Search

We extend the discussion of the recently discovered 'anomaly poles' in QCD Compton scattering. We perform the complete one-loop calculation of the Compton amplitude using momentum transfer $t$ as the regulator of collinear divergences. In the gluon channel, we confirm the presence of poles $1/t$ in both the real and imaginary parts of the amplitude. In the quark channel, we find unexpected infrared single $1/\epsilon$ and double $1/\epsilon^2$ poles. We then perform the one-loop calculation of the leading-twist quark generalized parton distributions (GPDs) for quark and gluon external states with the same regulators and find that all these singular terms can be systematically absorbed into the GPDs, showing that QCD factorization is restored to this order. Having established this, we discuss the fate of the $1/t$ poles. We argue that they become the nonperturbative building blocks of GPDs that encode the chiral and trace anomalies of QCD, in a way consistent with the known constraints these anomalies impose on the nucleon axial and gravitational form factors. The scope of research on GPDs can therefore be expanded to address the manifestation and implications of quantum anomalies in high-energy exclusive processes., Comment: 22 pages, 2 figures, Finite terms in the one-loop calculation of GPDs in the ERBL region included, version to appear in PRD

We compute the gravitational form factor $D(t)$ of various nuclei in the generalized Skyrme model where nuclei are described as solitonic field configurations each with a definite baryon number $B$. We separately discuss the cases $B=1$ (nucleons), $B=2$ (deuteron), $B=3$ (helium-3 and tritium) and extrapolate to larger $B$-values. Configurations with $B>1$ are in general not spherically symmetric, and we demonstrate how group theory helps to extract the form factor. Numerical results are presented for the configurations with $B=1,2,3,4,5,6,7,8,32,108$. We find that the $B$-dependence is consistent with a power-law $D(0)\propto B^{\beta}$ with $\beta=1.7\sim 1.8$. Other gravitational form factors can be calculated in the same framework, and we show the result for the $J(t)$ form factor associated with angular momentum for the $B=3$ solution., Comment: 15 pages, 7 figures

We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance., Comment: 44 pages, ReVTeX, White Paper on EIC Theory Alliance

The D-term is one of the conserved charges of hadrons defined as the forward limit of the gravitational form factor $D(t)$. We calculate the nucleon's D-term in a holographic QCD model in which the nucleon is described as a soliton in five dimensions. We show that the form factor $D(t)$ is saturated by the exchanges of infinitely many $0^{++}$ and $2^{++}$ glueballs dual to transverse-traceless metric fluctuations on the Wick rotated AdS$_7$ black hole geometry. We refer to this phenomenon as `glueball dominance', in perfect analogy to the vector meson dominance of the electromagnetic form factors. However, the value at vanishing momentum transfer $D(t=0)$ can be interpreted as due to the exchange of pairs of pions and infinitely many vector and axial-vector mesons without any reference to glueballs. We find that the D-term is slightly negative as a result of a cancellation between the isovector and isoscalar meson contributions., 40 pages

We study the small-$x$ evolution equation for the gluon generalized parton distribution (GPD) $E_g$ of the nucleon. It is shown that $E_g$ at vanishing skewness exhibits the Regge behavior identical to the BFKL Pomeron, despite its association with nucleon helicity-flip processes. We also consider the effect of gluon saturation and demonstrate that $E_g$ gets saturated in the same way as its helicity-nonflip counterpart $H_g$. Our result has a direct impact on the modeling of $E_g$ as well as the small-$x$ contribution to nucleon spin sum rules., Comment: 5 pages, 1 figure, v2 matches PRL version

Motivated by a novel origin of transverse single spin asymmetry (SSA) in semi-inclusive Deep Inelastic Scattering (SIDIS) uncovered by some of us, we quantitatively investigate its impact on the theoretical understanding of the mechanism responsible for SSA. This new contribution from the quark-initiated channel first appears in two-loop perturbation theory and involves the $g_T(x)$ distribution. We point out another entirely analogous piece from the gluon-initiated channel proportional to the gluon helicity distribution $\Delta G(x)$. Both contributions are solely expressed in terms of twist-two polarized parton distribution functions and twist-two fragmentation functions in the Wandzura-Wilczek approximation, such that they can be unambiguously evaluated without introducing free parameters. We make predictions for measurements of the asymmetries $A_{UT}$ at the future Electron-Ion Collider (EIC), and find that $A_{UT}$ associated with the $\sin (\phi_h-\phi_S)$, $\sin \phi_S$ and $\sin (2\phi_h-\phi_S)$ harmonics can reach up to 1-2\% even at the top EIC energy., Comment: 28 pages, 8 figures

We present a model of exclusive $��$-meson lepto-production $ep \to e'p'��$ near threshold which features the strangeness gravitational form factors of the proton. We argue that the shape of the differential cross section $d��/dt$ is a sensitive probe of the strangeness D-term of the proton., 9 pages

