Next-to-leading-logarithm threshold resummation for exclusive B meson decays

We extend the threshold resummation of the large logarithms $$\ln x$$ ln x which appear in factorization formulas for exclusive B meson decays, x being a spectator momentum fraction, to the next-to-leading-logarithm (NLL) accuracy. It is shown that the NLL resummation effect provides suppression in the end-point region with $$x\sim 0$$ x ∼ 0 stronger than the leading-logarithm (LL) one, and thus improves perturbative analyses of the above processes. We revisit the $$B\rightarrow K\pi $$ B → K π decays under the NLL resummation in the perturbative QCD approach, and find that it induces up to 20% variation of the direct CP asymmetries in various modes relative to the LL results. Our method to avoid the Landau singularity in the inverse Mellin transformation causes at most 10% theoretical uncertainty.

Unpolarized quark and gluon TMD PDFs and FFs at N3LO

In this paper we calculate analytically the perturbative matching coefficients for unpolarized quark and gluon Transverse-Momentum-Dependent (TMD) Parton Distribution Functions (PDFs) and Fragmentation Functions (FFs) through Next-to-Next-to-Next-to-Leading Order (N3LO) in QCD. The N3LO TMD PDFs are calculated by solving a system of differential equation of Feynman and phase space integrals. The TMD FFs are obtained by analytic continuation from space-like quantities to time-like quantities, taking into account the probability interpretation of TMD PDFs and FFs properly. The coefficient functions for TMD FFs exhibit double logarithmic enhancement at small momentum fraction z. We resum such logarithmic terms to the third order in the expansion of αs. Our results constitute important ingredients for precision determination of TMD PDFs and FFs in current and future experiments.

Erratum to: Effective field theory after a new-physics discovery

The two linear relations between operators shown in eq. (3.29) were missing an integral over the momentum fraction u on the right-hand side. In the one-particle anomalous dimensions in eq. (5.7) two fractions were mistyped.

Nucleon momentum fraction, helicity and transversity from 2+1-flavor lattice QCD

A detailed analysis of the systematic uncertainties in the calculation of the isovector momentum fraction, 〈x〉u − d, helicity moment, 〈x〉Δu − Δd, and the transversity moment, 〈x〉δu − δd, of the nucleon is presented using high-statistics data on seven ensembles of gauge configurations generated by the JLab/W&M/LANL/MIT collaborations using 2 + 1-flavors of dynamical Wilson-clover quarks. The much higher statistics have facilitated better control over all systematics compared to previous lattice calculations. The least understood systematic — excited-state contamination — is quantified by studying the variation of the results as a function of different estimates of the mass gap of the first excited state, obtained from two- and three-point correlation functions, and as a function of the pion mass Mπ. The final results are obtained using a simultaneous fit in the lattice spacing a, pion mass Mπ and the finite volume parameter MπL keeping leading order corrections. The data show no significant dependence on the lattice spacing and some evidence for finite-volume corrections. Our final results, in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme at 2 GeV, are 〈x〉u − d = 0.155(17)(20), 〈x〉Δu − Δd = 0.183(14)(20) and 〈x〉δu − δd = 0.220(18)(20), where the first error is the overall analysis uncertainty assuming excited-state contributions have been removed, and the second is an additional systematic uncertainty due to possible residual excited-state contributions. These results are consistent with phenomenological global fit values.

Dynamics of diffractive dissociation

We describe a QCD based model which incorporates the main properties of the inclusive particle distributions expected for diffractive processes, including the diffractive dissociation at high energies. We study, in turn, the total cross section, $$\sigma _\mathrm{tot}$$ σ tot , the differential elastic, $$d\sigma _\mathrm{el}/dt$$ d σ el / d t , cross section, the dependence of the single proton dissociation cross section, $$\xi d\sigma ^\mathrm{SD}/d\xi $$ ξ d σ SD / d ξ , on the momentum fraction, $$\xi =1-x_L$$ ξ = 1 - x L , lost by the leading proton, the multiplicity distributions in inelastic (non-diffractive) collisions and in the processes of dissociation. Besides this we calculate the mean transverse momenta of the ‘wee partons’ (secondaries) produced in the case of dissociation (that is in the processes with a large rapidity gap) and compare it with that in inelastic interactions.

Two-loop coefficient function for DVCS: vector contributions

Using the approach based on conformal symmetry we calculate the two-loop coefficient function for the vector flavor-nonsinglet contribution to deeply-virtual Compton scattering (DVCS). The analytic expression for the coefficient function in momentum fraction space is presented in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme. The corresponding next-to-next-to-leading order correction to the Compton form factor ℋ for a simple model of the generalized parton distribution appears to be rather large: a factor two smaller than the next-to-leading order correction, approximately ∼ 10% of the tree level result in the bulk of the kinematic range, for Q2 = 4 GeV2.

T-odd generalized and quasi transverse momentum dependent parton distribution in a scalar spectator model

Generalized transverse momentum dependent parton distributions (GTMDs), as mother funtions of transverse momentum dependent parton distributions (TMDs) and generalized parton distributions (GPDs), encode the most general parton structure of hadrons. We calculate four twist-two time reversal odd GTMDs of pion in a scalar spectator model. We study the dependence of GTMDs on the longitudinal momentum fraction x carried by the active quark and the transverse momentum $$|\vec k_T|$$ | k → T | for different values of skewness $$\xi $$ ξ defined as the longitudinal momentum transferred to the pion as well as the total momentum $$|\vec \Delta _T|$$ | Δ → T | transferred to the pion. In addition, the quasi-TMDs and quasi-GPDs of pion have also been investigated in this paper.

Recent progress on the study of nucleon structure from lattice QCD and future perspectives

We review the progress achieved within the last five years in the simulations of lattice QCD, as well as in the analysis for selected quantities probing nucleon structure. In particular, we discuss results on the nucleon electromagnetic form factors, \sigmaσ-terms, the momentum fraction carried by quark in the nucleon and the helicity and transversity moments. All quantities are obtained using simulations generated with quark masses fixed to their physical values. In addition, we review the on-going effort to extract parton distribution functions (PDFs) directly from lattice QCD using the quasi-PDF approach.