Low-energy effective field theory below the electroweak scale: anomalous dimensions

153

231

We perform a general model-independent analysis of b → cτν τ transitions, including measurements of R D , R D * , their q 2 differential distributions, the recently measured longitudinal D * polarization F D * L , and constraints from the B c → τν τ lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected b → cτν τ observables, such as the baryonic transition Λ b → Λ c τν τ , the ratio R J/ψ , the forward-backward asymmetries A D ( * ) FB , the τ polarization asymmetries P D ( * ) τ , and the longitudinal D * polarization fraction F D * L . The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary R D ( * ) measurement by the Belle collaboration.

Section: Interpretation Of Resultsmentioning

confidence: 99%

“…In order to relate both EFTs, the matching between the Spin Q.N. Nature Allowed couplings SMEFT WET WET theory and the SMEFT has to be performed at the EW scale [74,75,109,110,113,114]. The matching onto the basis in the non-linear case [115,116] is given in Ref.…”

Section: Interpretation Of Resultsmentioning

confidence: 99%

Global fit to b → cτν transitions

Murgui

Peñuelas

Jung

et al. 2019

153

231

“…The SMEFT at dimension six is well studied; see Refs. [22,23,[81][82][83][84][85][86][87] and refs. therein.…”

Section: Lower-dimension Operatorsmentioning

confidence: 99%

Consistency of the standard model effective field theory

Remmen¹,

Rodd²

2019

113

115

We derive bounds on couplings in the standard model effective field theory (SMEFT) as a consequence of causality and the analytic structure of scattering amplitudes. In the SMEFT, there are 64 independent operators at mass dimension eight that are quartic in bosons (either Higgs or gauge fields) and that contain four derivatives and/or field strengths, including both CP-conserving and CP-violating operators. Using analytic dispersion relation arguments for two-to-two bosonic scattering amplitudes, we derive 27 independent bounds on the sign or magnitude of the couplings. We show that these bounds also follow as a consequence of causality of signal propagation in nonvacuum SM backgrounds. These bounds come in two qualitative forms: i) positivity of (various linear combinations of) couplings of CP-even operators and ii) upper bounds on the magnitude of CP-odd operators in terms of (products of) CP-even couplings. We exhibit various classes of example completions, which all satisfy our EFT bounds. These bounds have consequences for current and future particle physics experiments, as part of the observable parameter space is inconsistent with causality and analyticity. To demonstrate the impact of our bounds, we consider applications both to SMEFT constraints derived at colliders and to limits on the neutron electric dipole moment, highlighting the connection between such searches suggested by infrared consistency.

“…We match the Z model directly onto the Weak effective theory (WET) at the electroweak scale. The Wilson coefficients of the WET are then evolved to the corresponding scales via the one-loop QCD anomalous dimensions [38,39]. In the following we report the lepton flavour violating observables used in the numerical analysis.…”

Section: Considered Observables 41 Preliminariesmentioning

confidence: 99%

Quark-lepton connections in Z′ mediated FCNC processes: gauge anomaly cancellations at work

Aebischer

Buras

Cerdà-Sevilla

et al. 2020

We consider scenarios with a heavy Z gauge boson with flavour non-universal quark and lepton couplings with the goal to illustrate how the cancellation of gauge anomalies generated by the presence of an additional U(1) gauge symmetry would imply correlations between FCNC processes within the quark sector, within the lepton sector and most interestingly between quark flavour and lepton flavour violating processes. To this end we present simple scenarios with only left-handed flavour-violating Z couplings and those in which also right-handed flavour-violating couplings are present. The considered scenarios are characterized by a small number of free parameters but in contrast to gauge anomaly cancellation in the Standard Model, in which it takes place separately within each generation, in our scenarios anomaly cancellation involves simultaneously quarks and leptons of all three generations. Our models involve, beyond the ordinary quarks and leptons, three heavy right-handed neutrinos. The models with only left-handed FCNCs of Z involve beyond g Z and M Z two real parameters characterizing the charges of all fermions under the U(1) gauge symmetry and the CKM and PMNS ones in the quark and lepton sectors, respectively. The models with the right-handed FCNCs of Z involve few additional parameters. Imposing constraints from well measured ∆F = 2 observables we identify a number of interesting correlations that involve e.g. ε /ε, B s,d → µ + µ − , B → K(K * ) + − , K + → π + νν, K L → π 0 νν and purely lepton flavour violating decays like µ → eγ, µ → 3e, τ → 3µ and µ − e conversion among others. Also (g − 2) µ,e are considered. The impact of the experimental µ → eγ, µ → 3e and in particular µ − e conversion bounds on rare K and B decays is emphasized.