scholarly journals Two-photon exchange corrections to γ*NΔ form factors for Q2≤4(GeV/c)2

2017 ◽  
Vol 96 (5) ◽  
Author(s):  
Hai-Qing Zhou ◽  
Shin Nan Yang
Keyword(s):  
Form Factors ◽  
Photon Exchange ◽  
Two Photon

scholarly journals Two-photon exchange in leptophilic dark matter scenarios

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Raghuveer Garani ◽  
Federico Gasparotto ◽  
Pierpaolo Mastrolia ◽  
Henrik J. Munch ◽  
Sergio Palomares-Ruiz ◽  
...  
Keyword(s):  
Dark Matter ◽  
Momentum Transfer ◽  
Direct Detection ◽  
Form Factors ◽  
Scalar Particle ◽  
Analytical Form ◽  
Photon Exchange ◽  
Two Photon ◽  
Zero Momentum ◽  
Pseudo Scalar

Abstract In leptophilic scenarios, dark matter interactions with nuclei, relevant for direct detection experiments and for the capture by celestial objects, could only occur via loop-induced processes. If the mediator is a scalar or pseudo-scalar particle, which only couples to leptons, the dominant contribution to dark matter-nucleus scattering would take place via two-photon exchange with a lepton triangle loop. The corresponding diagrams have been estimated in the literature under different approximations. Here, we present new analytical calculations for one-body two-loop and two-body one-loop interactions. The two-loop form factors are presented in closed analytical form in terms of generalized polylogarithms up to weight four. In both cases, we consider the exact dependence on all the involved scales, and study the dependence on the momentum transfer. We show that some previous approximations fail to correctly predict the scattering cross section by several orders of magnitude. Moreover, we quantitatively show that form factors in the range of momentum transfer relevant for local galactic dark matter, can be significantly smaller than their value at zero momentum transfer, which is the approach usually considered.

Proton form factors and two-photon exchange in elastic electron-proton scattering

2015 ◽  
Vol 78 (3) ◽  
pp. 394-403 ◽  
Author(s):  
D. M. Nikolenko ◽  
J. Arrington ◽  
L. M. Barkov ◽  
H. de Vries ◽  
V. V. Gauzshtein ◽  
...  
Keyword(s):  
Form Factors ◽  
Elastic Electron ◽  
Proton Scattering ◽  
Photon Exchange ◽  
Two Photon ◽  
Proton Form ◽  
Proton Form Factors

scholarly journals Two-Photon Exchange in Elastic Electron Scattering on Hadronic Systems

2021 ◽  
Vol 66 (1) ◽  
pp. 3
Author(s):  
D. Borisyuk ◽  
A. Kobushkin
Keyword(s):  
Charge Asymmetry ◽  
Form Factors ◽  
Photon Exchange ◽  
Spin Asymmetries ◽  
Single Spin ◽  
Two Photon ◽  
Double Spin ◽  
Theoretical Approaches ◽  
Single Spin Asymmetries ◽  
Proton Form Factors

In the present review, we discuss different aspects of the two-photon exchange (TPE) physics in elastic ep scattering at high Q2, as well as at low Q2. The imaginary part of the TPE amplitude gives rise to beam and target single-spin asymmetries. Different theoretical approaches to the calculation of these observables are considered. The real part of the TPE amplitude influences the unpolarized cross-section and double-spin observables and is, most likely, responsible for the discrepancy between two methods of measurements of the proton form factors. We review different methods of calculations of the TPE amplitudes in the framework of the “hadron” and “quark-gluon” approaches. We discuss the dispersion approach suitable for low and intermediate Q2, which includes elastic and inelastic intermediate hadronic states, as well as the connection of TPE with the proton radius puzzle. The present situation with direct experimental searches for the TPE amplitude in the e+p/e−p charge asymmetry is also discussed, as well as attempts to extract the TPE amplitudes from existing experimental data obtained by the Rosenbluth and double polarization techniques. The TPE physics in other processes such as elastic мp, e-nucleus, and еп scattering is also reviewed.

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