Related papers: Calculating the Two-photon Contribution to $\pi^0 …
A direct calculation of the complex $\Delta I=1/2$ kaon decay amplitude is notoriously difficult because of the presence of disconnected graphs. Here we describe and demonstrate two practical methods to defeat this problem: the EigCG…
Recent theoretical and numerical progresses of the lattice calculations of $K\to\pi\pi$ decay amplitude are reviewed.
We report on the calculation of the two-loop electroweak, two-photon mediated short-distance dispersive K_L \to \mu^+\mu^- decay amplitude. QCD corrections change the sign of this contribution and reduce it by an order of magnitude. The…
We consider electromagnetic corrections to the non-leptonic kaon decay, $K^+\to\pi^+\pi^0\pi^0$, due to explicit virtual photons only. The decay amplitude is calculated at one-loop level in the framework of Chiral Perturbation Theory. The…
A QCD based calculation of the photon spectrum in semi-inclusive $\eta_Q$ decays is performed. The method applied is an effective theory based on a 1/m_Q expansion of QCD.
We report on the first realistic \emph{ab initio} calculation of a hadronic weak decay, that of the amplitude $A_2$ for a kaon to decay into two \pi-mesons with isospin 2. We find Re$A_2=(1.436\pm 0.063_{\textrm{stat}}\pm…
We develop a method for lattice QCD calculation of the two-photon exchange (TPE) contribution to the muonic-hydrogen Lamb shift. To demonstrate the feasibility of this method, we also present an exploratory study with a gauge ensemble at…
We present the results of our lattice QCD study of the $\pi\gamma\to\pi\pi$ process, where the $\rho$ 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…
We perform a lattice QCD calculation of the \pi^0\to\gamma\gamma transition form factor and the associated decay width. We use a Euclidean time integral of the relevant three-point function to compute the decay amplitude for two-photon…
Based on quantum electrodynamics, we reexamine the two-photon decay of one-electron atoms. Special attention is paid to the calculation of the (two-photon) total decay rates which can be viewed as the imaginary part of the two-loop…
The two-photon-exchange (TPE) contribution in $ep\rightarrow ep\pi ^0$ with $W=M_{\Delta}$ and small $Q^2$ is calculated and its corrections to the ratios of electromagnetic transition form factors $R_{EM} = E_{1+}^{(3/2)}/M_{1+}^{(3/2)} $…
The rare kaon decays $K\to\pi\nu\bar{\nu}$ are strongly suppressed in the standard model and widely regarded as processes in which new phenomena, not predicted by the standard model, may be observed. Recognizing such new phenomena requires…
We present a lattice QCD calculation of the $\rho$ meson decay width via the $P$-wave scattering phase shift for the I=1 two-pion system. Our calculation uses full QCD gauge configurations for $N_f=2$ flavors generated using a…
In the traditional non-relativistic bound state calculation, the two-photon decay amplitudes of the $P$-wave $\chi_{c0,2}$ and $\chi_{b0,2}$ states depend on the derivative of the wave function at the origin which can only be obtained from…
In this work, we perform a lattice QCD calculation of the branching ratios and the form factors of radiative leptonic decays $P \to \ell \nu_\ell \gamma$ ($P = \pi, K$) using $N_f=2+1$ domain wall fermion ensembles generated by the RBC and…
We describe a first-principles method to apply lattice QCD to compute the order $\alpha_{\mathrm{EM}}$ corrections to $K\to\pi\ell\nu_\ell$ decay. This method formulates the calculation in infinite volume with the conventional…
In this contribution, we present recent progress from the RBC/UKQCD collaboration on the first calculation of the long-distance two-photon contribution to the decay amplitude of a long-lived kaon into a pair of charged muons.
We present a full account of the two-loop electroweak, two-photon mediated short-distance dispersive $K_L \to\mu^+\mu^-$ decay amplitude. QCD corrections change the sign of this amplitude and reduce it by an order of magnitude. Thus, the…
We develop a methodology for the computation of the $K\to \ell\nu_\ell \ell'^+ \ell'^-$ decay width using lattice QCD and present an exploratory study here. We use a scalar function method to account for the momentum dependence of the decay…
We give a more complete calculation of $b \to s e^+e^- $ decay including leading log QCD corrections from $m_{top}$ to $M_W$ in addition to corrections from $M_{W}$ to $m_b$. The differential decay rate is found to be slightly suppressed…