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تسجيل مستخدم جديدChallenges for New Physics in the Flavour Sector
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Andreas Crivellin
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In these proceedings I present a personal perspective of the challenges for new physics (NP) searches in the flavour sector. Since the CKM mechanism of flavour violation has been established to a very high precision, we know that physics beyond the Standard Model can only contribute sub-dominantly. Therefore, any realistic model of physics beyond the Standard Model (SM) must respect the stringent constrains from flavour observables like $bto s gamma$, $B_stomu^+mu^-$, $Delta F=2$ processes etc., in a first step. In a second step, it is interesting to ask the question if some deviations from the SM predictions (like the anomalous magnetic moment of the muon or recently observed discrepancies in tauonic $B$ decays or $Bto K^*mu^+mu^-$) can be explained by a model of NP without violating bounds from other observables.
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Several experiments observed deviations from the Standard Model (SM) in the flavour sector: LHCb found a $4-5,sigma$ discrepancy compared to the SM in $bto smu^+mu^-$ transitions (recently supported by an Belle analysis) and CMS reported a non-zero m
easurement of $htomutau$ with a significance of $2.4,sigma$. Furthermore, BELLE, BABAR and LHCb founds hints for the violation of flavour universality in $Bto D^{(*)}tau u$. In addition, there is the long-standing discrepancy in the anomalous magnetic moment of the muon. Interestingly, all these anomalies are related to muons and taus, while the corresponding electron channels seem to be SM like. This suggests that these deviations from the SM might be correlated and we briefly review some selected models providing simultaneous explanations.
LHCb found hints for physics beyond the Standard Model (SM) in $Bto K^*mu^+mu^-$, $R(K)$ and $B_stophimu^+mu^-$. These intriguing hints for NP have recently been confirmed by the LHCb measurement of $R(K^*)$ giving a combined significance for NP abov
e the $5,sigma$ level. In addition, the BABAR, BELLE and LHCb results for $Bto D^{(*)}tau u$ also point towards lepton flavour universality (LFU) violating new physics (NP). Furthermore, there is the long-standing discrepancy between the measurement and the theory prediction of the anomalous magnetic moment of the muon ($a_mu$) at the $3,sigma$ level. Concerning NP effects, $bto smu^+mu^-$ data can be naturally explained with a new neutral gauge bosons, i.e. a $Z^prime$ but also with heavy new scalars and fermions contributing via box diagrams. Another promising solution to $bto smu^+mu^-$, which can also explain $Bto D^{(*)}tau u$, are leptoquarks. Interestingly, leptoquarks provide also a viable explanation of $a_mu$ which can be tested via correlated effects in $Ztomu^+mu^-$ at future colliders. Considering leptoquark models, we show that an explanation of $Bto D^{(*)}tau u$ predicts an enhancement of $bto stau^+tau^-$ processes by around three orders of magnitude compared to the SM. In case of a simultaneous explanation of $Bto D^{(*)}tau u$ and $bto smu^+mu^-$ data, sizable effects in $bto staumu$ processes are predicted.
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