We propose a new method of the determination of $R^{D}=sigma_{L}^{D}/sigma_{T}^{D}$ from the dependence of the diffractive cross section on the azimuthal angle between the electron scattering and proton scattering planes. The method is based on our finding of the model independence of the ratio of the $LT$ interference and transverse diffractive structure functions. The predicted azimuthal asymmetry is substantial and can be measured at HERA. We show that the accuracy of our reconstruction of $R^{D}$ is adequate for a reliable test of an important pQCD prediction of $R^{D}gsim 1$ for large $beta$.
LPS provides access to new fundamental observables: the diffraction cone and azimuthal asymmetries. Diffraction cone has a unique rise of $B_T$ from the exclusive limit to excitation of continuum $M^2 approx Q^2$ which is in striking contrast to experience with real photoproduction and hadronic diffraction. Azimuthal asymmetry is large and pQCD calculable at large $beta$ and can be measured with LPS. It allows testing of the pQCD prediction of $L/T >> 1$.
We investigate a charge asymmetry in $t bar t gamma$ production at the LHC that provides complementary information to the measured asymmetries in $t bar t$ production. We estimate the experimental uncertainty in its measurement at the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce the asymmetry excess in $t bar t$ at the Tevatron and the SM-like asymmetry at the LHC, the measurement in $t bar t gamma$ at the LHC could exhibit significant deviations with respect to the SM prediction.
We discuss thw relations between the elastic and inelastic cross-sections valid for the shadow and reflective modes of the elastic scattering. Considerations are based on the unitarity arguments. It is shown that the redistribution of the total interaction probability between the elastic and inelastic interactions can lead to increasing ratio of $sigma_{el}(s)/sigma_{tot}(s)$ at the LHC energies in presence of the reflective scattering mode. The form of the inelastic overlap function becomes peripheral due to the negative feedback. In the absorptive scattering mode, the mechanism of this increase is a different one since the impact parameter dependence of the inelastic interactions probability is central in this case. A short notice is also given on the slope parameter and the leading contributions to its energy dependence in the both modes.
The empirical scaling law, wherein the total photoabsorption cross section depends on the single variable eta=(Q^2+m_0^2)/Lambda^2(W^2), provides empirical evidence for saturation in the sense of sigma_{gamma* p}(W^2,Q^2)/sigma_{gamma p}(W^2) --> 1 for W^2 --> infinity at fixed Q^2. The total photoabsorption cross section is related to elastic diffraction in terms of a sum rule. The excess of diffractive production over the elastic component is due to inelastic diffraction that contains the production of hadronic states of higher spins. Motivated by the diffractive mass spectrum, the generalized vector dominance/color dipole picture (GVD/CDP) is extended to successfully describe the DIS data in the full region of x=<0.1, all Q^2>=0, where the diffractive two-gluon-exchange mechanism dominates.
In this work, the two-photon-exchange (TPE) effects in $eprightarrow enpi^+$ at small $-t$ are discussed within a hadronic model. The TPE contributions to the amplitude and the unpolarized differential cross section are both estimated and we find that the TPE corrections to the unpolarized differential cross section are about $-4%sim-15%$ at $Q^2=1$GeV$^2sim1.6$GeV$^2$. After considering the TPE corrections to the experimental data sets of unpolarized differential cross section, we analyse the TPE corrections to the separated cross sections $sigma_{textrm{L,T,LT,TT}}$. We find that the TPE corrections (at $Q^2=1$GeV$^2sim1.6$GeV$^2$) to $sigma_{textrm{L}}$ are about $-10%sim -20%$, to $sigma_{textrm{T}}$ are about $20%$ and to $sigma_{textrm{LT,TT}}$ are much larger. By these analysis, we conclude that the TPE contributions in $eprightarrow enpi^+$ at small $-t$ are important to extract the separated cross sections $sigma_{textrm{L,T,LT,TT}}$ and the electromagnetic magnetic form factor of $pi^+$ in the experimental analysis.