arXiv subjects

Kay Schönwald

Publications and source records attributed to Kay Schönwald.

At least 19 recordsLinked to original sources

arXiv2026

Heavy-Quark Production in DIS: Mellin Moments for Phenomenology

Heavy-quark production in deep-inelastic scattering probes the gluon distribution, and the precision of current and future data requires predictions beyond next-to-leading order. We calculate the even Mellin moments $N = 2$ to $22$ of the next-to-leading-order heavy-quark coefficient functions for $F_2$ and $F_L$, retaining the full heavy-quark mass dependence. This includes the gluon channel, for which no analytic result is available. They provide a test of the parametrisations used in phenomenology: at a representative kinematic point these are accurate to better than one per cent in the gluon channel, whereas in the quark channels we find deviations of up to $20\%$ over a wide range of Mellin moments, signalling significant differences in the corresponding $x$-space distributions. As a new result at next-to-next-to-leading order, the lowest moment $N = 2$ has been determined exactly.

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arXiv2026

Higgs Boson Pair Production via Gluon Fusion: Higher-Order Corrections and Theoretical Uncertainties

In this contribution, the higher-order QCD and electroweak corrections to Standard Model Higgs boson pair production via the gluon-fusion mechanism, $gg\to hh$, are summarized and the different sources of theoretical uncertainty are assessed. The discussion includes finite top quark mass effects, matching to parton showers, approximate NNLO and N$^3$LO QCD corrections, NLO electroweak effects, and uncertainties associated with the top quark mass scheme and perturbative scale choices. In addition, we provide an updated state-of-the-art recommendation for the inclusive gluon-fusion Higgs boson pair production cross section and the corresponding Higgs boson pair invariant-mass distribution.

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arXiv2026

Three-loop QCD corrections to heavy-to-light form factors and applications to inclusive $B$ decays

We report on the calculation of heavy-to-light form factors at $\mathcal{O}(α_s^3)$ and on selected phenomenological applications in inclusive $B$-decays. After outlining the loop calculation, we extract the hard function in $\bar B \to X_s γ$, and discuss our recent progress and preliminary results for the N$^3$LO corrections to partial decay rates in $\bar B \to X_u l \bar ν_l$, important for the inclusive determination of $|V_{ub}|$. In particular, we establish relations for heavy-quark parameters in the shape-function scheme to four loops and improve a particular model of the $B$ meson shape-function.

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arXiv2026

The electron parton distribution functions at the NNLO in QED

The electron Parton Distribution Functions (PDFs) are essential components in the calculations of cross sections within a collinear-factorisation framework at lepton colliders. We compute them at the next-to-next-to-leading order (NNLO) in QED by working in two different factorisation schemes, namely the standard $\overline{\rm MS}$ one and the so-called $Δ$ scheme, which was originally defined at the next-to-leading order, and which we generalise in this work by extending its definition to all orders. We present analytical results relevant to the large-$z$ behaviour of the PDFs in both factorisation schemes, and thus show how the soft-logarithm enhancement of the $\overline{\rm MS}$ electron PDF is completely absent in the $Δ$ scheme. The latter therefore constitutes a natural choice that helps significantly reduce the complexity not only of numerical simulations in phenomenological applications, but also that of analytical computations necessary to achieve the soft resummation of physical observables. We argue that NNLO PDFs are necessary to attain relative-precision targets of $10^{-4}$ or better, for colliders whose centre-of-mass energies are in the hundred-GeV range.

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arXiv2026

Muon lifetime and Fermi constant: an update

We present an updated prediction for the lifetime of the muon including a detailed analysis of all relevant uncertainties. Our prediction includes QED corrections up to order $α^3$ and state-of-the-art hadronic contributions based on dispersive methods. Radiative corrections and finite-electron-mass effects are parametrized by the correction factor $Δq$ in $τ_μ^{-1}=G_F^2m_μ^5(1+Δq)/(192π^3)$, for which we obtain $Δq=(-4\, 384\, 678 \pm 34)\times 10^{-9}$. This reduces the uncertainty associated with $Δq$ by an order of magnitude compared to the previous prediction at order $α^2$. We use our results to provide an updated value of the Fermi coupling constant, $G_F=1.166\,378\, 59 \, (59) \times 10^{-5} \, \mathrm{GeV}^{-2}$. Further improvements will require better measurements of the muon lifetime and mass.

