arXiv subjects

Daniel Stremmer

Publications and source records attributed to Daniel Stremmer.

16 recordsLinked to original sources

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

ggxy: Fast and flexible NLO QCD corrections to gluon-initiated processes

We present the C++ library ggxy, which can be used for the fast and flexible calculation of partonic and hadronic cross sections to gluon-initiated top-mediated processes such as $gg\to HH$, as well as the newly derived processes $gg\to ZH$ and $gg\to ZZ$, at NLO QCD including full top-quark mass dependence. The two-loop virtual amplitudes are implemented using analytical approximations in different kinematic regions, while all other parts of the calculation are exact. This implementation allows to freely modify all input parameters, such as the top-quark mass and its renormalization scheme and the masses of the external $Z$/Higgs bosons. In addition, ggxy has been interfaced to Powheg, which allows the matching to parton showers.

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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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arXiv2025

Complete NLO corrections to off-shell $\boldsymbol{t\bar{t}}$ production in the $\boldsymbol{\ell+j}$ decay channel

We present the calculation of the complete NLO corrections to the off-shell top-quark pair production in the $\ell+j$ decay channel, denoted as $pp \to \ell^- \bar{\nu}_l\, j_b j_b \,jj + X$, where $\ell^- = e^-,\, \mu^-$. The calculation consistently preserves the finite-width effects of the top quarks and massive gauge bosons, as well as takes into account all doubly-, singly-, and non-resonant contributions along with their interference effects. All Born-level contributions, at the perturbative orders from ${\cal O}(\alpha_s^4\alpha^2)$ to ${\cal O}(\alpha_s^0\alpha^6)$, are included and corrected by both NLO QCD and NLO EW effects. Furthermore, all possible partonic initial states are taken into account. Particular attention is paid to the infrared safety in the presence of photons and jets. This requires the use of the so-called parton-to-photon fragmentation function and the photon-to-jet conversion function, which makes the democratic photon-parton clustering and the $\gamma \to q\bar{q}$ splittings finite. We present our findings at the integrated and differential fiducial cross-section levels for the LHC Run III centre-of-mass energy of $\sqrt{s}= 13.6$ TeV. In addition, we quantify the impact of subleading NLO effects, in particular, electroweak Sudakov logarithms and non-resonant QCD backgrounds. Two analysis strategies are employed and compared, namely with and without the resonance-enhancing requirement on the invariant mass of the two light jets, $|M_{jj}-m_W|<{\cal Q}_{\text{cut}} = 20$ GeV, illustrating the relationship between QCD background suppression, off-shell effects, interferences, and complete NLO corrections.

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arXiv2025

ggxy: NLO QCD corrections to loop induced gg initiated processes

We present the program package ggxy, which in its first version can be used to calculate partonic and hadronic cross sections to Higgs boson pair production at NLO QCD and it offers a direct interface to POWHEG-BOX. The 2-loop virtual amplitudes are implemented using analytical approximations in different kinematic regions, while all other parts of the calculation are exact. This implementation allows to freely modify all input parameter, such as the three Higgs coupling, the masses of the top quark and the Higgs boson, and the top-quark mass renormalization scheme.

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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

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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arXiv2024

Complete NLO corrections to $t\bar{t}\gamma$ and $t\bar{t}\gamma\gamma$

In this contribution we discuss recent progress in associated top-quark pair production with one or two isolated photons, $pp\to t\bar{t}\gamma(\gamma)$. The focus is the simultaneous inclusion of higher-order effects and photon radiation in the production of the top-quark pair and in the decay processes. This allows us to quantify the importance of photon radiation in decay processes and the size of the so-called complete NLO corrections in realistic final states.

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arXiv2024

NLO QCD predictions for $\boldsymbol{t\bar{t}\gamma}$ with realistic photon isolation

We present a complete description of top quark pair production in association with a hard photon in the di-lepton decay channel. The calculation is performed at NLO QCD and includes all resonant and non-resonant Feynman diagrams, interferences, and finite-width effects of the top quarks and $W^\pm/Z$ gauge bosons. We provide the results for the $pp\to e^+\nu_e \,\mu^- \bar{\nu}\, b\bar{b}\,\gamma+X$ process using the fixed-cone, smooth-cone and hybrid-photon isolation criteria. The fixed-cone isolation criterion allows contributions from collinear photon radiation off QCD partons, which requires the inclusion of parton-to-photon fragmention processes. To this end, we include the latter contributions into our computational framework. We quantify the impact of different photon-isolation prescriptions on the integrated and differential cross-section predictions for the LHC at a centre-of-mass energy of $\sqrt{s}=13.6$ TeV. Our state-of-the-art NLO QCD results with the fixed-cone criterion allow us to reproduce the photon-isolation prescription employed in ATLAS and CMS. This will help to improve future comparisons with the LHC data.

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arXiv2024

Complete NLO corrections to top-quark pair production with isolated photons

We compute for the first time the so-called complete NLO corrections to top-quark pair production with one and two isolated photons in the di-lepton top-quark decay channel. The Narrow Width Approximation is used for the modeling of unstable top quarks and $W$ bosons. Higher-order QCD and EW effects as well as photon bremsstrahlung are consistently included at all stages: in production and top-quark decays. We present results at the integrated and differential fiducial cross-section level for both processes for the LHC Run II center-of-mass energy of $\sqrt{s}=13$ TeV. In addition, we investigate the scale choice in photonic observables. Finally, the individual size of each subleading contribution is discussed in detail and the origin of the main subleading corrections is scrutinised. For the latter case, alternative calculations are performed in which the subleading NLO corrections are included only in the production of $t\bar{t}\gamma$ and $t\bar{t}\gamma\gamma$.

