arXiv subjects

Leandro Cieri

Publications and source records attributed to Leandro Cieri.

At least 19 recordsLinked to original sources

arXiv2026

Understanding IR singularities in the Loop-Tree Duality

One of the main advantages of the Loop-Tree Duality representation of scattering amplitudes is that it makes the origin of infrared and threshold singularities particularly transparent. This talk reviews recent progress in describing how singularities emerge and cancel at the level of scattering and vacuum amplitudes, discusses a novel strategy to efficiently construct finite integrals, and presents a complementary perspective based on encoding the underlying causal and singular structure in terms of qubits and quantum circuits.

hep-ph↗

arXiv2026

Four fermion soft emission in QCD hard scattering

We consider the radiation of two distinguishable soft quark-antiquark pairs ($\mathrm{q}\bar{\mathrm{q}}\mathrm{Q}\bar{\mathrm{Q}}$) in a generic process for multiparton hard scattering in QCD. We evaluate the corresponding soft current at tree level in terms of an independent-emission contribution and an irreducible correlation component, which includes strictly non-abelian terms and also terms with an abelian character. The squared current for soft $\mathrm{q}\bar{\mathrm{q}}\mathrm{Q}\bar{\mathrm{Q}}$ emission produces colour dipole and colour tripole interactions between the hard-scattering partons, with structures similar to soft gluon-quark-antiquark emission. The colour tripole interactions are odd under charge conjugation and lead to charge asymmetry effects. We extend our analysis by including QED interactions, the emission of two distinguishable soft lepton-antilepton pairs, and mixed quark-antiquark-lepton-antilepton soft emission.

hep-ph↗

arXiv2025

Transverse-momentum resummation at mixed QCD$\otimes$QED NNLL accuracy for Z boson production at hadron colliders

We consider the transverse momentum ($q_T$) distribution of neutral charged bosons at hadron colliders. We perform the resummation of the logarithmically-enhanced effects due to simultaneous QCD and QED initial-state radiation, up to mixed next-to-next-to-leading logarithmic (NNLL) accuracy. We study the impact of such mixed QCD$\otimes$QED resummed contributions on top of pure QCD corrections, finding percent-level effects.

hep-ph↗

arXiv2025

Gauge theory approach to describe ice crystals habit evolution in ice clouds

Ice clouds, particularly cirrus clouds, significantly influence Earth's radiative balance but remain poorly characterized in current climate models. A major uncertainty arises from the variability of their microphysical properties, especially the evolution of ice crystal habits under depositional growth. We propose a heuristic method to describe habit evolution based on four fundamental shapes identified in the literature and from in situ observations: droxtals, plates, columns, and rosettes. These represent the primary forms that are relevant under depositional growth, excluding aggregation. In this study, we employ a non-Abelian gauge theory within a field-theoretical framework, imposing an SU(2) $\otimes$ U(1) symmetry on the fields associated with each habit probability growth. This symmetry enables the derivation of a modified system of coupled Fokker-Planck equations, capturing the stochastic growth dynamics of ice crystals while incorporating phenomenological mutual influences among habits. This framework outlines a novel theoretical direction for integrating symmetry principles and field-theoretical tools into the modelling of habit dynamics in ice clouds.

physics.ao-ph↗

arXiv2024

Vacuum amplitudes and time-like causal unitary in the loop-tree duality

We present the first proof-of-concept application to decay processes at higher perturbative orders of LTD causal unitary, a novel methodology that exploits the causal properties of vacuum amplitudes in the loop-tree duality (LTD) and is directly well-defined in the four physical dimensions of the space-time. The generation of loop- and tree-level contributions to the differential decay rates from a kernel multiloop vacuum amplitude is shown in detail, and explicit expressions are presented for selected processes that are suitable for a lightweight understanding of the method. Specifically, we provide a clear physical interpretation of the local cancellation of soft, collinear and threshold singularities, and of the local renormalisation of ultraviolet singularities. The presentation is illustrated with numerical results that showcase the advantages of the method.

