The leading-order electromagnetic and strong isospin-breaking corrections to the ratio of K_{μ2} and π_{μ2} decay rates are evaluated for the first time on the lattice, following a method recently ...proposed. The lattice results are obtained using the gauge ensembles produced by the European Twisted Mass Collaboration with N_{f}=2+1+1 dynamical quarks. Systematic effects are evaluated and the impact of the quenched QED approximation is estimated. Our result for the correction to the tree-level K_{μ2}/π_{μ2} decay ratio is -1.22(16)%, to be compared to the estimate of -1.12(21)% based on chiral perturbation theory and adopted by the Particle Data Group.
We present a nonperturbative lattice calculation of the form factors which contribute to the amplitudes for the radiative decays P → ℓνℓγ, where P is a pseudoscalar meson and ℓ is a charged lepton. ...Together with the nonperturbative determination of the corrections to the processes P → ℓνℓ due to the exchange of a virtual photon, this allows accurate predictions at O(αem) to be made for leptonic decay rates for pseudoscalar mesons ranging from the pion to the Ds meson. We are able to separate unambiguously and nonpertubatively the pointlike contribution, from the structure-dependent, infrared-safe, terms in the amplitude. The fully nonperturbative O(a) improved calculation of the inclusive leptonic decay rates will lead to the determination of the corresponding Cabibbo-Kobayashi-Maskawa matrix elements also at O(αem). Prospects for a precise evaluation of leptonic decay rates with emission of a hard photon are also very interesting, especially for the decays of heavy D and B mesons for which currently only model-dependent predictions are available to compare with existing experimental data.
The leading electromagnetic (e.m.) and strong isospin-breaking corrections to the π+→μ+νγ and K+→μ+νγ leptonic decay rates are evaluated for the first time on the lattice. The results are obtained ...using gauge ensembles produced by the European Twisted Mass Collaboration with Nf=2+1+1 dynamical quarks. The relative leading-order e.m. and strong isospin-breaking corrections to the decay rates are 1.53(19)% for πμ2 decays and 0.24(10)% for Kμ2 decays. Using the experimental values of the πμ2 and Kμ2 decay rates and updated lattice QCD results for the pion and kaon decay constants in isosymmetric QCD, we find that the Cabibbo-Kobayashi-Maskawa matrix element |Vus|=0.22538(46), reducing by a factor of about 1.8 the corresponding uncertainty in the particle data group review. Our calculation of |Vus| allows also an accurate determination of the first-row Cabibbo-Kobayashi-Maskawa unitarity relation |Vud|2+|Vus|2+|Vub|2=0.99988(46). Theoretical developments in this paper include a detailed discussion of how QCD can be defined in the full QCD+QED theory and an improved renormalization procedure in which the bare lattice operators are renormalized nonperturbatively into the regularization independent momentum subtraction (RI'-MOM) scheme and subsequently matched perturbatively at O(αemαs(MW)) into the W-regularization scheme appropriate for these calculations.
We present a lattice computation of the isospin-breaking corrections to pseudoscalar meson masses using the gauge configurations produced by the European Twisted Mass Collaboration with Nf=2+1+1 ...dynamical quarks at three values of the lattice spacing (a≃0.062, 0.082, and 0.089 fm) with pion masses in the range Mπ≃210–450 MeV. The strange and charm quark masses are tuned at their physical values. We adopt the RM123 method based on the combined expansion of the path integral in powers of the d- and u-quark mass difference (m^d−m^u) and of the electromagnetic coupling αem. Within the quenched QED approximation, which neglects the effects of the sea-quark charges, and after the extrapolations to the physical pion mass and to the continuum and infinite volume limits, we provide results for the pion, kaon, and (for the first time) charmed-meson mass splittings, for the prescription-dependent parameters επ0, εγ(MS¯,2 GeV), εK0(MS¯,2 GeV), related to the violations of the Dashen’s theorem, and for the light quark mass difference (m^d−m^u)(MS¯,2 GeV).
A
bstract
In this paper we show, for the first time, that charged-hadron masses can be calculated on the lattice without relying on gauge fixing at any stage of the calculations. In our simulations ...we follow a recent proposal and formulate full QCD+QED on a finite volume, without spoiling locality, by imposing C-periodic boundary conditions in the spatial directions. Electrically charged states are interpolated with a class of operators, originally suggested by Dirac and built as functionals of the photon field, that are invariant under local gauge transformations. We show that the quality of the numerical signal of charged-hadron masses is the same as in the neutral sector and that charged-neutral mass splittings can be calculated with satisfactory accuracy in this setup. We also discuss how to describe states of charged hadrons with real photons in a fully gauge-invariant way by providing a first evidence that the proposed strategy can be numerically viable.
