Ran Zhou, Thomas Blum, Takumi Doi, Masashi Hayakawa, Taku Izubuchi, Norikazu Yamada
We investigate the electromagnetic mass splittings in the pseudoscalar meson and nucleon systems by combining 2+1 flavor domain wall fermion gauge configurations, generated by the RBC and UKQCD collaborations, and quenched, non-compact, lattice QED configurations. We analyze finite volume effects by using $16^3\times 32$ and $24^3\times 64$ lattices.
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We present a lattice calculation of the leading corrections to the masses of nucleons and $Δ$ resonances. These are obtained in QCD+QED at $1$st order in the Isospin Breaking parameters $α_{EM}$, the electromagnetic coupling, and $\frac{\hat{m}_d - {\hat{m}}_u}{Λ_{QCD}}$, coming from the mass difference between $u$ and $d$ quarks.
Curve collapse for the isospin-2 pion scattering length from QCD with 3, 4, and 5 colors
本文通过比较3、4和5色QCD模拟中的同位旋-2π介子散射长度，验证了其按1/Nc变化的曲线坍缩行为，符合大Nc计数预期。
Pion condensation at non-zero isospin chemical potential with Wilson fermions
本文利用Wilson费米子格点模拟研究非零同位旋化学势下π介子玻色-爱因斯坦凝聚相的起始点，弥补现有结果仅基于交错费米子的不足。
Isospin 0 and 2 two-pion scattering at physical pion mass using distillation with periodic boundary conditions in lattice QCD
本文利用distillation技术构建多粒子插值算符，在物理质量下计算了同位旋0和2两π介子散射相移与长度，减除真空和热污染后，最精细系综结果与唯象学在统计误差内一致。
We present the three-pion spectrum with maximal isospin in a finite volume determined from lattice QCD, including excited states in addition to the ground states across various irreducible representations at zero and nonzero total momentum. The required correlation functions, from which the spectrum is extracted, are computed using a newly implemented algorithm which speeds up the computation by more than an order of magnitude. On a subset of the data we extract a nonzero value of the three-pion threshold scattering amplitude using the $1/L$ expansion of the three-particle quantization conditi…
An Update on the Isospin-Breaking Effects in the Pion Decay Constant with Staggered Quarks
本文基于双重费米子衰变常数中宇称破缺效应的计算，使用N_f=2+1+1的阶梯夸克进行研究，更新了对称值和梯度流尺度的确定，并讨论了后续计划。
Implementing the RFT finite-volume formalism for three pions across all non-maximal isospins
本文数值实现RFT有限体积形式体系，在三粒子相互作用为零的非物理设置下，计算三π介子在所有非最大同位旋、不同总动量及对称群不可约表示中的离散能谱，为格点QCD提取三体相互作用提供基线。
In this paper, we consider two-flavor QCD at zero temperature and finite isospin chemical potential ($μ_I$) using a model-independent analysis within chiral perturbation theory at next-to-leading order. We calculate the effective potential, the chiral condensate and the pion condensate in the pion-condensed phase at both zero and nonzero pionic source. We compare our finite pionic source results for the chiral condensate and the pion condensate with recent (2+1)-flavor lattice QCD results and find that they are in excellent agreement.
We investigate pion superfluidity and its effect on meson properties and equation of state at finite temperature and isospin and baryon densities in the frame of standard flavor SU(2) NJL model. In mean field approximation to quarks and random phase approximation to mesons, the critical isospin chemical potential for pion superfluidity is exactly the pion mass in the vacuum, and corresponding to the isospin symmetry spontaneous breaking, there is in the pion superfluidity phase a Goldstone mode which is the linear combination of the normal sigma and charged pion modes. We calculate numerically…
Implementing the finite-volume three-pion scattering formalism across all non-maximal isospins
该研究探索了所有非最大同位旋下三π介子的相对论场论形式，通过通用同位旋扩展及开源Python库实现框架，预测了有限体积下带非零总动量的三π介子能量基线，为未来格点量子色动力学中三体效应研究提供参考。
Strong isospin breaking in the spectrum of the nucleons and deltas can be studied in lattice QCD with the help of chiral perturbation theory. At leading order in the chiral expansion, the mass splittings between the proton and neutron and between the deltas are linear in the quark mass difference. The next-to-leading order contributions to these splittings vanish even away from the strong-isospin limit. Therefore, any non-linear quark mass dependence of these mass splittings is a signal of the next-to-next-to-leading order mass contributions, thus providing access to LECs at this order. We det…
Pion-pion elastic scattering in the isospin I=2 channel is investigated in two-flavor dynamical lattice QCD. Six ensembles are used with lattices elongated in one of the spatial dimensions at two quark masses corresponding to a pion mass of 315 MeV and 226 MeV. The energy of the low-lying states below the inelastic threshold are extracted in each case using the standard variational method.The extracted finite-volume spectrum is fitted by the inverse amplitude method simultaneously for both quark masses and extrapolated thereafter to the physical point. The resulting phase-shifts and scattering…
Isospin-breaking in the $ππ$ scattering amplitude I: Effects due to the pion mass difference
本文作为系列首篇，分析ππ散射振幅的同位旋破缺效应，推导带电与中性π介子质量差对Roy方程的修正，匹配手征表示后数值求解并讨论结果，为后续研究奠定基础。
We study the phase diagram of QCD at finite isospin density using two flavors of staggered quarks. We investigate the low temperature region of the phase diagram where we find a pion condensation phase at high chemical potential. We started a basic analysis of the spectrum at finite isospin density. In particular, we measured pion, rho and nucleon masses inside and outside of the pion condensation phase. In agreement with previous studies in two-color QCD at finite baryon density we find that the Polyakov loop does not depend on the density in the staggered formulation.
We show that there exist two types of universal phenomena for three-boson systems with isospin degrees of freedom. In the isospin symmetric limit, there is only one universal three-boson bound state with the total isospin one, whose binding energy is proportional to that of the two-boson bound state. With large isospin symmetry breaking, the standard Efimov states of three identical bosons appear at low energies. Both phenomena can be realized by three pions with the pion mass appropriately tuned in lattice QCD simulations, or by spin-one bosons in cold atom experiments. Implication to the in-…
On the role of isospin violation in the pion-nucleon $σ$-term
本研究发现π-核子$σ$-项的唯象与格点QCD测定因同位旋约定不同存在张力，计算得3.1(5)MeV修正可缓解矛盾，还更新了π原子提取值与核子标量耦合。
The extraction of meson-baryon scattering parameters from lattice QCD is complicated by the necessity, in some channels, of including annihilation diagrams. We consider a strategy to avoid the need for these extremely costly and noisy contributions. The strategy is based on simulations with an isospin chemical potential which, contrary to a baryon chemical potential, has no sign problem. When the isospin chemical potential is larger than a critical value, a charged pion condensate forms. Baryons propagating in the pion condensate will have their masses modified by pion-baryon scattering parame…
QCD at finite isospin chemical potential $μ_{\text I}$ possesses a positively definite fermion determinant and the lattice simulation can be successfully performed. While the two-flavor effective models may be sufficient to describe the phenomenon of pion condensation, it is interesting to study the roles of the strangeness degree of freedom and the U$_{\rm A}(1)$ anomaly. In this paper, we present a systematic study of the three-flavor Nambu--Jona-Lasinio model with a Kobayashi-Maskawa-'t Hooft (KMT) term that mimics the U$_{\rm A}(1)$ anomaly at finite isospin chemical potential. In the mean…
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