hep-ph↗

arXiv2024

Catani's generalization of collinear factorization breaking

We consider the most general form of soft and collinear factorization for hard-scattering amplitudes to all orders in perturbative Quantum Chromodynamics. Specifically, we present the generalization of collinear factorization to configurations with several collinear directions, where the most singular behaviour is encoded by generalized collinear splitting amplitudes that manifestly embed the breaking of strict collinear factorization in space-like collinear configurations. We also extend the analysis to the simultaneous soft-collinear factorization with multiple collinear directions where na\"{\i}ve multiplicative factorization does not hold. As an illustrative example of factorization breaking, we present explicit results at the one-loop level in the soft-collinear limit.

hep-ph↗

arXiv2024

Loop Feynman integration on a quantum computer

This work investigates in detail the performance and advantages of a new quantum Monte Carlo integrator, dubbed Quantum Fourier Iterative Amplitude Estimation (QFIAE), to numerically evaluate for the first time loop Feynman integrals in a near-term quantum computer and a quantum simulator. In order to achieve a quadratic speedup, QFIAE introduces a Quantum Neural Network (QNN) that efficiently decomposes the multidimensional integrand into its Fourier series. For a one-loop tadpole Feynman diagram, we have successfully implemented the quantum algorithm on a real quantum computer and obtained a reasonable agreement with the analytical values. One-loop Feynman diagrams with more external legs have been analyzed in a quantum simulator. These results thoroughly illustrate how our quantum algorithm effectively estimates loop Feynman integrals and the method employed could also find applications in other fields such as finance, artificial intelligence, or other physical sciences.

hep-ph↗

arXiv2023

Two-loop form factors for diphoton production in quark annihilation channel with heavy quark mass dependence

We present the computation of the two-loop form factors for diphoton production in the quark annihilation channel. These quantities are relevant for the NNLO QCD corrections to diphoton production at LHC recently presented in arXiv:2308.10885. The computation is performed retaining full dependence on the mass of the heavy quark in the loops. The master integrals are evaluated by means of differential equations which are solved exploiting the generalised power series technique.

hep-ph↗

arXiv2023

Full top-quark mass dependence in diphoton production at NNLO in QCD

In this paper we consider the diphoton production in hadronic collisions at the next-to-next-to-leading order (NNLO) in perturbative QCD, taking into account for the first time the full top quark mass dependence up to two loops (full NNLO). We show selected numerical distributions, highlighting the kinematic regions where the massive corrections are more significant. We make use of the recently computed two-loop massive amplitudes for diphoton production in the quark annihilation channel. The remaining massive contributions at NNLO are also considered, and we comment on the weight of the different types of contributions to the full and complete result.

hep-ph↗

arXiv2023

Quantum Fourier Iterative Amplitude Estimation

Monte Carlo integration is a widely used numerical method for approximating integrals, which is often computationally expensive. In recent years, quantum computing has shown promise for speeding up Monte Carlo integration, and several quantum algorithms have been proposed to achieve this goal. In this paper, we present an application of Quantum Machine Learning (QML) and Grover's amplification algorithm to build a new tool for estimating Monte Carlo integrals. Our method, which we call Quantum Fourier Iterative Amplitude Estimation (QFIAE), decomposes the target function into its Fourier series using a Parametrized Quantum Circuit (PQC), specifically a Quantum Neural Network (QNN), and then integrates each trigonometric component using Iterative Quantum Amplitude Estimation (IQAE). This approach builds on Fourier Quantum Monte Carlo Integration (FQMCI) method, which also decomposes the target function into its Fourier series, but QFIAE avoids the need for numerical integration of Fourier coefficients. This approach reduces the computational load while maintaining the quadratic speedup achieved by IQAE. To evaluate the performance of QFIAE, we apply it to a test function that corresponds with a particle physics scattering process and compare its accuracy with other quantum integration methods and the analytic result. Our results show that QFIAE achieves comparable accuracy while being suitable for execution on real hardware. We also demonstrate how the accuracy of QFIAE improves by increasing the number of terms in the Fourier series. In conclusion, QFIAE is a promising end-to-end quantum algorithm for Monte Carlo integrals that combines the power of PQC with Fourier analysis and IQAE to offer a new approach for efficiently approximating integrals with high accuracy.

