arXiv subjects

Giovanni Antonio Chirilli

Publications and source records attributed to Giovanni Antonio Chirilli.

10 recordsLinked to original sources

arXiv2026

Sub-eikonal Structure of High-Energy Deep-Inelastic Scattering

I develop a mixed-space formulation of high-energy deep-inelastic scattering in the shock-wave formalism at sub-eikonal order. Starting from the quark propagator in the background field, I derive the corresponding mixed-space Feynman rules from the LSZ reduction formula in the presence of a shock wave, including the instantaneous contributions generated by the presence of the shock-wave. As a first check of the formalism, I rederive the standard eikonal dipole cross sections for longitudinal and transverse photon polarization. I then use the same framework to compute the first sub-eikonal corrections to the dipole structure functions. In particular, I obtain the sub-eikonal contributions to the longitudinal and transverse structure functions $F_L$ and $F_T$, as well as to the helicity-sensitive asymmetry related to $g_1$, and organize the result in terms of a gauge-invariant operator basis. The resulting operator combinations are naturally written in dipole form and vanish in the zero-dipole-size limit, making the unitarity property and the small-dipole behavior manifest. Finally, I analyze the divergence structure of the sub-eikonal dipole corrections. I show that the longitudinal structure function is finite at this order, whereas the transverse and helicity-dependent structure functions contain only logarithmic divergences.

hep-ph↗

arXiv2026

From Sub-eikonal DIS to Quark Distributions and their High-Energy Evolution

Relating the high-energy dipole description of deep-inelastic scattering to the standard light-ray operator formulation at finite Bjorken $x_B$ is essential for connecting the small-$x$ framework to the usual partonic description. I demonstrate that this connection already emerges at the first sub-eikonal order. At the differential level, the first sub-eikonal correction is governed by a quark TMD-like light-ray operator. In the inclusive limit, after complete phase-space integration, it reconstructs the standard nonlocal quark and helicity distributions at nonzero $x_B$. I then show independently that the same inclusive operator content follows from the high-energy limit of the leading-twist non-local operator product expansion, thereby establishing an explicit operator-level bridge between the shock-wave formalism and the non-local light-cone expansion. I further discuss the high-energy evolution of the corresponding operators at $x_B=0$. Rewriting the evolution equations in terms of dipole-type operator combinations, I identify an operator basis whose bilocal building blocks vanish in the zero-dipole-size limit, making the small-dipole behavior and the leading-logarithmic structure manifest. In the double-logarithmic approximation the evolution equations admit the usual mixed longitudinal-transverse Bessel-type solution when the transverse phase space is treated independently. When the transverse phase space is instead constrained by longitudinal ordering, the second logarithm is converted into a logarithm of energy, and in the symmetric double-logarithmic regime one recovers the fixed-coupling Kirschner-Lipatov exponent with the full finite-$N_c$ color factor $C_F$.

hep-ph↗

arXiv2023

Pseudo and quasi quark PDF in the BFKL approximation

I examine the high-energy behavior of the Ioffe-time distribution for the quark bi-local space-like separated operator using the high-energy operator product expansion. These findings have significant implications for lattice calculations, which require extrapolation for large Ioffe-time values. I perform an explicit Fourier transform for both the pseudo-PDF and quasi-PDF, and investigate their behavior within the first two leading twist contributions. I show that the quark pseudo-PDF captures the BFKL resummation (resummation of all twists) and exhibits a rising behavior for small $x_B$ values, while the quasi-PDF presents a different behavior. I demonstrate that an appropriate small-$x_B$ behavior cannot be achieved solely through DGLAP dynamics, emphasizing the importance of all-twist resummation. This study provides valuable insights into quark non-local operators' high-energy behavior and the limitations of lattice calculations in this context.

hep-ph↗

arXiv2023

Small-x behavior of quark pseudo- and quasi-PDFs

The pseudo- and the quasi-PDFs defined through space-like separated bilocal operators allow direct access to the parton distribution functions (PDFs) from first principles within lattice gauge theory. This formalism, however, leaves the small Bjorken $x$ regime inaccessible. In view of the future Electron-Ion Collider, the study of the PDFs at small-$x$ is timely. For this reason, we calculate the quark pseudo- and quasi-PDF in the high-energy limit and show that they have rather different behavior. In particular, we show that the quark pseudo-PDF has the expected small-$x$ rising behavior while the quasi-PDF becomes ill-defined at this regime. Moreover, we also obtain the leading and next-to-leading twist corrections for each of the two distributions. For the pseudo-PDF, although the first two twist corrections follow the same small-$x$ behavior as the one with BFKL resummation, unexpectedly, the next-to-leading correction appears to be only a small shift with respect to the leading one. Unlike the pseudo-PDF, the quasi-PDF exhibits rather unusual behavior at small-$x$.

