Hard and thermal probes of QGP from the perspective of Lattice QCD

In this talk I review the current status of lattice QCD results on the hard and thermal probes of QGP, including jet quenching parameters, the melting of quarkonia and open heavy flavours, thermal photon/dilepton rates, electrical conductivity as well as heavy quark diffusion coefficients.Comment: 6 pages, plenary talk given at the 6th International Conference on Hard and Electromagnetic Probes of High-energy Nuclear Collisions (Hard Probes 2013), accepted version to appear in NP

Exploring QCD phase diagram at vanishing baryon density on the lattice

I report on the current status of QCD phase diagram at vanishing baryon density. I focus on the QCD phase diagram with three degenerate quark flavor using Highly Improved Staggered Quarks on $N_{\tau}=6$ lattices. No evidence of a first order phase transition in the pion mass window of $80\lesssim m_{\pi} \lesssim 230$MeV is found. The pion mass at the critical point where the chiral first order phase transition ends is estimated to be $m^c_{\pi} \lesssim 45$ MeV.Comment: proceedings for Extreme QCD (XQCD 2012), August 21-23, 2012, The George Washington University, Washington DC, US

Momentum dependences of charmonium properties from lattice QCD

Charmonia produced in initial hard parton scatterings during heavy ion collisions move with respect to the medium rather than flow with the medium. Lattice studies suggest that charmonium bound states at the rest are dissociated at $T\gtrsim 1.5 T_c$. We present results on momentum dependences of charmonium properties in a hot medium from lattice QCD Monte Carlo simulations. The dispersion relation of the screening mass and the change of correlation and spectral functions at various temperatures and momenta are discussed.Comment: parallel talk given at the Quark Matter 2012 International Conference, August 13-18, Washington D.C., US

Recent lattice QCD results and phase diagram of strongly interacting matter

I review recent lattice QCD results on a few selected topics which are relevant to the heavy ion physics community. Special emphasis is put on the QCD equation of state at vanishing and nonzero baryon chemical potential, the onset of deconfinement of open strange and charmed hadrons, the contribution from experimentally not yet observed hadrons to the thermodynamics of the hadronic gas and their influence on freeze-out conditions of strange and light-quark hadrons.Comment: plenary talk given at Quark Matter 2014, Darmstadt, May 2014, 8 page

Chiral phase transition of NfN_f=2+1 and 3 QCD at vanishing baryon chemical potential

We present updated results on chiral phase structure in (2+1)-flavor ($N_f$=2+1) and 3-flavor ($N_f=3$) QCD based on the simulations using Highly Improved Staggered Quarks on lattices with temporal extent $N_\tau$ =6 at vanishing baryon chemical potential. In $N_f$=2+1 QCD we have performed simulations with a strange quark fixed to its physical value and two degenerate light quarks whose values are adjusted to have 5 values of Goldstone pion masses in the region of 160 - 80 MeV in the continuum limit. The universal scaling behavior of chiral condensates as well as chiral susceptibilities is discussed and the tri-critical point is suggested to be located below the physical point, i.e. at smaller than physical strange quark mass. In $N_f$=3 QCD simulations with 6 different masses of 3 degenerate quarks corresponding to the Goldstone pion masses in the region of 230 - 80 MeV have also been performed. Our results suggest that the QCD transition with these values of quark masses is of crossover type and an upper bound of the critical pion mass where the first order phase transition starts is estimated to be about 50 MeV.Comment: Proceedings of the 33rd International Symposium on Lattice Field Theory, July 14-18, 2015, Kobe, Japa

The curvature of the chiral phase transition line for small values of μB\mu_B

We present preliminary results from an ongoing calculation to determine the curvature of the chiral phase transition line in the chiral limit along the light-light, light-strange and strange-strange chemical potential directions. We do this by studying the appropriate $\mu$-derivatives of the chiral condensate as a function of the quark mass and comparing them to the scaling predictions of $3d$-$O(N)$ theory. We work at a fixed lattice spacing, $N_\tau=6$ and at four different quark masses $m_\pi\approx$ 140, 110, 90 and 80 MeV. For the light quark curvature, we obtain a value 0.03$\leqslant\kappa_{ll}\leqslant$0.11. We also find that both strange and light-strange curvatures are around an order of magnitude smaller. Currently, the light-strange curvature is the least constrained curvature and could have either sign, though our results seem to prefer a slightly negative value.Comment: Contribution to the proceedings of the 33rd International Symposium on Lattice Field Theory, July 14-18, Kobe Japa