quant-ph↗

arXiv2023

Drell-Yan lepton-pair production: $q_T$ resummation at approximate N$^4$LL+N$^4$LO accuracy

We consider Drell-Yan lepton pairs produced in hadronic collisions. We present high-accuracy QCD predictions for the transverse-momentum ($q_T$) distribution and fiducial cross sections in the small $q_T$ region. We resum to all perturbative orders the logarithmically enhanced contributions up to the next-to-next-to-next-to-next-to-leading logarithmic (N$^4$LL) accuracy and we include the hard-virtual coefficient at the next-to-next-to-next-to-leading order (N$^3$LO) (i.e. $\mathcal{O}(\alpha_S^3)$) with an approximation of the N$^4$LO coefficients. The massive axial-vector and vector contributions up to three loops have also been consistently included. The resummed partonic cross section is convoluted with approximate N$^3$LO parton distribution functions. We show numerical results at LHC energies of resummed $q_T$ distributions for $Z/\gamma^*, W^\pm$ production and decay, including the $W^\pm$ and $Z/\gamma^*$ ratio, estimating the corresponding uncertainties from missing higher orders corrections and from incomplete or missing perturbative information coefficients at N$^4$LL and N$^4$LO. Our resummed calculation has been encoded in the public numerical program DYTurbo.

hep-ph↗

arXiv2023

Combining QED and QCD transverse-momentum resummation for W and Z boson production at hadron colliders

In this article, we consider the transverse momentum ($q_T$) distribution of $W$ and $Z$ bosons produced in hadronic collisions. We combine the $q_T$ resummation for QED and QCD radiation including the QED soft emissions from the $W$ boson in the final state. In particular, we perform the resummation of enhanced logarithmic contributions due to soft and collinear emissions at next-to-leading accuracy in QED, leading-order accuracy for mixed QED-QCD and next-to-next-to-leading accuracy in QCD. In the small-$q_T$ region we consistently include in our results the next-to-next-to-leading order (i.e.\ two loops) QCD corrections and the next-to-leading order (i.e.\ one loop) electroweak corrections. The matching with the fixed-order calculation at large $q_T$ has been performed at next-to-leading order in QCD (i.e.\ at $\mathcal{O}(\alpha_S^2)$) and at leading order in QED. We show numerical results for $W$ and $Z$ production at the Tevatron and the LHC. Finally, we consider the effect of combined QCD and QED resummation for the ratio of $W$ and $Z$ $q_T$ distributions, and we study the impact of the QED corrections providing an estimate of the corresponding perturbative uncertainties.

hep-ph↗

arXiv2022

Soft gluon-quark-antiquark emission in QCD hard scattering

We consider the radiation of a soft gluon ($g$) and a soft quark-antiquark ($q{\bar q}$) pair in QCD hard scattering. In the soft limit the scattering amplitude has a singular behaviour that is factorized and controlled by a soft current, which has a process-independent structure in colour space. We evaluate the soft $gq{\bar q}$ current at the tree level for an arbitrary multiparton scattering process. The irreducible correlation component of the current includes strictly non-abelian terms and also terms with an abelian character. Analogous abelian correlations appear for soft photon-lepton-antilepton emission in QED. The squared current for soft $gq{\bar q}$ emission produces colour dipole and colour tripole interactions between the hard-scattering partons. The colour tripole interactions are odd under charge conjugation and lead to charge asymmetry effects. We consider the specific applications to processes with two and three hard partons, and we discuss the structure of the corresponding charge asymmetry contributions. We also generalize our QCD results to the cases of QED and mixed QCD$\times$QED radiative corrections.

hep-ph↗

arXiv2022

Quantum jet clustering with LHC simulated data

We study the case where quantum computing could improve jet clustering by considering two new quantum algorithms that might speed up classical jet clustering algorithms. The first one is a quantum subroutine to compute a Minkowski-based distance between two data points, while the second one consists of a quantum circuit to track the rough maximum into a list of unsorted data. When one or both algorithms are implemented in classical versions of well-known clustering algorithms (K-means, Affinity Propagation and $k_T$-jet) we obtain efficiencies comparable to those of their classical counterparts. Furthermore, in the first two algorithms, an exponential speed up in dimensionality and data length can be achieved when applying the distance or the maximum search algorithm. In the $k_T$ algorithm, a quantum version of the same order as FastJet is achieved.

