Recently JLab has carried out several measurement on the spin structure of the nucleon which contradicted the predictions of chiral perturbation theory. I would like to summarize their experimental result and give my own comment on this bizarre situation.
We study violation of quark-hadron duality for B → Xuℓν decays in the presence of the right-handed current (RHC). In this model, it is shown that duality violation has some characteristic aspects different from the standard model (SM) due to the existence of an instanton. In particular, the fermionic zero mode of an intermediate light quark plays a pronounced role for the RHC, whereas the same contribution is prohibited due to wrong chirality in the SM. Within a certain approximation relying on the single instanton, the finite distance singularity, which causes violation of quark-hadron duality, is extracted analytically. As a result, it is shown that duality violation for the lepton energy distribution in B → Xuℓν decays is possibly comparable to the leading perturbative contribution in the RHC, for a particular region in the phase space.
I present progress on lattice computation of the pion distribution amplitude from the HOPE collaboration. Status of numerical calculations for the 2nd and the 4th Mellin moments will be discussed.
I briefly discuss the method of pseudo distributions in extracting parton distrubtion functions (PDFs) from lattice QCD. Then, I describe the background field approach and present the calculation of matching relations connecting gluon PDFs to gluon pseudo-PDFs.
It is important to understand the nature of quark matter in high T QCD, which is crucial for the mechanism of matter creation in the early universe, as well as in the heavy-ion collision experiments at RHIC and LHC. A first step toward this goal is to find out the symmetries of high T QCD, since the nature of matter can be unveiled from its symmetries. I study meson correlators in $N_f = 2 + 1 + 1$ lattice QCD with dynamical domain-wall quarks at the physical point, for $T \simeq (190−770)$ MeV. The meson correlators include a complete set of Dirac bilinears, and each for six combinations of quark flavors. I discuss the implications of these results for the effective restoration of various symmetries in high T QCD, in particular, the emergent SU(2) chiral-spin symmetry.
Deeply Virtual Compton Scattering (DVCS) and Hard Exclusive Meson Production (HEMP) are valuable processes to study Generalized Parton Distributions (GPDs). By correlating the longitudinal momentum of the partons to their transverse spatial distribution inside the nucleon, GPDs reveal the 3-dimensional structure of the nucleon in QCD. Following a test run in 2012, dedicated exclusive measurements were performed at COMPASS in 2016 and 2017, using the 160 GeV muon beam at the M2 beamline of the CERN SPS. The current progress on the study of the exclusive channels will be presented.
The Schwinger effect, whereby particle anti-particle pairs are generated from the quantum field theoretic vacuum in a strong electric field, is studied for massive fermions in U(1) × SU(2) background fields mimicking the early stages of a heavy-ion collision. The background configuration, moreover, possesses a net angular momentum, that by virtue of the Schwinger effect, we find is transported to the produced fermion pairs. To achieve this we analyze a heuristic and classical model stemming from Wong’s equations, as well as an out-of-equilibrium in-in quantum model to one-loop.
We derive the dependence of the leading-twist pion light-cone distribution amplitude (LCDA) on a parton momentum fraction x by directly solving the dispersion relations for the moments with inputs from the operator product expansion (OPE) of the corresponding correlation function. It is noticed that these dispersion relations must be organized into those for the Gegenbauer coefficients first in order to avoid the ill-posed problem appearing in the conversion from the moments to the Gegenbauer coefficients. Given the values of various condensates in the OPE, we find that a solution for the pion LCDA, which is stable in the Gegenbauer expansion, exists. Moreover, the solution from summing contributions up to 18 Gegenbauer polynomials is smooth, and can be well approximated by a function proportional to xp(1−x)p with p ∼ 0.45 at the scale μ = 2 GeV.
Chimera baryons are an important feature of composite Higgs models, since they play role of top partner in partial top compositeness. In the realisation of the mechanism provided by Sp(4) gauge theory, such exotic objects are composed of two fundamental and one antisymmetric fermion constituents. We perform lattice computations for the chimera baryon spectrum both in the quenched approximation and with three dynamical antisymmetric Dirac fermions. Masses of various chimera baryons with different quantum number will be presented, including the one known as the top partner.