arXiv subjects

Johannes Heinrich Weber

Publications and source records attributed to Johannes Heinrich Weber.

At least 19 recordsLinked to original sources

arXiv2026

Scale Setting and Strong Coupling Determination in the Gradient Flow Scheme for 2+1 Flavor Lattice QCD

We report on the determination of the gradient flow scales in $N_f=2+1$ QCD using highly improved staggered quark (HISQ) ensembles generated by the HotQCD Collaboration for bare gauge couplings ranging from $β= 6.423$ to $8.400$. Using bottomonium splittings, kaon decay constant, the decay constant of unmixed $η_s$ meson and the $ϕ$ meson mass we obtained the values of the gradient flow scales in physical units, $\sqrt{t_0} = 0.14446 (76)$ fm and $w_0 = 0.17429 (83)$ fm. Using the same physical inputs we revisit the determination of the potential $r_1$ scale and find $r_1 = 0.3118(26)$~fm. As a byproduct of our study we obtain the running of the gauge coupling in the gradient flow scheme. We find that within the uncertainties the running of the gradient flow coupling obtained on the lattice is compatible with the perturbative results up to flow radius $\sqrt{8 τ_F}=0.15$ fm.

hep-lat↗

arXiv2026

Highly improved staggered quarks on anisotropic lattices

We present a study of tuning of the anisotropic highly improved staggered quark (aHISQ) action on pure gauge ensembles with the renormalized anisotropy ranging from 1 to 8. We discuss multiple gradient flow schemes for tuning the gauge anisotropy and comment on what scheme may be optimal for anisotropic simulations. Next, we compare tuning of the fermion anisotropy for the naive staggered and aHISQ actions. Finally, we study the dependence of the staggered pion taste mass splittings on anisotropy for the two actions and develop an empirical model that captures the main features of the aHISQ spectrum. We observe qualitatively different behavior of the naive and aHISQ taste spectrum with anisotropy.

hep-lat↗

arXiv2026

Fluctuation-Dissipation Relation for Hard Partons in a Gluonic Plasma

We derive a fluctuation dissipation relation connecting the drag and diffusion jet transport coefficients for an energetic light quark traversing a non-perturbative thermalized gluon plasma. The hard quark is taken to be close to on-shell, with an energy scale parametrically larger than the medium temperature. We introduce a general complex-valued function for each transport coefficient. Evaluating these in the deep Euclidean momentum region enables their expression in terms of local operators. Using contour-integration techniques, we relate these local operators, after vacuum subtraction, to the physical transport coefficients that arise along a branch cut, close to light-like dispersion. The derived relation relates the longitudinal drag coefficient to the longitudinal and transverse diffusion coefficients, and the thermal gluon condensate.

hep-ph↗

arXiv2025

Temperature Dependence of Heavy Quark Diffusion from (2+1)-flavor Lattice QCD

We present a lattice determination of the heavy-quark diffusion coefficient in (2+1)-flavor QCD with almost physical quark masses. The momentum and spatial diffusion coefficients are extracted for a wide temperature range, from $T=163$ MeV to $10$ GeV. The results are in agreement with previous works from the HotQCD collaboration, and show fast thermalization of the heavy quark inside the QGP. Near the chiral crossover temperature $T_c\simeq150$ MeV, our results are close to the AdS/CFT estimation computed at strong coupling.

hep-lat↗

arXiv2025

Towards dynamical simulations with the anisotropic HISQ action

The primary goal of this project is the reconstruction of quarkonium spectral functions from thermal lattice correlators, relevant for the study of Quark-Gluon Plasma in heavy-ion collisions. To this end, we pursue the generation of fully dynamical anisotropic HISQ (aHISQ) ensembles, aiming at a physical strange quark and a heavier-than-physical light quark mass, corresponding to a 300 MeV continuum pion mass. We report on tuning the gauge anisotropy and the lattice spacing of anisotropic pure gauge ensembles with the tree-level Symanzik-improved action using the gradient flow and compare various tuning schemes. We also discuss the simultaneous tuning of the strange quark mass and the quark anisotropy with aHISQ, using spectrum measurements on quenched ensembles. We compare different ways to tune the quark anisotropy and discuss pion taste splittings for aHISQ at anisotropies up to 8. Finally, we present the expressions for the aHISQ fermion force required for dynamical simulations.

hep-lat↗

arXiv2025

Spin-taste representation of minimally doubled fermions from first principles: Karsten-Wilczek fermions

