## About

88

Publications

2,421

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2,315

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Citations since 2017

Introduction

Andreas Krassnigg is a researcher based in Graz Austria.
Andreas does research in the areas of Applied Mathematics, Elementary Particle Physics, Computational Physics, and Machine Learning.
His main recent interest are numerical approaches to various problems in science, wirh his original research background being the highly specialized field of theoretical hadron physics.

Additional affiliations

February 2020 - December 2021

**Innophore GmbH**

Position

- Senior AI Strategist

Description

- Strategic, theoretical, and hands-on work for the company's AI and related projects and workflows in the field of bioinformatics.

Education

September 1993 - July 2002

## Publications

Publications (88)

Treatment of COVID-19 with a soluble version of ACE2 that binds to SARS-CoV-2 virions before they enter host cells is a promising approach, however it needs to be optimized and adapted to emerging viral variants. The computational workflow presented here consists of molecular dynamics simulations for spike RBD-hACE2 binding affinity assessments of...

Introduction
The current coronavirus pandemic is being combated worldwide by nontherapeutic measures and massive vaccination programs. Nevertheless, therapeutic options such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main-protease (M pro ) inhibitors are essential due to the ongoing evolution toward escape from natural or induc...

To date, more than 263 million people have been infected with SARS-CoV-2 during the COVID-19 pandemic. In many countries, the global spread occurred in multiple pandemic waves characterized by the emergence of new SARS-CoV-2 variants. Here we report a sequence and structural-bioinformatics analysis to estimate the effects of amino acid substitution...

Treatment of COVID-19 with a soluble version of ACE2 that binds to SARS-CoV-2 virions before they enter host cells is a promising approach, but it needs to be optimized and adapted to emerging viral variants. The computational workflow presented here consists of molecular dynamics simulations for RBD-ACE2 binding affinity assessments of ACE2 or RBD...

The current COVID-19 pandemic poses a challenge to medical professionals and the general public alike. In addition to vaccination programs and nontherapeutic measures being employed worldwide to encounter SARS-CoV-2, great efforts have been made towards drug development and evaluation. In particular, the main protease (M pro ) makes an attractive d...

The current coronavirus pandemic is being combated worldwide by nontherapeutic measures and massive vaccination programs. Nevertheless, therapeutic options such as SARS-CoV-2 main-protease (M pro ) inhibitors are essential due to the ongoing evolution toward escape from natural or induced immunity. While antiviral strategies are vulnerable to the e...

The monkeypox virus (MPX) belongs to the orthopoxvirus genus of the Poxviridae family, is endemic in parts of Africa, and causes a disease in humans similar to smallpox. The most recent outbreak of MPX in 2022 is already affecting 19 countries on different continents and has consequently become a focus of interest. In particular, a molecular unders...

To date, more than 263 million people have been infected with SARS-CoV-2 during the COVID-19 pandemic. In many countries, the global spread came in several pandemic waves characterized by the emergence of new SARS-CoV-2 variants. Here, we report on a sequence- and structural-bioinformatics analysis by which we estimate the impact of amino acid exch...

Recently, we completed a comprehensive investigation of a huge part of the entire meson spectrum by considering both quarkonia and open-flavour mesons by means of a single common framework which unites the homogeneous Bethe-Salpeter equation that describes mesons as quark-antiquark bound states and the Dyson-Schwinger equation that governs the full...

Exploiting an interplay of the Bethe-Salpeter equation enabling us to regard mesons as bound states of quark and antiquark and the Dyson-Schwinger equation controlling the dressed quark propagator, we amend existing studies of quarkonia by a comprehensive description of open-flavour mesons composed of all conceivable combinations of quark flavour....

Exploiting an interplay of the Bethe-Salpeter equation enabling us to regard mesons as bound states of quark and antiquark and the Dyson-Schwinger equation controlling the dressed quark propagator, we amend existing studies of quarkonia by a comprehensive description of open-flavour mesons composed of all conceivable combinations of quark flavour....