hep-ph↗

arXiv2022

Pseudo and quasi gluon PDF in the BFKL approximation

I study the behavior of the gauge-invariant gluon bi-local operator with space-like separation at large longitudinal distances. Performing the Fourier transform, I also calculate the behavior of the pseudo and quasi gluon PDF at low Bjorken $x$ and compare it with the leading and next-to-leading twist approximation. I show that the pseudo-PDF and quasi-PDF are very different in this regime and that the higher twist corrections of the quasi-PDF come in not as inverse powers of $P$ but as inverse powers of $x_B P$.

hep-ph↗

arXiv2021

High-energy Operator Product Expansion at sub-eikonal level

The high energy Operator Product Expansion for the product of two electromagnetic currents is extended to the sub-eikonal level in a rigorous way. I calculate the impact factors for polarized and unpolarized structure functions, define new distribution functions, and derive the evolution equations for unpolarized and polarized structure functions in the flavor singlet and non-singlet case.

hep-ph↗

arXiv2019

Sub-eikonal corrections to scattering amplitudes at high energy

Most of the progress in high-energy Quantum Chromodynamics has been obtained within the eikonal approximation and infinite Wilson-line operators. Evolution equations of Wilson lines with respect to the rapidity parameter encode the dynamics of the hadronic processes at high energy. However, even at high energy many interesting aspects of hadron dynamics are not accessible within the eikonal approximation, the spin physics being an obvious example. The higher precision reached by the experiments and the possibility to probe spin dynamics at future Electron Ion Colliders make the study of deviations from eikonal approximation especially timely. In this paper I derive the sub-eikonal quark and gluon propagators which can serve as a starting point of studies of these effects.

hep-ph↗

arXiv2012

High-Energy QCD factorization from DIS to pA collisions

The high-energy QCD factorization for Deep Inelastic Scattering and for proton-nucleus collisions using Wilson line formalism and factorization in rapidity is discussed. We show that in DIS the factorization in rapidity reduces to the $k_{\rm T}$-factorization when the 2-gluon approximation is applied, provided that the composite Wilson line operator is used in the high-energy Operator Product Expansion. We then show that the inclusive forward cross-section in proton-nucleus collisions factorizes in parton distribution functions, fragmentation functions and dipole gluon distribution function at one-loop level.

hep-ph↗

arXiv2010

High-energy amplitudes and impact factors at next-to-leading order

To study scattering amplitudes at high-energy, the T-product of two currents can be expanded in terms of coefficient functions (impact factors) and matrix elements of ``composite color dipoles'' made of Wilson line operators with rapidity cutoff preserving conformal invariance. In the leading order, the high-energy evolution of color dipoles is governed by the non-linear Balitsky-Kovchegov (BK) equation. To describe the high-energy amplitudes in the next-to-leading order (NLO) one needs to know the coefficient function (``impact factor'') and the evolution of corresponding Wilson-line operators. Using the high-energy OPE, we find the next-to-leading order (NLO) correction to the BK equation and calculate the impact factor for virtual photons in deep inelastic scattering.

hep-ph↗

arXiv2010

Small-x Evolution in the Next-to-Leading Order

After a brief introduction to Deep Inelastic Scattering in the Bjorken limit and in the Regge Limit we discuss the operator product expansion in terms of non local string operator and in terms of Wilson lines. We will show how the high-energy behavior of amplitudes in gauge theories can be reformulated in terms of the evolution of Wilson-line operators. In the leading order this evolution is governed by the non-linear Balitsky- Kovchegov (BK) equation. In order to see if this equation is relevant for existing or future deep inelastic scattering (DIS) accelerators (like Electron Ion Collider (EIC) or Large Hadron electron Collider (LHeC)) one needs to know the next-to-leading order (NLO) corrections. In addition, the NLO corrections define the scale of the running-coupling constant in the BK equation and therefore determine the magnitude of the leading-order cross sections. In Quantum Chromodynamics (QCD), the next-to-leading order BK equation has both conformal and non-conformal parts. The NLO kernel for the composite operators resolves in a sum of the conformal part and the running-coupling part. The QCD and ${\cal N}=4$ SYM kernel of the BK equation is presented.

hep-ph↗