We present a lattice calculation of the leading-order electromagnetic and strong isospin-breaking corrections to the hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment ...of the muon. We employ the gauge configurations generated by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks at three values of the lattice spacing (a≃0.062,0.082,0.089 fm) with pion masses between ≃210 and ≃450 MeV. The results are obtained by adopting the RM123 approach in the quenched-QED approximation, which neglects the charges of the sea quarks. Quark disconnected diagrams are not included. After the extrapolations to the physical pion mass and to the continuum and infinite-volume limits the contributions of the light, strange, and charm quarks are, respectively, equal to δaμHVP(ud)=7.1(2.5)×10−10, δaμHVP(s)=−0.0053(33)×10−10, and δaμHVP(c)=0.0182(36)×10−10. At leading order in αem and (md−mu)/ΛQCD we obtain δaμHVP(udsc)=7.1(2.9)×10−10, which is currently the most accurate determination of the isospin-breaking corrections to aμHVP.
We present a lattice calculation of the masses and decay constants of D(s)* and B(s)* mesons using the gauge configurations produced by the European Twisted Mass Collaboration (ETMC) with Nf=2+1+1 ...dynamical quarks at three values of the lattice spacing a∼(0.06−0.09) fm. Pion masses are simulated in the range Mπ≃(210–450) MeV, while the strange and charm sea-quark masses are close to their physical values. We compute the ratios of vector to pseudoscalar masses and decay constants for various values of the heavy-quark mass mh in the range 0.7mcphys≲mh≲3mcphys. In order to reach the physical b-quark mass, we exploit the heavy quark effective theory prediction that, in the static limit of infinite heavy-quark mass, the considered ratios are equal to one. At the physical point our results are MD*/MD=1.0769(79), MDs*/MDs=1.0751(56), fD*/fD=1.078(36), fDs*/fDs=1.087(20), MB*/MB=1.0078(15), MBs*/MBs=1.0083(10), fB*/fB=0.958(22) and fBs*/fBs=0.974(10). Combining them with the experimental values of the pseudoscalar meson masses (used as input to fix the quark masses) and the values of the pseudoscalar decay constants calculated by ETMC, we get MD*=2013(14), MDs*=2116(11), fD*=223.5(8.4), fDs*=268.8(6.6), MB*=5320.5(7.6), MBs*=5411.36(5.3), fB*=185.9(7.2) and fBs*=223.1(5.4) MeV.
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.
A
bstract
We present a lattice calculation of the Hadronic Vacuum Polarization (HVP) contribution of the strange and charm quarks to the anomalous magnetic moment of the muon including leading-order ...electromagnetic corrections. We employ the gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with
N
f
= 2 + 1 + 1 dynamical quarks at three values of the lattice spacing (
a
≃ 0
.
062
,
0
.
082
,
0
.
089 fm) with pion masses in the range
M
π
≃ 210-450 MeV. The strange and charm quark masses are tuned at their physical values. Neglecting disconnected diagrams and after the extrapolations to the physical pion mass and to the continuum limit we obtain:
a
μ
s
(
α
em
2
) = (53.1 ± 2.5) · 10
− 10
,
a
μ
s
(
α
em
3
) = (−0.018 ± 0.011) · 10
− 10
and
a
μ
c
(
α
em
2
) = (14.75 ± 0.56) · 10
− 10
,
a
μ
c
(
α
em
3
) = (−0.030 ± 0.013) · 10
− 10
for the strange and charm contributions, respectively.
We review lattice results related to pion, kaon, D- and B-meson physics with the aim of making them easily accessible to the particle-physics community. More specifically, we report on the ...determination of the light-quark masses, the form factor \f_+(0)\, arising in the semileptonic \K \rightarrow \pi \ transition at zero momentum transfer, as well as the decay constant ratio \f_K/f_\pi \ 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 \SU(2)_L\times SU(2)_R\ and \SU(3)_L\times SU(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. The latter quantities are an addition compared to the previous review. For the heavy-quark sector, we provide results for \m_c\ and \m_b\ (also new compared to the previous review), as well as those for D- and B-meson-decay constants, form factors, and mixing parameters. These are the heavy-quark quantities most relevant for the determination of CKM matrix elements and the global CKM unitarity-triangle fit. Finally, we review the status of lattice determinations of the strong coupling constant \\alpha _s\.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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
We present the calculation of the short-distance power corrections to the CP-violation parameter
ε
K
coming from dimension-8 operators in the ∆
S
= 2 effective Hamiltonian. A first estimate ...of this contribution, obtained for large-
N
c
and in the chiral limit, was provided in ref.
1
. Here we evaluate and include the
O
m
K
2
/
m
c
2
and
O
Λ
QCD
2
/
m
c
2
contributions that, a priori, could induce
O
(1) corrections to previous estimates, as
m
K
is numerically of order Λ
QCD
. Our computation shows that there are several dimension-8 operators besides the one considered before. Their effect on
ε
K
, however, accidentally cancels out to a large extent, leaving the final correction at the level of 1%.
We review lattice results relevant for pion and kaon physics with the aim of making them easily accessible to the particle physics community. Specifically, we review the determination of the ...light-quark masses, the form factor
f
+
(0), relevant for the semileptonic
K
→
π
transition at zero momentum transfer as well as the ratio
f
K
/
f
π
of decay constants and discuss the consequences for the elements
V
us
and
V
ud
of the CKM matrix. Furthermore, we describe the results obtained on the lattice for some of the low-energy constants of SU(2)
L
×SU(2)
R
and SU(3)
L
×SU(3)
R
Chiral Perturbation Theory and review the determination of the
B
K
parameter of neutral kaon mixing. We introduce quality criteria and use these when forming averages. Although subjective and imperfect, these criteria may help the reader to judge different aspects of current lattice computations. Our main results are summarized in Sect. 1.2, but we stress the importance of the detailed discussion that underlies these results and constitutes the bulk of the present review.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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