We revisit earlier calculations of leptonic decay constants of vector charmonia and present and illustrate our decomposition of the corresponding covariant Bethe-Salpeter amplitudes in terms of orbital angular momentum as interpreted in the meson's rest frame. Our results confirm our previous conclusions drawn from the magnitudes of vector-meson le...

We investigate the light-quarkonium spectrum using a covariant Dyson–Schwinger–Bethe–Salpeter-equation approach to QCD. We discuss splittings among as well as orbital angular momentum properties of various states in detail and analyze common features of mass splittings with regard to properties of the effective interaction. In particular, we predic...

Open-flavour meson studies are the necessary completion to any comprehensive investigation of quarkonia. We extend recent studies of quarkonia in the Dyson-Schwinger-Bethe-Salpeter equation approach to explore their results for all possible flavour combinations. Within the inherent limitations of the setup, we present the most comprehensive results...

We discuss charmed mesons in the covariant Dyson-Schwinger-Bethe-Salpeter-equation approach. In particular we computed masses, leptonic decay constants, and an orbital-angular-momentum decomposition for a basic set of states. We also report an efficient way to treat the two coupled quark propagator dressing functions via a single
function.

Meson states with exotic quantum numbers arise naturally in a covariant bound-state framework in QCD. We investigate the consequences of shifting quark masses such that the states are no longer restricted to certain C-parities, but only by J^P. Then, a priori, one can no longer distinguish exotic or conventional states. In order to identify signatu...

We extend earlier investigations of heavy-light pseudoscalar mesons to the vector case, using a simple model in the context of the Dyson-Schwinger-Bethe-Salpeter approach. We investigate the effects of a dressed quark-gluon vertex in a systematic fashion and illustrate and attempt to quantify corrections beyond the phenomenologically very useful an...

We give a short and basic introduction to our covariant Dyson-Schwinger-Bethe-Salpeter-equation approach using a rainbow-ladder truncated model of QCD, in which we investigate the leptonic decay properties of heavy quarkonium states in the pseudoscalar and vector channels. Comparing the magnitudes of decay constants, we identify radial 1-- excitati...

We investigate the light quarkonium spectrum using a covariant
Dyson-Schwinger-Bethe-Salpeter-equation approach with a rainbow-ladder
truncated model of quantum chromodynamics. We attempt to tie properties of the
effective interaction in this setup to features in the spectrum and draw
conclusions about the applicability of the rainbow-ladder trunca...

Using a simple model in the context of the Dyson-Schwinger-Bethe-Salpeter
approach, we investigate the effects of a dressed-quark-gluon vertex on
pseudoscalar meson masses. In particular, we focus on the unequal-mass case and
investigate heavy-light meson masses; in addition, we study the premise of the
effective treatment of heavy quarks in our ap...

We investigate the properties of mesons with the exotic J^PC = 1^-+ quantum
numbers. Starting out from the light-quark domain, where the \pi_1 states are
used as references, we predict the masses of analogous quarkonia for c\bar{c}
and b\bar{b} configurations. We employ a covariant
Dyson-Schwinger-Bethe-Salpeter-equation approach with a rainbow-lad...

In a covariant Bethe-Salpeter-equation approach and with a rainbow-ladder truncated model of quantum chromodynamics (QCD), we investigate the use of an effective interaction with the goal of reproducing QCD phenomenology. We extend previous studies and present results for ground and excited meson states in the bottomonium and charmonium systems, wh...

Following up on earlier work, we investigate possible effects of a dressed
quark-gluon vertex in heavy-light mesons. In particular, we study corrections
to the popular rainbow-ladder truncation of the Dyson-Schwinger-Bethe-Salpeter
equation system. We adopt a simple interaction kernel which reduces the
resulting set of coupled integral equations to...

We investigate capabilities of the effective interaction in a rainbow-ladder
truncated meson model of QCD within a covariant Landau-gauge
Bethe-Salpeter-equation approach. Based upon past success for the light- as
well as heavy-quark domains, we discuss the range of applicability and features
of an effort with comprehensive phenomenological claim a...

