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Giovanni Salmè

Publications and source records attributed to Giovanni Salmè.

16 recordsLinked to original sources
arXiv2026

Double parton scattering off nuclei and the double-EMC effect

The double-parton scattering process off light and heavy nuclei is proposed as an effective tool to open a novel window for accurately studying the effects of nuclear binding on the internal structure of the nucleon, in the spirit of the European Muon Collaboration (EMC) effect. The key ingredient is the actual calculation of nuclear double-parton distributions that contain information about double-parton distributions and generalized-parton distributions of the nucleon, folded with nuclear light-front distributions. It allows to introduce a new quantity, which we call double-EMC ratio that appears to be much more sensitive than the standard EMC effect to both the nucleon partonic structure and to the nuclear binding. Hence, it could help solving long-standing questions about how nucleons change when they are bound in atomic nuclei.

hep-ph↗
arXiv2025

Theoretical insights on nuclear double parton distributions

In this paper, we address double parton scattering (DPS) in pA collisions. Within the Light-Front approach, we formally derive the two contributions to the nuclear double parton distribution (DPD), namely: DPS1, involving two partons from the same nucleon, and DPS2, where the two partons belong to different parent nucleons. We then generalize the sum rule for hadron DPDs to the nuclear case and analytically show how all contributions combine to give the expected results. In addition partial sum rules for the DPDs related to DPS1 and DPS2 mechanisms are discussed for the first time. The deuteron system is considered for the first calculation of the nuclear DPD by using a realistic wave function obtained from the very refined nucleon-nucleon AV18 potential, embedded in a rigorous Poincaré covariant formalism. Results are used to test sum rules and properly verify that DPS1 contribution compares with the DPS2 one, although smaller. We also introduce EMC-like ratios involving nuclear and free DPDs to address the potential role of DPS in understanding in depth the EMC effect.

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arXiv2024

$^3$He spin-dependent structure functions within the relativistic Light-Front Hamiltonian dynamics

$^3$He spin-dependent structure functions, $g^3_1(x)$ and $g^3_2(x)$, which parametrize the hadronic tensor in polarized deep-inelastic scattering, were evaluated within the Poincaré covariant light-front framework. The Bakamjian-Thomas construction of the Poincaré generators allows us to make use of a realistic $^3$He wave function, obtained from refined nuclear phenomenological potentials. The same approach was already successfully applied to the $^3$He and $^4$He unpolarized deep-inelastic scattering. To investigate the neutron polarized structure functions, $g^n_1$ and $g^n_2$, a readily implementable procedure, aimed at extracting the neutron spin structure functions from those of $^3$He, is shown to hold. Moreover, the first moment of $g^3_1(x)$ was evaluated, aiming at providing a valuable check of the Bjorken sum rule. The present analysis is relevant for experiments nvolving polarized beams planned at the future facilities, like the Electron Ion Colliders.

nucl-th↗
arXiv2023

The EMC effect for few-nucleon bound systems in Light-Front Hamiltonian Dynamics

The light-front formalism for a covariant description of the European Muon Collaboration (EMC) effect, already applied to $^3$He, is formally extended to any nucleus, and used for actually calculating the $^3$H and $^4$He cases. The realistic and accurate nuclear description of few-nucleon bound systems, obtained with both phenomenological and chiral potentials, has been properly combined with the Poincare' covariance and macroscopic locality, automatically satisfying both number of particles and momentum sum rule. While retaining the on-mass-shell nucleon structure functions, one is then able to predict a sizable EMC effect for $^4$He, as already observed for $^3$He. Moreover, the impact on the EMC effect of both i) the short-range correlations, such as those generated by modern nuclear interactions, and ii) the ratio between the neutron and proton structure functions has been studied. The short-range correlations generated by retaining only the standard nuclear degrees of freedom act on the depth of the minimum in the EMC ratio, while the uncertainties linked to the ratio of neutron to proton structure functions are found to be very small. These light-front results facilitates ascribing deviations from experimental data due to genuine QCD effects, not included in a standard nuclear description, and initiating unbiased investigations.

