Search

In the framework of large-momentum effective theory at one-loop matching accuracy, we perform a lattice calculation of the Collins-Soper kernel, which governs the rapidity evolution of transverse-momentum-dependent (TMD) distributions. We first obtain the quasi-TMD wave functions at three different meson momenta, on a lattice with valence clover quarks on a dynamical highly improved staggered quark sea and lattice spacing a=0.12 fm from the MILC Collaboration, and renormalize the pertinent linear divergences using Wilson loops. Through one-loop matching to the light-cone wave functions, we determine the Collins-Soper kernel with transverse separation up to 0.6 fm. We study the systematic uncertainties from operator mixing and scale dependence, as well as the impact from higher power corrections. Our results potentially allow for a determination of the soft function and other transverse-momentum-dependent quantities at one-loop accuracy.

We complete the procedure of extracting parton distribution functions (PDFs) using large momentum effective theory (LaMET) at leading power accuracy in the hadron momentum. We derive a general factorization formula for the quasi PDFs in the presence of mixing, and give the corresponding hard matching kernel at $\mathcal O(\alpha_s)$, both for the unpolarized and for the polarized quark and gluon quasi-PDFs. Our calculation is performed in a regularization-independent momentum subtraction scheme. The results allow us to match the nonperturbatively renormalized quasi-PDFs to normal PDFs in the presence of mixing, and therefore can be used to extract flavor-singlet quark PDFs as well as gluon PDFs from lattice simulations., Comment: 29 pages, 5 figures. Errors in Eq. (90) are corrected

We present the first lattice-QCD calculation of the pion distribution amplitude using the large- momentum effective field theory (LaMET) approach, which allows us to extract lightcone parton observables from a Euclidean lattice. The mass corrections needed to extract the pion distribution amplitude from this approach are calculated to all orders in $m^2_{\pi} /P_z^2$. We also implement the Wilson- line renormalization which is crucial to remove the power divergences in this approach, and find that it reduces the oscillation at the end points of the distribution amplitude. Our exploratory result at 310-MeV pion mass favors a single-hump form broader than the asymptotic form of the pion distribution amplitude., Comment: 11 pages, 4 figures

Recent developments showed that light-cone parton distributions can be studied by investigating the large momentum limit of the hadronic matrix elements of spacelike correlators, which are known as quasiparton distributions. Like a light-cone parton distribution, a quasiparton distribution also contains ultraviolet divergences and therefore needs renormalization. The renormalization of nonlocal operators in general is not well understood. However, in the case of quasi-quark distribution, the bilinear quark operator with a straight-line gauge link appears to be multiplicatively renormalizable by the quark wave function renormalization in the axial gauge. We first show that the renormalization of the self-energy correction to the quasi-quark distribution is equivalent to that of the heavy-light quark vector current in the heavy quark effective theory at one-loop order. Assuming this equivalence at two-loop order, we then show that the multiplicative renormalizability of the quasi-quark distribution is true at two-loop order.

We present the one-loop matching condition for the unpolarized and polarized generalized quark distributions in the nonsinglet case. The matching condition links the quasi distributions defined in terms of spacelike correlators at finite nucleon momentum to the light-cone distributions, and it is useful for extracting the latter from the former in a lattice QCD calculation. Our results show that at one-loop and leading power accuracy the matching for the light-cone generalized quark distribution $H$ ($\stackrel{\texttildelow{}}{H}$) is nontrivial, whereas no matching is required for $E$ ($\stackrel{\texttildelow{}}{E}$). Therefore, $E$ ($\stackrel{\texttildelow{}}{E}$) can be smoothly approached by its quasi counterpart in the large momentum limit. We also present the matching for the distribution amplitude of the pion.

The electroweak $\mathcal O(\alpha)$ radiative corrections to the decay of the heavy CP-even MSSM Higgs boson to weak gauge bosons are presented. Due to the suppression of the tree-level $H^0WW/H^0ZZ$ coupling, the electroweak contributions to the partial decay width are significant. Although the effective Born decay width can be rather small for certain $M_{A^0}$ values (especially for large $\tan\beta$), the corrected partial widths at different values of $M_{A^0}$ are of comparable size.