1,067 research outputs found
Social Computing: An Overview
A collection of technologies termed social computing is driving a dramatic evolution of the Web, matching the dot-com era in growth, excitement, and investment. All of these share high degree of community formation, user level content creation, and computing, and a variety of other characteristics. We provide an overview of social computing and identify salient characteristics. We argue that social computing holds tremendous disruptive potential in the business world and can significantly impact society, and outline possible changes in organized human action that could be brought about. Social computing can also have deleterious effects associated with it, including security issues. We suggest that social computing should be a priority for researchers and business leaders and illustrate the fundamental shifts in communication, computing, collaboration, and commerce brought about by this trend
`Unhinging' the surfaces of higher-order topological insulators and superconductors
We show that the chiral Dirac and Majorana hinge modes in three-dimensional
higher-order topological insulators (HOTIs) and superconductors (HOTSCs) can be
gapped while preserving the protecting symmetry
upon the introduction of non-Abelian surface topological order. In both cases,
the topological order on a single side surface breaks time reversal symmetry,
but appears with its time-reversal conjugate on alternating sides in a
preserving pattern. In the absence of the
HOTI/HOTSC bulk, such a pattern necessarily involves gapless chiral modes on
hinges between -conjugate domains. However, using a
combination of -matrix and anyon condensation arguments, we show that on the
boundary of a 3D HOTI/HOTSC these topological orders are fully gapped and hence
`anomalous'. Our results suggest that new patterns of surface and hinge states
can be engineered by selectively introducing topological order only on specific
surfaces
Testing the no-hair nature of binary black holes using the consistency of multipolar gravitational radiation
Gravitational-wave (GW) observations of binary black holes offer the best probes of the relativistic, strong-field regime of gravity. Gravitational radiation in the leading order is quadrupolar. However, nonquadrupole (higher order) modes make appreciable contribution to the radiation from binary black holes with large mass ratios and misaligned spins. The multipolar structure of the radiation is fully determined by the intrinsic parameters (masses and spin angular momenta of the companion black holes) of a binary in quasicircular orbit. Following our previous work [S. Dhanpal, A. Ghosh, A. K. Mehta, P. Ajith, and B. S. Sathyaprakash, Phys. Rev. D 99, 104056 (2019).], we develop multiple ways of testing the consistency of the observed GW signal with the expected multipolar structure of radiation from binary black holes in general relativity. We call this a no-hair test of binary black holes as this is similar to testing the no-hair theorem for isolated black holes through mutual consistency of the quasinormal mode spectrum. We use Bayesian inference on simulated GW signals that are consistent/inconsistent with binary black holes in general relativity to demonstrate the power of the proposed tests. We also make estimate systematic errors arising as a result of neglecting companion spins
Dipolar bogolons: from superfluids to Pfaffians
We study the structure of Bogoliubov quasiparticles, 'bogolons,' the
fermionic excitations of paired superfluids that arise from fermion (BCS)
pairing, including neutral superfluids, superconductors, and paired quantum
Hall states. The naive construction of a stationary quasiparticle in which the
deformation of the pair field is neglected leads to a contradiction: it carries
a net electrical current even though it does not move. However, treating the
pair field self-consistently resolves this problem: In a neutral superfluid, a
dipolar current pattern is associated with the quasiparticle for which the
total current vanishes. When Maxwell electrodynamics is included, as
appropriate to a superconductor, this pattern is confined over a penetration
depth. For paired quantum Hall states of composite fermions, the Maxwell term
is replaced by a Chern-Simons term, which leads to a dipolar charge
distribution and consequently to a dipolar current pattern.Comment: 5 pages main text + 5 pages supplementary material; 1 figure. Version
published in PRL under different title; typos corrected, references adde
The Weakly Coupled Pfaffian as a Type I Quantum Hall Liquid
The Pfaffian phase of electrons in the proximity of a half-filled Landau
level is understood to be a p+ip superconductor of composite fermions. We
consider the properties of this paired quantum Hall phase when the pairing
scale is small, i.e. in the weak-coupling, BCS, limit, where the coherence
length is much larger than the charge screening length. We find that, as in a
Type I superconductor, the vortices attract so that, upon varying the magnetic
field from its magic value at \nu=5/2, the system exhibits Coulomb frustrated
phase separation. We propose that the weakly and strongly coupled Pfaffian
states exemplify a general dichotomy between Type I and Type II quantum Hall
fluids.Comment: 4 pages, 1 figur
A Typology for Quantum Hall Liquids
There is a close analogy between the response of a quantum Hall liquid (QHL)
to a small change in the electron density and the response of a superconductor
to an externally applied magnetic flux - an analogy which is made concrete in
the Chern-Simons Landau-Ginzburg (CSLG) formulation of the problem. As the
Types of superconductor are distinguished by this response, so too for QHLs: a
typology can be introduced which is, however, richer than that in
superconductors owing to the lack of any time-reversal symmetry relating
positive and negative fluxes. At the boundary between Type I and Type II
behavior, the CSLG action has a "Bogomol'nyi point," where the quasi-holes
(vortices) are non-interacting - at the microscopic level, this corresponds to
the behavior of systems governed by a set of model Hamiltonians which have been
constructed to render exact a large class of QHL wavefunctions. All Types of
QHLs are capable of giving rise to quantized Hall plateaux.Comment: 4 +epsilon pages, 1 figure; v2 has added references and minor
changes, version published in Phys. Rev. B. (Rapid Communications
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