arXiv subjects

Michael Fucilla

Publications and source records attributed to Michael Fucilla.

At least 19 recordsLinked to original sources

arXiv2026

NLO corrections to the NEik DIS structure functions

We summarize the next-to-leading order (NLO) corrections to next-to-eikonal (NEik) quark background contributions to DIS structure functions. At NEik accuracy, in addition to corrections arising from the gluon background field of the target, DIS structure functions receive contributions from the $t$-channel quark exchanges, represented by insertions of the quark background field of the target. The latter provide the lowest order contributions in $\alpha_s$ at NEik accuracy. We show that the NLO corrections to the longitudinal NEik structure functions are finite, whereas those to the transverse NEik structure functions exhibit rapidity and ultraviolet (UV) divergences. We analyze these divergences and extract the finite contributions.

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arXiv2026

Reggeization of quarks from next-to-eikonal high-energy QCD

We develop a comprehensive Wilson-line formulation of quark Reggeization in QCD. Starting from a next-to-eikonal operator built from a semi-infinite Wilson line and a background-quark insertion, we identify an interpolating operator for the Reggeized quark and derive its nonlinear rapidity evolution using the background-field method. In the dilute regime, its positive-signature component exhibits Regge-pole evolution governed by the quark Regge trajectory, whereas the negative-signature sector displays mixing between quark and gluon degrees of freedom, in accordance with its known Regge-cut structure. In the planar limit, this mixing is suppressed, and Reggeization emerges without an explicit signature projection, recovering signature degeneracy. We illustrate the universality of the construction by extracting the same Reggeized-quark operator from a more general Wilson-line operator describing a gluon-to-quark transition. Furthermore, we extend the formalism to massive quarks, deriving a coordinate-space evolution kernel whose Fourier transform reproduces the massive-quark Regge trajectory. Finally, from the leading operator-mixing structure of the evolution equation and signature arguments, we show that the Reggeized-quark interpolating operator is expected to remain an eigenstate of the rapidity evolution up to next-to-leading logarithmic accuracy.

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arXiv2026

Quark Reggeization in QCD from the Wilson line formalism

We establish a Wilson-line formulation of quark Reggeization in QCD. An interpolating operator for the Reggeized quark is identified in terms of semi-infinite Wilson lines, and its nonlinear rapidity evolution is derived. We provide strong evidence that this operator remains an eigenstate of the rapidity evolution up to next-to-leading logarithmic accuracy. Within the leading logarithmic accuracy, we explicitly recover the one-loop quark Regge trajectory. Our results provide a first-principles operator framework for quark Reggeization and pave the way for a systematic all-order description of high-energy QCD amplitudes with $t$-channel quark exchange in terms of Wilson lines.

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arXiv2026

Quantum entanglement in electron-nucleus collisions: Role of the linearly polarized gluon distribution

We calculate the spin density matrix of a back-to-back quark-antiquark pair inclusively produced in electron-nucleus scattering, taking into account the gluon saturation effect and the linearly polarized gluon distribution. We then investigate concurrence and stabilizer R\'enyi entropy, quantifying entanglement, Bell-nonlocality, and magic. We find that the linearly polarized gluon distribution tends to enhance the entanglement of a heavy quark pair when the total and relative transverse momenta of the pair are orthogonal.

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arXiv2026

Deeply virtual meson production at HERA and at the EIC within the Color Glass Condensate EFT

Continuing our previous study of Deeply Virtual Meson Production (DVMP) at twist-3 accuracy, we derive compact expressions for all helicity amplitudes. We perform a phenomenological analysis of the helicity-amplitude ratio $\mathcal{A}^{11}/\mathcal{A}^{00}$ and of the spin-density matrix element $r_{00}^{04}$ within the Color Glass Condensate framework. Small-$x$ evolution is incorporated by numerically solving the running-coupling-and-collinearly-improved Balitsky-Kovchegov and Balitsky-Fadin-Kuraev-Lipatov equations with the McLerran-Venugopalan model as the initial condition. By capturing a relevant subset of next-to-leading order corrections, we provide the most theoretically accurate description of these observables to date. Our results are compared to HERA data, and predictions are presented for electron-lead collisions at the future Electron-Ion Collider. We discuss the impact of non-linear effects at low photon virtuality and the role of genuine higher-twist contributions associated with light vector meson distribution amplitudes, corresponding to higher-Fock-state components of the projectile.

