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Seminar
CP-violating single scalar-leptoquark solutions for the $(g-2)_{e,\mu}$ puzzles and their implications for lepton EDMs
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Australia/Sydney
Description
Ever since the announcement of the first results from the Muon g$-$2 at Fermilab~(FNAL) in early 2021, leading to an updated 4.2 sigma deviation from the Standard Model, the number of potential solutions to the muon g$-$2 anomaly has exploded in the literature. A lesser focus has surrounded the anomalous magnetic moment~(AMM) of the electron, which until December 2020 demonstrated a 2.5 sigma deviation from the SM — but in the \emph{opposite} direction to that of the muon. In late 2020, a second result indicated that the AMM of the electron was actually 1.6 sigma and with \emph{common} sign to the muon AMM. The results for the electron AMM remain in unresolved disparity, but nevertheless it appears that it may not only be the muon that has strange behaviour in its effective dipolar interaction. Models that permit violation of lepton flavour universality could suggest a common origin for these anomalies, and we can invoke Occam’s razor to argue that the simplest of these is likely the best. Single scalar leptoquarks provide such a simple solution. We study the two scalar leptoquarks capable of generating chirally-enhanced, sign-dependent contributions to lepton AMMs and electric dipole moments~(EDMs).
We consider the case in which the electron and muon sectors are decoupled, and leptoquark couplings are assigned complex values. Adopting the coupling anzatz that the electron dipole operator is generated by charm-containing loops, and muon dipole operator by top-containing loops, we identified novel parameter space where these leptoquark models remain viable solutions for reconciling both muon and electron AMMs, accounting for either of the two disparate electron AMM results. We also examine the correlated corrections to the muon and electron masses generated by these models, and argue that to minimise fine-tuning this introduces an upper bound on viable LQ $\phi$ masses, $m_{\phi}<\mathcal{O}(4)$ TeV. Similar arguments allow us to make a prediction for the upper bound of the muon EDM generated by these models, $|d_\mu|< \mathcal{O}(10^{-22})\; e$ cm, which could be within reach of upcoming experimental programs, including FNAL ,and muEDM at Paul Scherrer Institut~(PSI).
