16,521 research outputs found
Fluctuations and correlations of net baryon number, electric charge and strangeness in a background magnetic field
We present results on the second-order fluctuations of and correlations among
net baryon number, electric charge and strangeness in (2+1)-flavor lattice QCD
in the presence of a background magnetic field. Simulations are performed using
the tree-level improved gauge action and the highly improved staggered quark
(HISQ) action with a fixed scale approach ( 0.117 fm). The light quark
mass is set to be 1/10 of the physical strange quark mass and the corresponding
pion mass is about 220 MeV at vanishing magnetic field. Simulations are
performed on lattices with 9 values of varying
from 96 to 6 corresponding to temperatures ranging from zero up to 281 MeV. The
magnetic field strength is simulated with 15 different values up to
2.5 GeV at each nonzero temperature. We find that quadratic
fluctuations and correlations do not show any singular behavior at zero
temperature in the current window of while they develop peaked structures
at nonzero temperatures as grows. By comparing the electric charge-related
fluctuations and correlations with hadron resonance gas model calculations and
ideal gas limits we find that the changes in degrees of freedom start at lower
temperatures in stronger magnetic fields. Significant effects induced by
magnetic fields on the isospin symmetry and ratios of net baryon number and
baryon-strangeness correlation to strangeness fluctuation are observed, which
could be useful for probing the existence of a magnetic field in heavy-ion
collision experiments.Comment: 12 pages, 7 figures, invited contribution to The European Physical
Journal A-Hadrons and Nuclei: Topical Issue on "QCD Phase Diagram in Strong
Magnetic Fields", minor revisio
Geometric entanglement from matrix product state representations
An efficient scheme to compute the geometric entanglement per lattice site
for quantum many-body systems on a periodic finite-size chain is proposed in
the context of a tensor network algorithm based on the matrix product state
representations. It is systematically tested for three prototypical critical
quantum spin chains, which belong to the same Ising universality class. The
simulation results lend strong support to the previous claim [Q.-Q. Shi, R.
Or\'{u}s, J. O. Fj{\ae}restad, and H.-Q. Zhou, New J. Phys \textbf{12}, 025008
(2010); J.-M. St\'{e}phan, G. Misguich, and F. Alet, Phys. Rev. B \textbf{82},
180406R (2010)] that the leading finite-size correction to the geometric
entanglement per lattice site is universal, with its remarkable connection to
the celebrated Affleck-Ludwig boundary entropy corresponding to a conformally
invariant boundary condition.Comment: 4+ pages, 3 figure
Dynamical and sequential decay effects on isoscaling and density dependence of the symmetry energy
The isoscaling properties of the primary and final products are studied via
isospin dependent quantum molecular dynamics
(IQMD) model and the followed sequential decay model GEMINI, respectively. It
is found that the isoscaling parameters of both primary and final
products keep no significant change for light fragments, but increases with the
mass for intermediate and heavy products. The dynamical effects on isoscaling
are exhibited by that value decreases a little with the evolution time
of the system, and opposite trend for the heavy products. The secondary decay
effects on isoscaling are reflected in the increasing of the value for
the final products which experiences secondary decay process.
Furthermore the density dependence of the symmetry energy has also been
explored, it is observed that in the low densities the symmetry energy
coefficient has the form of ,
where for both primary and final products, but
have different values for primary and final products. It is also suggested that
it might be more reasonable to describe the density dependence of the symmetry
energy coefficient by the
with , and constant
parameters.Comment: 10 pages, 10 figure
Alfvenic Ion Temperature Gradient Activities in a Weak Magnetic Shear Plasma
We report the first experimental evidence of Alfvenic ion temperature
gradient (AITG) modes in HL-2A Ohmic plasmas. A group of oscillations with
kHz and is detected by various diagnostics in high-density
Ohmic regimes. They appear in the plasmas with peaked density profiles and weak
magnetic shear, which indicates that corresponding instabilities are excited by
pressure gradients. The time trace of the fluctuation spectrogram can be either
a frequency staircase, with different modes excited at different times or
multiple modes may simultaneously coexist. Theoretical analyses by the extended
generalized fishbone-like dispersion relation (GFLDR-E) reveal that mode
frequencies scale with ion diamagnetic drift frequency and , and they
lie in KBM-AITG-BAE frequency ranges. AITG modes are most unstable when the
magnetic shear is small in low pressure gradient regions. Numerical solutions
of the AITG/KBM equation also illuminate why AITG modes can be unstable for
weak shear and low pressure gradients. It is worth emphasizing that these
instabilities may be linked to the internal transport barrier (ITB) and H-mode
pedestal physics for weak magnetic shear.Comment: 9 pages, 7 figure
Competitions of magnetism and superconductivity in FeAs-based materials
Using the numerical unrestricted Hartree-Fock approach, we study the ground
state of a two-orbital model describing newly discovered FeAs-based
superconductors. We observe the competition of a mode spin-density
wave and the superconductivity as the doping concentration changes. There might
be a small region in the electron-doping side where the magnetism and
superconductivity coexist. The superconducting pairing is found to be spin
singlet, orbital even, and mixed s + d wave (even
parity).Comment: 5 pages, 3 figure
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