361 research outputs found
Shear induced polarization: Collisional contributions
It has been realized that thermal shear plays a similar role as thermal
vorticity in polarizing spin of particles in heavy ion collisions. We point out
that shear has a fundamental difference that it leads to particle
redistribution in the medium. The redistribution gives rise to an additional
contribution to spin polarization through the self-energy, which is
parametrically the same order as the one considered so far in the literature.
The self-energy contribution is in general gauge dependent. We introduce double
gauge links stretching along the Schwinger-Keldysh contour to restore gauge
invariance. We also generalize the straight path to adapt to the
Schwinger-Keldysh contour. We find another contribution associated with the
gauge link, which is also parametrically the same order. We illustrate the two
contributions with a massive probe fermion in massless QED plasma with shear. A
modest suppression of spin polarization is found from the combined
contributions when the probe fermion has momentum much greater than the
temperature.Comment: 29 pages, 5 figure
C.E.O. academic experience and firm sustainable growth
Chief executive officers (C.E.O.s) play a dominant role in firm decision-
makings and operations, and their characteristics will affect
firm sustainable growth. This study investigates whether C.E.O.
academic experience affects firm sustainable growth. Using a sample
from China, we find that C.E.O. academic experience is positively
related to firm sustainable growth, and the effect is
pronounced for high-tech firms. Further analyses demonstrate
that the results are robust to alternative measures and controlling
for endogeneity problems. Finally, the channel analysis shows
that the effect is partially driven by firm innovation and
internal control
Local Equilibrium Spin Distribution From Detailed Balance
As the core ingredient for spin polarization, the local equilibrium spin
distribution function is derived from the detailed balance principle. The
kinetic theory for interacting fermionic systems is applied to the
Nambu--Jona-Lasinio model at quark level. Under the semi-classical expansion
with respect to and non-perturbative expansion with respect to ,
the kinetic equations for the vector and axial-vector distribution functions
are derived with collision terms. It is found that, for an initially
unpolarized system, non-zero spin polarization can be generated at the order of
from the coupling between the vector and axial-vector charges. The
local equilibrium spin polarization is derived from the requirement of detailed
balance. It arises from the thermal vorticity and is orthogonal to the particle
momentum.Comment: 13 page
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