hep-ph↗

arXiv2022

Quantum clustering and jet reconstruction at the LHC

Clustering is one of the most frequent problems in many domains, in particular, in particle physics where jet reconstruction is central in experimental analyses. Jet clustering at the CERN's Large Hadron Collider (LHC) is computationally expensive and the difficulty of this task will increase with the upcoming High-Luminosity LHC (HL-LHC). In this paper, we study the case in which quantum computing algorithms might improve jet clustering by considering two novel quantum algorithms which may speed up the classical jet clustering algorithms. The first one is a quantum subroutine to compute a Minkowski-based distance between two data points, whereas the second one consists of a quantum circuit to track the maximum into a list of unsorted data. The latter algorithm could be of value beyond particle physics, for instance in statistics. When one or both of these algorithms are implemented into the classical versions of well-known clustering algorithms (K-means, Affinity Propagation and $k_T$-jet) we obtain efficiencies comparable to those of their classical counterparts. Even more, exponential speed-up could be achieved, in the first two algorithms, in data dimensionality and data length when the distance algorithm or the maximum searching algorithm are applied.

hep-ph↗

arXiv2022

Higgs boson production at the LHC: fast and precise predictions in QCD at higher orders

We present a new numerical program, HTurbo, which provides fast and numerically precise predictions for Higgs boson production cross sections. The present version of the code implements the perturbative QCD expansion up to the next-to-next-to-leading order also combined with the resummation of the large logarithmic corrections at small transverse momenta up to next-to-next-to-leading logarithmic accuracy and it includes the Higgs boson production through gluon fusion and decay in two photons with the full dependence on the final-state kinematics. Arbitrary kinematical cuts can be applied to the final states in order to obtain fiducial cross sections and associated kinematical distributions. We present a benchmark comparison with the predictions obtained with the numerical programs HRes and HNNLO programs for which HTurbo represents an improved reimplementation.

hep-ph↗

arXiv2021

Fiducial perturbative power corrections within the q$_{\bf T}$ subtraction formalism

We consider higher-order QCD corrections to the production of high-mass systems in hadron collisions within the transverse-momentum (q$_{\rm T}$) subtraction formalism. We present a method to consistently remove the linear power corrections in q$_{\rm T}$ which appears when fiducial kinematical cuts are applied on the final state system. We consider explicitly the case of fiducial cross sections for Drell-Yan lepton pair production at the Large Hadron Collider up to next-to-next-to-next-to-leading order (N$^3$LO) in QCD. We have implemented our method within the DYTurbo numerical program and we have obtained perturbative predictions which are in agreement at the per mille level with those obtained with local subtraction formalisms up to the next-to-next-to-leading order (NNLO). At the N3LO we are able to provide predictions for fiducial cross sections with numerical accuracy at the per mille level.

hep-ph↗

arXiv2021

Multiple soft radiation at one-loop order and the emission of a soft quark-antiquark pair

We consider the radiation of two or more soft partons in QCD hard-scattering at one-loop order. The corresponding scattering amplitude is singular, and the singular behaviour is controlled by a process-independent soft current. Using regularization in $d=4 - 2\epsilon$ space-time dimensions, we explicitly evaluate the ultraviolet and infrared divergent ($\epsilon$-pole) terms of the one-loop soft current for emission of an arbitrary number of soft partons in a generic hard-scattering process. Then we consider the specific case of soft quark-antiquark ($q{\bar q}$) emission and we compute the one-loop current by including the finite terms. We find that the one-loop soft-$q{\bar q}$ current exhibits a new type of transverse-momentum singularity, which has a quantum (absorptive) origin and a purely non-abelian character. At the squared amplitude (cross section) level, this transverse-momentum singularity produces contributions to multijet production processes in hadron collisions. The one-loop squared current also leads to charge asymmetry terms, which are a distinctive features of soft-$q{\bar q}$ radiation. We also extend these results to the cases of QED and mixed QCD$\times$QED radiative corrections for soft fermion-antifermion emission.

hep-ph↗