56,624 research outputs found
[Colored solutions of Yang-Baxter equation from representations of U_{q}gl(2)]
We study the Hopf algebra structure and the highest weight representation of
a multiparameter version of . The commutation relations as well as
other Hopf algebra maps are explicitly given. We show that the multiparameter
universal matrix can be constructed directly as a quantum double
intertwiner, without using Reshetikhin's transformation. An interesting feature
automatically appears in the representation theory: it can be divided into two
types, one for generic , the other for being a root of unity. When
applying the representation theory to the multiparameter universal
matrix, the so called standard and nonstandard colored solutions of the Yang-Baxter equation is obtained.Comment: [14]pages, latex, no figure
Effects of turbulent dust grain motion to interstellar chemistry
Theoretical studies have revealed that dust grains are usually moving fast
through the turbulent interstellar gas, which could have significant effects
upon interstellar chemistry by modifying grain accretion. This effect is
investigated in this work on the basis of numerical gas-grain chemical
modeling. Major features of the grain motion effect in the typical environment
of dark clouds (DC) can be summarised as follows: 1) decrease of gas-phase
(both neutral and ionic) abundances and increase of surface abundances by up to
2-3 orders of magnitude; 2) shifts of the existing chemical jumps to earlier
evolution ages for gas-phase species and to later ages for surface species by
factors of about ten; 3) a few exceptional cases in which some species turn out
to be insensitive to this effect and some other species can show opposite
behaviors too. These effects usually begin to emerge from a typical DC model
age of about 10^5 yr. The grain motion in a typical cold neutral medium (CNM)
can help overcome the Coulomb repulsive barrier to enable effective accretion
of cations onto positively charged grains. As a result, the grain motion
greatly enhances the abundances of some gas-phase and surface species by
factors up to 2-6 or more orders of magnitude in the CNM model. The grain
motion effect in a typical molecular cloud (MC) is intermediate between that of
the DC and CNM models, but with weaker strength. The grain motion is found to
be important to consider in chemical simulations of typical interstellar
medium.Comment: 20 pages, 10 figures and 2 table
Ground states of stealthy hyperuniform potentials. II. Stacked-slider phases
Stealthy potentials, a family of long-range isotropic pair potentials,
produce infinitely degenerate disordered ground states at high densities and
crystalline ground states at low densities in d-dimensional Euclidean space
R^d. In the previous paper in this series, we numerically studied the
entropically favored ground states in the canonical ensemble in the
zero-temperature limit across the first three Euclidean space dimensions. In
this paper, we investigate using both numerical and theoretical techniques
metastable stacked-slider phases, which are part of the ground-state manifold
of stealthy potentials at densities in which crystal ground states are favored
entropically. Our numerical results enable us to devise analytical models of
this phase in two, three, and higher dimensions. Utilizing this model, we
estimated the size of the feasible region in configuration space of the
stacked-slider phase, finding it to be smaller than that of crystal structures
in the infinite-system-size limit, which is consistent with our recent previous
work. In two dimensions, we also determine exact expressions for the pair
correlation function and structure factor of the analytical model of
stacked-slider phases and analyze the connectedness of the ground-state
manifold of stealthy potentials in this density regime. We demonstrate that
stacked-slider phases are distinguishable states of matter; they are
nonperiodic, statistically anisotropic structures that possess long-range
orientational order but have zero shear modulus. We outline some possible
future avenues of research to elucidate our understanding of this unusual phase
of matter
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Ground states of stealthy hyperuniform potentials: I. Entropically favored configurations
Systems of particles interacting with "stealthy" pair potentials have been
shown to possess infinitely degenerate disordered hyperuniform classical ground
states with novel physical properties. Previous attempts to sample the
infinitely degenerate ground states used energy minimization techniques,
introducing algorithmic dependence that is artificial in nature. Recently, an
ensemble theory of stealthy hyperuniform ground states was formulated to
predict the structure and thermodynamics that was shown to be in excellent
agreement with corresponding computer simulation results in the canonical
