Tests of lepton-universality as rate ratios in b → sll transitions can be predicted very accurately in the Standard Model. The deficits with respect to expectations reported by the LHCb experiment in muon-toelectron ratios of the B → K ðÃÞ ll decay rates thus point to genuine manifestations of lepton nonuniversal new physics. In this paper, we analyze these measurements in the context of effective field theory. First, we discuss the interplay of the different operators in R K and R K à and provide predictions for R K à in the Standard Model and in new-physics scenarios that can explain R K . We also provide approximate numerical formulas for these observables in bins of interest as functions of the relevant Wilson coefficients. Secondly, we perform frequentist fits to R K and R K à . The Standard Model disagrees with these measurements at 3.7σ significance. We find excellent fits in scenarios with combinations ofwith pulls relative to the Standard Model in the region of 4σ. An important conclusion of our analysis is that a lepton-specific contribution to O 10 is important to understand the data. Under the hypothesis that new-physics couples selectively to the muons, we also present fits to other b → sμμ data with a conservative error assessment and comment on more general scenarios. Finally, we discuss new lepton universality ratios that, if new physics is the origin of the observed discrepancy, should contribute to the statistically significant discovery of new physics in the near future.

We study the ground-state octet baryon masses and sigma terms using the covariant baryon chiral perturbation theory (ChPT) with the extended-on-mass-shell (EOMS) renormalization scheme up to next-to-next-to-next-to-leading order (N 3 LO). By adjusting the available 19 low-energy constants (LECs), a reasonable fit of the n f = 2+1 lattice quantum chromodynamics (LQCD) results from the PACS-CS, LHPC, HSC, QCDSF-UKQCD and NPLQCD collaborations is achieved. Finite-volume corrections to the lattice data are calculated self-consistently. Our study shows that the N 3 LO BChPT describes better the light quark mass evolution of the lattice data than the NNLO BChPT does and the various lattice simulations seem to be consistent with each other. We also predict the pion and strangeness sigma terms of the octet baryons using the LECs determined in the fit of their masses. The predicted pion-and strangeness-nucleon sigma terms are σ πN = 43(1)(6) MeV and σ sN = 126(24)(54) MeV, respectively.

The scalar strangeness content of the nucleon, characterized by the so-called strangeness-nucleon sigma term, is of fundamental importance in understanding its sea-quark flavor structure. We report a determination of the octet baryon sigma terms via the Feynman-Hellmann theorem by analyzing the latest high-statistics $n_f=2+1$ lattice QCD simulations with covariant baryon chiral perturbation theory up to next-to-next-to-next-to-leading order. In particular, we predict $\sigma_{\pi N}=55(1)(4)$ MeV and $\sigma_{sN}=27(27)(4)$ MeV, while the first error is statistical and the second systematic due to different lattice scales. The predicted $\sigma_{sN}$ is consistent with the latest LQCD results and the results based on the next-to-next-to-leading order chiral perturbation theory. Several key factors in determining the sigma terms are systematically taken into account and clarified for the first time, including the effects of lattice scale setting, systematic uncertainties originating from chiral expansion truncations, and constraint of strong-interaction isospin breaking effects.Comment: 6 pages, 2 figures; version to appear in Physical Review

Motivated by the successes of relativistic theories in studies of atomic/molecular and nuclear systems and the need for a relativistic chiral force in relativistic nuclear structure studies, we explore a new relativistic scheme to construct the nucleon-nucleon interaction in the framework of covariant chiral effective field theory. The chiral interaction is formulated up to leading order with covariant power counting and a Lorentz invariant chiral Lagrangian. We find that the relativistic scheme induces all six spin operators needed to describe the nuclear force. A detailed investigation of the partial wave potentials shows a better description of the 1 S0 and 3 P0 phase shifts than the leading order Weinberg approach, and similar to that of the next-to-leading order Weinberg approach. For the other partial waves with angular momenta J ≥ 1, the relativistic results are almost the same as their leading order non-relativistic counterparts.

The axial-vector mesons a 1 (1260), b 1 (1235), f 1 (1285), h 1 (1170), h 1 (1380), and K 1 (1270) are dynamically generated in the unitized chiral perturbation theory. Such a picture has been tested extensively in the past few years. In this work, we calculate the interaction kernel up to O(p 2 ) and study the impact on the dynamically generated axial-vector states. In anticipation of future lattice QCD simulations, we calculate the scattering lengths and the pole positions as functions of the pion mass, with the light-quark mass dependence of the kaon, the eta, and the vector mesons determined by the n f = 2 + 1 lattice QCD simulations of the PACS-CS Collaboration.

We study finite-volume effects on the masses of the ground-state octet baryons using covariant baryon chiral perturbation theory (ChPT) up to next-to-leading order by analyzing the latest n f = 2 + 1 lattice Quantum ChromoDynamics (LQCD) results from the NPLQCD collaboration. Contributions of virtual decuplet baryons are taken into account using the "consistent" coupling scheme. We compare our results with those obtained from heavy baryon ChPT and show that, although both approaches can describe well the lattice data, the underlying physics is different: In HBChPT, virtual decuplet baryons play a more important role than they do in covariant ChPT. This is because the virtual octet baryon contributions to finite-volume corrections are larger in covariant ChPT than in HBChPT, while the contributions of intermediate decuplet baryons are smaller, because of relativistic effects. We observe that for the octet baryon masses, at fixed m π L (≫ 1) finite-volume corrections decrease as m π approaches its physical value, provided that the strange quark mass is at or close to its physical value, as in most LQCD setups.

We extend a previous analysis of the lowest-lying octet baryon masses in covariant baryon chiral perturbation theory (ChPT) by explicitly taking into account the contribution of the virtual decuplet baryons. Up to next-to-next-to-next-to-leading order (N 3 LO), the effects of these heavier degrees of freedom are systematically studied. Their effects on the light-quark mass dependence of the octet baryon masses are shown to be relatively small and can be absorbed by the available low-energy constants up to N 3 LO. Nevertheless, a better description of the finite-volume corrections of the lattice QCD data can be achieved, particularly those with small M φ L (< 4), which is demonstrated by a careful study of the NPLQCD and QCDSF-UKQCD small-volume data. Finally, we show that the predicted pion-and strangeness-baryon sigma terms are only slightly changed by the inclusion of the virtual decuplet baryons.

Inspired by the recent discovery of the pentaquark states P c (4450) and P c (4380), which can be viewed as excited nucleon states with hidden charm, we study the three-body interaction of a kaon and a pair of DD * in isospin 0 and 1. We show that the two body interactions stringently constrained by the existence of the D * s0 (2317), D * s1 (2460), X(3872), and Z c (3900), which are widely believed to contain large DK, D * K, and DD * components, inevitably lead to the existence of a heavy K * meson with hidden charm. Concrete coupled channel three-body calculations yield its mass and width as (4307 ± 2) − i(9 ± 2) MeV with I(J P ) = 1/2(1 − ). This state, if found experimentally, definitely cannot be accommodated in a qq picture, and therefore presents a clear case of an exotic hadron.