Anomalous gauge-boson couplings and the Higgs-boson mass

We study anomalous gauge-boson couplings induced by a locally SU(2) x U(1) invariant effective Lagrangian containing ten operators of dimension six built from the boson fields of the Standard Model (SM) before spontaneous symmetry breaking (SSB). After SSB some operators lead to new three- and four-gauge-boson interactions, some contribute to the diagonal and off-diagonal kinetic terms of the gauge bosons and to the mass terms of the W and Z bosons. This requires a renormalisation of the gauge-boson fields, which, in turn, modifies the charged- and neutral-current interactions, although none of the additional operators contain fermion fields. Bounds on the anomalous couplings from electroweak precision measurements at LEP and SLD are correlated with the Higgs-boson mass m_H. Rather moderate values of anomalous couplings allow m_H up to 500 GeV. At a future linear collider the triple-gauge-boson couplings gammaWW and ZWW can be measured in the reaction e+e- --> WW. We compare three approaches to anomalous gauge-boson couplings: the form-factor approach, the addition of anomalous coupling terms to the SM Lagrangian after and, as outlined above, before SSB. The translation of the bounds on the couplings from one approach to another is not straightforward. We show that it can be done for the process e+e- --> WW by defining new effective ZWW couplings.Comment: 50 pages, 4 figures; version to appear in EPJ

Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation

We study in detail the renomalization group evolution of Yukawa couplings and soft supersymmetry breaking trilinear couplings in the minimal supersymmetric standard model with baryon and lepton number violation. We obtain the exact solutions of these equations in a closed form, and then depict the infrared fixed point structure of the third generation Yukawa couplings and the highest generation baryon and lepton number violating couplings. Approximate analytical solutions for these Yukawa couplings and baryon and lepton number violating couplings, and the soft supersymmetry breaking couplings are obtained in terms of their initial values at the unification scale. We then numerically study the infrared fixed surfaces of the model, and illustrate the approach to the fixed points.Comment: 16 pages REVTeX, figures embedded as epsfigs, replaced with version to appear in Physical Review D, minor typographical errors eliminated and references reordered, figures correcte

Measurement of Boson Self Couplings at LEP and Search for Anomalies

With center of mass energies up to 209 GeV of LEP II, massive W and Z bosons can be produced in pairs and jointly with photons. This allows to study boson-boson couplings. Since the W and Z bosons are unstable and decay into fermions, two- and four-fermion final states, accompanied possibly by photons, play an important role for these measurements. The couplings of the W to other bosons have been measured to be g1Z = 0.990+0.023-0.024, kappa_gamma = 0.896+0.058-0.056, and lambda_gamma = -0.023 +0.025 -0.023. They are in agreement with the Standard Model expectation of g1Z = 1, kappa_gamma = 1, and lambda_gamma = 0. No sign for couplings of three neutral bosons, parametrized by the couplings f_i^V and h_i^V, and for anomalous couplings of four gauge bosons, parametrized by a_0, a_n and a_c has been found.Comment: LaTex, 6 pages, 9 figures, to appear in the proceedings of the Conference: XXXVII Rencontres de Moriond: Electroweak Interactions and Unified Theories. Systematics added, more recent values for the neutral triple gauge boson couplings, sign swap correction for quartic boson couplings, new limits for quartic couplings from the Z gamma gamma final state, reference adde

Anomalies, Anomalous U(1)'s and generalized Chern-Simons terms

A detailed analysis of anomalous U(1)'s and their effective couplings is performed both in field theory and string theory. It is motivated by the possible relevance of such couplings in particle physics, as well as a potential signal distinguishing string theory from other UV options. The most general anomaly related effective action is analyzed and parameterized. It contains Stuckelberg, axionic and Chern-Simons-like couplings. It is shown that such couplings are generically non-trivial in orientifold string vacua and are not in general fixed by anomalies. A similar analysis in quantum field theories provides similar couplings. The trilinear gauge boson couplings are also calculated and their phenomenological relevance is advocated. We do not find qualitative differences between string and field theory in this sector.Comment: 52 pages, 2 eps figures, LaTeX, feynmf & youngtab packages (v2 - Minor corrections, references added