A strongly momentum-dependent dressed-quark mass function is basic to QCD. It is central to the appearance of a constituent-quark mass-scale and an existential prerequisite for Goldstone modes. Dyson-Schwinger equation (DSEs) studies have long emphasised this importance, and have proved that QCD's Goldstone modes are the only pseudoscalar mesons to...

We study pseudoscalar and scalar mesons using a practical and symmetry preserving truncation of QCD's Dyson-Schwinger equations. We investigate and compare properties of ground and radially excited meson states. In addition to exact results for radial meson excitations we also present results for meson masses and decay constants from the chiral lim...

Using a well-established effective interaction in a rainbow-ladder truncation
model of QCD, we fix the remaining model parameter to the bottomonium
ground-state spectrum in a covariant Bethe-Salpeter equation approach and find
surprisingly good agreement with the available experimental data including the
2^{--} Upsilon(1D) state. Furthermore, we in...

In the functional approach to quantum chromodynamics, the properties of hadronic bound states are accessible via covariant integral equations, e.g. the Bethe-Salpeter equation for mesons. In particular, one has to deal with linear, homogeneous integral equations which, in sophisticated model setups, use numerical representations of the solutions of...

We study hadronic decays of mesons and baryons in the context of the
Dyson-Schwinger equations of QCD. Starting from a well-established effective
interaction in rainbow-ladder truncation, we consistently calculate all
ingredients of the appropriate decay diagrams. The resulting strong couplings
are presented as functions of the quark mass from the...

We investigate tensor mesons as quark-antiquark bound states in a fully
covariant Bethe-Salpeter equation. As a first concrete step we report results
for masses of J^{PC}=2^{++} mesons from the chiral limit up to bottomonium and
sketch a comparison to experimental data. All covariant structures of the
fermion-antifermion system are taken into accou...

We discuss how to extract observables from an inhomogeneous vertex
Bethe-Salpeter equation without resorting to the corresponding homogeneous
equation. As an example we present a prediction for the $e^+e^-$ decay width of
the $\rho(1450)$ or $\rho'$ meson. We also attempt to identify the momentum
range contributing to a vector meson's decay constan...

We examine the nucleon's electromagnetic form factors in a Poincare-covariant
Faddeev framework. The three-quark core contributions to the form factors are
obtained by employing a quark-diquark approximation. We implement the
self-consistent solution for the quark-photon vertex from its inhomogeneous
Bethe-Salpeter equation. We find that the result...

We present a calculation of the three-quark core contribution to nucleon and
Delta-baryon masses and Delta electromagnetic form factors in a
Poincare-covariant Faddeev approach. A consistent setup for the dressed-quark
propagator, the quark-quark, quark-'diquark' and quark-photon interactions is
employed, where all ingredients are solutions of thei...

The Bethe-Salpeter equation in QCD connects the gauge-dependent gluon and
quark degrees of freedom with the gauge-invariant properties of mesons. We
study the rho meson mass and decay constant for various versions of the
gauge-dependent input functions discussed in the literature, which start to
differ generically below the hadronic scale, and show...

We report the first study of the nucleon where the full Poincaré-covariant structure of the three-quark amplitude is implemented in the Faddeev equation. We employ an interaction kernel which is consistent with contemporary studies of meson properties and aspects of chiral symmetry and its dynamical breaking, thus yielding a comprehensive approach...

We analyze the chiral phase transition with the help of the QCD gap equation. Various models for the effective interaction in rainbow truncation are contrasted with regard to the resulting chiral transition temperatures. In particular, we investigate possible systematic relations of the details of the effective interaction and the value of T_c. In...

Employing an approach based on the Green functions of Landau-gauge QCD, some selected results from a calculation of meson and baryon properties are presented. A rainbow-ladder truncation to the quark Dyson-Schwinger equation is used to arrive at a unified description of mesons and baryons by solving BetheSalpeter and covariant Faddeev equations, re...