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arXiv2026

The photon-energy spectrum in $B\to X_sγ$ to N$^3$LO: light-fermion and large-$N_{\rm c}$ corrections

We calculate the photon-energy spectrum of the inclusive radiative decay $B\to X_sγ$, induced by the electromagnetic dipole operator $O_7$, to next-to-next-to-next-to-leading order and consider the complete corrections for light fermions, for the contributions with two closed massive fermion loops, and for the limit of large QCD colour factors $N_{\rm c}$ in the remaining part. We discuss the total decay rate both without and with a cut on the photon energy. In addition to the on-shell renormalization of the bottom-quark mass, we also consider the kinetic mass and the MSR mass schemes. The latter two lead to an improved perturbative behaviour of the decay rate.

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arXiv2026

$gg \to ZH$ at NLO matched to parton showers with ggxy and POWHEG

We implement the recently-calculated analytic expressions for the next-to-leading order QCD corrections to $gg\to ZH$ in ggxy. This provides a flexible framework for investigating partonic and hadronic cross sections for various top quark mass renormalization schemes. We augment the $Z$ boson with leptonic decays, including spin correlations and off-shell effects, and furthermore provide an interface to POWHEG. This enables simulations with parton showers, performed using Pythia.

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arXiv2026

Analytic next-to-leading order electroweak corrections to Higgs boson pair production at high energies

We compute the complete next-to-leading order electroweak corrections to the form factors entering gluon-induced Higgs boson pair production. We consider the top quark contribution in the limit where the Mandelstam variables are much larger than all other scales involved in the process and compute about a hundred expansion terms in analytic form. They are used to obtain precise numerical results even for fairly low values of the transverse momentum of the Higgs boson. We show that these electroweak corrections at high energies are of the order of $-10\%$. We also discuss the leading logarithmic corrections of the analytic expressions.

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arXiv2026

Heavy-quark production in deep-inelastic scattering -- Mellin moments of structure functions

We compute Mellin moments of the heavy-quark structure functions in deep-inelastic scattering at next-to-leading order in quantum chromodynamics, retaining their full dependence on the heavy-quark mass. Using the optical theorem and the operator product expansion, we derive analytic results for fixed Mellin moments $N = 2$ to $22$ of the structure functions $F_2$ and $F_L$. Our results reproduce the known expressions in the relevant asymptotic limits, in particular for virtualities of the exchanged photon $Q^2$ much larger than the heavy-quark mass squared $m^2$, and are in agreement with existing parametrisations of the next-to-leading-order coefficient functions. The computational set-up developed in this work also provides a direct pathway toward extending these calculations to next-to-next-to-leading order.

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arXiv2025

Three-loop corrections to $gg\to ZH$ in the large top quark mass limit

We compute three-loop virtual corrections to the associated production of a Higgs boson with a $Z$ boson in the large-$m_t$ limit. We describe in detail the application of the asymptotic expansion and provide, for all form factors, analytic results for the first three terms in the $1/m_t$ expansion. We also provide numerical routines implemented in the C++ library ggxy.

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arXiv2025

Identified Hadron Production in Deeply Inelastic Neutrino-Nucleon Scattering

The production of identified hadrons in semi-inclusive deep-inelastic scattering (SIDIS) is sensitive to parton distribution functions and hadron fragmentation functions. Neutrino-induced SIDIS processes probe combinations of these functions different from their charged-lepton-induced counterparts. We compute charged pion production in (anti-)neutrino induced SIDIS up to second order in perturbative QCD and compare our predictions to precise legacy fixed-target data. We demonstrate the high sensitivity of these data on the parametrization of the fragmentation functions and discuss future SIDIS probes at the LHC Forward Physics Facility.

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arXiv2025

Neutral and Charged Current Semi-Inclusive Deep-Inelastic Scattering at NNLO QCD

Semi-inclusive hadron production in deep inelastic lepton-nucleon scattering (SIDIS) provides important probes of parton distributions and fragmentation functions. We compute the next-to-next-to-leading order (NNLO) massless QCD corrections to the full set of SIDIS coefficient functions in analytical form, accounting for electroweak neutral current and charged current exchange. Focusing on the kinematical setting of SIDIS measurements at the future Electron-Ion Collider (EIC), we quantify the impact of these corrections on the phenomenological predictions and their associated uncertainties. We study the impact of electroweak interference in the neutral current SIDIS process and investigate lepton polarisation asymmetries designed to enhance the sensitivity on charged current SIDIS.

