Sergey Syritsyn

Using forward matrix elements of local leading-twist operators, we present a determination of the isovector third Mellin moments ⟨ x 2 ⟩ of nucleon unpolarized, polarized, and transversity parton distribution functions. Two lattice QCD ensembles at the physical pion mass are used, which were generated using a tree-level Symanzik-improved gauge action and 2 + 1 flavor tree-level improved Wilson clover fermions coupling via two-level HEX smearing. Leveraging a wide set of operators, two extraction methods for the matrix elements, and the automatic inclusion of model uncertainties via bootstrapped model averages, we extract values of the third Mellin moments. This is the first direct calculation of these observables performed at the physical pion mass.

A bstract: We investigate the entangling properties of the color flux tube between a static quark-antiquark pair in pure gauge Yang-Mills theory. In earlier works, we defined a gauge-invariant flux tube entanglement entropy (FTE ² ), the excess entanglement entropy of a region of gluon fields that can be attributed to the color flux tube, and demonstrated that it is finite in the continuum limit. FTE ² was shown to have two contributions, one from the vibrations of the QCD string, and the other from its internal (color) degrees of freedom. In this work, we further explore the internal color component in (2+1)D Yang-Mills theory for SU ( N _c ) gauge groups, varying 2 ≤ N _c ≤ 5. We identify a novel physical scale in the theory, the entanglement radius ξ ₀ . This radius characterizes the transverse extent of the flux tube that must be completely severed by an entangling region to capture the entanglement entropy of color degrees of freedom. The key feature underlying this phenomenon is its topological nature. This is revealed through systematic studies of multi-slab entangling regions in which FTE ² changes sharply when boundaries of the slabs completely cross-cut the flux tube. We find that ξ ₀ increases approximately linearly with N _c and is independent of both Rényi replica number and the inter-quark separation length. We also study FTE ² as a function of the entangling region’s transverse displacement from the static quark pair and observe behavior consistent with a previously identified intrinsic width λ of the flux tube. The extracted value is in agreement with the inverse mass of the lightest glueball for the gauge groups studied.

Processes that violate baryon number, most notably proton decay and n n ¯ transitions, are promising probes of physics beyond the Standard Model (BSM) needed to understand the lack of antimatter in the Universe. To interpret current and forthcoming experimental limits, theory input from nuclear matrix elements to UV complete models enters. Thus, an interplay of experiment, effective field theory, lattice QCD, and BSM model building is required to develop strategies to accurately extract information from current and future data and maximize the impact and sensitivity of next-generation experiments. Here, we briefly summarize the main results and discussions from the workshop ‘INT-25-91W: Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics,’ held at the Institute for Nuclear Theory, University of Washington, Seattle, WA, 13–17 January 2025.

In this work, we report a lattice calculation of x-dependent valence pion generalized parton distributions (GPDs) at zero skewness with multiple values of the momentum transfer −t. The calculations are based on an N _f = 2 + 1 gauge ensemble of highly improved staggered quarks with Wilson-Clover valence fermion. The lattice spacing is 0.04 fm, and the pion valence mass is tuned to be 300 MeV. We determine the Lorentz-invariant amplitudes of the quasi-GPD matrix elements for both symmetric and asymmetric momenta transfers with similar values and show the equivalence of both frames. Then, focusing on the asymmetric frame, we utilize a hybrid scheme to renormalize the quasi-GPD matrix elements obtained from the lattice calculations. After the Fourier transforms, the quasi-GPDs are then matched to the light-cone GPDs within the framework of large momentum effective theory with improved matching, including the next-to-next-to-leading order perturbative corrections, and leading renormalon and renormalization group resummations. We also present the 3-dimensional image of the pion in impact-parameter space through the Fourier transform of the momentum transfer −t.

A bstract: We construct a novel flux tube entanglement entropy (FTE ² ), defined as the excess entanglement entropy relative to the vacuum of a region of color flux stretching between a heavy quark-anti-quark pair in pure gauge Yang-Mills theory. We show that FTE ² can be expressed in terms of correlators of Polyakov loops, is manifestly gauge-invariant, and therefore free of the ambiguities in computations of the entanglement entropy in gauge theories related to the choice of the center algebra. Employing the replica trick, we compute FTE ² for SU(2) Yang-Mills theory in (2+1)D and demonstrate that it is finite in the continuum limit. We explore the properties of FTE ² for a half-slab geometry, which allows us to vary the width and location of the slab, and the extent to which the slab cross-cuts the color flux tube. Following the intuition provided by computations of FTE ² in (1+1)D, and in a thin string model, we examine the extent to which our FTE ² results can be interpreted as the sum of an internal color entropy and a vibrational entropy corresponding to the transverse excitations of the string.