Calculating the Two-photon Contribution to $π^0 \rightarrow e^+ e^-$ Decay Amplitude

无中微子双β衰变来自格点QCD：短距离 $\pi^-\rightarrow\pi^+ e^- e^-$ 振幅

Neutrinoless Double Beta Decay from Lattice QCD: The Short-Distance $π^-\rightarrowπ^+ e^- e^-$ Amplitude

本研究通过格点QCD计算非物理 $\pi^-\rightarrow\pi^+ e^- e^-$ 衰变的短距离贡献，外推得到手征有效场论低能常数，为无中微子双β衰变提供关键输入。

QED-corrected Lellouch-Lüscher formula for $K \rightarrow ππ$ decay

A precise SM prediction for the direct CP violation in the $K \rightarrow ππ$ decay process is of great importance in confronting experiments and constraining new physics. The state-of-art lattice QCD study of this process will soon achieve a precision that QED effects can no longer be neglected. The inclusion of QED in such calculations is planned, and the formalism to relate the finite-volume matrix element obtained from these calculations to the physical amplitude is underway. Here, we report on the progress towards an extension of the Lellouch-Lüscher formalism in presence of QED, with the…

Neutrinoless Double Beta Decay from Lattice QCD: The Long-Distance $π^{-} \rightarrow π^{+} e^{-} e^{-}$ Amplitude

Neutrinoless double beta decay (\( 0 νββ\)) is a hypothetical nuclear decay mode with important implications. In particular, observation of this decay would demonstrate that the neutrino is a Majorana particle and that lepton number conservation is violated in nature. Relating experimental constraints on \(0 νββ\) decay rates to the neutrino masses requires theoretical input in the form of non-perturbative nuclear matrix elements which remain difficult to calculate reliably. This work marks a first step toward providing a general lattice QCD framework for computing long-distance \(0 νββ\) matr…

$K \rightarrow ππ$ $ΔI=3/2$ decay amplitude in the continuum limit

We present new results for the amplitude $A_2$ for a kaon to decay into two pions with isospin $I=2$: Re$A_2 = 1.50(4)_\mathrm{stat}(14)_\mathrm{syst}\times 10^{-8}$ GeV; Im$A_2 = -6.99(20)_\mathrm{stat}(84)_\mathrm{syst}\times 10^{-13}$ GeV. These results were obtained from two ensembles generated at physical quark masses (in the isospin limit) with inverse lattice spacings $a^{-1}=1.728(4)$ GeV and $2.358(7)$ GeV. We are therefore able to perform a continuum extrapolation and hence largely to remove the dominant systematic uncertainty from our earlier results, that due to lattice artefacts. …

Calculating the $ρ$ radiative decay width with lattice QCD

We present the results of our lattice QCD study of the $πγ\toππ$ process, where the $ρ$ resonance appears as an enhancement in the transition amplitude. We use $N_f=2+1$ clover fermions on a lattice of $L=3.6$ fm and a pion mass of $320$ MeV. Using a combination of forward, stochastic, and sequential propagators, we calculate the two-point and three-point functions that allow us to determine the $πγ\toππ$ matrix elements for several values of the invariant mass $s$ and momentum transfer $q^2$. To fit the $q^2$ and $s$ dependence of the $πγ\toππ$ amplitude, we explore a set of general parametri…

$Ω_c γ\rightarrowΩ_c^\ast$ transition in lattice QCD

We study the electromagnetic $Ω_c γ\rightarrowΩ_c^\ast$ transition in 2+1 flavor lattice QCD, which gives access to the dominant decay mode of $Ω_c^\ast$ baryon. The magnetic dipole and the electric quadrupole transition form factors are computed. The magnetic dipole form factor is found to be mainly determined by the strange quark and the electric quadrupole form factor to be negligibly small, in consistency with the quark model. We also evaluate the helicity amplitudes and the decay rate.

Hadron tomography by generalized distribution amplitudes in pion-pair production process $γ^* γ\rightarrow π^0 π^0 $ and gravitational form factors for pion

Hadron tomography can be investigated by three-dimensional structure functions such as generalized parton distributions (GPDs), transverse-momentum-dependent parton distributions, and generalized distribution amplitudes (GDAs). Here, we extract the GDAs, which are $s$-$t$ crossed quantities of the GPDs, from cross-section measurements of hadron-pair production process $γ^* γ\rightarrow π^0 π^0$ at KEKB. This work is the first attempt to obtain the GDAs from the actual experimental data. The GDAs are expressed by a number of parameters and they are determined from the data of $γ^* γ\rightarrow …

Holographic Corrections to the Veneziano Amplitude

We propose a holographic computation of the $2\rightarrow 2$ meson scattering in a curved string background, dual to a QCD-like theory. We recover the Veneziano amplitude and compute a perturbative correction due to the background curvature. The result implies a small deviation from a linear trajectory, which is a requirement of the UV regime of QCD.

三粒子散射振幅来自格点QCD

Three-particle scattering amplitudes from lattice QCD

本文基于格点QCD研究三粒子散射振幅及共振性质，通过有限体积光谱和积分方程计算，探索复平面中的共振极点。