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arXiv2026

Complete NLO BFKL impact factors for quarkonium hadroproduction in NRQCD: the case of ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$ states

We present the first complete next-to-leading-order calculation of the impact factors for hadroproduction of the ${}^1S_0^{[1]}$, ${}^1S_0^{[8]}$, and ${}^3S_1^{[8]}$ NRQCD states within the BFKL formalism. We complete the recent virtual-correction computation presented in JHEP 12 (2024) 129 by that of the real-emission contributions. We observe the cancellation of the soft divergences between these real- and virtual-emission contributions and we note that the surviving collinear singularities are compatible with factorisation up to one loop for a novel class of processes where BFKL resummation can be applied. Our work indeed represents the first complete NLO quarkonium impact factor in the BFKL framework and paves the way to first next-to-leading-logarithmic-precision studies for hadroproduction of forward-backward quarkonium associated production at hadron colliders.

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arXiv2025

Next-to-Leading Order corrections to the Next-to-Eikonal DIS structure functions

We compute next-to-leading order (NLO) corrections to next-to-eikonal (NEik) quark background contributions to DIS structure functions. Among NEik corrections, $t$-channel quark exchanges provide the lowest order contributions in $\alpha_s$, and can be represented as insertions of the quark background field of the target. At NLO, we compute NEik corrections induced by both quark and gluon background fields, and suppressed by an explicit factor of $\alpha_s$. We show that the NLO corrections to the NEik longitudinal structure function are finite, while those to the NEik transverse structure function exhibit rapidity and UV divergences. These divergences are analyzed, and the finite contributions are extracted.

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arXiv2025

Exclusive photoproduction of a $\pi^0\gamma $ pair in the saturation framework

We consider the exclusive photoproduction of a $\pi^0 \gamma$ pair with large invariant mass, as a promising channel to study the effects of gluon saturation. It has recently been demonstrated that this process is incompatible with a collinear factorization approach in terms of generalized parton distributions (GPDs) at the leading twist. In such a situation, a (generalized) $k_T$-dependent factorization at small $x$ is a valid alternative approach. We perform this calculation using the shockwave formalism, which resums multiple gluon exchanges between the projectile and the dense nuclear target. We find that the polarized amplitude changes sign as a function of back-to-back transverse momentum $|\vec{p}_t|$ of the pion-photon pair, resulting in a dip-like structure in the fully differential cross section as a function of $|\vec{p}_t|$.

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arXiv2025

Spin-spin entanglement in diffractive heavy quark production

We calculate the spin density matrix of a heavy quark-antiquark pair ($b\bar{b}$, $c\bar{c}$ or $s\bar{s}$) diffractively produced in Deep Inelastic Scattering and Ultraperipheral Collisions. We show that the Pomeron exchange leaves characteristic imprints on the entanglement pattern between the quark and the antiquark. For the longitudinally polarized virtual photon, the pair always exhibits maximal entanglement and maximal violation of the Bell-CHSH inequality. For the transversely polarized photon, the pair is always entangled and Bell-violating, reaching maximal entanglement and maximal violation simultaneously when the transverse momentum approximately equals the quark mass.

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arXiv2025

High-energy factorization via eigenfunctions of the next-to-leading-order BFKL kernel

We present a general formula for the amplitude of forward exclusive hadronic processes in the semihard regime of perturbative Quantum Chromodynamics (QCD), by means of the {\em next-to-leading order} eigenfunctions of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) kernel, as constructed by Chirilli and Kovchegov. We discuss some formal subtleties in the check of compatibility with the similar formula based on the use of the {\em leading-order} BFKL eigenfunctions. Finally, in the specific case of the electroproduction of two light vector mesons, we consider the numerical stability of the amplitude when one or the other set of eigenfunctions is adopted.

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arXiv2025

The real corrections to the Higgs impact factor at next-to-leading order with finite top mass

This work presents the computation of real corrections to the impact factor for forward Higgs boson production, preserving the full dependence on the top-quark mass. The results are shown to align with the BFKL factorization framework, particularly in reproducing the expected rapidity divergence. Additionally, the subtraction of this divergence has been demonstrated using the appropriate counterterm within the BFKL scheme. In the infinite-top-mass limit, our findings reproduce the previously established result.

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arXiv2025

Exclusive leptoproduction of a light vector meson at the twist-3 in a GTMD framework

We provide the most general description of the exclusive leptoproduction of a light vector meson, at high center-of-mass energy, within the CGC/shockwave formalism. We keep a twist-3 accuracy in $s$ channel, thus being able to describe all possible helicity amplitudes, including the ones for the production of a transversally polarized meson. In this latter case, we overcome the well-known issue of endpoint singularities by promoting the GPD to a GTMD given by matrix elements of dipole and double dipole operators. The all-twists treatment of the proton (nucleon) target allow to safely twist-expand the general vacuum-to-meson matrix elements. Therefore, unlike previous attempts in the modified perturbative approach, our final results are expressed in terms of the twist-3 collinear distribution amplitudes, introduced in the context of the higher-twist collinear formalism.

