This is probably the most important discrepancy between theory and experiment in fundamental physics at the moment. The pulls on the Wilson coefficients mentioned exceed five sigma (before any proper look elsewhere effect analysis). There are new theories to explain it, explored below, but not good ones.

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B-decay discrepancies after Moriond 2019

(Submitted on 25 Mar 2019)

Following the updated measurement of the lepton flavour universality (LFU) ratio R_K in B -> Kll decays by LHCb, as well as a number of further measurements, e.g. R_K* by Belle and B_s -> mu mu by ATLAS, **we analyse the global status of new physics in b -> s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory at the electroweak scale, and in simplified models of new physics. **

We find that **the data continues to strongly prefer a solution with new physics** in semi-leptonic Wilson coefficients. A purely muonic contribution to the combination C_9 = -C_10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C_9 only. An even better fit is obtained by allowing an additional LFU shift in C_9. **Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b -> c transitions.** This scenario is naturally realized in the simplified U_1 leptoquark model. We also analyse simplified models where a LFU effect in b -> sll is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.

It is less significant because the predicted value is uncertain:

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Implications on the first observation of charm CPV at LHCb

(Submitted on 26 Mar 2019)

Very recently, the LHCb Collaboration observed the CP violation (CPV) in the charm sector for the first time, with ΔAdirCP≡ACP(D0→K+K−)−ACP(D0→π+π−)=(−1.54±0.29)×10−3. **This result is consistent with our prediction of ΔASMCP=(−0.57∼−1.87)×10−3 obtained in the factorization-assisted topological-amplitude (FAT) approach in [PRD86,036012(2012)]. It implies that the current understanding of the penguin dynamics in charm decays in the Standard Model is reasonable.** Motivated by the success of the FAT approach, we further suggest to measure the D+→K+K−π+ decay, which is the next potential mode to reveal the CPV of the same order as 10−3.

And there is a review of muon g-2 research:

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The muon g−2: a brief overview of hadronic cross section data

(Submitted on 22 Mar 2019)

The hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon, ahad,VPμ are evaluated dispersively via a combination of experimentally measured e+e−→hadrons cross section data. Many experiments have dedicated programmes to precisely measure these final states, meaning that a vast amount of data is now available and that, in some cases, overall precision has reached the sub-percent level. However, **data tensions are evident between measurements of the same hadronic channels from different experiments, which reduces the overall quality of the data combinations used **to determine ahad,VPμ. The inclusion of these data in the KNT18 analysis results in ahad,LOVPμ=(693.26±2.46)×10−10 and ahad,NLOVPμ=(−9.82±0.04)×10−10. The corresponding new estimate for the Standard Model prediction is found to be **aSMμ=(11 659 182.04±3.56)×10−10, which is 3.7σ below the current experimental measurement.**