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arXiv2025

Polarized Neutral and Charged Current Semi-Inclusive Deep-Inelastic Scattering at NNLO in QCD

The semi-inclusive production of identified hadrons in deeply inelastic lepton scattering on polarized nucleons allows to probe the spin structure of the nucleon target in a more detailed level than through fully inclusive processes. We compute the NNLO QCD corrections to longitudinally polarized semi-inclusive deep inelastic processes mediated by electroweak neutral and charged currents. We present the first calculation of polarized electroweak structure functions in the Larin scheme up to NNLO. Additionally, we reformulate the finite scheme transformation to the $\overline{\textrm{MS}}$ scheme in a quark flavour basis and identify issues in its assignment to partonic channels in previous calculations. Using our results we perform a detailed phenomenological study of polarized cross sections and of single and double spin asymmetries. We observe large electroweak effects, which need to be included in precision studies of polarized observables.

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arXiv2025

Polarized semi-inclusive deep-inelastic scattering at NNLO in QCD

Semi-inclusive hadron production in longitudinally polarized deep-inelastic lepton-nucleon scattering is a powerful tool for resolving the quark flavor decomposition of the proton's spin structure. We present the full next-to-next-to-leading order (NNLO) QCD corrections to the coefficient functions of polarized semi-inclusive deep-inelastic scattering (SIDIS) in analytical form, enabling the use of SIDIS measurements in precision studies of the proton spin structure. The numerical impact of these corrections is illustrated by a comparison with data of polarized single-inclusive hadron spectra from the DESY HERMES and CERN COMPASS experiments.

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arXiv2025

Two-loop QCD corrections to $ZH$ and off-shell $Z$ boson pair production in gluon fusion

We compute two-loop corrections to the associated production of a Higgs boson with a $Z$ boson and to off-shell $Z$ boson pair production in the gluon fusion channel, mediated by a heavy quark. We perform deep expansions in the high-energy region and around the forward limit and show that their combination covers the whole phase space. Our results constitute the next-to-leading order virtual corrections to these processes. Their numerical evaluation is fast and the dependence on all parameters is maintained, thus a change of parameter values or renormalization scheme is straightforward. As a by-product of our calculation, we also obtain the two-loop heavy quark mediated virtual corrections to the processes of off-shell di-photon and photon-$Z$ production.

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arXiv2025

{\tt ggxy}: a flexible library to compute gluon-induced cross sections

We present the library {\tt ggxy}, written in {\tt C++}, which can be used to compute partonic and hadronic cross sections for gluon-induced processes with at least one closed heavy quark loop. It is based on analytic ingredients which avoids, to a large extent, expensive numerical integration. This results in significantly shorter run-times than other similar tools. Modifying input parameters, changing the renormalization scheme and varying renormalization and factorization scales is straightforward. In Version~1 of {\tt ggxy} we implement all routines which are needed to compute partonic and hadronic cross sections for Higgs boson pair production up to next-to-leading order in QCD. We provide flexible interfaces and allow the user to interact with the built-in amplitudes at various levels.

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arXiv2025

Three-loop large-$N_c$ virtual corrections to $gg\to HH$ in the forward limit

We compute the three-loop form factors for $gg\to HH$ in the limit of vanishing transverse momentum of the Higgs boson which provides a reasonable approximation of the cross section. In our calculations we adopt the large-$N_c$ limit, which already includes non-trivial non-planar Feynman diagrams. We discuss the results for top quark masses in the pole and $\overline{\rm MS}$ schemes and show that the scheme dependence is significantly reduced at next-to-next-to-leading order.

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arXiv2025

Analytic next-to-leading order Yukawa and Higgs boson self-coupling corrections to $gg\to HH$ at high energies

We consider electroweak corrections to Higgs boson pair production, taking into account the top quark Yukawa and Higgs boson self couplings. Using differential equations we compute a deep expansion of all master integrals in the high-energy limit and present analytic results for the two-loop box-type form factors. We show that precise numerical results can be obtained even for relatively small values of the Higgs boson transverse momentum. We compare against recent numerical results and find good agreement.

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