This volume is a collection of contributions for the 7-week program "Probing Nucleons and Nuclei in High Energy Collisions" that was held at the Institute for Nuclear Theory in Seattle, WA, USA, from October 1 until November 16, 2018. The program was dedicated to the physics of the Electron Ion Collider (EIC), the world's first polarized electron-nucleon (ep) and electron-nucleus (eA) collider to be constructed in the USA. These proceedings are organized by chapters, corresponding to the weeks of the program: Week I, Generalized parton distributions; Week II, Transverse spin and TMDs; Week III, Longitudinal spin; Week IV, Symposium week; Weeks V & VI, eA collisions; Week VII, pA and AA collisions. We hope these proceedings will be useful to readers as a compilation of EIC-related science at the end of the second decade of the XXI century., Electron Ion Collider, INT 18-3 Program. Published by World Scientific. Duplicates content of arXiv:1912.10965, arXiv:1912.10724, arXiv:1910.03006, arXiv:1910.07982, arXiv:1912.13397, arXiv:1910.01979, arXiv:2001.07862, arXiv:2001.03700, arXiv:1910.01030, arXiv:1910.01273, arXiv:1912.13020, arXiv:1910.06003, arXiv:2001.03655, arXiv:1909.12591, arXiv:1909.09809, arXiv:1910.04806, arXiv:2001.05978

We study sub-threshold heavy quarkonium ($J/��$ and $��$) photo-productions in $��A$ collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the $��p$ threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for $J/��$ and $��$. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China., 7 pages, 5 figures

We update our previous calculation of $J/��$ photo-production near threshold \cite{Hatta:2018ina} by incorporating the recent developments in theory and the new experimental data from the GlueX collaboration at Jefferson Lab \cite{Ali:2019lzf}. We then propose to study the near threshold production of $��$ and $J/��$ in ultraperipheral $pA$ collisions at RHIC. These processes are sensitive to the gluon condensate in the proton which is related to the QCD trace anomaly. Our result emphasizes the role of gluons as the origin of the proton mass., 10 pages, 9 figures

It has been suggested that the production of a heavy quarkonium near threshold in electron-proton scattering can shed light on the origin of the proton mass via the QCD trace anomaly. We study the photoproduction of $J/��$ off the proton using gauge/string duality and demonstrate that the $t$-dependence of the differential cross section $d��/dt$ at small-$t$ is a sensitive probe of the trace anomaly., 17 pages, 7 figures. v2: Eq.(24,27) corrected, minor changes in numerical results

We show that the diffractive forward production of two quarkonia, especially the $��_{cJ}$ and $��_c$ states, in proton-proton or proton-ion collisions can access the Weizs��cker-Williams gluon Wigner distribution of the proton. We use the hybrid factorization approach where the collinear, double gluon PDF is applied for one of the protons and the $k_T$-dependent (Wigner or GTMD) distribution for the other. The production of quarkonia is treated in the NRQCD framework. A particularly concise formula is obtained for double $��_{J=1}$ production., 19 pages, 3 figures

We suggest inclusive hadron production in ultra-peripheral proton-nucleus collisions (UPCs) $p^\uparrow A \to h AX$ as a new channel to investigate single spin asymmetries (SSAs), in particular, to test the assumed dominance of the contribution from twist-three fragmentation functions. The UPC cross sections are obtained by considering the photoproduction limit of semi-inclusive deep inelastic scattering (SIDIS). In particular, we find simple formulas for the polarized UPC cross sections in the collinear twist-three framework. We then numerically calculate the fragmentation contribution to SSA in $p^\uparrow A \to \pi A X$ at $\sqrt{s} = 200$ GeV and find a few percent asymmetry in the forward region., Comment: minor corrections, matches the published version

We investigate the close connection between the quantum phase space Wigner distribution of small-$x$ gluons and the color dipole scattering amplitude, and propose to study it experimentally in the hard diffractive dijet production at the planned electron-ion collider. The angular correlation between the nucleon recoiled momentum and the dijet transverse momentum will probe the nontrivial correlation in the phase space Wigner distribution. This experimental study will not only provide us with three-dimensional tomographic pictures of gluons inside high energy proton, but also give a unique and interesting signal for the small-$x$ dynamics with QCD evolution effects., 6 pages, 1 figure

Motivated by the problem of thermalization in heavy-ion collisions, we present numerical simulations of the nonequilibrium evolution of the O(N) model in 1+2 dimensions with longitudinal expansion and in the presence of a background field. We work in the NLO approximation of the 1/N expansion and consider both the strong and weak coupling cases. Special emphasis is put on the difference between the 2PI formalism and the classical statistical approach. In the 2PI case at strong coupling, we find some evidence of the Bose-Einstein (exponential) distribution in the expanding system., 12 pages, 12 figures; v2 version published in PRD

We compute the inclusive spectrum of produced particles in e+e- annihilation in confining gauge theories that have a gravity dual and show that the momentum distribution exhibits the thermal behavior., Comment: 4 pages, revtex4; v2. discussion slightly expanded

This paper has been withdrawn by the author., Comment: 2pages, 1figure, revtex

We argue that the chiral phase transition and the deconfinement phase transition in finite temperature QCD are just different limits of a single crossover phase transition driven by the lightest scalar field which is a mixture of the glueball and the sigma meson. The key mechanism, the level repulsion between the sigma and the glueball, gives not only a unified description of the finite temperature phase transitions, but also a consistent characterization of the entire QCD phase diagram in the temperature-quark mass plane., 10 pages, 3 figures