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arXiv2021

Light-Front Transverse Momentum Distributions for ${\cal J}$=1/2 Hadronic Systems in Valence Approximation

The semi-inclusive correlator for a ${\cal J}$=1/2 bound-system, composed by A spin-1/2 fermions, is linearly expressed in terms of the light-front Poincaré covariant spin-dependent spectral function, in valence approximation. The light-front spin-dependent spectral function is fully determined by six scalar functions that allow for a complete description of the six T-even transverse-momentum distributions, suitable for a detailed investigation of the dynamics inside the bound system. The application of the developed formalism to a case with a sophisticated dynamical content, like $^3$He, reaches two goals: (i) to illustrate a prototype of an investigation path for gathering a rich wealth of information on the dynamics and also finding valuable constraints to be exploited from the phenomenological standpoint; (ii) to support for the three-nucleon system a dedicated experimental effort for obtaining a detailed 3D picture in momentum space. In particular, the orbital-angular momentum decomposition of the bound state can be studied through the assessment of relations among the transverse-momentum distributions, as well as the relevance of the relativistic effect generated by the implementation of macrocausality. A fresh evaluation of the longitudinal and transverse polarizations of the neutron and proton is also provided, confirming essentially the values used in the standard procedure for extracting the neutron structure functions from both deep-inelastic scattering and semi-inclusive reactions, in the same kinematical regime.

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arXiv2021

Fermion and Photon gap-equations in Minkowski space within the Nakanishi Integral Representation method

The approach based on the Nakanishi integral representation of n-leg transition amplitudes is extended to the treatment of the self-energies of a fermion and an (IR-regulated) vector boson, in order to pave the way for constructing a comprehensive application of the technique to both gap- and Bethe-Salpeter equations, in Minkowski space. The achieved result, namely a 6-channel coupled system of integral equations, eventually allows one to determine the three Källén-Lehman weights for fully dressing the propagators of fermion and photon. A first consistency check is also provided. The presented formal elaboration points to embed the characteristics of the non-perturbative regime at a more fundamental level. It yields a viable tool in Minkowski space for the phenomenological investigation of strongly interacting theories, within a QFT framework where the dynamical ingredients are made transparent and under control.

hep-ph↗
arXiv2020

EMC effect, few-nucleon systems and Poincaré covariance

An approach for a Poincaré covariant description of nuclear structure and of lepton scattering off nuclei is proposed within the relativistic Hamiltonian dynamics in the light-front form. Indeed a high level of accuracy is needed for a comparison with the increasingly precise present and future experimental data at high momentum transfer. Therefore, to distinguish genuine QCD effects or effects of medium modified nucleon structure functions from conventional nuclear structure effects, the commutation rules between the Poincaré generators should be satisfied. For the first time in this paper a proper hadronic tensor for inclusive deep inelastic scattering of electrons off nuclei is derived in the impulse approximation in terms of the single nucleon hadronic tensor. Our approach is based : i) on a light-front spectral function for nuclei, obtained taking advantage of the successful non-relativistic knowledge of nuclear interaction, and ii) on the free current operator that, if defined in the Breit reference frame with the momentum transfer, $\bf q$, parallel to the $z$ axis, fulfills Poincaré covariance and current conservation. Our results can be generalized : i) to exclusive processes or to semi-inclusive deep inelastic scattering processes; ii) to the case where the final state interaction is considered through a Glauber approximation; iii) to finite momentum transfer kinematics. As a first test, the hadronic tensor is applied to obtain the nuclear structure function F$_2^A$ and to evaluate the EMC effect for $^3He$ in the Bjorken limit. Encouraging results including only the two-body part of the light-front spectral function are presented.

nucl-th↗
arXiv2019

Few-body systems in Minkowski space: the Bethe-Salpeter Equation challenge

Solving the homogeneous Bethe-Salpeter equation directly in Minkowski space is becoming a very alive field, since, in recent years, a new approach has been introduced, and the reachable results can be potentially useful in various areas of research, as soon as the relativistic description of few-body bound systems is relevant. A brief review of the status of the novel approach, which benefits from the consistent efforts of different groups, will be presented, together with some recent results.

hep-th↗
arXiv2017

Neutron Parton Structure And The Light-Front Spectral Function Of 3He

Semi-inclusive deep inelastic electron scattering off polarized 3He is studied in a non-relativistic framework, using a distorted spin-dependent spectral function for 3He to take care of the final state interaction between the observed pion and the remnant. A simple procedure is shown to be valuable for the extraction of Sivers and Collins asymmetries for the neutron fromthe corresponding asymmetries for 3He. To extend this study in a relativistic framework, a novel approach for a Poincaré covariant description of nuclear dynamics is presented, based on the light-front Hamiltonian dynamics. The key quantity is the light-front spectral function, where both normalization and momentum sum rule can be satisfied at the same time. Preliminary results are discussed for an initial analysis of the role of relativity in the EMC effect in 3He, and the generalization of the procedure for the extraction of neutron asymmetries within the light-front dynamics is outlined.