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arXiv2023

$t\bar{t}jj$ -- NLO QCD corrections to top quark pair production and decays at the LHC

In these proceedings we present the calculation of NLO QCD corrections to $pp\to t\bar{t}jj$ in the dilepton decay channel. The narrow width approximation is used to model the decays of the top quark pair preserving spin correlations. Jet radiation and QCD corrections are consistently included in the production and decay of the top quarks. We discuss the size of NLO QCD corrections and the main theoretical uncertainties of fiducial cross sections at the integrated and differential level. In addition, we examine the contributions of jet radiation in the production and decay of the top-quark pair, as well as of a mixed configuration where jet radiation is present simultaneously in the production and decay stages.

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arXiv2023

Associated production of a top-quark pair with two isolated photons at the LHC through NLO in QCD

We report on the computation of NLO QCD corrections to top-quark pair production in association with two photons at the LHC. Higher-order effects and photon bremsstrahlung are taken into account in the production and decays of the top-quark pair. Top-quark and $W$-boson decays are treated in the Narrow Width Approximation conserving spin correlations up to NLO in QCD. This is the first time that the complete set of NLO QCD corrections to the $pp \to t\bar{t}\gamma\gamma$ process including top-quark decays is calculated. We present results at the integrated and differential cross-section level in the di-lepton and lepton $+$ jet channel. In addition, we investigate the effect of photon bremsstrahlung in $t\bar{t}$ production and top-quark decays, as well as the mixed contribution. The latter contribution, in which two photons occur simultaneously in the production and decay of the $t\bar{t}$ pair, proved to be significant at both the integrated and differential cross-section level.

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arXiv2022

A study of additional jet activity in top quark pair production and decay at the LHC

We report on the calculation of the NLO QCD corrections to top quark pair production in association with two hard jets at the LHC. We take into account higher-order effects in both the production and decays of the top-quark pair. The latter are treated in the narrow width approximation and $t\bar{t}$ spin correlations are preserved throughout the calculation. This is the first time that such a complete study for this process is conducted at NLO in QCD. We present results for fiducial cross sections at the integrated and differential level. Furthermore, we investigate kinematic properties of the additional light jets and their distribution in the $pp\to t\bar{t}jj$ process. We examine jets in production and top-quark decays as well as the mixed contribution, where the two hardest non-$b$ jets are present simultaneously in the production and decay processes.

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arXiv2022

${\cal CP}$ structure of the top-quark Yukawa interaction: NLO QCD corrections and off-shell effects

Since its discovery at the Large Hadron Collider in 2012 the Higgs boson has arguably become the most famous of the Standard Model particles and many measurements have been performed in order to assess its properties. Among others, these include measurements of the Higgs boson's ${\cal CP}$ state which is predicted to be ${\cal CP}$-even. Even though a pure ${\cal CP}$-odd state has been ruled out, a possible admixture of a ${\cal CP}$-odd Higgs state has yet to be excluded. In this work we present predictions for the associated production of a leptonically decaying top quark pair and a stable Higgs boson $p p \to e^+ \nu_e\, \mu^- \bar{\nu}_\mu\,b\bar{b}\,H$ with possible mixing between ${\cal CP}$-even and ${\cal CP}$-odd states at NLO in QCD for the LHC with $\sqrt{s} = 13$ TeV. Finite top-quark and gauge boson width effects as well as all double-, single- and non-resonant Feynman diagrams including their interference effects are taken into account. We compare the behaviour of the ${\cal CP}$-even, -odd and -mixed scenarios for the integrated fiducial cross-sections as well as several key differential distributions. In addition, we show that both NLO corrections and off-shell effects play an important role even at the level of integrated fiducial cross-sections and that these are further enhanced in differential distributions. Even though we focus here on the Standard Model Higgs boson, the calculations could be straightforwardly applied to models that have an extended Higgs-boson sector and predict the existence of ${\cal CP}$-odd Higgs-like particles, such as the two-Higgs-doublet model.

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arXiv2021

Production and decay of the Higgs boson in association with top quarks

We report on the calculation of the next-lo-leading order QCD corrections to Higgs boson production and decay in association with top quarks. We consider leptonic decays of top quarks leading to the hadronic process $pp\to e^+\nu_e\, \mu^-\bar{\nu}_\mu \, b\bar{b}\,H\, (H\to X)$ at the LHC with $\sqrt{s}=13$ TeV. All resonant as well as non-resonant Feynman diagrams, interferences and off-shell effects are included for the top quark and $W$ gauge boson. Decays of the Higgs boson, on the other hand, are included in the narrow-width-approximation. Specifically, we consider Higgs boson decays into $b\bar{b}$, $\tau^+\tau^-$, $\gamma\gamma$ and $e^+e^-e^+e^-$. Numerical results are given at the integrated and differential fiducial level for various factorisation and renormalisation scale choices and different PDF sets. We study the main theoretical uncertainties that are associated with neglected higher order terms in the perturbative expansion and with different parametrisations of the PDFs. Furthermore, we examine the size of the off-shell effects by an explicit comparison to the calculation in the full narrow-width-approximation. Finally, the impact of the contributions induced by the bottom-quark parton density is investigated.

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