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Herschel A. Chawdhry

Publications and source records attributed to Herschel A. Chawdhry.

14 recordsLinked to original sources
arXiv2025

Quantum simulation of scattering amplitudes and interferences in perturbative QCD

A flagship application of quantum computers is the simulation of other quantum systems, including quantum field theories. In this article, we show how quantum computers can be employed to naturally calculate Feynman diagrams and their interferences in Quantum Chromodynamics (QCD). We simulate the colour parts of the interactions directly on the quantum computer, while the kinematic parts are for now pre-computed classically. For processes where some of the external particles are identical, we find the first hints of a potential quantum advantage. We validate our techniques using simulated quantum computers. Furthermore, for toy examples we also demonstrate our algorithms on a 56-qubit trapped-ion quantum computer. The work constitutes a further key step towards a full quantum simulation of generic perturbative QCD processes.

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arXiv2024

Quantum algorithms for the simulation of QCD processes in the perturbative regime

Theoretical predictions for high-energy collision processes at particle colliders, such as the Large Hadron Collider (LHC), rely on calculations in perturbative Quantum Chromodynamics (QCD), which are often computationally challenging. In these conference proceedings, we explore the possibility of using quantum computers to simulate QCD processes in the perturbative QCD regime. In particular, as a first step towards that goal, we present quantum circuits to simulate the colour part of perturbative QCD. The circuits are validated by implementing them on a simulated quantum computer and verifying the colour factors for several example Feynman diagrams.

hep-ph↗
arXiv2024

Rational-function interpolation from p-adic evaluations in scattering amplitude calculations

Numerical interpolation techniques are widely employed for calculating large rational functions in scattering amplitude computations. It has been observed in recent years that these rational functions greatly simplify upon partial fractioning. In this conference proceedings paper, based on the article [H. A. Chawdhry, Phys. Rev. D 110, 056028 (2024)], a technique is presented to interpolate such rational functions directly in partial-fractioned form, from evaluations at special integer points chosen for their properties under a p-adic absolute value. It is shown that the technique can require 25 times fewer numerical probes than conventional finite-field-based techniques and can produce results that are more compact in size by 2 orders of magnitude. The reconstructed results moreover exhibit additional patterns that could be exploited in future work to further improve the size of the results and the number of required numerical probes.

hep-ph↗
arXiv2024

Interpolation of rational functions in loop calculations by using p-adic numbers

The calculation and manipulation of large multi-variable rational functions is a key bottleneck in multi-loop calculations. In these conference proceedings, based on my article [Chawdhry (2023) arXiv:2312.03672], I present a technique to interpolate such rational functions in a compact form by evaluating them at special integer points chosen for their properties under a $p$-adic absolute value. I apply the technique to examples of large rational functions appearing in 2-loop 5-point massless non-planar amplitude calculations in Quantum Chromodynamics (QCD). The number of required numerical probes (per field) is found to be around 25 times smaller than in conventional techniques, and the obtained result is 130 times smaller.

hep-th↗
arXiv2024

p-adic reconstruction of rational functions in multi-loop amplitudes

Numerical reconstruction techniques are widely employed in the calculation of multi-loop scattering amplitudes. In recent years, it has been observed that the rational functions in multi-loop calculations greatly simplify under partial fractioning. In this article, we present a technique to reconstruct rational functions directly in partial-fractioned form, by evaluating the functions at special integer points chosen for their properties under a p-adic metric. As an application, we apply this technique to reconstruct the largest rational function in the integration-by-parts reduction of one of the rank-5 integrals appearing in 2-loop 5-point full-colour massless amplitude calculations in Quantum Chromodynamics (QCD). The number of required numerical probes (per prime field) is found to be around 25 times smaller than in conventional techniques, and the obtained result is 130 times smaller. The reconstructed result displays signs of additional structure that could be used to further reduce its size and the number of required probes.

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arXiv2023

Quantum simulation of colour in perturbative quantum chromodynamics

Quantum computers are expected to give major speed-ups for the simulation of quantum systems. In this work, we present quantum gates that simulate the colour part of the interactions of quarks and gluons in perturbative quantum chromodynamics (QCD). As a first application, we implement these circuits on a simulated noiseless quantum computer and use them to calculate colour factors for various examples of Feynman diagrams. This work constitutes a first key step towards a quantum simulation of generic scattering processes in perturbative QCD.

hep-ph↗
arXiv2023

Quantum algorithms for the simulation of perturbative QCD processes

Quantum computers are expected to give major speed-ups for the simulation of quantum systems. In these conference proceedings, we discuss quantum algorithms for the simulation of perturbative Quantum Chromodynamics (QCD) processes. In particular, we describe quantum circuits for simulating the colour part of the interactions of quarks and gluons. We implement our circuits on a simulated noiseless quantum computer and validate them by calculating colour factors for various examples of Feynman diagrams.

