parameter space of this singlet extension is examined extensively, while it is restricted by numerous phenomenological constraints, such as the invisible Higgs decay width.