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High Energy Physics Lattice

Berezinskii-Kosterlitz-Thouless transitions in two-dimensional lattice SO(Nc) gauge theories with two scalar flavors

We study the phase diagram and critical behavior of a two-dimensional lattice SO(Nc) gauge theory (Nc≥3) with two scalar flavors, obtained by partially gauging a maximally O(2Nc) symmetric scalar model. The model is invariant under local SO(Nc) and global O(2) transformations. We show that, for anyNc≥3, it undergoes finite-temperature Berezinskii-Kosterlitz-Thouless (BKT) transitions, associated with the global Abelian O(2) symmetry. The transition separates a high-temperature disordered phase from a low-temperature spin-wave phase where correlations decay algebraically (quasi-long range order). The critical properties at the finite-temperature BKT transition and in the low-temperature spin-wave phase are determined by means of a finite-size scaling analysis of Monte Carlo data.

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High Energy Physics Lattice

Bethe-Salpeter amplitudes of Upsilons

Based on lattice non-relativistic QCD (NRQCD) studies we present results for Bethe-Salpeter amplitudes forΥ(1S),Υ(2S)andΥ(3S)in vacuum as well as in quark-gluon plasma. Our study is based on 2+1 flavor483×12lattices generated using the Highly Improved Staggered Quark (HISQ) action and with a pion mass of161MeV. At zero temperature the Bethe-Salpeter amplitudes follow the expectations based on non-relativistic potential models. At non-zero temperatures, the interpretation of Bethe-Salpeter amplitudes turns out to be more nuanced, but consistent with our previous lattice QCD study of excited Upsilons in quark-gluon plasma.

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High Energy Physics Lattice

Bottomonium precision tests from full lattice QCD: hyperfine splitting,Υleptonic width andbquark contribution toe+e????hadrons

We calculate the mass difference between theΥandηband theΥleptonic width from lattice QCD using the Highly Improved Staggered Quark formalism for thebquark and includingu,d,sandcquarks in the sea. We have results for lattices with lattice spacing as low as 0.03 fm and multiple heavy quark masses, enabling us to map out the heavy quark mass dependence and determine values at thebquark mass. Our results are:MΥ??Mηb=57.5(2.3)(1.0)MeV(where the second uncertainty comes from neglect of quark-line disconnected correlation functions) and decay constants,fηb=724(12)MeV andfΥ=677.2(9.7)MeV, giving?(Υ??e+e??)=1.292(37)(3)keV. The hyperfine splitting and leptonic width are both in good agreement with experiment, and provide the most accurate lattice QCD results to date for these quantities by some margin. At the same time results for the time moments of the vector-vector correlation function can be compared to values for thebquark contribution to?(e+e???�hadrons)determined from experiment. Moments 4--10 provide a 2\% test of QCD and yield abquark contribution to the anomalous magnetic moment of the muon of 0.300(15)?10??0. Our results, covering a range of heavy quark masses, may also be useful to constrain QCD-like composite theories for beyond the Standard Model physics.

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High Energy Physics Lattice

Calculating the Two-photon Contribution toπ0→e+e−Decay Amplitude

We develop a new method that allows us to deal with two-photon intermediate states in a lattice QCD calculation. We apply this method to perform a first-principles calculation of theπ0→e+e−decay amplitude. Both the real and imaginary parts of amplitude are calculated. The imaginary part is compared with the prediction of optical theorem to demonstrate the effectiveness of this method. Our result for the real part of decay amplitude is19.68(52)(1.10) eV, where the first error is statistical and the second is systematic.

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High Energy Physics Lattice

Calculation of PCAC mass with Wilson fermion using gradient flow

We calculate the PCAC mass for(2+1)flavor full QCD with Wilson-type quarks. We adopt the Small Flow-time eXpansion (SFtX) method based on the gradient flow which provides us a general way to compute correctly renormalized observables even if the relevant symmetries for the observable are broken explicitly due to the lattice regularization, such as the Poincáre and chiral symmetries. Our calculation is performed on heavyu,dquarks mass (mπ/mρ≃0.63) and approximately physicalsquark mass with fine latticea≃0.07~fm. The results are compared with those computed with the Schrödinger functional method.

