17,612 research outputs found
Weyl points and topological nodal superfluids in a face-centered cubic optical lattice
We point out that a face-centered cubic (FCC) optical lattice, which can be
realised by a simple scheme using three lasers, provides one a highly
controllable platform for creating Weyl points and topological nodal
superfluids in ultracold atoms. In non-interacting systems, Weyl points
automatically arise in the Floquet band structure when shaking such FCC
lattices, and sophisticated design of the tunnelling is not required. More
interestingly, in the presence of attractive interaction between two hyperfine
spin states, which experience the same shaken FCC lattice, a three-dimensional
topological nodal superfluid emerges, and Weyl points show up as the gapless
points in the quasiparticle spectrum. One could either create a double Weyl
point of charge 2, or split it to two Weyl points of charge 1, which can be
moved in the momentum space by tuning the interactions. Correspondingly, the
Fermi arcs at the surface may be linked with each other or separated as
individual ones.Comment: 5 pages, 2 figures in the main text; 2 pages, 2 figures in the
supplemental materia
Log-aesthetic Curves as Similarity Geometric Analogue of Euler's Elasticae
In this paper we consider the log-aesthetic curves and their generalization
which are used in CAGD. We consider those curves under similarity geometry and
characterize them as stationary integrable flow on plane curves which is
governed by the Burgers equation. We propose a variational formulation of those
curves whose Euler-Lagrange equation yields the stationary Burgers equation.
Our result suggests that the log-aesthetic curves and their generalization can
be regarded as the similarity geometric analogue of Euler's elasticae
General considerations of matter coupling with the self-dual connection
It has been shown for low-spin fields that the use of only the self-dual part
of the connection as basic variable does not lead to extra conditions or
inconsistencies. We study whether this is true for more general chiral action.
We generalize the chiral gravitational action, and assume that half-integer
spin fields are coupled with torsion linearly. The equation for torsion is
solved and substituted back into the generalized chiral action, giving
four-fermion contact terms. If these contact terms are complex, the imaginary
part will give rise to extra conditions for the gravitational and matter field
equations. We study the four-fermion contact terms taking spin-1/2 and spin-3/2
fields as examples.Comment: 16 pages, late
Will Nonlinear Peculiar Velocity and Inhomogeneous Reionization Spoil 21cm Cosmology from the Epoch of Reionization?
The 21cm background from the epoch of reionization is a promising
cosmological probe: line-of-sight velocity fluctuations distort redshift, so
brightness fluctuations in Fourier space depend upon angle, which linear theory
shows can separate cosmological from astrophysical information. Nonlinear
fluctuations in ionization, density and velocity change this, however. The
validity and accuracy of the separation scheme are tested here for the first
time, by detailed reionization simulations. The scheme works reasonably well
early in reionization ( 80% ionized).Comment: 2 figures, matches published PRL versio
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