4,295 research outputs found
Topological Phases of One-Dimensional Fermions: An Entanglement Point of View
The effect of interactions on topological insulators and superconductors
remains, to a large extent, an open problem. Here, we describe a framework for
classifying phases of one-dimensional interacting fermions, focusing on
spinless fermions with time-reversal symmetry and particle number parity
conservation, using concepts of entanglement. In agreement with an example
presented by Fidkowski \emph{et. al.} (Phys. Rev. B 81, 134509 (2010)), we find
that in the presence of interactions there are only eight distinct phases,
which obey a group structure. This is in contrast to the
classification in the non-interacting case. Each of these eight
phases is characterized by a unique set of bulk invariants, related to the
transformation laws of its entanglement (Schmidt) eigenstates under symmetry
operations, and has a characteristic degeneracy of its entanglement levels. If
translational symmetry is present, the number of distinct phases increases to
16.Comment: 12 pages, 1 figure; journal ref. adde
Management of mental illness by the British Army
Background: The Ministry of Defence has its own hospital for soldiers requiring admission for mental health problems.
Aims: To assess the efficiency of the army psychiatric hospital at restoring patients to full active duty. To assess whether a new military training and rehabilitation unit (MTRU) that emphasises military-skills training, improves outcome.
Method: A 2-year, inception-cohort outcome study of hospital in-patients. A 12-month, case-matched, ‘before and after’ outcome study compared MTRU patients with hospital in-patients.
Results: I (hospital in-patients, n=309): at 2-year follow-up 67 (22%) were fully fit for active duty. Military psychiatrists' success rate at predicting recovery to active duty was 27%. 2: the odds of a soldier in the MTRU cohort (n=35) returning to active duty were 14 times greater than for the hospital cohort (n=35). The odds of remaining in the army while unfit for active duty were 20 times less for the MTRU than for the hospital cohort.
Conclusions: The army hospital is inefficient at rehabilitation to active duty. The MTRU significantly increased the odds of returning to active duty and reduced the odds of remaining in the army while still unfit. These findings may be applicable to the emergency services
Symmetry protection of topological order in one-dimensional quantum spin systems
We discuss the characterization and stability of the Haldane phase in integer
spin chains on the basis of simple, physical arguments. We find that an odd-
Haldane phase is a topologically non-trivial phase which is protected by any
one of the following three global symmetries: (i) the dihedral group of
-rotations about and axes; (ii) time-reversal symmetry
; (iii) link inversion symmetry (reflection
about a bond center), consistently with previous results [Phys. Rev. B
\textbf{81}, 064439 (2010)]. On the other hand, an even- Haldane phase is
not topologically protected (i.e., it is indistinct from a trivial,
site-factorizable phase). We show some numerical evidence that supports these
claims, using concrete examples.Comment: 9 pages, 6 figures, extended version: several new examples and
numerical results added. Journal reference adde
Detection of Symmetry Protected Topological Phases in 1D
A topological phase is a phase of matter which cannot be characterized by a
local order parameter. It has been shown that gapped phases in 1D systems can
be completely characterized using tools related to projective representations
of the symmetry groups. We show how to determine the matrices of these
representations in a simple way in order to distinguish between different
phases directly. From these matrices we also point out how to derive several
different types of non-local order parameters for time reversal, inversion
symmetry and symmetry, as well as some more general cases
(some of which have been obtained before by other methods). Using these
concepts, the ordinary string order for the Haldane phase can be related to a
selection rule that changes at the critical point. We furthermore point out an
example of a more complicated internal symmetry for which the ordinary string
order cannot be applied.Comment: 12 pages, 9 Figure
Axion Cosmology and the Energy Scale of Inflation
We survey observational constraints on the parameter space of inflation and
axions and map out two allowed windows: the classic window and the inflationary
anthropic window. The cosmology of the latter is particularly interesting;
inflationary axion cosmology predicts the existence of isocurvature
fluctuations in the CMB, with an amplitude that grows with both the energy
scale of inflation and the fraction of dark matter in axions. Statistical
arguments favor a substantial value for the latter, and so current bounds on
isocurvature fluctuations imply tight constraints on inflation. For example, an
axion Peccei-Quinn scale of 10^16 GeV excludes any inflation model with energy
scale > 3.8*10^14 GeV (r > 2*10^(-9)) at 95% confidence, and so implies
negligible gravitational waves from inflation, but suggests appreciable
isocurvature fluctuations.Comment: 10 PRD pages, 4 figs, V3: updated to match published versio
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