Relaxation time for strange quark spin in rotating quark-gluon plasma

The properties of a massive fermion field undergoing rigid rotation at finite temperature and chemical potential are discussed. The polarisation imbalance is taken into account by considering a helicity chemical potential, which is dual to the helicity charge operator. The advantage of the proposed approach is that, as opposed to the axial current, the helicity charge current remains conserved at finite mass. A computation of thermal expectation values of the vector, helicity and axial charge currents, as well as of the fermion condensate and stress-energy tensor is provided. In all cases, analytic constitutive equations are derived for the non-equilibrium transport terms, as well as for the quantum corrections to the equilibrium terms (which are derived using an effective relativistic kinetic theory model for fermions with helicity imbalance) in the limit of small masses. In the context of the parameters which are relevant to relativistic heavy ion collisions, the expressions derived in the massless limit are shown to remain valid for masses up to the thermal energy, except for the axial charge conductivity in the azimuthal direction, which presents strong variations with the particle mass.

Section: Jhep08(2020)016mentioning

confidence: 99%

Helical massive fermions under rotation

Ambruş

2020

“…[54], the spin-diffusion term at O( 0 ) in collisions was computed in perturbative QCD (see also refs. [55,56] for other studies of collisions). Nonetheless, the inclusion of O( 1 ) corrections to the collisional effects, which is responsible for generating the spin polarization, has never been achieved.…”

Section: Jhep07(2020)070 Introductionmentioning

confidence: 99%

Effective quantum kinetic theory for spin transport of fermions with collsional effects

Yang

Hattori

Hidaka

2020

109

We systematically derive the collision term for the axial kinetic theory, a quantum kinetic theory delineating the coupled dynamics of the vector/axial charges and spin transport carried by the massive spin-1/2 fermions traversing a medium. We employ the Wigner-function approach and propose a consistent power-counting scheme where the axial-charge distribution function, a non-conserved quantity for massive particles, is accounted as the first-order quantity in the expansion, while the vector-charge distribution function the zeroth-order quantity. This specific power-counting scheme allows us to organize a reduced expansion for the collision term and to formally identity the spindiffusion effect and the spin-polarization effect at the same order. We confirm that the obtained collisional axial kinetic theory smoothly reduces to the chiral kinetic theory in the massless limit, serving as a consistency check. In the absence of electromagnetic fields, we further present the simplified axial kinetic equations suitable for tracking dynamical spin polarization of heavy and light fermions, respectively. As an application to the weakly coupled quark-gluon plasma at high temperature, we compute the spin-diffusion term for massive quarks within the leading-log approximation. The formal expression for the firstorder terms provides a path toward evaluation of the spin polarization effect in quantum chromodynamics.

“…This would pave the way to future study of entangled spin transport of quarks and gluons in QGP. Motivated by recent experimental observations of global polarization of Λ hyperons in heavy ion collisions [61][62][63], this direction should be important to understand how the dynamical evolution of the quark spin will be converted to the local spin polarization of hadrons [60,[64][65][66][67][68][69][70] along the direction of the strong vorticity generated in peripheral collisions; see other theoretical works on developments of hydrodynamics with spin [71][72][73][74][75] and statistical quantum field theory [76][77][78], which also aim at exploring underlying mechanisms and reconciling the existing tension between theoretical predictions and experimental observations for local spin polarization in heavy ion collisions (see ref. [79] for a recent review and more references therein).…”

Section: Introductionmentioning

confidence: 99%

Wigner functions and quantum kinetic theory of polarized photons

Hattori

Hidaka

Yamamoto

et al. 2021

We derive the Wigner functions of polarized photons in the Coulomb gauge with the ħ expansion applied to quantum field theory, and identify side-jump effects for massless photons. We also discuss the photonic chiral vortical effect for the Chern-Simons current and zilch vortical effect for the zilch current in local thermal equilibrium as a consistency check for our formalism. The results are found to be in agreement with those obtained from different approaches. Moreover, using the real-time formalism, we construct the quantum kinetic theory (QKT) for polarized photons. By further adopting a specific power counting scheme for the distribution functions, we provide a more succinct form of an effective QKT. This photonic QKT involves quantum corrections associated with self-energy gradients in the collision term, which are analogous to the side-jump corrections pertinent to spin-orbit interactions in the chiral kinetic theory for massless fermions. The same theoretical framework can also be directly applied to weakly coupled gluons in the absence of background color fields.