Minimally doubled fermions realize one pair of Dirac fermions on the lattice. Similarities to Kogut-Susskind fermions exist, namely, spin and taste degrees of freedom become intertwined, and a peculiar non-singlet chiral symmetry and ultralocality are maintained. However, charge conjugation, some space-time reflection symmetries and isotropy are broken by the cutoff. We address the most simple variant, Karsten-Wilczek fermions, in its parallel and in its perpendicular version. We derive the correct spin-taste representation from first principles. The spin-taste representation on the quark level permits construction of local or extended hadron interpolating operators for any spin-taste combination, albeit with contamination by parity partners and taste-symmetry breaking. We classify all interpolating operator for mesons and diquarks, and give examples for baryons. We also discuss the appropriate discretizations for taste-singlet or taste-isovector mass or chemical potential terms. We explain the counterterms in the spin-taste framework, and derive generic constraints on the parametric form and cutoff effects from the KW determinant and hadronic correlation functions. We derive how and why non-perturbative tuning schemes for the counterterms work, and obtain analytic, assumption-free, non-perturbative predictions for taste-symmetry breaking and other hadronic properties from first principles. In particular, we identify the origin and nature of two different types of taste-symmetry breaking cutoff effects. The few available numerical results for KW fermions validate these predictions.

hep-lat↗

arXiv2025

Jet transport coefficient $\hat{q}$ in lattice QCD

We present the first calculation of the jet transport coefficient $\hat{q}$ in quenched and (2+1)-flavor QCD on a 4-D Euclidean lattice. The light-like propagation of an energetic parton is factorized from the mean square gain in momentum transverse to the direction of propagation, which is expressed in terms of the thermal field-strength field-strength correlator. The leading-twist term in its operator product expansion is calculated on the lattice. Continuum extrapolated quenched results, and full QCD estimates based on un-renormalized lattice data, over multiple lattice sizes, are compared with (non) perturbative calculations and phenomenological extractions of $\hat{q}$. The lattice data for $\hat{q}$ show a temperature dependence similar to the entropy density. Within uncertainties, these are consistent with phenomenological extractions, contrary to calculations using perturbation theory.

hep-lat↗

arXiv2025

Strong coupling in (2+1+1)-flavor QCD

The strong coupling $α_\mathrm{s}$ can be obtained from the static energy as shown in previous lattices studies. For short distances, the static energy can be calculated both on the lattice with the use of Wilson line correlators, and with the perturbation theory up to three loop accuracy with leading ultrasoft log resummation. Comparing the perturbative expression and lattice data allows for precise determination of $α_\mathrm{s}(m_Z)$. We will present preliminary results for the determination of $α_\mathrm{s} {(M_Z)}$ in (2+1+1)-flavor QCD using the configurations made availableby the MILC-collaboration with smallest lattice spacing reaching 0.0321fm.

hep-lat↗

arXiv2024

An update on supersphere non linear sigma model on the lattice

We consider the discretized version of the sigma-model with supersphere target space $OSp(N+2m|2m)/OSp(N+2m-1|2m)$ and present a preliminary numerical study of bosonic and fermionic two-point functions for the cases $OSp(3|2)$ and $OSp(5|2)$. We observe consistency with the expectations of this supersymmetric setup and discuss the sign problem.

hep-lat↗

arXiv2024

Un-screened forces in Quark-Gluon Plasma?

We study the correlator of temporal Wilson lines at non-zero temperature in 2+1 flavor lattice QCD with the aim to define the heavy quark-antiquark potential at non-zero temperature. For temperatures $153~{\rm MeV} \leq T \leq 352~{\rm MeV}$ the spectral representation of this correlator is consistent with a broadened peak in the spectral function, position or width of which then defines the real or imaginary parts of the heavy quark-antiquark potential at non-zero temperature, respectively. We find that the potential's real part is not screened contrary to the widely-held expectations. We comment on how this fact may modify the picture of quarkonium melting in the quark-gluon plasma.

hep-lat↗

arXiv2024

In-medium static inter-quark potential on high resolution quenched lattices

We re-investigate the interactions between static color sources in a finite temperature gluonic medium using both high resolution isotropic and anisotropic quenched lattice QCD ensembles. The underlying ill-posed inverse problem, related to the extraction of spectral functions, is attacked with a range of different methods, including Bayesian inference, Padé interpolation and model fits. Among the latter we include a tail amended Gaussian ansatz and a HTL-inspired fit ansatz. We reconfirm the presence of a dominant low-lying spectral feature that supports the existence of a potential picture for the in-medium evolution of the static charges at late real times. Using the raw unmodified lattice data, all applicable methods show clear signs of screening of the real-part of the potential. After applying a subtraction procedure featured in a previous study we find however that screening disappears from the extracted potential. Paths towards the resolution of this puzzle are discussed.

