Register to reply

W boson vertices

by kaksmet
Tags: boson, vertices
Share this thread:
kaksmet
#1
Dec12-12, 05:04 AM
P: 83
Hi,

a simple question on W boson vertices (and I guess field theory in general). If I have a W boson vertex for incoming particles, i.e.

W^+ ubar d and W^- u dbar

how do I change this for outgoing W's. The first interaction contains a CKM matrix element Vud and the second a Vud^*, and I want to figure out which one of them has the complex conjugate in the case of outgoing W's.

Thanks!
Phys.Org News Partner Physics news on Phys.org
New complex oxides could advance memory devices
Nature's designs inspire research into new light-based technologies
UCI team is first to capture motion of single molecule in real time
ofirg
#2
Dec12-12, 05:58 AM
P: 93
First of all remember that an interaction vertex in the lagrangian can represent several different processes in feynman diagrams.

the [itex]W^{-}u\bar{d}[/itex] term in the lagrangian can be the decay [itex]W^{+}\rightarrow u\bar{d}[/itex] or the annhilation [itex]d\bar{u}\rightarrow W^{-}[/itex] , both with the same coupling (including the same phase)

the conjugate decay and annihilation processes will come from the hermitian conjugate term in the lagrangian, and they will have opposite phase.

A useful way to remember which processes will have the same phase and which will not is to remember that the CPT inversed process has the same coupling (including the same phase).
In our case [itex]W^{+}\rightarrow u\bar{d}[/itex] is the CPT inversed process of [itex]d\bar{u}\rightarrow W^{-}[/itex] , since each particle is replaced by its antiparticle and the time direction is reversed.


Register to reply

Related Discussions
If the Boson Higgs Boson only exists for >.< long... High Energy, Nuclear, Particle Physics 1
Pair production in boson-boson collision Advanced Physics Homework 2
Cause of boson-boson repulsion Atomic, Solid State, Comp. Physics 0
Massless boson vs massive boson High Energy, Nuclear, Particle Physics 1
Number of Graphs on n vertices without isolated vertices Calculus & Beyond Homework 0