103,034 research outputs found
Electromagnetic and strong isospin-breaking corrections to the muon g-2 from lattice QCD+QED
No full textWe 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
HVP contributions to the muon (g−2) including QED corrections with twisted-mass fermions
No full textWe 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 (e.m.) corrections. We employ the gauge configurations generated by the European Twisted Mass Collaboration (ETMC) 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 in the range Mπ ≃ 210 - 450 MeV. The strange and charm quark masses are tuned at their physical values. Neglecting discon-nected diagrams and after the extrapolations to the physical pion mass and to the continuum limit we obtain: aμsαem2=53.1±2.5⋅10−10,aμsαem3=−0.018±0.011⋅10−10 and aμcαem2=14.75±0.56⋅10−10,aμcαem3=−0.030±0.013⋅10−10 for the strange and charm contributions, respectively.
Neutron electric dipole moment on the lattice: a theoretical reappraisal
No full textWe present a strategy for a lattice evaluation of the neutron electric dipole moment induced by the strong CP violating term of the QCD lagrangian. Our strategy is based on the standard definition of the electric dipole moment, involving the charge density operator J(0), in case of three flavors with non-degenerate masses. We present a complete diagrammatic analysis showing how the axial chiral Ward identities can be used to replace the topological charge operator with the flavor-singlet pseudoscalar density P-S. Our final result is characterized only by disconnected diagrams, where the disconnected part can be either the single insertion of P-S or the separate insertions of both P-S and J(0). The applicability of our strategy to the case of lattice formulations that explicitly break chiral symmetry, like the Wilson and Clover actions, is discussed
The impact of automated support for linking equivalent requirements based on similarity measures
No full textWhen developing systems of systems, requirements tend to be redundant especially when running large numbers of projects,
with many requirements per project, and diverse sources of requirements. It is therefore necessary to consolidate requirements by identifying
the ones that are equivalent in order to avoid redundant work. The aim of this paper is to evaluate requirement similarity measurement to
support analysts when linking equivalent requirements. The evaluation is conducted based on the requirements management process of an
Italian company in the defense and aerospace domain. Our empirical investigation combines a controlled experiment with graduate students
and an industrial case study. Results clearly show that one cannot expect any significant advantage in general. The level of support provided
by similarity measures significantly depends on their level of credibility, that is the extent to which similarity measurement reliably indicates
the equivalence of requirements. On average, given the credibility distribution observed in our industrial case study, showing similarity
measurement to analysts is expected to: 1) improve by 20% the number of equivalence links identified per minute and 2) decrease by 40%
the number of incorrect links. Finally, we investigate whether there is an effective way to combine human judgment and similarity
measurement to effectively determine equivalence links. Based on machine learning, our approach yielded positive results both in terms of
the correctness of the links and the speed at which they are established. Moreover, this hybrid solution is effective even when the credibility
of similarity measurement is half the average we observed in our industrial case study. In conclusion, our results confirm and complement
past empirical studies on the practical benefit, in terms of both quality and speed, of adopting requirement similarity measurement for linking
equivalent requirements
Strange and charm HVP contributions to the muon (g-2) including QED corrections with twisted-mass fermions
No full textWe 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 Nf= 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 Mpi = 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: amu^s(alpha_em^2) = (53.1 ± 2.5) · 10^(-10), amu^s(alpha_em^3) = (-0.018 ± 0.011) · 10^(-10) and amu^c(alpha_em^2) = (14.75 ± 0.56) · 10^(-10), amu^c(alpha_em^3) =(-0.030 ± 0.013) · 10^(-10) for the strange and charm contributions, respectively
Rotated twisted-mass: a convenient regularization scheme for isospin breaking QCD and QED lattice calculations
No full textWe propose a scheme of lattice twisted-mass fermion regularization which is particularly convenient for application to isospin breaking (IB) QCD and QED calculations, based in particular on the so called RM123 approach, in which the IB terms of the action are treated as a perturbation. The main, practical advantage of this scheme is that it allows the calculation of IB effects on some mesonic observables, like e.g. the pi+ - pi0 mass splitting, using lattice correlation functions in which the quark and antiquark fields in the meson are regularized with opposite values of the Wilson parameter r. These correlation functions are found to be affected by much smaller statistical fluctuations, with respect to the analogous functions in which quark and antiquark fields are regularized with the same value of r. Two numerical application of this scheme, that we call "rotated twisted-mass", within pure QCD and QCD+QED respectively, are also provided for illustration
First direct lattice calculation of the chiral perturbation theory low-energy constant l7
No full textWe evaluate by means of lattice QCD calculations the low-energy constant l7 which parametrizes strong isospin effects at next-to-leading order (NLO) in SU(2) chiral perturbation theory. Among all low-energy constants at NLO, l7 is the one known less precisely, and its uncertainty is currently larger than 50%. Our strategy is based on the RM123 approach in which the lattice path-integral is expanded in powers of the isospin breaking parameter Δm=(md-mu)/2. In order to evaluate the relevant lattice correlators we make use of the recently proposed rotated twisted-mass (RTM) scheme. Within the RM123 approach, it is possible to cleanly extract the value of l7 from either the pion mass splitting Mπ+-Mπ0 induced by strong isospin breaking at order O((Δm)2) (mass method), or from the coupling of the neutral pion π0 to the isoscalar operator (u ̄γ5u+d ̄γ5d)/2 at order O(Δm) (matrix element method). In this pilot study we limit the analysis to a single ensemble generated by the Extended Twisted Mass Collaboration (ETMC) with Nf=2+1+1 dynamical quark flavors, which corresponds to a lattice spacing a≃0.095 fm and to a pion mass Mπ≃260 MeV. We find that the matrix element method outperforms the mass method in terms of resulting statistical accuracy. Our determination, l7=2.5(1.4)×10-3, is in agreement and improves previous calculations
Lattice calculation of the pion mass difference at order
No full textWe present a lattice calculation of the charged/neutral pion mass difference
at order using the gauge
configurations produced by the Extended Twisted Mass Collaboration with
dynamical quark flavours at three values of the lattice spacing
() and pion masses in the range . We employ the RM123 method and expand the
path-integral around the isospin symmetric point at leading order in the
electromagnetic coupling . Making use of the recently proposed RTM
scheme, we evaluate the full contribution, with the
inclusion of the disconnected diagram. At the physical point, after performing
the continuum and infinite volume extrapolation, we obtain the value
which is in good agreement with
the experimental result .Comment: 13 pages, 5 figures, 1 tabl
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