11,224 research outputs found
On a question of Babadi and Tarokh
In a recent remarkable paper, Babadi and Tarokh proved the "randomness" of
sequences arising from binary linear block codes in the sense of spectral
distribution, provided that their dual distances are sufficiently large.
However, numerical experiments conducted by the authors revealed that Gold
sequences which have dual distance 5 also satisfy such randomness property.
Hence the interesting question was raised as to whether or not the stringent
requirement of large dual distances can be relaxed in the theorem in order to
explain the randomness of Gold sequences. This paper improves their result on
several fronts and provides an affirmative answer to this question
Determine the galaxy bias factors on large scales using bispectrum method
We study whether the bias factors of galaxies can be unbiasedly recovered
from their power spectra and bispectra. We use a set of numerical N-body
simulations and construct large mock galaxy catalogs based upon the
semi-analytical model of Croton et al. (2006). We measure the reduced bispectra
for galaxies of different luminosity, and determine the linear and first
nonlinear bias factors from their bispectra. We find that on large scales down
to that of the wavenumber k=0.1h/Mpc, the bias factors b1 and b2 are nearly
constant, and b1 obtained with the bispectrum method agrees very well with the
expected value. The nonlinear bias factor b2 is negative, except for the most
luminous galaxies with M<-23 which have a positive b2. The behavior of b2 of
galaxies is consistent with the b2 mass dependence of their host halos. We show
that it is essential to have an accurate estimation of the dark matter
bispectrum in order to have an unbiased measurement of b1 and b2. We also test
the analytical approach of incorporating halo occupation distribution to model
the galaxy power spectrum and bispectrum. The halo model predictions do not fit
the simulation results well on the precision requirement of current
cosmological studies.Comment: 9 pages, 8 figures, accepted for publication in Ap
Topological Kondo Insulators
This article reviews recent theoretical and experimental work on a new class
of topological material - topological Kondo insulators, which develop through
the interplay of strong correlations and spin-orbit interactions. The history
of Kondo insulators is reviewed along with the theoretical models used to
describe these heavy fermion compounds. The Fu-Kane method of topological
classification of insulators is used to show that hybridization between the
conduction electrons and localized f-electrons in these systems gives rise to
interaction-induced topological insulating behavior. Finally, some recent
experimental results are discussed, which appear to confirm the theoretical
prediction of the topological insulating behavior in Samarium hexaboride, where
the long-standing puzzle of the residual low-temperature conductivity has been
shown to originate from robust surface states.Comment: Accepted as an article in the Annual Review of Condensed Matter
Physics, Volume 7 (2016
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