hep-lat↗

arXiv2024

Exploring the anisotropic HISQ (aHISQ) action

The fate of heavy quarkonia states in quark-gluon plasma is encoded in the temperature dependence of their spectral functions. Reconstruction of spectral functions from Euclidean lattice correlators is an ill-posed problem. Despite a variety of techniques developed recently, many questions remain unresolved. It is known that the situation may be improved using anisotropic ensembles that provide finer resolution in the temporal direction. To date, the effort focused on Wilson fermions. We report on our first study with anisotropic improved staggered quarks. To compute the spectrum of the anisotropic Highly Improved Staggered Quarks (aHISQ) we generated a library of anisotropic pure gauge ensembles. We discuss the gauge anisotropy tuning that is performed with the Wilson and Symanzik gradient flow, as well as tuning of the strange quark mass and quark anisotropy with aHISQ, using spectrum measurements on quenched ensembles. Finally, we discuss the impact of anisotropy on pion taste splittings for aHISQ.

hep-lat↗

arXiv2022

Supersphere non-linear sigma model on the lattice

Two-dimensional $O(N)$ non-linear sigma models are exactly solvable theories and have many applications, from statistical mechanics to their use as QCD toy models. We consider a supersymmetric extension, the non-linear sigma model on the supersphere~$S^{N+2m-1|2m}\equiv \frac{OSP(N+2m|2m)}{OSP(N+2m-1|2m)}$. We briefly describe its renormalization properties and lattice discretization, and present a strategy for numerical simulations together with some preliminary numerical results.

hep-lat↗

arXiv2022

Charm mass effects in the static energy computed in 2+1+1 flavor lattice QCD

We report our analysis for the static energy in (2+1+1)-flavor QCD over a wide range of lattice spacings and several quark masses. We obtain results for the static energy out to distances of nearly 1 fm, allowing us to perform a simultaneous determination of the lattice scales $r_2$, $r_1$ and $r_0$ as well as the string tension, $σ$. While our results for ${r_0}/{r_1}$ and $r_0$ $\sqrtσ$ agree with published (2+1)-flavor results, our result for ${r_1}/{r_2}$ differs significantly from the value obtained in the (2+1)-flavor case, likely due to the effect of the charm quark. We study in detail the effect of the charm quark on the static energy by comparing our results on the finest lattices with the previously published (2+1)-flavor QCD results at similar lattice spacing. The lattice results agree well with the two-loop perturbative expression of the static energy incorporating finite charm mass effects.

hep-lat↗

arXiv2022

Static quark anti-quark interactions at non-zero temperature from lattice QCD

We present results on the in-medium interactions of static quark anti-quark pairs using realistic 2+1 HISQ flavor lattice QCD. Focus is put on the extraction of spectral information from Wilson line correlators in Coulomb gauge using four complementary methods. Our results indicate that on HISQ lattices, the position of the dominant spectral peak associated with the real-part of the interquark potential remains unaffected by temperature. This is in contrast to prior work in quenched QCD and we present follow up comparisons to newly generated quenched ensembles.

hep-lat↗

arXiv2022

Static quark anti-quark interactions at non-zero temperature from lattice QCD

We study the interactions of a static quark antiquark pair at non-zero temperature using realistic 2+1 flavor lattice QCD calculations. The study consists of two parts: the first investigates the properties of Wilson line correlators in Coulomb gauge and compares to predictions of hard-thermal loop perturbation theory. As a second step we extract the spectral functions underlying the correlators using four conceptually different methods: spectral function fits, a HTL inspired fit for the correlation function, Padé rational approximation and the Bayesian BR spectral reconstruction. We find that our high statistics Euclidean lattice data are amenable to different hypotheses for the shapes of the spectral function and we compare the implications of each analysis method for the existence and properties of a well defined ground state spectral peak.

hep-lat↗

arXiv2022

Strong coupling constant from moments of quarkonium correlators revisited

We revisit previous determination of the strong coupling constant from moments of quarkonium correlators in (2+1)-flavor QCD. We use previously calculated moments obtained with Highly Improved Staggered Quark (HISQ) action for five different quark masses and several lattice spacings. We perform a careful continuum extrapolations of the moments and from the comparison of these to the perturbative result we determine the QCD Lambda parameter, $Λ_{\overline{MS}}^{n_f=3}=332 \pm 17 \pm 2(scale)$ MeV. This corresponds to $α_s^{n_f=5}(μ=M_Z)=0.1177(12)$.

hep-lat↗

arXiv2022

Heavy quarks at finite temperature

New incarnations of heavy-ion collision experiments are turning our attention to hard processes and a more fine-grained resolution of the QGP. In this endeavor quarkonia or open heavy flavors turn out to be versatile probes, which are usually described through models based on perturbative QCD, AdS, and effective field theories. The lattice provides nonperturbative input and constraints to such models.\newline In-medium bottomonia, the complex static quark-antiquark potential, and the heavy-quark momentum diffusion coefficient are key quantities where lattice gauge theory has recently achieved significant progress with impact for heavy-ion phenomenology. We review these lattice results, relate them to phenomenological applications, and close with an outlook.

hep-lat↗