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1. Incoherent diffractive dijet production and gluon Bose enhancement in the nuclear wave function

   https://doi.org/10.1007/JHEP07(2024)134  

   Kar, Tiyasa; Kovner, Alexander; Li, Ming; Skokov, Vladimir V (July 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> We investigate the effect of gluon Bose enhancement in the nuclear wave function on the dijet production in incoherent diffractive processes in DIS and ultraperipheral collisions. We demonstrate that Bose enhancement leads to an enhancement of diffractive dijet production cross section when the transverse momenta of the two jets are aligned at zero relative angle. This enhancement is maximal when the magnitude of the transverse momenta of the two jets are equal, and disappears rather quickly as a function of the ratio of the two momenta. We study both the dilute limit and fully nonlinear dense regime where the nuclear wave function is evolved with the leading order JIMWLK equation. In both cases we observe a visible effect, with it being enhanced by the evolution due to the dynamical generation of the color neutralization scale. 

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2. Direct quarkonium production in DIS from a joint CGC and NRQCD framework

   https://doi.org/10.1103/PhysRevD.110.094039  

   Cheung, Vincent; Kang, Zhong-Bo; Salazar, Farid; Vogt, Ramona (November 2024, Physical Review D)

   We compute the differential cross section for direct quarkonium production in high-energy electron-nucleus collisions at small $x$. Our computation is performed within the nonrelativistic QCD factorization formalism that separates the calculation into short distance coefficients and long distance matrix elements that depend on the color and spin of the state. We obtain the short distance coefficients of the production of the heavy quark pair within the framework of the color glass condensate effective field theory, which resums coherent multiple interactions of the heavy quark pair with the nucleus to all orders. Our results are expressed as the convolution of perturbatively calculable functions with multipoint lightlike Wilson line correlators. In the correlation limit, we establish the correspondence between our color glass condensate formulation with calculations employing the transverse momentum dependent (TMD) framework. We extend this correspondence by resumming kinematic power corrections within the improved TMD framework, which interpolates between the TMD formalism and $k_{\perp }$-factorization formalism. We present a detailed numerical analysis, focusing on $J/\psi$production in the kinematics accessible at the future Electron-Ion Collider, highlighting the importance of genuine higher-order saturation contributions when the electron collides with a large nucleus. Our results are also valid in the photoproduction limit where we expect the largest contribution from genuine higher-order saturation contributions which could be accessed in ultraperipheral collisions of relativistic heavy ions. Published by the American Physical Society2024 

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3. Subleading power corrections to heavy quarkonium production in QCD factorization approach

   https://doi.org/10.1051/epjconf/202227404005  

   Lee, Kyle; Qiu, Jian-Wei; Sterman, George; Watanabe, Kazuhiro (January 2022, EPJ Web of Conferences)

   Rothkopf, A.; Brambilla, N.; Tolos, L.; Tranberg, A.; Kurkela, A.; Roehrich, D.; Andersen, J.O.; Tywoniuk, K.; Antonov, D.; Greensite, J. (Ed.)

   We report the current understanding of heavy quarkonium production at high transverse momentum ( p T ) in hadronic collisions in terms of QCD factorization. In this presentation, we highlight the role of subleading power corrections to heavy quarkonium production, which are essential to describe the p T spectrum of quarkonium at a relatively lower p T . We also introduce prescription to match QCD factorization to fixed-order NRQCD factorization calculations for quarkonium production at low p T . 

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4. Non-perturbative quarkonium dissociation rates in strongly coupled quark-gluon plasma

   https://doi.org/10.1007/JHEP07(2025)162  

   Wu, Biaogang; Tang, Zhanduo; Rapp, Ralf (July 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> Heavy quarks and quarkonia are versatile probes of the transport properties of the hot QCD medium produced in ultra-relativistic heavy-ion collisions (URHICs). A robust description of heavy-flavor transport coefficients requires a microscopic approach that treats the open and hidden heavy-flavor sectors on the same footing. Here, we employ the quantum many-bodyT-matrix formalism to evaluate the dissociation rates of heavy quarkonia in the quark-gluon plasma (QGP). The basic ingredient is the heavy-lightT-matrix, which utilizes a nonperturbative driving kernel constrained by lattice-QCD data. Its resummation in a ladder series provides a much enhanced interaction strength compared to a previously used perturbative coupling to the quasiparticle partons in the QGP. The in-medium quarkonium properties, particularly their temperature-dependent binding energies, are obtained from selfconsistent calculations with the same interaction kernel, including interference effects (also referred to as the imaginary part of the heavy-quark potential) as well as off-shell parton spectral functions. We systematically investigate the interplay of these effects and elaborate on the connections to the dipole approximation used in effective field theory. 

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5. All-loop group-theory constraints for four-point amplitudes of SU(N), SO(N), and Sp(N) gauge theories

   https://doi.org/10.1007/JHEP10(2024)221  

   Naculich, Stephen G; Osathapan, Athis (October 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> In the decomposition of gauge-theory amplitudes into kinematic and color factors, the color factors (at a given loop orderL) span a proper subspace of the extended trace space (which consists of single and multiple traces of generators of the gauge group, graded by powers ofN). Using an iterative process, we systematically construct theL-loop color space of four-point amplitudes of fields in the adjoint representation of SU(N), SO(N), or Sp(N). We define the null space as the orthogonal complement of the color space. For SU(N), we confirm the existence of four independent null vectors (forL≥ 2) and for SO(N) and Sp(N), we establish the existence of seventeen independent null vectors (forL≥ 5). Each null vector corresponds to a group-theory constraint on the color-ordered amplitudes of the gauge theory. 

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