User:Bierlich/sandbox

The idea is, that since the Standard Model is a very successful theory, it can be taken as a low energy approximation of the theory of new physics. The deviations from the Standard Model at higher energies are modeled much in the same way as one would make a series expansion of a function in the neighborhood of a minimum. The parametrization that will be considered in this thesis takes as its starting point the vertex where a W particle radiates a Z. This vertex is parametrized in triple gauge boson couplings, and the end result of the conducted study is to set a limit on these. As the model considered is a general parametrization of an existing vertex using only Standard Model particle content, limits on triple gauge boson couplings truly are model independent limits on deviations from Standard Model physics.

charged One can write out the electroweak Lagrangian of equation (2.23) in terms of the physical fields introduced in equation (2.24). The bilinear term becomes [11]: 1Wi Wμν = ig [Wμν−W+ − Wμν+W−][cos(Θ )Z + sin(Θ )A ] 4μνi 1 μ μ Wμ Wμ + ig1 [cos(ΘW )Zμν + sin(ΘW )Aμν][Wμ−Wν+ − Wμ+Wν−] + O(g2), 2 (2.27) ￼￼expressing the triple gauge boson vertices allowed in the SM. Multiplying the terms together, it is clear, that the only two triple gauge boson vertices allowed, are W+W−Z and W+W−γ. The strength of these vertices are the same as the coupling to the fermions. The neglected terms of O(g2) are the so-called quadruple gauge boson vertices; γγW+W−, ZZW+W−, γZW+W−, W+W−W+W−. The quadruple gauge boson vertices are not considered in this thesis. The triple gauge boson vertex part, however, can be rearranged to an expression where the WWZ and the WWγ vertices are separated, but symmetric in the exchange of photons and Zs:

￼￼￼WWγ part + ig 􏰂gZ(W− W+μZν − W+ W−μZν) + κ W−W+Zμν􏰃, WWZ 1 μν μν Z μ ν 􏱨 􏱧􏱦 􏱩 ￼￼where gWWγ = e and gWWZ = ecot(ΘW). As seen, the emergence of the TGCs resides both on the non-Abelian structure of the electroweak theory, but also very much on the Higgs mechanism. The two triple gauge boson vertices described in equation (2.27) and (2.28) is part of the SM, and has been experimentally confirmed both at Lep [12] and TeVatron [13]. neutral