Search

We systematically analyze the effects of the derivatives of the hydrodynamic fields on axial Wigner function that describes the spin polarization vector in phase space. We have included all possible first-order derivative contributions that are allowed by symmetry and compute the associated transport functions at one-loop using the linear response theory. In addition to reproducing known effects due to the temperature gradient and vorticity, we have identified a number of potentially significant contributions that are overlooked previously. In particular, we find that the shear strength, the symmetric and traceless part of the flow gradient, will induce a quadrupole for spin polarization in the phase space. We refer to this novel effect as the shear-induced polarization (SIP). Our results, together with hydrodynamic gradients obtained from hydrodynamic simulations, can be employed as a basis for the interpretation of the $\Lambda$ (anti-$\Lambda$) spin polarization measurement in heavy-ion collisions., Comment: 18 pages, 2 figures, matched to the published version

We discuss the theory of the spin polarizations induced by hydrodynamic gradients, which includes a newly discovered shear-induced polarization (SIP) term. In the phenomenological study using a hydrodynamic model, we discover that the local polarization contributed by SIP is substantial and has the “same sign” as the experimental measurements. Also, we find that the “sign” property of the local polarization observed in experiments seems to be related to “memory” effects on the polarizations of strange quarks in quark-gluon plasma.

Quark number susceptibilities as computed in lattice QCD are commonly believed to provide insights into the microscopic structure of QCD matter, in particular its degrees of freedom. We generalize a previously constructed partonic $T$-matrix approach to finite chemical potential to calculate various susceptibilities, in particular for configurations containing a heavy charm quark. At vanishing chemical potential and moderate temperatures, this approach predicts large collisional widths of partons generated by dynamically formed hadronic resonance states which lead to transport parameters characteristic for a strongly coupled system. The quark chemical potential dependence is implemented into the propagators and the in-medium color potential, where two newly introduced parameters for the thermal and screening masses are fixed through a fit to the baryon number susceptibility, $\chi^B_2$. With this setup, we calculate heavy-light susceptibilities without further tuning; the results qualitatively agree with the lattice-QCD (lQCD) data for both $\chi^{uc}_{11}$ and $\chi^{uc}_{22}$. This implies that the lQCD results are compatible with a significant content of broad $D$-meson and charm-light diquark bound states in a moderately hot QGP., Comment: 6 pages, 4 figures

We study the spin polarization generated by the hydrodynamic gradients. In addition to the widely studied thermal vorticity effects, we identify an undiscovered contribution from the fluid shear. This shear-induced polarization (SIP) can be viewed as the fluid analog of strain-induced polarization observed in elastic and nematic materials. We obtain the explicit expression for SIP using the quantum kinetic equation and linear response theory. Based on a realistic hydrodynamic model, we compute the differential spin polarization along both the beam direction $\hat{z}$ and the out-plane direction $\hat{y}$ in non-central heavy-ion collisions at $\sqrt{s_{NN}}=200$ GeV, including both SIP and thermal vorticity effects. We find that SIP contribution always shows the same azimuthal angle dependence as experimental data and competes with thermal vorticity effects. In the scenario that $\Lambda$ inherits and memorizes the spin polarization of strange quark, SIP wins the competition, and the resulting azimuthal angle dependent spin polarization $P_y$ and $P_z$ agrees qualitatively with the experimental data., Comment: 6 pages, 3 figures

Spin Hall effect (SHE) is the generation of spin current due to an electric field, and has been observed in a variety of materials. The analogous spin Hall current can be induced by chemical potential and temperature gradient, both of which are present in hot and dense nuclear matter created in heavy-ion collisions. In this letter, we investigate the perspective of detecting spin Hall current experimentally. We propose to measure "directed spin flow", the first Fourier coefficients of local spin polarization of $\Lambda$ ($\bar{\Lambda}$) hyperon, at central collisions to probe spin Hall current. To quantify induced spin current, we evaluate relevant transport coefficients using thermal field theory. We benchmark the magnitude of the induced "directed spin flow" at two representatively collisions energies, namely $\sqrt{s}_{NN}=200~{\rm GeV}$ and $\sqrt{s}_{NN}=19.6~{\rm GeV}$, by employing a phenomenologically motivated freeze-out prescription. At both beam energies, the resulting "directed spin flow" ranges from $10^{-4}$ to $10^{-3}$, and is very sensitive to the rapidity., Comment: 8 pages, 4 figures; published version

Using a covariant and angular-momentum-conserved chiral transport model, which takes into account the spin-orbit interactions of chiral fermions in their scatterings via the side jumps, we study the quark spin polarization in quark matter. For a system of rotating and unpolarized massless quarks in an expanding box, we find that side jumps can dynamically polarize the quark spin and result in a final quark spin polarization consistent with that of thermally equilibrated massless quarks in a self-consistent vorticity field. For the quark matter produced in noncentral relativistic heavy ion collisions, we find that in the medium rest frame both the quark local spin polarizations in the direction perpendicular to the reaction plane and along the longitudinal beam direction show an azimuthal angle dependence in the transverse plane similar to those observed in experiments for the Lambda hyperon., 6 pages, 3 figures