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Robert Harlander

Publications and source records attributed to Robert Harlander.

At least 19 recordsLinked to original sources
arXiv2025

The life cycle of scientific principles -- a template for characterizing physical principles

Scientific principles can undergo various developments. While philosophers of science have acknowledged that such changes occur, there is no systematic account of the development of scientific principles. Here we propose a template for analyzing the development of scientific principles called the 'life cycle' of principles. It includes a series of processes that principles can go through: prehistory, elevation, formalization, generalization, and challenge. The life cycle, we argue, is a useful heuristic for the analysis of the development of scientific principles. We illustrate this by discussing examples from foundational physics including Lorentz invariance, Mach's principle, the naturalness principle, and the perfect cosmological principle. We also explore two applications of the template. First, we propose that the template can be employed to diagnose the quality of scientific principles. Second, we discuss the ramifications of the life cycle's processes for the empirical testability of principles.

physics.hist-ph↗
arXiv2024

Determining the Quark Mass with the Gradient Flow

We propose a new method to determine the quark mass by using bilinear operators of the flowed quark field defined within the gradient-flow formalism. This method enables the quark mass determination through a comparison of perturbative calculations with lattice data. The gauge-invariant nature of the observable should allow clear control over perturbative errors. At the same time, the gradient flow suppresses the noise in the lattice measurements of the observable, which simply consists of one-point functions. Concerning the perturbative input in this framework, we study the mass dependence of the flowed quark condensate $\langle \bar{\chi}(t,x) \chi(t,x) \rangle$ at the two-loop level. For this purpose, we develop a novel approach for expanding massive gradient-flow integrals in the limit of small and large $(m^2t)$. We also present a fully numerical result which includes the full mass dependence.

hep-lat↗
arXiv2024

Gradient Flow Renormalisation for Meson Mixing and Lifetimes

Fermionic gradient flow in combination with the short-flow-time expansion provides a computational method where the renormalisation of hadronic matrix elements on the lattice can be simplified to address e.g. the issue that operators with different mass dimension can mix. We demonstrate our gradient flow renormalisation procedure by determining matrix elements of four-quark operators describing neutral meson mixing or meson lifetimes. While meson mixing calculations are well-established on the lattice and serve to validate our procedure, a lattice calculation of matrix elements for heavy meson lifetimes is still outstanding. Preliminary results for mesons formed of a charm and strange quark are presented.

hep-lat↗
arXiv2024

FeynGame-2.1 -- Feynman diagrams made easy

FeynGame is an open-source software tool to draw Feynman diagrams, but also to get acquainted with their structure. This article reports on a number of new features which have been added to FeynGame since its first release. These include full support of LaTeX for the line and vertex labels, the possibility to automatically include momentum arrows, new graphical elements, and new pedagogical features. FeynGame is freely available as jar or MacOS app file from https://web.physik.rwth-aachen.de/user/harlander/software/feyngame, and as source code from https://gitlab.com/feyngame/FeynGame.

hep-ph↗
arXiv2023

Using Gradient Flow to Renormalise Matrix Elements for Meson Mixing and Lifetimes

Neutral meson mixing and meson lifetimes are theory-side parametrised in terms four-quark operators which can be determined by calculating weak decay matrix elements using lattice Quantum Chromodynamics. While calculations of meson mixing matrix elements are standard, determinations of lifetimes typically suffer from complications in renormalisation procedures because dimension-6 four-quark operators can mix with operators of lower mass dimension and, moreover, quark-line disconnected diagrams contribute. We present work detailing the idea to use fermionic gradient flow to non-perturbatively renormalise matrix elements describing meson mixing or lifetimes, and combining it with a perturbative calculation to match to the $\overline{\rm MS}$ scheme using the shoft-flow-time expansion.

hep-lat↗
arXiv2021

The gradient flow at higher orders in perturbation theory

Various results for higher-order perturbative calculations in the gradient-flow formalism are reviewed, including the gradient-flow beta function and the small-flow-time expansion of the hadronic vacuum polarization and the energy-momentum tensor. In addition, the strategy of regions is outlined in order to obtain systematic expansions of gradient-flow integrals, for example at large and small flow times.

hep-lat↗
arXiv2021

The electroweak Hamiltonian in the gradient flow formalism

Over the last decade the gradient flow formalism has become an important tool for lattice simulations of Quantum Chromodynamics. It offers remarkable renormalization properties which pave the way for cross-fertilization between perturbative and lattice calculations. In this contribution we report on the construction of the flowed operator product expansion for the current-current operators of the electroweak Hamiltonian at NNLO QCD. This allows for simpler transformations between lattice and perturbative schemes and might reduce the uncertainties of theoretical predictions for low-energy flavor observables.

hep-lat↗
arXiv2018

Naturalness, Wilsonian Renormalization, and "Fundamental Parameters" in Quantum Field Theory