ensemble (in the zero-temperature limit). In this paper, we provide details and
justifications of the simulation procedure, which involves performing molecular
dynamics simulations at sufficiently low temperatures and minimizing the energy
of the snapshots for both the high-density disordered regime, where the theory
applies, as well as lower densities. We also use numerical simulations to
extend our study to the lower-density regime. We report results for the pair
correlation functions, structure factors, and Voronoi cell statistics. In the
high-density regime, we verify the theoretical ansatz that stealthy disordered
ground states behave like "pseudo" disordered equilibrium hard-sphere systems
in Fourier space. These results show that as the density decreases from the
high-density limit, the disordered ground states in the canonical ensemble are
characterized by an increasing degree of short-range order and eventually the
system undergoes a phase transition to crystalline ground states. We also
provide numerical evidence suggesting that different forms of stealthy pair
potentials produce the same ground-state ensemble in the zero-temperature
limit. Our techniques may be applied to sample this limit of the canonical
ensemble of other potentials with highly degenerate ground states
Floquet Topological Polaritons in Semiconductor Microcavities
We propose and model Floquet topological polaritons in semiconductor
microcavities, using the interference of frequency detuned coherent fields to
provide a time periodic potential. For arbitrarily weak field strength, where
the Floquet frequency is larger than the relevant bandwidth of the system, a
Chern insulator is obtained. As the field strength is increased, a topological
phase transition is observed with an unpaired Dirac cone proclaiming the
anomalous Floquet topological insulator. As the relevant bandwidth increases
even further, an exotic Chern insulator with flat band is observed with
unpaired Dirac cone at the second critical point. Considering the polariton
spin degree of freedom, we find that the choice of field polarization allows
oppositely polarized polaritons to either co-propagate or counter-propagate in
chiral edge states.Comment: Accepted by PR
Anti-chiral edge states in an exciton polariton strip
We present a scheme to obtain anti-chiral edge states in an exciton-polariton
honeycomb lattice with strip geometry, where the modes corresponding to both
edges propagate in the same direction. Under resonant pumping the effect of a
polariton condensate with nonzero velocity in one linear polarization is
predicted to tilt the dispersion of polaritons in the other, which results in
an energy shift between two Dirac cones and the otherwise flat edge states
become tilted. Our simulations show that due to the spatial separation from the
bulk modes the edge modes are robust against disorder.Comment: 6 pages, 5 figure
Synthetic horizontal branch morphology for different metallicities and ages under tidally enhanced stellar wind
It is believed that, except for metallicity, some other parameters are needed
to explain the horizontal branch (HB) morphology of globular clusters (GCs).
Furthermore, these parameters are considered to be correlated with the mass
loss of the red giant branch (RGB) stars. In our previous work, we proposed
that tidally enhanced stellar wind during binary evolution may affect the HB
morphology by enhancing the mass loss of the red giant primary. As a further
study, we now investigate the effects of metallicity and age on HB morphology
by considering tidally enhanced stellar winds during binary evolution. We
incorporated the tidally enhanced-stellar-wind model into Eggleton's stellar
evolution code to study the binary evolution. To study the effects of
metallicity and age on our final results, we conducted two sets of model
calculations: (i) for a fixed age, we used three metallicities, namely
Z=0.0001, 0.001, and 0.02. (ii) For a fixed metallicity, Z=0.001, we used five
ages in our model calculations: 14, 13, 12, 10, and 7 Gyr. We found that HB
morphology of GCs becomes bluer with decreasing metallicity, and old GCs
present bluer HB morphology than young ones. These results are consistent with
previous work. Although the envelope-mass distributions of zero-age HB stars
produced by tidally enhanced stellar wind are similar for different
metallicities, the synthetic HB under tidally enhanced stellar wind for Z=0.02
presented a distinct gap between red and blue HB. However, this feature was not
seen clearly in the synthetic HB for Z=0.001 and 0.0001. We also found that
higher binary fractions may make HB morphology become bluer, and we discussed
the results with recent observations.Comment: 16 pages, 6 figures, 3 tables, accepted for publication in Astronomy
& Astrophysic
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