Effects of longitudinal short-distance constraints on the hadronic light-by-light contribution to the muon $$\mathbf {g-2}$$

The short-distance behaviour of the hadronic light-by-light (HLbL) contribution to (g − 2)μ has recently been studied by means of an operator product expansion in a background electromagnetic field. The leading term in this expansion has been shown to be given by the massless quark loop, and the non-perturbative corrections are numerically very suppressed. Here, we calculate the perturbative QCD correction to the massless quark loop. The correction is found to be fairly small compared to the quark loop as far as we study energy scales where the perturbative running for the QCD coupling is well-defined, i.e. for scales μ ≳ 1 GeV. This should allow to reduce the large systematic uncertainty associated to high-multiplicity hadronic states.

Section: The Two-loop Perturbative Correctionsupporting

confidence: 83%

The two-loop perturbative correction to the (g − 2)μ HLbL at short distances

Bijnens

Hermansson-Truedsson

Laub

et al. 2021

“…Some recent developments include refs [34][35][36][37][38][39][40]. for hadronic vacuum polarization and refs [41][42][43][44][45][46][47][48]. for hadronic light-by-light scattering.…”

mentioning

confidence: 99%

Consequences of chirally enhanced explanations of (g − 2)μ for h → μμ and Z → μμ

Crivellin

Hoferichter

2021

With the long-standing tension between experiment and Standard-Model (SM) prediction in the anomalous magnetic moment of the muon aμ recently reaffirmed by the Fermilab experiment, the crucial question becomes which other observables could be sensitive to the underlying physics beyond the SM to which aμ may be pointing. While from the effective field theory (EFT) point of view no direct correlations exist, this changes in specific new physics models. In particular, in the case of explanations involving heavy new particles above the electroweak (EW) scale with chiral enhancement, which are preferred to evade exclusion limits from direct searches, correlations with other observables sensitive to EW symmetry breaking are expected. Such scenarios can be classified according to the SU(2)L representations and the hypercharges of the new particles. We match the resulting class of models with heavy new scalars and fermions onto SMEFT and study the resulting correlations with h → μμ and Z → μμ decays, where, via SU(2)L symmetry, the latter process is related to Z → νν and modified W-μ-ν couplings.

“…Applying the projectors given in appendix A and reducing the (ultraviolet finite) integrals, the result is left in terms of scalar tadpole, self-energy and triangle integrals. Expanding these in the masses, 14 one findŝ…”

Section: Jhep10(2020)203mentioning

confidence: 99%

“…In the latter approach one considers individual intermediate states, for which short-distance constraints such as those derived herein can be used, examples are refs. [7,8,13,14,16,20]. One should of course be careful in comparing at the correct kinematics.…”

Section: Introductionmentioning

confidence: 99%

Short-distance HLbL contributions to the muon anomalous magnetic moment beyond perturbation theory

Bijnens

Hermansson-Truedsson

Laub

et al. 2020

The hadronic light-by-light contribution to the muon anomalous magnetic moment depends on an integration over three off-shell momenta squared ($$ {Q}_i^2 $$ Q i 2 ) of the correlator of four electromagnetic currents and the fourth leg at zero momentum. We derive the short-distance expansion of this correlator in the limit where all three $$ {Q}_i^2 $$ Q i 2 are large and in the Euclidean domain in QCD. This is done via a systematic operator product expansion (OPE) in a background field which we construct. The leading order term in the expansion is the massless quark loop. We also compute the non-perturbative part of the next-to-leading contribution, which is suppressed by quark masses, and the chiral limit part of the next-to-next-to leading contributions to the OPE. We build a renormalisation program for the OPE. The numerical role of the higher-order contributions is estimated and found to be small.