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arXiv2024

Heavy-quark mass effects in off-light-cone distributions

We compute the one-loop correction to the forward matrix element of an off-light-cone bi-local quark correlator characterised by a space-like separation $z^2$ in the presence of heavy quarks with mass $m$. This calculation allows us to extract the one-loop matching kernel, necessary to connect quasi and pseudo-distributions to collinear parton distribution functions (PDFs), accounting for heavy-quark mass effects. Our result is exact in that it includes all powers of $z^2m^2$ at one loop in $\alpha_s$. In the limit $z^2m^2\rightarrow 0$, it consistently reduces to the known massless result. We also carry out an implementation of our expression, which allows us to compute the charm pseudo-distribution of the proton given its PDF. We finally comment on the quantitative impact of heavy-quark mass corrections.

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arXiv2024

Prospective report of the French QCD community to the ESPPU 2025 with respect to the program of the LHC Run 5 and beyond and future colliders at CERN

This document summarizes the prospective physics plans of the French QCD and Heavy-Ion community, including the experimental programs at the LHC Run 5 and beyond and future colliders at CERN, within the context of the French contribution to the update of the European Strategy in Particle Physics (ESPPU 2025), as discussed in the workshop on European Strategy for Particle Physics Update 2025 organised by the QCD GdR in Oct. 2024.

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arXiv2024

The next-to-leading order Higgs impact factor at physical top mass: The real corrections

We compute the real corrections to the impact factor for the production of a forward Higgs boson, retaining full top-mass dependence. We demonstrate that the rapidity divergence is the one predicted by the BFKL factorization and perform the explicit subtraction in the BFKL scheme. We show that the IR-structure of the impact factor is the expected one and that, in the infinite-top-mass approximation, the previously known result is recovered. We also verify that the impact factor vanishes when the transverse momenta of the $t$-channel Reggeon goes to zero, in agreement with its gauge-invariant definition, exploiting the $m_t \rightarrow \infty$ expansion up to the next-to-next-to-leading order.

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arXiv2024

Gluon tomography through diffractive processes in a saturation framework

We discuss a series of results aimed at bringing saturation physics and gluon tomography into an era of precision. In particular, the NLO treatment of diffractive: 1) exclusive dijet, 2) exclusive longitudinally polarized light vector meson and 3) semi-inclusive single or double hadron photo- or electroproduction with large $p_T$, on a nucleon or a nuclei. Finally, we discuss the more complicated 4) exclusive transversely polarized light vector meson production, which starts at the next-to-leading power and therefore requires a beyond leading twist treatment. This new class of processes provides an access to precision physics of gluon saturation dynamics, with very promising future phenomenological studies at the EIC, or, at the LHC in $p A$ and $A A$ scattering, using Ultra Peripheral Collisions (UPC).

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arXiv2024

Higgs production at NLL accuracy in the BFKL approach

Precision physics in the Higgs sector has been one of the main challenges of particle physics in the recent years. The pure fixed-order calculations entering the collinear factorization framework, which have been pushed up to next-cube-leading-order, are not able to describe the entire kinematic spectrum. In particular sectors, they have to be necessarily enhanced by all-order resummations. In the so-called semi-hard regime, large energy-type logarithms spoil the perturbative convergence of the series and must be resummed to all orders. This resummation is a core ingredient for a correct description of the inclusive hadroproduction of a forward Higgs boson in the limit of small Bjorken $x$, as well as for a precision study of inclusive forward emissions of a Higgs boson in association with a backward identified object. A complete resummation for these processes can be achieved at the at next-to-leading logarithmic accuracy thanks to the Balitsky-Fadin-Kuraev-Lipatov approach. In the present work we present and discuss a series of recent phenomenological results within a partial next-to-leading accuracy. They include the analysis of rapidity and azimuthal-angle differential rates for Higgs plus jet and Higgs plus charm reactions in forward and ultraforward directions of rapidity at the LHC.

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arXiv2024

Towards Higgs and $Z$ boson plus jet distributions at NLL/NLO$^+$

We present novel predictions for rapidity and transverse-momentum distributions sensitive to the emission of a Higgs boson accompanied by a jet in proton collisions, calculated within the NLO fixed order in QCD and matched with the next-to leading energy-logarithmic accuracy. We also highlight first advancements in the extension of our analysis to the $Z$-boson case. We come out with the message that the improvement of fixed-order calculations on Higgs- and $Z$-boson plus jet distributions is a required step to reach the precision level of the description of observables relevant for Higgs and electroweak physics at current LHC energies and nominal FCC ones.

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