New developments in lattice QCD on equilibrium physics and phase diagram

I review recent new lattice QCD results on a few selected topics which are relevant to the heavy ion physics community. Special emphasis is put on the QCD phase diagram towards the chiral limit and at nonzero baryon density as well as the fate of quarkonia and heavy quark drag coefficients.Comment: 8 pages, 5 figures, plenary talk given at the XXVIIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2019), November 4th-9th 2019, Wuhan, Chin

Vector spectral functions and transport properties in quenched QCD

We present new results on the reconstruction of mesonic spectral functions for three temperatures $1.1T_c$, $1.2T_c$ and $1.4T_c$ in quenched QCD. Making use of non-perturbatively improved clover Wilson valence quarks allows for a clean extrapolation of correlator data to the continuum limit. For the case of vanishing momentum the spectral function is obtained by fitting the data to a well motivated ansatz, using the full covariance matrix of the continuum extrapolated data in the fit. We found that vector correlation function is almost temperature independent in the current temperature window. The electrical conductivity of the hot medium, related to the origin of the vector spectral function at zero momentum, is computed from the resulting parameters at all three temperatures, leading to an estimate of $0.2C_{em}\lesssim \sigma/T\lesssim0.4C_{em}$. The dilepton rates resulting from the obtained spectral functions show no significant temperature dependence.Comment: 7 pages, 5 figures, PoS LATTICE 201

Imprints of relic gravitational waves on pulsar timing

Relic gravitational waves (RGWs) , a background originated during inflation, would give imprints on the pulsar timing residuals. This makes RGWs be one of important sources for detection using the method of pulsar timing. In this paper, we discuss the effects of RGWs on the single pulsar timing, and give quantitively the timing residuals caused by RGWs with different model parameters. In principle, if the RGWs are strong enough today, they can be detected by timing a single millisecond pulsar with high precision after the intrinsic red noise in pulsar timing residuals were understood, even though observing simultaneously multiple millisecond pulsars is a more powerful technique in extracting gravitational wave signals. We corrected the normalization of RGWs using observations of the cosmic microwave background (CMB), which leads to the amplitudes of RGWs being reduced by two orders of magnitude or so compared to our previous works. We made new constraints on RGWs using the recent observations from the Parkes Pulsar Timing Array, employing the tensor-to-scalar ratio $r=0.2$ due to the tensor-type polarization observations of CMB by BICEP2 as a referenced value even though it has been denied. Moreover, the constraints on RGWs from CMB and BBN (Big Bang nucleosynthesis) will also be discussed for comparison.Comment: 17 pages, 6 figures, accepted by RA

Meson masses in external magnetic fields with HISQ fermions

We studied the temporal correlation function of mesons in the pseudo-scalar channel in (2+1)-flavor QCD in the presence of external magnetic fields at zero temperature. The simulations were performed on $32^3 \times 96$ lattices using the Highly Improved Staggered Quarks (HISQ) action with $m_{\pi} \approx$ 230 MeV. The strength of magnetic fields $|eB|$ ranges from 0 to around 3.3 GeV$^2$ ($\sim 60 m_\pi^2$). We found that the masses of neutral pseudo-scalar particles, e.g. neutral pion and kaon, monotonouslly decrease as the magnetic field grows and then saturate at a nonzero value. It is observed that heavier neutral pseudo-scalars are less affected by magnetic fields. Moreover, we found a non-monotonous behavior of charged pion and kaon mass in magnetic field for the first time. In the case of small magnetic field (0 $\leq~|eB| \lesssim$ 0.3 GeV$^2~\sim 6m_\pi^2$ ) the mass of charged pseudo-scalar grows with magnetic field and can be well described by the Lowest Landau Level approximation, while for $|eB|$ larger than 0.3 GeV$^2$ the mass starts to decrease. The possible connection between $|eB|$ dependences of neutral pion mass and the decreasing behavior of pseudo-critical temperature in magnetic field is discussed. Due to the nonzero value of neutral pion mass our simulation indicates that the superconducting phase of QCD does not exist in the current window of magnetic field.Comment: 7 pages, 7 figures; Proceedings of the 37th International Symposium on Lattice Field Theory - Lattice 2019, Wuhan (China