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Register a new userConstraints on Four Fermion Contact Interactions from Precise Electroweak Measurements
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We establish constraints on a general four-fermion contact interaction from precise measurements of electroweak parameters. We compute the one-loop contribution for the leptonic $Z$ width, anomalous magnetic, weak-magnetic, electric and weak dipole moments of leptons in order to extract bounds on the energy scale of these effective interactions.
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The Large Hadron Collider can do precision physics at a level that is competitive with electroweak precision constraints when probing physics beyond the Standard Model. We present a simple yet general parameterization of the effect of an arbitrary number of lepton-quark contact interactions on any di-lepton observable at hadron colliders. This parameterization can be easily adopted by the experimental collaborations to put bounds on arbitrary combinations of lepton-quark contact interactions. We compute the corresponding bounds from current di-lepton resonance searches at the LHC and find that they are competitive with and often complementary to indirect constraints from electroweak precision data. We combine all current constraints in a global analysis to obtain the most stringent bounds on lepton-quark contact interactions. We also show that the high-energy phase of the LHC has a unique potential in terms of discovery and discrimination power among different types of lepton-quark contact interactions.
The recently completed calculation of the full electroweak O(alpha) corrections to the charged-current four-fermion production processes e+e- --> nu_tau tau+ mu- anti-nu_mu, u anti-d mu- anti-nu_mu, and u anti-d s anti-c is briefly reviewed. The calculation is performed using complex gauge-boson masses, supplemented by complex couplings to restore gauge invariance. The evaluation of the occurring one-loop tensor integrals, which include 5- and 6-point functions, requires new techniques. The effects of the complete O(alpha) corrections to the total cross section and to some differential cross sections of physical interest are discussed and compared to predictions based on the double-pole approximation, revealing that the latter approximation is not sufficient to fully exploit the potential of a future linear collider in an analysis of W-boson pairs at high energies.
We investigate from first principles the introduction of isospin-1 vector and axial-vector fields into the nonlinear sigma model. Chiral symmetry is nonlinearly realised and spin-1 fields are assumed to transform homogeneously under chiral rotations. By requiring the Hamiltonian of the theory to be bounded from below we find inequalities relating three- and four-point meson couplings. This leads to a low-energy phenomenological Lagrangian for the nonanomalous sector of $pirho a_1$ strong interactions.
We set constraints on the trilinear Higgs boson self-coupling, $lambda_3$, by combining the information coming from the $W$ mass and leptonic effective Weinberg angle, electroweak precision observables, with the single Higgs boson analyses targeting the $gamma gamma,, ZZ^*,, WW^*, ,tau^+ tau^-$ and $bar{b} b$ decay channels and the double Higgs boson analyses in the $bbar{b}bbar{b}, , bbar{b}b tau^+ tau^-$ and $bbar{b}b gamma gamma$ decay channels, performed by the ATLAS collaboration. With the assumption that the new physics affects only the Higgs potential, values outside the interval $ -1.8, lambda_3^{rm SM} < lambda_3 < 9.2 , lambda_3^{rm SM}$ are excluded at $95%$ confidence level. With respect to similar analyses that do not include the information coming from the electroweak precision observables our analysis shows a stronger constraint on both positive and negative values of $lambda_3$.
We compute bounds on coefficients of effective operators in the Standard Model that can be inferred from observations of neutrino scattering by the COHERENT experiment. While many operators are bound extremely well by past experiments the full future data set from COHERENT will provide modest improvements for some operators.
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