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- Fred Jegerlehner, Andreas Nyffeler
- 2009

The muon anomalous magnetic moment is one of the most precisely measured quantities in particle physics. In a recent experiment at Brookhaven it has been measured with a remarkable 14-fold improvement of the previous CERN experiment reaching a precision of 0.54ppm. Since the first results were published, a persistant “discrepancy” between theory and… (More)

Starting from the study of the low-energy and high-energy behaviours of the QCD three-point functions 〈VAP 〉, 〈V VP 〉 and 〈AAP 〉, several O(p6) low-energy constants of the chiral Lagrangian are evaluated within the framework of the lowest meson dominance (LMD) approximation to the large-NC limit of QCD. In certain cases, values that differ substantially… (More)

The correction to the muon anomalous magnetic moment from the pion-pole contribution to the hadronic light-by-light scattering is considered using a description of the π−γ−γ transition form factor based on the large-NC and short-distance properties of QCD. The resulting twoloop integrals are treated by first performing the angular integration analytically,… (More)

- Markus Knecht, Andreas Nyffeler, Michel Perrottet, Eduardo De Rafael
- Physical review letters
- 2002

The hadronic light-by-light contribution to a(mu), the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a… (More)

We analyse hadronically quiet trilepton signatures in the T-parity conserving Littlest Higgs model and in R-parity conserving supersymmetry at the Large Hadron Collider. We identify the regions of the parameter space where such signals can reveal the presence of these new physics models above the Standard Model background and distinguish them from each… (More)

In this paper we reanalyze the electroweak chiral Lagrangian with particular focus on two issues related to gauge invariance. Our analysis is based on a manifestly gauge-invariant approach that we introduced recently. It deals with gauge-invariant Green’s functions and provides a method to evaluate the corresponding generating functional without fixing the… (More)

- Thomas Appelquist, Andreas Nyffeler, Stephen B. Selipsky
- 1997

We compare gap equation predictions for the spontaneous breaking of global symmetries in supersymmetric Yang-Mills theory to nonperturbative results from holomorphic effective action techniques. In the theory without matter fields, both approaches describe the formation of a gluino condensate. With Nf flavors of quark and squark fields, and with Nf below a… (More)

- Andreas Nyffeler
- 2008

We briefly review the current status of the hadronic light-by-light scattering correction to the muon g−2. Then we present our semi-analytical evaluation of the pion-pole contribution, using a description of the pion-photonphoton form factor based on large-NC and short-distance properties of QCD. We also sketch an effective field theory approach to hadronic… (More)

- Andreas Nyffeler
- 2009

We summarize our recent new evaluation of the pion-exchange contribution to hadronic lightby-light scattering in the muon g− 2. We first derive a new short-distance constraint on the off-shell pion-photon-photon form factor at the external vertex in aμ which relates the form factor to the quark condensate magnetic susceptibility in QCD. We then evaluate the… (More)

We use the chiral Lagrangian to investigate the global properties of the N -flavor QCD vacuum as a function of the θ parameter. In the case of exact quark degeneracy we find evidence for first order phase transitions at θ = π · (odd integer). The first order transitions are smoothed by quark mass splittings, although interesting effects remain at realistic… (More)