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High Energy Physics Lattice

Calculation of theKL−KSmass difference for physical quark masses

In this article, I will present the status of our calculation of the difference between the masses of the long- and short-lived neutral K mesons,ΔmKpredicted by the Standard Model. This calculation is performed on an ensemble of 152,643×128gauge configurations with an inverse lattice spacing of 2.36 GeV and physical quark masses. The results from different methods of analysis and our progress toward obtaining a final result will be discussed.

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High Energy Physics Lattice

Casimir effect for lattice fermions

We propose a definition of the Casimir energy for free lattice fermions. From this definition, we study the Casimir effects for the massless or massive naive fermion, Wilson fermion, and (Möbius) domain-wall fermion in1+1dimensional spacetime with the spatial periodic or antiperiodic boundary condition. For the naive fermion, we find an oscillatory behavior of the Casimir energy, which is caused by the difference between odd and even lattice sizes. For the Wilson fermion, in the small lattice size ofN≥3, the Casimir energy agrees very well with that of the continuum theory, which suggests that we can control the discretization artifacts for the Casimir effect measured in lattice simulations. We also investigate the dependence on the parameters tunable in Möbius domain-wall fermions. Our findings will be observed both in condensed matter systems and in lattice simulations with a small size.

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High Energy Physics Lattice

Charged multi-hadron systems in lattice QCD+QED

Systems with the quantum numbers of up to twelve charged and neutral pseudoscalar mesons, as well as one-, two-, and three-nucleon systems, are studied using dynamical lattice quantum chromodynamics and quantum electrodynamics (QCD+QED) calculations and effective field theory. QED effects on hadronic interactions are determined by comparing systems of charged and neutral hadrons after tuning the quark masses to remove strong isospin breaking effects. A non-relativistic effective field theory, which perturbatively includes finite-volume Coulomb effects, is analyzed for systems of multiple charged hadrons and found to accurately reproduce the lattice QCD+QED results. QED effects on charged multi-hadron systems beyond Coulomb photon exchange are determined by comparing the two- and three-body interaction parameters extracted from the lattice QCD+QED results for charged and neutral multi-hadron systems.

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High Energy Physics Lattice

Charged particles interaction in both a finite volume and a uniform magnetic field

A formalism for describing charged particles interaction in both a finite volume and a uniform magnetic field is presented. In the case of short-range interaction between charged particles, we show that the factorization between short-range physics and finite volume long-range correlation effect is possible, a Lüscher formula-like quantization condition is thus obtained.

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High Energy Physics Lattice

Charmed andϕmeson decay constants from 2+1-flavor lattice QCD

On a lattice with 2+1-flavor dynamical domain-wall fermions at the physical pion mass, we calculate the decay constants ofD(∗)s,D(∗)andϕ. The lattice size is483×96, which corresponds to a spatial extension of∼5.5fm with the lattice spacinga≈0.114fm. For the valence light, strange and charm quarks, we use overlap fermions at several mass points close to their physical values. Our results at the physical point arefD=213(5)MeV,fDs=249(7)MeV,fD∗=234(6)MeV,fD∗s=274(7)MeV, andfϕ=241(9)MeV. The couplings ofD∗andD∗sto the tensor current (fTV) can be derived, respectively, from the ratiosfTD∗/fD∗=0.91(4)andfTD∗s/fD∗s=0.92(4), which are the first lattice QCD results. We also obtain the ratiosfD∗/fD=1.10(3)andfD∗s/fDs=1.10(4), which reflect the size of heavy quark symmetry breaking in charmed mesons. The ratiosfDs/fD=1.16(3)andfD∗s/fD∗=1.17(3)can be taken as a measure of SU(3) flavor symmetry breaking.

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