1、,3/18,4/18,5/18,The Weak Nuclear Force,Tao HaniSTEP 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 th
2、e 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 cou
3、ld 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 be
4、en applied to leptons. (Chris Cooper, Physics).,6/18,7/18,8/18,is not SU(2) invariant,9/18,arbitrary matrix not hermitian,10/18,Unitary rotations:,diagonalized by bi-unitary transformation,Quark mass matrix & Yukawa couplings,simultaneously diagonalized,黑格斯没有树图的FCNC Yukawa 耦合,11/18,also unitary,Ferm
5、ions unitary rotations have only one impact in gauge couplings:,Charged current coupling:,t,d, s, b,For example: top decays,t W d |Vtd|2,t W s |Vts|2,t W b |Vtb|2,distinguishablee.g., b-tagging,production cross section or decay rate,undistinguishablemissing energy,detectable,Now, look at lepton flav
6、or rotation any impact in gauge couplings ?,Mass:,转动对耦合和可观测量没影响,转动对可观测量没影响,:,13/18,source,propagation,detection,lepton flavor rotation （类似CKM的矩阵）引起的物理现象只是：neutrino oscillation,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,14/18,15/18,QCD interactions:,16/18,EW gauge interactions:,17/18,Higgs gauge+Yukawa interactions:,18/18,休息一会儿,