We provide details on a recent solution of the nucleon's covariant Faddeev equation in an explicit three-quark approach. The full Poincare-covariant structure of the three-quark amplitude is implemented through an orthogonal basis obtained from a partial-wave decomposition. We employ a rainbow-ladder gluon exchange kernel which allows for a compari...

The Bethe-Salpeter equation is used to comprehensively study mesons with J=0, 1 and equal-mass constituents for quark masses from the chiral limit to the b-quark mass. The survey contains masses of the ground states in all corresponding J{sup PC} channels including those with 'exotic' quantum numbers. The emphasis is put on each particular state's...

We present a Poincare covariant Faddeev equation, which enables the simultaneous prediction of meson and baryon observables using the leading order in a truncation of the Dyson-Schwinger equations that can systematically be improved. The solution describes a nucleon's dressed-quark core. The evolution of the nucleon mass with current-quark mass is...

In theoretical hadron physics mesons are a center of attention. Constructed in a simpler way than baryons in the quark model, they still present a considerable challenge if one aims at an understanding of all their aspects in terms of quarks and gluons in the context of Quantum Chromodynamics, the quantum field theory of the strong interaction. Com...

We present selected results from a calculation of meson and nucleon observables in a Green-function approach. A rainbow-ladder truncation of QCD's Dyson-Schwinger equations is used to solve the respective meson, diquark and quark-diquark Bethe-Salpeter equations. It allows for a simultaneous description of meson and nucleon masses and electromagnet...

We present a calculation of the three-quark core contribution to the mass of the Delta-baryon in a Poincare-covariant Faddeev framework. A consistent setup for the dressed-quark propagator, the quark-quark and quark-diquark interactions is used, where all the ingredients are solutions of their respective Dyson-Schwinger or Bethe-Salpeter equations...

We present a calculation of the three-quark core contribution to the mass of the Delta-baryon in a Poincare-covariant Faddeev framework. A consistent setup for the dressed-quark propagator, the quark-quark and quark-diquark interactions is used, where all the ingredients are solutions of their respective Dyson-Schwinger or Bethe-Salpeter equations...

Established results for the quark propagator in Landau gauge QCD, together with a detailed comparison to lattice data, are used to formulate a Poincaré-covariant Faddeev approach to the nucleon. The resultant three-quark amplitudes describe the quark core of the nucleon. The nucleon’s mass and its electromagnetic form factors are calculated as func...

Established results for the quark propagator of Landau gauge QCD, together with a detailed comparison to lattice data, are implemented in a Poincaré-covariant Faddeev approach to the nucleon. The nucleon mass and its electromagnetic form factors, together with charge radii and magnetic moments, are calculated as a function of the current-quark mass...

Prima facie the systematic implementation of corrections to the rainbow-ladder truncation of QCD's Dyson-Schwinger equations will uniformly reduce in magnitude those calculated mass-dimensioned results for pseudoscalar and vector meson properties that are not tightly constrained by symmetries. The aim and interpretation of studies employing rainbow...

We provide a snapshot of Dyson-Schwinger equation applications to the theory and phenomenology of hadrons. Exact results for pseudoscalar mesons are highlighted, with details relating to the U_A(1) problem. Calculated masses of the lightest J=0,1 states are discussed. We recapitulate upon studies of nucleon properties and give a perspective on the...

In this summary of the application of Dyson-Schwinger equations to the theory and phenomenology of hadrons, some deductions following from a nonperturbative, symmetry-preserving truncation are highlighted, notable amongst which are results for pseudoscalar mesons. We also describe inferences from the gap equation relating to the radius of convergen...

We examine the applicability and viability of methods to obtain knowledge about bound-states from information provided solely in Euclidean space. Rudimentary methods can be adequate if one only requires information about the ground and first excited state and assumptions made about analytic properties are valid. However, to obtain information from...

