Jon-Ivar Skullerud

A quantitative investigation into the modification of ground-state field structures in two-color QCD ( QC 2 D ) is presented at finite chemical potential. Using lattice simulations with Wilson gauge and fermion actions, we explore the chromo-electromagnetic field strengths under varying matter densities. To ensure accurate measurements, we develop and calibrate two highly improved topological charge operators and evaluate four gradient flow actions. Our results reveal a finite-volume crossover in the regime of the anticipated phase boundary at μ = m π / 2 , with both chromoelectric and chromomagnetic field strengths suppressed before recovering and exceeding vacuum values at higher chemical potentials. We find the difference between the squared chromoelectric and chromomagnetic field strengths, E 2 − B 2 , to increase in magnitude monotonically with increasing chemical potential. At a μ = 0.7 , we find an 11% suppression of E 2 , a relatively small effect. A systematic analysis using sigmoid fits of lattice simulations in the crossover regime is performed to confirm the critical chemical potential obtained from the field structure is in agreement with the phase boundary at m π / 2 . These findings provide new insight into non-Abelian ground-state vacuum field structures and offer a foundation for future studies in real QCD.

In the QCD phase diagram, the dependence of the pseudocritical temperature, T pc , on the baryon chemical potential, μ B , is of fundamental interest. The variation of T pc with μ B is normally captured by κ , the coefficient of the leading (quadratic) term of the polynomial expansion of T pc with μ B . In this work, we present the first calculation of κ using hadronic quantities. Simulating N f = 2 + 1 flavors of Wilson fermions on astsum ensembles, we calculate the O ( μ B 2 ) correction to mesonic correlation functions. By demanding degeneracy in the vector and axial-vector channels we obtain T pc ( μ B ) and hence κ . While lacking a continuum extrapolation and being away from the physical point, our results are consistent with previous works using thermodynamic observables (renormalized chiral condensate, strange quark number susceptibility) from lattice QCD simulations with staggered fermions.

We investigate spectral features of bottomonium at high temperature, in particular the thermal mass shift and width of ground state S-wave and P-wave state. We employ and compare a range of methods for determining these features from lattice NRQCD correlators, including direct correlator analyses (multi-exponential fits and moments of spectral functions), linear methods (Backus-Gilbert, Tikhonov and HLT methods), and Bayesian methods for spectral function reconstruction (MEM and BR). We comment on the reliability and limitations of the various methods.

The FASTSUM collaboration has a long-standing project examining hadronic properties using anisotropic lattice QCD. We determine the spectral properties of bottomonia at finite temperature using lattice NRQCD and describe how our newer simulations improve our control over systematic errors. Motivated by these efforts, the temperature dependence of charm hadron masses is determined where it is found that temperature effects can extend into the confining phase and that some species remain stable deep past the pseudo-critical temperature.

We investigate spectral features of bottomonium at high temperature, in particular the thermal mass shift and width of ground state S-wave and P-wave state. We employ and compare a range of methods for determining these features from lattice NRQCD correlators, including direct correlator analyses (multi-exponential fits and moments of spectral functions), linear methods (Backus-Gilbert, Tikhonov and HLT methods), and Bayesian methods for spectral function reconstruction (MEM and BR). We comment on the reliability and limitations of the various methods.

We study the impact of Gribov copies on the quark propagator in lattice 2-color quantum chromodynamics (QCD). We find that the Gribov noise is comparable to the gauge noise for smaller volumes but becomes less significant for larger spatial volumes. The Gribov noise in the quark propagator is found to be comparable to, but smaller than in the gluon propagator on the same ensembles. No correlation is found between the values of either of the quark propagator form factors and the value of the gauge fixing functional, nor between the two form factors. Published by the American Physical Society 2025