arXiv subjects

Jon-Ivar Skullerud

Publications and source records attributed to Jon-Ivar Skullerud.

At least 91 records · Page 5Linked to original sources

arXiv2012

Non-relativistic spectrum of two-color QCD at non-zero baryon density

The heavy quarkonium spectrum of Two Color QCD (QC$_2$D) at non-zero quark chemical potential $μ$ and temperature $T$ with $μ/T\gg1$ has been calculated in both $S$- and $P$-wave channels using a lattice non-relativistic formulation of QC$_2$D. As $μ$ is varied, the quarkonium spectra reveal three separate regions, corroborating previous findings that there are three distinct physical regimes of QC$_2$D at low temperature and high baryon density: hadronic matter, quark/quarkyonic matter, and deconfined matter. The results are interpreted in terms of the formation of heavy-light $Qq$ states in the two-color baryonic medium.

hep-lat↗

arXiv2011

What happens to the Upsilon and eta_b in the quark-gluon plasma? Bottomonium spectral functions from lattice QCD

We study bottomonium spectral functions in the quark-gluon plasma in the Upsilon and eta_b channels, using lattice QCD simulations with two flavours of light quark on highly anisotropic lattices. The bottom quark is treated with nonrelativistic QCD (NRQCD). In the temperature range we consider, 0.42 < T/T_c < 2.09, we find that the ground states survive, whereas the excited states are suppressed as the temperature is increased. The position and width of the ground states are compared to analytical effective field theory (EFT) predictions. Systematic uncertainties of the maximum entropy method (MEM), used to construct the spectral functions, are discussed in some detail.

hep-lat↗

arXiv2011

Quark number susceptibility at finite density and low temperature

We study the quark number susceptibility in SU(2) lattice gauge theory with two Wilson quark flavours at non-zero chemical potential and low temperature. We present some technical aspects of the issue and numerical results obtained at different lattices and different parameters. We discuss what this observable can teach us about the phase diagram of the model and in particular about the relation between susceptibility and Polyakov loop

hep-lat↗

arXiv2011

Bottomonium at Non-zero Temperature from Lattice Non-relativistic QCD

The temperature dependence of bottomonium states at temperatures above and below $T_c$ is presented, using non-relativistic dynamics for the bottom quark and full relativistic lattice QCD simulations for two light flavors on a highly anisotropic lattice. We find that the S-waves ($Υ$ and $η_b$) show little temperature dependence in this range while the P wave propagators show a crossover from the exponential decay characterizing the hadronic phase to a power-law behavior consistent with nearly-free dynamics at approximately twice the critical temperature.

hep-ph↗

arXiv2011

Lattice Study of Dense Matter with Two Colors and Four Flavors

We present results from a simulation of SU(2) lattice gauge theory with N_f=4 flavors of Wilson fermion and non-zero quark chemical potential mu, using the same 12^3x24 lattice, bare gauge coupling, and pion mass in cut-off units as a previous study with N_f=2. The string tension for N_f=4 is found to be considerably smaller implying smoother gauge field configurations. Thermodynamic observables and order parameters for superfluidity and color deconfinement are studied, and comparisons drawn between the two theories. Results for quark density and pressure as functions of mu are qualitatively similar for N_f=2 and N_f=4; in both cases there is evidence for a phase in which baryonic matter is simultaneously degenerate and confined. Results for the stress-energy tensor, however, suggest that while N_f=2 has a regime where dilute matter is non-relativistic and weakly-interacting, N_f=4 matter is relativistic and strongly-interacting for all values of mu above onset.

hep-lat↗

arXiv2010

A Quarkyonic Phase in Dense Two Color Matter?

We present results from simulations of Two Color QCD with two Wilson quark flavors in the presence of a quark chemical potential mu at two different lattice spacings. The equation of state, conformal anomaly, superfluid order parameter and Polyakov line are all discussed. Our results suggest that the transition from hadronic to quark matter, and that from confined to deconfined matter occur at distinct values of mu, consistent with the existence of a quarkyonic phase in this model.

hep-lat↗

arXiv2009

Gluons, quarks and deconfinement at high density

We compute gluon and quark propagators in 2-colour QCD at large baryon chemical potential mu. The gluon propagator is found to be antiscreened in the superfluid, confined phase and screened in the large-mu, deconfined phase. We present the first attempt to determine corresponding electric and magnetic gluon masses. The quark propagator undergoes dramatic modifications in the superfluid region as a result of the formation of a superfluid gap. These modifications include the appearance of zero crossings in the vector part of the (normal) quark propagator, a large suppression of the scalar part, and the emergence of anomalous propagation.

hep-lat↗

arXiv2008

Quarks and gluons in dense two-colour QCD

We compute quark and gluon propagators in 2-colour QCD at large baryon chemical potential mu. The gluon propagator is found to be antiscreened at intermediate mu and screened at large mu. The quark propagator is drastically modified in the superfluid region as a result of the formation of a superfluid gap.