This Dyson-Schwinger equation (DSE) aperçu highlights recent applications to mesons. It reports features of, and results for, pseudoscalar and scalar bound-state residues in vacuum polarisations, and exhibits how a restoration of chiral symmetry in meson trajectories could be manifest in a relationship between them. It also touches on nucleon studi...

We study pseudoscalar and scalar mesons using a practical and symmetry preserving truncation of QCD's Dyson-Schwinger equations. We investigate and compare properties of ground and radially excited meson states. In addition to exact results for radial meson excitations we also present results for meson masses and decay constants from the chiral lim...

Phenomenological consequences of the infrared singular, instantaneous part of the gluon propagator in the Coulomb gauge are investigated. The corresponding quark Dyson-Schwinger equation is solved, neglecting retardation and transverse gluons and regulating the resulting infrared singularities. While the quark propagator vanishes as the infrared re...

Electron scattering at large Q2 probes a nucleon's quark core. This core's contribution to electromagnetic form factors may be calculated using Poincaré covariant Faddeev amplitudes combined with a nucleon-photon vertex that automatically fulfills a Ward-Takahashi identity for on-shell nucleons. The calculated behaviour of on Q2∈[2,6] GeV2 agrees w...

We report an investigation of the pion’s first excited state using QCD’s Dyson-Schwinger equations. Exact results and a numerical study are presented.

Aspects of the dressed-quark-gluon vertex and their role in the gap and Bethe-Salpeter equations are briefly surveyed using an intuitive model. The model allows one to elucidate why a linear extrapolation to the chiral limit of extant lattice data on the dressed-quark mass-function overestimates this function and hence the value of the vacuum quark...

The axial-vector Ward-Takahashi identity places constraints on particular properties of every pseudoscalar meson. For example, in the chiral limit all pseudoscalar mesons, except the Goldstone mode, decouple from the axial-vector current. Nevertheless, all neutral pseudoscalar mesons couple to two photons. The strength of the \pi_n^0 \gamma \gamma...

A Poincar-covariant Faddeev equation, which describes baryons as composites of confined-quarks and -nonpointlike-diquarks, is solved to obtain masses and Faddeev amplitudes for the nucleon and Δ. The amplitudes are a component of a nucleon-photon vertex that automatically fulfills the Ward-Takahashi identity for on-shell nucleons. These elements ar...

Two-body bound states such as mesons are described by solutions of the Bethe-Salpeter equation. We discuss recent results for the pseudoscalar and vector meson masses and leptonic decay constants, ranging from pions up to cbar c bound states. Our results are in good agreement with data. Essential in these calculation is a momentum-dependent quark m...

The Poincare invariant coupled-channel formalism for two-particle systems interacting via one-particle exchange, which has been developed and applied to vector mesons in Ref. [1] is applied to axial vector mesons. We thereby extend the previous study of a dynamical treatment of the Goldstone-boson exchange by comparison with the commonly used insta...

Goldstone modes are the only pseudoscalar mesons to possess a nonzero leptonic decay constant in the chiral limit when chiral symmetry is dynamically broken. The decay constants of their radial excitations vanish. These features and aspects of their impact on the meson spectrum are illustrated using a manifestly covariant and symmetry preserving mo...

Features of the dressed-quark-gluon vertex and their role in the gap and Bethe-Salpeter equations are explored. It is argued that quenched lattice data indicate the existence of net attraction in the colour-octet projection of the quark-antiquark scattering kernel. This attraction affects the uniformity with which solutions of truncated equations c...

An hallmark of present-day Dyson-Schwinger equation applications in hadron physics is the existence of a systematic and symmetry preserving truncation scheme. This enables the proof of exact results; e.g., the leptonic decay constant of every pseudoscalar meson except the pion vanishes in the chiral limit. Calculations using the scheme's leading-or...