The Higgs naturalness principle served as the basis for the so far failed prediction that signatures of physics beyond the Standard Model (SM) would be discovered at the LHC. One influential formulation of the principle, which prohibits fine tuning of bare Standard Model (SM) parameters, rests on the assumption that a particular set of values for these parameters constitute the "fundamental parameters" of the theory, and serve to mathematically define the theory. On the other hand, an old argument by Wetterich suggests that fine tuning of bare parameters merely reflects an arbitrary, inconvenient choice of expansion parameters and that the choice of parameters in an EFT is therefore arbitrary. We argue that these two interpretations of Higgs fine tuning reflect distinct ways of formulating and interpreting effective field theories (EFTs) within the Wilsonian framework: the first takes an EFT to be defined by a single set of physical, fundamental bare parameters, while the second takes a Wilsonian EFT to be defined instead by a whole Wilsonian renormalization group (RG) trajectory, associated with a one-parameter class of physically equivalent parametrizations. From this latter perspective, no single parametrization constitutes the physically correct, fundamental parametrization of the theory, and the delicate cancellation between bare Higgs mass and quantum corrections appears as an eliminable artifact of the arbitrary, unphysical reference scale with respect to which the physical amplitudes of the theory are parametrized. While the notion of fundamental parameters is well motivated in the context of condensed matter field theory, we explain why it may be superfluous in the context of high energy physics.

physics.hist-ph↗
arXiv2014

Resummed Higgs $p_T$ distribution at NNLL + NNLO in bottom-quark annihilation

The resummed transverse-momentum distribution for Higgs bosons produced via bottom-quark annihilation at the LHC is presented. Our results are obtained in the five-flavor scheme to NNLO+NNLL accuracy. We present a theoretical prediction which consistently matches the cross section at small and large transverse momenta. Theoretical uncertainties are derived from a variation of the unphysical scales entering the calculation. Their size is significantly reduced with respect to lower orders.

hep-ph↗
arXiv2011

Bottom-quark associated Higgs-boson production: reconciling the four- and five-flavour scheme approach

The main arguments in the discussion of the proper treatment of the total inclusive cross section for bottom-quark associated Higgs-boson production are briefly reviewed. A simple and pragmatic formula for the combination of the so-called four- and five-flavour schemes is suggested, including the treatment of the respective theory error estimates. The numerical effects of this matching formula are discussed.

hep-ph↗
arXiv2011

Top-Quark Mediated Effects in Hadronic Higgs-Strahlung

Novel contributions to the total inclusive cross section for Higgs-Strahlung in the Standard Model at hadron colliders are evaluated. Although formally of order $α_s^2$, they have not been taken into account in previous NNLO predictions. The terms under consideration are induced by Higgs radiation off top-quark loops and thus proportional to the top-quark Yukawa coupling. At the Tevatron, their effects to HW production are below 1% in the relevant Higgs mass range, while for HZ production, we find corrections between about 1% and 2%. At the LHC, the contribution of the newly evaluated terms to the cross section is typically of the order of 1%-3%. Based on these results, we provide updated predictions for the total inclusive Higgs-Strahlung cross section at the Tevatron and the LHC.

hep-ph↗
arXiv2010

Higgs production in gluon fusion at NNLO for finite top quark mass

The evaluation of the top quark mass suppressed terms to the Higgs production cross section in gluon fusion at next-to-next-to-leading order is reported on. In the region below threshold, the Feynman diagrams are evaluated using asymptotic expansions. The result is then matched to the high-energy limit derived from kT factorization. The result shows that the heavy-top limit used so far approximates the full result to better than 1%.

hep-ph↗
arXiv2008

Gluon-Induced Weak Boson Fusion

The gluon-gluon induced terms for Higgs production through weak boson fusion (WBF) are computed. Formally, these are of NNLO in the strong coupling constant. This is the lowest order at which non-zero color exchange occurs between the scattering quarks, leading to a color field and thus additional hadronic activity between the outgoing jets. Using a minimal set of cuts, the numerical impact of these terms is at the percent level with respect to the NLO rate for weak boson fusion. Applying the so-called WBF cuts leads to an even stronger suppression, so that we do not expect a significant deterioration of the WFB signal by these color exchange effects.

hep-ph↗
arXiv2007

Dimensional Reduction applied to QCD at higher orders

Recent developments in higher order calculations within the framework of Dimensional Reduction, the preferred regularization scheme for supersymmetric theories, are reported on. Special emphasis is put on the treatment of evanescent couplings, the equivalence to Dimensional Regularization, and the evaluation of $α_s(M_GUT)$ from $α_s(M_Z)$.

hep-ph↗
arXiv2006

Standard and SUSY Higgs production at the LHC

Recent theoretical developments concerning Higgs production at the Large Hadron Collider are reviewed, both in the Standard Model and in the MSSM. Emphasis is put on the inclusive and exclusive cross sections for gluon fusion, as well as on the associated production with bottom quarks.

hep-ph↗
arXiv2005

Higgs production and decay: Analytic results at next-to-leading order QCD

The virtual two-loop corrections for Higgs production in gluon fusion are calculated analytically in QCD for arbitrary Higgs and quark masses. Both scalar and pseudo-scalar Higgs bosons are considered. The results are obtained by expanding the known one-dimensional integral representation in terms of m_H/m_q, and matching it with a suitably chosen ansatz of Harmonic Polylogarithms. This ansatz is motivated by the known analytic result for the Higgs decay rate into two photons. The method also allows us to check this result and to extend it to the pseudo-scalar decay rate.

hep-ph↗
arXiv2003

Supersymmetric Higgs production at the Large Hadron Collider

We review the status of theoretical predictions for the production of neutral Higgs bosons at the LHC. Special emphasis is put on the role of bottom quarks in the gluon fusion process and in the associated production of Higgs bosons with bb-bar pairs.

hep-ph↗