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The Weak Nuclear Force Tao Han iSTEP 2017
The Idea of EW Unification Partial-symmetries of weak interactions
The birth of the Standard Model In 1967, Weinberg produced a gauge theory that correctly predicted electromagnetic and weak nuclear forces. This was later to become known as the electroweak theory. In his paper, 'A model of leptons', he showed that although electromagnetism is much stronger than the weak force of everyday energies, the only way to devise a theory of the weak force is to include the electromagnetic force. Weinberg showed how what was seemingly impossible could be achieved and the forces could be unified through the interchange of particles in spite of the difference in their strengths. Abdus Salam had independently reached the same conclusions and what became known as the Weinberg-Salam model was a major advance on earlier models that had originally been applied to leptons... (Chris Cooper, Physics).
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9/18 is not SU(2) invariant
10/18 arbitrary matrix not hermitian
11/18 Unitary rotations: 黑格斯没有树图的 FCNC Yukawa 耦合 diagonalized by bi-unitary transformation Quark mass matrix & Yukawa couplings 黑格斯没有树图的 FCNC Yukawa 耦合 simultaneously diagonalized
t Fermions’ unitary rotations have only one impact in gauge couplings: Fermions’ unitary rotations have only one impact in gauge couplings: Charged current coupling: also unitary For example: top decays t W d ~ |Vtd|2 t d, s, b distinguishable e.g., b-tagging t W s ~ |Vts|2 t W b ~ |Vtb|2
Now, look at lepton flavor rotation – any impact in gauge couplings ? 13/18 : Mass: undistinguishable missing energy detectable production cross section or decay rate 转动对耦合和 可观测量没影响 转动对可观测量没影响
source propagation detection lepton flavor rotation （类似CKM的矩阵） 14/18 引起的物理现象只是：neutrino oscillation 14/18 为了简单，可以选取一个basis: 自发破缺前把带电轻子的Yukawa耦合对角化 这样只有中微子的质量是非对角的、需要对角化 左手中微子的转动矩阵（类似CKM矩阵）导致‘中微子震荡’ source propagation detection
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EW gauge interactions: 17/18
Higgs gauge+Yukawa interactions: 18/18
休息一会儿