Dyson-Schwinger equations furnish a Poincaré covariant approach to hadron physics. They reveal that dynamical chiral symmetry breaking is tied to the long-range behaviour of the strong interaction and make predictions corroborated by modern lattice-QCD simulations. A hallmark in the contemporary use of DSEs is the existence of a nonperturvative, sy...

We recapitulate on aspects of Dyson-Schwinger equation studies relevant to pseudoscalar mesons: lattice confirmation of the DSE prediction that propagators are nonperturbatively dressed in the infrared; and exact results, e.g., in the chiral limit the leptonic decay constant vanishes for every pseudoscalar meson except the pion. Comment: 8 pages; L...

The proton’s elastic electromagnetic form factors are calculated using an ansatz for the nucleon’s Poincaré covariant Faddeev amplitude that only retains scalar diquark correlations. A spectator approximation is employed for the current. On the domain of q
2 accessible in modern precision experiments these form factors are a sensitive probe of nonp...

We apply the point form of relativistic quantum mechanics to develop a Poincare invariant coupled-channel formalism for two-particle systems interacting via one-particle exchange. This approach takes the exchange particle explicitly into account and leads to a generalized eigenvalue equation for the Bakamjian-Thomas type mass operator of the system...

We develop a formalism for the treatment of a two-particle system interacting via one-boson exchange in the point form of relativistic quantum mechanics. A Poincaré invariant coupled-channel treatment leads to a generalized eigenvalue equation for the mass operator of the system. The formalism is applied to vector mesons in a constituent-quark pict...

When calculating meson and baryon spectra within constituent quark models, not only ground states but also excited states are usually treated as stable quark-antiquark and three-quark configurations. Resonance widths are then often obtained in first-order perturbation theory by employing a particular model for the decay vertex [1]. Moreover, the co...

Starting from a one-body front-form equation with Lepage- Brodsky spinors we show, with a fair amount of new technology, how an integral equation in standard momentum space with Bjorken-Drell spinors can be obtained. The integral equation decouples for singlets and triplets.

Interacting Poincaré generators for both front form (FF) and point form (PF) are obtained by integrating interaction Lagragians over appropriate space-like surfaces. For finite degree of freedom systems mass operators in both FF and PF can be constructed using the Bakamjian-Thomas (BT) procedure. Velocity states are used to calculate matrix element...

We propose a method that allows for the efficient solution of the three-body Faddeev equations in the presence of infinitely rising confinement interactions. Such a method is useful in calculations of nonrelativistic and especially semirelativistic constituent quark models. The convergence of the partial wave series is accelerated and possible spur...

This article was written by Andreas Krassnigg and Timo Thonhauser in February 1998 referring to a lecture given by C.B. Lang on "Introduction to Lattice Gauge Theory" in the winter-semester 1997 at the "Karl-FranzensUniversit at" in Graz, Austria. The typesetting was done in L

We report further results from a study of hadronic decays of light and strange baryon resonances within a recently proposed constituent-quark model whose hyperfine interaction is derived from Goldstone-boson ex-change. Three-quark wave functions generated by solution of a semirelativistic Schrödinger-type equation with the stochastic variational me...

The recently proposed semirelativistic constituent-quark model whose hyperfine interaction relies on Goldstone-boson-exchange dynamics is applied to study hadronic decays of light and strange baryon resonances. Three-quark wave functions produced with the stochastic variational method are used to calculate partial decay widths of π and η decays wit...

Free Electron Laser. Noise. Will there be a muon-muon collider? Use of crystals to produce high energy polorized photons.

We investigate hadronic decays of mesons in a Dyson-Schwinger-Bethe-Salpeter ap-proach. This complements the studies of hadron spectra and electromagnetic properties of hadrons, which have been performed over the past years in this setup. First example results are presented for light mesons, the beginning of a systematic investigation of decays for...

We study strong decays of mesons in a Green-function approach, using the coupled system of Bethe-Salpeter and quark Dyson-Schwinger equations. We present results for the ρ → ππ-transition and range the quark masses from the chiral limit up to the strange quark mass.

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