nucl-th↗
arXiv2017

Three--Dimensional parton structure of light nuclei

Two promising directions beyond inclusive deep inelastic scattering experiments, aimed at unveiling the three dimensional structure of the bound nucleon, are reviewed, considering in particular the $^3$He nucleus. The 3D structure in coordinate space can be accessed through deep exclusive processes, whose non-perturbative part is encoded in generalized parton distributions (GPDs). In this way, the distribution of partons in the transverse plane can be obtained. As an example, coherent deeply virtual Compton scattering (DVCS) off $^3$He nuclei, important to access the neutron GPDs, will be discussed. In Impulse Approximation (IA), the sum of two GPDs of $^3$He, $H$ and $E$, at low momentum transfer, turns out to be dominated by the neutron contribution. Besides, a technique, able to take into account the nuclear effects included in the Impulse Approximation analysis, has been developed. The spin dependent GPD $\tilde H$ of $^3$He is also found to be largely dominated, at low momentum transfer, by the neutron contribution. Semi-inclusive deep inelastic scattering processes access the momentum space 3D structure parameterized through transverse momentum dependent parton distributions. A distorted spin-dependent spectral function has been recently introduced for $^3$He, in a non-relativistic framework, to take care of the final state interaction between the observed pion and the remnant in semi-inclusive deep inelastic electron scattering off transversely polarized $^3$He. The calculation of the Sivers and Collins single spin asymmetries for $^3$He, and a straightforward procedure to effectively take into account nuclear dynamics and final state interactions, will be reviewed. The Light-front dynamics generalization of the analysis is also addressed.

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arXiv2016

Polarized $^3$He target and final state interactions in SiDIS

Jefferson Lab (JLab) is starting a wide experimental program aimed at studying the neutron's structure, with a great emphasis on the extraction of the parton transverse-momentum distributions (TMDs). To this end, Semi-inclusive deep-inelastic scattering (SiDIS) experiments on polarized $^3$He will be carried out, providing, together with proton and deuteron data, a sound flavor decomposition of the TMDs. Given the expected high statistical accuracy, it is crucial to disentangle nuclear and partonic degrees of freedom to get an accurate theoretical description of both initial and final states. In this contribution, a preliminary study of the Final State Interaction (FSI) in the standard SiDIS, where a pion (or a Kaon) is detected in the final state is presented, in view of constructing a realistic description of the nuclear initial and final states.

nucl-th↗
arXiv2016

Light-Front spin-dependent Spectral Function and Nucleon Momentum Distributions for a Three-Body System

Poincare' covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian-Thomas construction of the Poincare' generators, that allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, like the ones needed for evaluating the EMC effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, since remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. It is also shown a straightforward generalization of the definition of the light-front spectral function to an A-nucleon system.

nucl-th↗
arXiv2016

The 3He spectral function in light-front dynamics

A distorted spin-dependent spectral function for 3He is considered for the extraction of the transverse-momentum dependent parton distributions in the neutron from semi-inclusive deep inelastic electron scattering off polarized 3He at finite momentum transfers, where final state interactions are taken into account. The generalization of the analysis to a Poincaré covariant framework within the light-front dynamics is outlined.

nucl-th↗
arXiv2014

A Light-Front approach to the $^3$He spectral function

The analysis of semi-inclusive deep inelastic electron scattering off polarized $^3$He at finite momentum transfers, aimed at the extraction of the quark transverse-momentum distributions in the neutron, requires the use of a distorted spin-dependent spectral function for $^3$He, which takes care of the final state interaction effects. This quantity is introduced in the non-relativistic case, and its generalization in a Poincaré covariant framework, in plane wave impulse approximation for the moment being, is outlined. Studying the light-front spin-dependent spectral function for a J=1/2 system, such as the nucleon, it is found that, within the light-front dynamics with a fixed number of constituents and in the valence approximation, only three of the six leading twist T-even transverse-momentum distributions are independent.

nucl-th↗
arXiv2011

Two-body scattering states in Minkowski space and the Nakanishi integral representation onto the null plane

The Nakanishi perturbative integral representation of the four-dimensional T-matrix is investigated in order to get a workable treatment for scattering states, solutions of the inhomogeneous Bethe-Salpeter Equation, in Minkowski space. The projection onto the null-plane of the four-dimensional inhomogeneous Bethe-Salpeter Equation plays a key role for devising an equation for the Nakanishi weight function (a real function), as in the homogeneous case that corresponds to bound states and it has been already studied within different frameworks. In this paper, the whole formal development is illustrated in detail and applied to a system, composed by two massive scalars interacting through the exchange of a massive scalar. The explicit expression of the scattering integral equations are also obtained in ladder approximation, and, as simple applications of our formalism, some limiting cases, like the zero-energy limit and the Wick-Cutkosky model in the continuum, are presented.

hep-ph↗