FLAG Review 2021 Aoki, Y.; Blum, T.; Colangelo, G. ...
The European physical journal. C, Particles and fields,
10/2022, Letnik:
82, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We review lattice results related to pion, kaon,
D
-meson,
B
-meson, and nucleon physics with the aim of making them easily accessible to the nuclear and particle physics communities. More ...specifically, we report on the determination of the light-quark masses, the form factor
f
+
(
0
)
arising in the semileptonic
K
→
π
transition at zero momentum transfer, as well as the decay constant ratio
f
K
/
f
π
and its consequences for the CKM matrix elements
V
us
and
V
ud
. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of
S
U
(
2
)
L
×
S
U
(
2
)
R
and
S
U
(
3
)
L
×
S
U
(
3
)
R
Chiral Perturbation Theory. We review the determination of the
B
K
parameter of neutral kaon mixing as well as the additional four
B
parameters that arise in theories of physics beyond the Standard Model. For the heavy-quark sector, we provide results for
m
c
and
m
b
as well as those for the decay constants, form factors, and mixing parameters of charmed and bottom mesons and baryons. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. We review the status of lattice determinations of the strong coupling constant
α
s
. We consider nucleon matrix elements, and review the determinations of the axial, scalar and tensor bilinears, both isovector and flavor diagonal. Finally, in this review we have added a new section reviewing determinations of scale-setting quantities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We propose a method to expand correlation functions with respect to the spatial components of external momenta. From the coefficients of the expansion it is possible to extract Lorentz-invariant form ...factors at zero spatial momentum transfer avoiding model dependent extrapolations. These objects can be profitably calculated on the lattice. We have explicitly checked the validity of the proposed procedure by considering two-point correlators with insertions of the axial current, the form factors of the semileptonic decay of pseudoscalar mesons, and the hadronic vacuum polarization tensor entering, for example, the lattice calculation of the anomalous magnetic moment of the muon.
We present a comparison of existing experimental data for the radiative leptonic decays P → ℓνℓγ, where P = K or π and ℓ = e or μ, from the KLOE, PIBETA, E787, ISTRA+ and OKA collaborations with ...theoretical predictions based on the recent non-perturbative determinations of the structure-dependent vector and axial-vector form factors, FV and FA respectively. These were obtained using lattice QCD + QED simulations at order O(αem) in the electromagnetic coupling. We find good agreement with the KLOE data on K → eνeγ decays from which the form factor F+ = FV + FA can be determined. For K → μνμγ decays we observe differences of up to –34 standard deviations at large photon energies between the theoretical predictions and the data from the E787, ISTRA + and OKA experiments and similar discrepancies in some kinematical regions with the PIBETA experiment on radiative pion decays. A global study of all the kaon-decay data within the Standard Model results in a poor fit, largely because at large photon energies the KLOE and E787 data cannot be reproduced simultaneously in terms of the same form factor F+. The discrepancy between the theoretical and experimental values of the form factor F− = FV − FA is even more pronounced. These observations motivate future improvements of both the theoretical and experimental determinations of the structure-dependent form factors F+ and F−, as well as further theoretical investigations of models of "new physics" which might for example, include possible flavor changing interactions beyond V − A and/or nonuniversal corrections to the lepton couplings.
We demonstrate that the leading and next-to-leading finite-volume effects in the evaluation of leptonic decay widths of pseudoscalar mesons at O(α) are universal; i.e. they are independent of the ...structure of the meson. This is analogous to a similar result for the spectrum but with some fundamental differences, most notably the presence of infrared divergences in decay amplitudes. The leading nonuniversal, structure-dependent terms are of O(1/L2) compared to the O(1/L3) leading nonuniversal corrections in the spectrum. We calculate the universal finite-volume effects, which requires an extension of previously developed techniques to include a dependence on an external three-momentum (in our case, the momentum of the final-state lepton). The result can be included in the strategy proposed in Ref. N. Carrasco et al.,Phys. Rev. D 91, 074506 (2015). for using lattice simulations to compute the decay widths at O(α), with the remaining finite-volume effects starting at order O(1/L2). The methods developed in this paper can be generalized to other decay processes, most notably to semileptonic decays, and hence open the possibility of a new era in precision flavor physics.
The adoption of two distinct boundary conditions for two fermions species on a finite lattice allows to deal with arbitrary relative momentum between the two particle species, in spite of the ...momentum quantization rule due to a limited physical box size. We test the physical significance of this topological momentum by checking in the continuum limit the validity of the expected energy–momentum dispersion relations.
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