hep-lat↗

arXiv2007

Charmonium at high temperature in two-flavor QCD

We compute charmonium spectral functions in 2-flavor QCD on anisotropic lattices using the maximum entropy method. Our results suggest that the S-waves (J/psi and eta_c) survive up to temperatures close to 2Tc, while the P-waves (chi_c0 and chi_c1) melt away below 1.2Tc.

hep-lat↗

arXiv2007

Hadron Spectrum in a Two-Colour Baryon-Rich Medium

The hadron spectrum of SU(2) lattice gauge theory with two flavours of Wilson quark is studied on an 8^3x16 lattice using all-to-all propagators, with particular emphasis on the dependence on quark chemical potential mu. As mu is increased from zero the diquark states with non-zero baryon number B respond as expected, while states with B=0 remain unaffected until the onset of non-zero baryon density at mu=m_pi/2. Post onset the pi-meson mass increases in accordance with chiral perturbation theory while the rho becomes lighter. In the diquark sector a Goldstone state associated with a superfluid ground state can be identified. A further consequence of superfluidity is an approximate degeneracy between mesons and baryons with the same spacetime and isospin quantum numbers. Finally we find tentative evidence for the binding of states with kaon quantum numbers within the baryonic medium.

hep-lat↗

arXiv2007

Quark-gluon vertex in general kinematics

We compute the quark-gluon vertex in quenched lattice QCD, in the Landau gauge using an off-shell mean-field O(a)-improved fermion action. The Dirac-vector part of the vertex is computed for arbitrary kinematics. We find a substantial infrared enhancement of the interaction strength regardless of the kinematics.

hep-lat↗

arXiv2006

Quark Matter in QC(2)D

Results are presented from a numerical study of lattice QCD with gauge group SU(2) and two flavors of Wilson fermion at non-zero quark chemical potential mu >> T. Studies of the equation of state, the superfluid condensate, and the Polyakov line all suggest that in addition to the low density phase of Bose-condensed diquark baryons, there is a deconfined phase at higher quark density in which quarks form a degenerate system, whose Fermi surface is only mildly disrupted by Cooper pair condensation.

nucl-th↗

arXiv2006

Dynamical QCD simulations on anisotropic lattices

The simulation of QCD on dynamical (Nf=2) anisotropic lattices is described. A method for nonperturbative renormalisation of the parameters in the anisotropic gauge and quark actions is presented. The precision with which this tuning can be carried out is determined in dynamical simulations on 8^3x48 and 8^3x80 lattices.

hep-lat↗

arXiv2006

Deconfinement in dense 2-color QCD

We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential mu and low temperature on a 8^3x16 system. We identify three regimes along the mu-axis. For mu<~m_pi/2 the system remains in the vacuum phase, and all physical observables considered remain essentially unchanged. The intermediate regime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose-Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined regime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of mu exhibits a minimum in the deconfined regime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter.

hep-lat↗

arXiv2005

Mesons at high temperature in Nf=2 QCD

We report first results for spectral functions of charmonium in 2-flavour QCD. The spectral functions are determined from vector and pseudoscalar correlators on a dynamical, anisotropic lattice. J/psi and eta_c are found to survive well into the deconfined phase before melting away at T<~2T_c. Current systematic uncertainties prevent us from drawing any definite conclusions at this stage.

hep-lat↗

arXiv2005

Static-light hadrons on a dynamical anisotropic lattice

We present preliminary results for the static-light meson and baryon spectra for $N_f=2$ QCD. The study is performed on an anisotropic lattice and uses a new all-to-all propagator method allowing us to determine particle masses to a high precision.

hep-lat↗

arXiv2005

The onset and deconfinement transitions in two-colour QCD

We study two-colour QCD with two flavours of Wilson fermion at non-zero chemical potential mu and zero temperature. We find evidence of two separate transitions: an onset transition at mu ~ m_pi/2 where quark number and energy densities increase from zero; and a deconfinement transition at higher mu. The mu-dependence of the number and energy densities and the diquark condensate indicate that a Fermi surface is formed and that BCS rather than Bose-Einstein condensation dominates at the quark mass considered here, especially beyond the deconfinement transition.

hep-lat↗

arXiv2005

Two Color QCD beyond the BEC regime

We present results of simulations of Two Color QCD using two flavors of Wilson quark in the fundamental representation, at non-zero quark chemical potential mu, on an 8^3x16 lattice. Results for the quark number density, quark and gluon energy densities, and superfluid condensate are qualitatively distinct from the behaviour expected on the assumption that the dominant degrees of freedom are tightly bound scalar diquarks which Bose condense; rather the scaling with mu is more suggestive of a Fermi surface disrupted by a Cooper pair condensate. We also present evidence both for screening of the static potential, and color deconfinement, arising solely as a result of a non-zero quark density.

hep-lat↗