Whereas the short time behaviour of an unstable quantum mechanical system is well understood from its theoretical as well as experimental side, the long time tail of the very same systems has neither been measured experimentally nor is there a theoretical agreement on how to handle it. We suggest a possible way out of this unsatisfactory state of art. Theoretically we suggest that the correct spectral function entering the Fock-Krylov method to calculate the survival amplitude is proportional to the density of states of a resonance. The latter is essentially the energy derivative of a phase shift. As a bonus, we can connect the survival probability to scattering data via the phase shift. The method then not only establishes the spectral function, but is per se a semi-empirical method to extract the large time behaviour from scattering data.
Non-linear Compton scattering of ultra-relativistic electrons traversing high-intensity laser pulses generates also hard photons. These photon high-energy tails are considered for parameters in reach at the forthcoming experiments LUXE and E-320. We consider the invariant differential cross sections $d σ/ du$ between the IR and UV regions and analyze the impact of the laser polarization and find q-deformed exponential shapes. (The variable $u$ is the light-cone momentum-transfer from initial electron to final photon.) Optical laser pulses of various durations are compared with the monochromati…
Spectator scattering at NLO in non-leptonic B decays: Tree amplitudes
我们计算了非轻子B衰变树振幅中硬旁观者散射的单圈（α_s^2）修正。这形成了强子B衰变的QCD因子分解公式的NNLO贡献的一部分，并引入了一个新的再散射阶段，纠正了直接CP不对称的领先顺序的结果。在这些技术问题中，我们讨论了红外发散的消除，以及倏逝四夸克算符的处理。我们的结果的红外有限性建立在1圈顺序的观众散射的因式分解。根据强子输入参数的值，新的1-圈修正可能对树主导的衰变（如B -> pi pi）产生重大影响。
Measuring the a0-a2 pion scattering lengths through K to 3 pi decays
本文讨论了Cabibbo最近提出的从π 0-π 0能谱中的尖点效应测量π-π散射长度组合a0-a2的建议。我们估计了在非线性光学条件下a0-a2测定的理论不确定度，得到K ~+对（pi 0 pi 0 pi ~+）的理论不确定度不小于5%。如果使用低于阈值的中性KL至（pi 0 pi 0 pi 0）衰减数据，则得到类似的理论不确定性。对于这种衰减，由于消除，阈值以上存在非常大的理论不确定性，并且阈值以上的数据不能用于获得散射长度。
Hadronic light-by-light scattering in the muon g-2: impact of proposed measurements of the (pi^0 -> gamma gamma) decay width and the (gamma^* gamma -> pi^0) transition form factor with the KLOE-2 experiment