hep-ph↗
arXiv2022

Mixed QCD-electroweak corrections to dilepton production at the LHC in the high invariant mass region

We compute mixed QCD-electroweak corrections to the neutral-current Drell-Yan production of a pair of massless leptons in the high invariant mass region. Our computation is fully differential with respect to the final state particles. At relatively low values of the dilepton invariant mass, $m_{\ell \ell} \sim 200$ GeV, we find unexpectedly large mixed QCD-electroweak corrections at the level of -1%. At higher invariant masses, $m_{\ell \ell} \sim 1$ TeV, we observe that these corrections can be well approximated by the product of QCD and electroweak corrections. Hence, thanks to the well-known Sudakov enhancement of the latter, they increase at large invariant mass and reach e.g. -3% at $m_{\ell \ell} = 3$ TeV. Finally, we note that the inclusion of mixed corrections reduces the theoretical uncertainty related to the choice of electroweak input parameters to below the percent level.

hep-ph↗
arXiv2021

Two-loop leading-color helicity amplitudes for three-photon production at the LHC

We calculate all planar contributions to the two-loop massless helicity amplitudes for the process $q\bar q\to γγγ$. The results are presented in fully analytic form in terms of the functional basis proposed recently by Chicherin and Sotnikov. With this publication we provide the two-loop contributions already used by us in the NNLO QCD calculation of the LHC process $pp\to γγγ$ [Chawdhry et al. (2019)]. Our results agree with a recent calculation of the same amplitude [Abreu et al. (2020)] which was performed using different techniques. We combine several modern computational techniques, notably, analytic solutions for the IBP identities, finite-field reconstruction techniques as well as the recent approach [Chen (2019)] for efficiently projecting helicity amplitudes. Our framework appears well-suited for the calculation of two-loop multileg amplitudes for which complete sets of master integrals exist.

hep-ph↗
arXiv2021

NNLO QCD corrections to diphoton production with an additional jet at the LHC

We calculate the NNLO QCD corrections to diphoton production with an additional jet at the LHC. Our calculation represents the first NNLO-accurate prediction for the transverse momentum distribution of the diphoton system. The improvement in the accuracy of the theoretical prediction is significant, by a factor of up to four relative to NLO QCD. Our calculation is exact except for the finite remainder of the two-loop amplitude which is included at leading color. The numerical impact of this approximated contribution is small. The results of this work are expected to further our understanding of the Higgs boson sector and of the behavior of higher-order corrections to LHC processes.

hep-ph↗
arXiv2020

NNLO QCD corrections to three-photon production at the LHC

We compute the NNLO QCD corrections to three-photon production at the LHC. This is the first NNLO QCD calculation for a $2\to 3$ process. Our calculation is exact, except for the scale-independent part of the two-loop finite remainder which is included in the leading color approximation. We estimate the size of the missing two-loop corrections and find them to be phenomenologically negligible. We compare our predictions with available 8 TeV measurement from the ATLAS collaboration. We find that the inclusion of the NNLO corrections eliminates the existing significant discrepancy with respect to NLO QCD predictions, paving the way for precision phenomenology in this process.

hep-ph↗
arXiv2019

Ambiguities of the principle of maximum conformality procedure for hadron collider processes

In any calculation in perturbative Quantum Chromodynamics (QCD) a choice needs to be made for the unphysical renormalisation scale, $μ_R$. The Brodsky-Lepage-Mackenzie/Principle of Maximum Conformality (BLM/PMC) scale-setting procedure is one proposed method for selecting this scale. In this work we identify three ambiguities in the BLM/PMC procedure itself. Their numerical impact is studied using the example of the total cross-section for $t\bar{t}$ production through Next-to-Next-to-Leading Order in QCD. One ambiguity is the arbitrary choice of the value of the highest-order PMC scale. The numerical impact of this choice on the BLM/PMC prediction for the cross-section is found to be comparable to the impact of the choice of $μ_R$ in the conventional scale-setting approach. Another ambiguity relates to the definitions of the other PMC scales and is similarly found to have a large impact on the cross-section.

hep-ph↗
arXiv2019

Two-loop five-point massless QCD amplitudes within the IBP approach

We solve the integration-by-parts (IBP) identities needed for the computation of any planar two-loop five-point massless amplitude in QCD. We also derive some new results for the most complicated non-planar topology with irreducible numerators of power as high as six. We do this by applying a new strategy for solving the IBP identities which scales better for problems with a large number of scales and/or master integrals. Our results are a proof of principle that the remaining non-planar contributions for all two-loop five-point massless QCD amplitudes can be computed in analytic form.

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