[论文解读] Implications of the discovery of a Higgs boson with a mass of 125 GeV

Dario Buttazzo|arXiv (Cornell University)|Mar 26, 2014

Particle physics theoretical and experimental studies参考文献 3被引用 5

一句话总结

本论文研究了125 GeV Higgs玻色子的发现对费米能标物理学的影响，分析了在超对称理论、复合Higgs模型以及标准模型中自然性的问题。论文推导出两圈真空稳定性约束，并表明接近临界的Higgs四次耦合常数暗示了真空的亚稳态性，从而将电弱能标与普朗克能标物理联系起来。

ABSTRACT

The rather precise knowledge of the mass of the Higgs boson and of its couplings has important consequences for the physical phenomena taking place at the Fermi scale. We analyze some of these implications in the most motivated frameworks for physics at that energies - supersymmetry, models of a composite Higgs boson, and the Standard Model itself. At the same time, precision experiments in flavour physics require a highly non-generic structure of flavour and CP transitions. In any model of electroweak symmetry breaking with a relatively low scale of new phenomena, as motivated by naturalness, some mechanism has to be found in order to keep unwanted flavour effects under control. We devote particular attention to the consequences of the approximate U(2)^3 symmetry exhibited by the quarks of the Standard Model. The combined analysis of the indirect constraints from flavour, Higgs and electroweak physics will allow us to outline a picture of some most natural models of physics near the Fermi scale. Although non trivially, a few models emerge that look capable of accommodating a 125 GeV Higgs boson, consistently with all the other constraints, with new particles in an interesting range for discovery at the LHC, as well as associated flavour signals. This is particularly interesting in view of the forthcoming improvements in the direct experimental investigation of that energies. Finally, the measurement of the last parameter of the Standard Model - the Higgs quartic coupling - has important consequences even if no new physics is present close to the Fermi scale: its near-critical value, which puts the electroweak vacuum in a metastable state close to a phase transition, may have an interesting connection with Planck-scale physics. We derive the bound for electroweak vacuum stability with full two-loop precision, and explore some possible implication of near-criticality.

研究动机与目标

• 评估125 GeV Higgs玻色子对电弱对称性自发破缺模型的影响，特别是超对称理论与复合Higgs情景。
• 探讨味物理与CP破坏对费米能标新物理的约束，强调在夸克 sector 中近似 U(2)^3 对称性的作用。
• 推导两圈精度的真空稳定性约束，以评估电弱真空的亚稳态性质。
• 识别能够容纳125 GeV Higgs玻色子、满足间接约束条件，并在LHC上预测可探测新物理的可行模型。
• 研究Higgs四次耦合接近临界值与普朗克能标物理之间的联系，特别是在真空亚稳态背景下的意义。

提出的方法

• 使用两圈跑动方程计算有效Higgs四次耦合，包含完整的QCD与Yukawa修正。
• 应用 anomalous dimension γ(μ) 以在从 Mt 到 h 能标范围内重求和对数修正。
• 通过大对数的指数重求和推导有效耦合 λ_eff(h)：在 μ = h 处，a_eff(h) = e^{4Γ(h)}[λ + λ_eff^{(1)} + λ_eff^{(2)}]。
• 利用完整的两圈 β 函数与 polylogarithm 函数评估一阶与两阶修正 λ_eff^{(1)} 与 λ_eff^{(2)}。
• 在两圈有效势计算中纳入顶夸克、规范玻色子与Higgs自相互作用的贡献。
• 使用完整的两圈有效势确定电弱真空的稳定性边界，包含非微扰修正。

实验结果

研究问题

• RQ1 125 GeV Higgs玻色子如何约束超对称与复合Higgs模型中的自然性？
• RQ2 近似 U(2)^3 对称性在费米能标新物理模型中抑制味改变中性流的作用是什么？
• RQ3 Higgs四次耦合的两圈精度约束是什么？它们如何影响真空稳定性？
• RQ4 能否存在满足味物理、电弱物理与Higgs精度测量约束，同时在LHC上预测新粒子的模型？
• RQ5 Higgs四次耦合的近临界值与普朗克能标物理之间存在何种联系？

主要发现

• 观测到的125 GeV Higgs质量在最小超对称标准模型中要求显著的微调，更倾向于支持具有额外单态的NMSSM等更复杂的模型。
• 两圈有效势计算表明电弱真空是亚稳态的，其Higgs四次耦合接近一个临界值，该值区分了稳定与不稳定区域。
• 有效耦合 λ_eff(h) 以完整的两圈精度计算得出，包含 anomalous dimension 重求和与 dilogarithm 修正。
• 来自间接测量的味物理约束要求味与CP变换具有高度非通用的结构，而这种结构在具有近似 U(2)^3 对称性的模型中自然实现。
• Higgs耦合的近临界性暗示其可能与普朗克能标物理存在关联，真空衰变率对四次耦合的精确值高度敏感。
• 若干模型——尤其是具有复合Higgs或扩展标量结构的模型——能够容纳125 GeV Higgs玻色子，同时满足所有现有约束，并在LHC上预测可探测的信号。