Laub, Laetitia (2021). Shortdistance constraints on the hadronic lightbylight contribution to the muon g2. (Thesis). Universität Bern, Bern

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Abstract
The aim of this work is to investigate the information available from perturbative QCD to constrain the hadronic lightbylight contribution to $(g2)_\mu$ 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 $g2$ 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 nonperturbative 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 socalled MelnikovVainshtein constraint. A way to satisfy the shortdistance 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 modeldependence 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 
URI:  https://boristheses.unibe.ch/id/eprint/2816 
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