Dispersive analysis of the Primakoff reaction $γK \to K π$

Dispersion relation formalism for virtual Compton scattering and the generalized polarizabilities of the nucleon

A dispersion relation formalism for the virtual Compton scattering (VCS) reaction on the proton is presented, which for the first time allows a dispersive evaluation of 4 generalized polarizabilities at a four-momentum transfer $Q^2 \leq$ 0.5 GeV$^2$. The dispersive integrals are calculated using a state-of-the-art pion photo- and electroproduction analysis. The dispersion formalism provides a new tool to analyze VCS experiments above pion threshold, thus increasing the sensitivity to the generalized polarizabilities of the nucleon.

Data-driven dispersive analysis of the $ππ$ and $πK$ scattering

We present a data-driven analysis of the resonant S-wave $ππ\to ππ$ and $πK \to πK$ reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are accounted for using the Taylor expansion in a suitably constructed conformal variable. The fits are performed to experimental and lattice data as well as Roy analyses. For the $ππ$ scattering we present both a single- and coupled-channel analysis by including additionally the $K\bar{K}$ channel. For the latter the central result is the Omnès matrix, which is consistent with the most recent Roy and Roy-Steiner res…

Two photons into π^0π^0

We perform a theoretical study based on dispersion relations of the reaction γγ\to π^0π^0 emphasizing the low energy region. We discuss how the f_0(980) signal emerges in γγ\to ππwithin the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ\to ππamplitude above the K\bar{K} threshold. This allows us to make sharper predictions for the cross section at lower energies and our results could then be used to distinguish between different ππisoscalar S-wave parameterizations with the advent of new precise data on γγ\toπ^0π^0. We compare our dispersive appro…

Dispersive analysis of the $ππ$ and $πK$ scattering data

We present a data-driven analysis of the S-wave $ππ\to ππ\,(I=0,2)$ and $πK \to πK\,(I=1/2, 3/2)$ reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are parametrized using the expansion in a suitably constructed conformal variable, which accounts for its analytical structure. The partial-wave dispersion relation is solved numerically using the $N/D$ method. The fits to the experimental data supplemented with the constraints from chiral perturbation theory at threshold and Adler zero give the results consistent with Roy-like (Roy-Steiner) analyses. F…

The Reaction $γγ\toπ^0π^0$ in Generalized Chiral Perturbation Theory

The cross section for $γγ\toπ^0π^0$ and the pion polarizabilities are computed, within generalized chiral perturbation theory, in the full one loop approximation, {\it i.e.} up to and including order $O({p^5})$. The result depends on the parameter $α_{ππ}$ defining the tree level $π- π$ scattering amplitude and on an additional low energy constant. The latter is shown to be related by an exact sum-rule to the $e^+ e^-$ data. The parameter $α_{ππ}$ is related to the quark mass ratio $r = m_s /{\hat m}$ via the expansion of pseudoscalar meson masses. The generalized one loop $γγ\toπ^0π^0$ amplit…

Improved dispersion relations for γγ\to π^0π^0

We perform a dispersive theoretical study of the reaction γγ\to pi^0π^0 emphasizing the low energy region. The large source of theoretical uncertainty to calculate the γγ\toπ^0π^0 total cross section for \sqrt{s}\gtrsim 0.5 GeV within the dispersive approach is removed. This is accomplished by taking one more subtraction in the dispersion relations, where the extra subtraction constant is fixed by considering new low energy constraints, one of them further refined by taking into consideration the f_0(980) region. This allows us to make sharper predictions for the cross section for \sqrt{s}\les…

从壳振幅构建的有效场论中的氘生成

Deuterium Production in an Effective Field Theory Constructed from On-Shell Amplitudes

该研究构建从壳振幅出发的有效场论计算氘生成反应，经贝叶斯拟合确定热核反应率，降低了原初氘丰度预测的不确定度。