arXiv subjects

Qian-Qian Guo

Publications and source records attributed to Qian-Qian Guo.

5 recordsLinked to original sources

arXiv2026

Corrections to the Forward Limit Dispersion Relations for $γZ$-Exchange Contributions

The weak charge of the proton $Q_{\textrm{w}}$ is one of the most fundamental quantities in physics. It can be determined by measuring the parity asymmetry $A_{\textrm{PV}}$ in elastic $ep$ scattering, where the $γZ$-exchange contributions are crucial. For the past fifteen years, dispersion relations (DRs) in the forward limit have been widely used as a model-independent method to estimate these contributions. In this work, we study corrections to these forward-limit DRs. We first estimate these corrections using pointlike interactions as an illustrative example. We then estimate the $γZ$-exchange contributions for the upcoming P2 experiment through both direct calculation and the forward-limit DRs, within the framework of low-energy effective interactions. The results indicate that the correction to the forward-limit DR for $\Box_{γZ}^{V}$ is around 47\% for the upcoming P2 experiment, which will significantly modify the extracted value of $Q_{\textrm{w}}$.

hep-ph↗

arXiv2026

$γZ$-exchange contribution in elastic $ep$ scattering by perturbative QCD

In this study, we calculate the $γZ$-exchange contribution to elastic $ep$ scattering at large momentum transfer within perturbative QCD. We present analytical expressions for the $γZ$-exchange contributions to the amplitudes. We also estimate the asymptotic behaviors of the amplitude contributions and of the physical quantity $A_{\text{PV}}$ at high momentum transfer. These asymptotic behaviors determine the subtraction order in the dispersion relations (DRs) satisfied by the amplitudes. We find that the DR usually used in the literature for the axial-vector part of the amplitude is not valid at high $Q^2$ and should be modified to a once-subtracted form. Within the present pQCD framework and the adopted proton distribution amplitudes, these high-energy properties also provide nontrivial constraints on low-energy DR assumptions.

hep-ph↗

arXiv2026

Axion-like particle production from lepton-nucleon scattering in chiral effective theory

In this work we study the axion/axion-like particle production from the lepton-nucleon scattering in the low-energy region, i.e., the $\ell N\to \ell N a$ processes, $\ell$ being the electron or muon and $N$ the proton or neutron. We simultaneously include three different types of axion interaction couplings within the chiral effective field theory, namely the axion-nucleon-nucleon couplings $g_{aNN}$, axion-photon-photon coupling $g_{aγγ}$ and axion-photon-vector meson resonances couplings $g_{ρaγ}$ and $g_{ωaγ}$. Vast inputs from the lattice QCD and hadron phenomenological studies are used to fix the unknown couplings. The relative strengths of different axion interactions in the $\ell N\to \ell N a$ processes are then revealed. We provide detailed predictions for the differential cross sections with respect to various angles and axion energy, as well as the total cross sections in the low-energy region around production thresholds, both for the Kim-Shifman-Vainstein-Zakharov (KSVZ) and Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) axion models.

hep-ph↗

arXiv2024

$γZ$-Exchange Contributions in Low-Energy Parity-Violating $ep$ Scattering

In this work, the $γZ$-exchange contributions in the low-energy elastic parity-violating $ep$ scattering are discussed with the approximation $m_e=0$. By expanding the $γpp$ and $Zpp$ interactions on the momentum of photon and considering both the leading-order and the next-to-leading order interactions, we calculate the amplitudes of the $γZ$-exchange diagrams. After performing the loop integral, we expand the results in the low energy limit, and obtain the analytic expressions for the amplitudes. Numerical comparisons show that the analytic expressions are very close to the full results over a large region. We investigate the power behaviors of these contributions and find that some are enhanced by a kinematic factor in the low energy limit. Additionally, in some cases, the imaginary parts of the contributions from the next-to-leading-order interactions are at the same order as those from the leading-order interactions. Furthermore, the corresponding contributions to the physical observable quantity $A_{\textrm{PV}}$ are also discussed. Combining all the properties together, we conclude that these analytic expressions describe the leading-order contributions of all $γZ$-exchange helicity amplitudes in the region with $α_e\ll Q/M_N\sim δ/M_N^2\ll 1$, where $α_{e}$ is the fine structure constant, $M_N$ is the mass of proton, $Q$ and $δ$ are the small quantities related to the momentum transfer and the center-of-mass energy.

hep-ph↗

arXiv2022

Two-Photon-Exchange effect in $ep\rightarrow enπ^+$ at small $-t$ with the hadronic model and dispersion relation approach

In this work, the two-photon-exchange (TPE) effect in $ep\rightarrow enπ^+$ at small $-t$ is discussed. In the previous work, the TPE contribution with one $π$ intermediate state is estimated numerically within a hadronic model under the pion-dominance approximation. Here we extend the discussion to include one $ρ$ intermediate state. The TPE contribution can be described by one scalar function in the limit $m_e\rightarrow 0$, the dispersion relation (DR) satisfied by this scalar function is analysed. The analytic expressions for the imaginary parts of the TPE contributions from one $π$ or one $ρ$ intermediate state are given within the hadronic model. Combining these analytic expressions and the DR, the corresponding real parts of the TPE contributions can be estimated easily at any available region. This can help the further experimental analysis to include the TPE contributions in a convenient way. The numeric results show that the TPE correction with one $ρ$ intermediate state is much smaller than that with one $π$ intermediate state in the current energy region. These results suggest that the TPE contribution with an elastic state is the main TPE contribution in $ep\rightarrow enπ^+$ at small $-t$.

hep-ph↗