BORIS Theses

BORIS Theses
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Short-distance constraints on the hadronic light-by-light contribution to the muon g-2

Laub, Laetitia (2021). Short-distance constraints on the hadronic light-by-light contribution to the muon g-2. (Thesis). Universität Bern, Bern

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The aim of this work is to investigate the information available from perturbative QCD to constrain the hadronic light-by-light contribution to $(g-2)_\mu$ and to implement it in a way that is compatible with the dispersive description. The first regime of interest is the one where three photon virtualities are large. Because the external photon is soft in the $g-2$ kinematics, an operator product expansion in presence of an external electromagnetic field needs to be used. The leading order in this expansion corresponds to the usual massless quark loop. In this work, it is shown that the non-perturbative corrections are small and that the $\alpha _s$-correction is negative and amounts to about 10\% of the quark loop. The second interesting regime is the one where two photon virtualities are much larger than the third. This leads to the so-called Melnikov-Vainshtein constraint. A way to satisfy the short-distance constraints using heavy pseudoscalars is then presented. This is done using a large-$N_c$ inspired Regge model for the transition form factors of the radially excited pseudoscalars. The contribution of the heavy pseudoscalars is then matched to the quark loop and its first gluonic correction in order to reduce the model-dependence of our estimation. With the recent results from Fermilab, the discrepancy between the experimental and theoretical determinations of the anomalous magnetic moment of the muon has been pushed to $4.2\sigma$. In order to reach the $5\sigma$-threshold, the experimental and theoretical uncertainties need to be reduced further.

Item Type: Thesis
Dissertation Type: Cumulative
Date of Defense: 18 June 2021
Subjects: 500 Science > 530 Physics
Institute / Center: 08 Faculty of Science > Institute of Theoretical Physics
10 Strategic Research Centers > Albert Einstein Center for Fundamental Physics (AEC)
Depositing User: Hammer Igor
Date Deposited: 06 Jul 2021 10:44
Last Modified: 06 Jul 2021 10:48

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