87 research outputs found
A Quantitative Approach to Understanding Online Antisemitism
A new wave of growing antisemitism, driven by fringe Web communities, is an
increasingly worrying presence in the socio-political realm. The ubiquitous and
global nature of the Web has provided tools used by these groups to spread
their ideology to the rest of the Internet. Although the study of antisemitism
and hate is not new, the scale and rate of change of online data has impacted
the efficacy of traditional approaches to measure and understand these
troubling trends. In this paper, we present a large-scale, quantitative study
of online antisemitism. We collect hundreds of million posts and images from
alt-right Web communities like 4chan's Politically Incorrect board (/pol/) and
Gab. Using scientifically grounded methods, we quantify the escalation and
spread of antisemitic memes and rhetoric across the Web. We find the frequency
of antisemitic content greatly increases (in some cases more than doubling)
after major political events such as the 2016 US Presidential Election and the
"Unite the Right" rally in Charlottesville. We extract semantic embeddings from
our corpus of posts and demonstrate how automated techniques can discover and
categorize the use of antisemitic terminology. We additionally examine the
prevalence and spread of the antisemitic "Happy Merchant" meme, and in
particular how these fringe communities influence its propagation to more
mainstream communities like Twitter and Reddit. Taken together, our results
provide a data-driven, quantitative framework for understanding online
antisemitism. Our methods serve as a framework to augment current qualitative
efforts by anti-hate groups, providing new insights into the growth and spread
of hate online.Comment: To appear at the 14th International AAAI Conference on Web and Social
Media (ICWSM 2020). Please cite accordingl
Disconnected Elementary Band Representations, Fragile Topology, and Wilson Loops as Topological Indices: An Example on the Triangular Lattice
In this work, we examine the topological phases that can arise in triangular
lattices with disconnected elementary band representations. We show that,
although these phases may be "fragile" with respect to the addition of extra
bands, their topological properties are manifest in certain nontrivial
holonomies (Wilson loops) in the space of nontrivial bands. We introduce an
eigenvalue index for fragile topology, and we show how a nontrivial value of
this index manifests as the winding of a hexagonal Wilson loop; this remains
true even in the absence of time-reversal or sixfold rotational symmetry.
Additionally, when time-reversal and twofold rotational symmetry are present,
we show directly that there is a protected nontrivial winding in more
conventional Wilson loops. Crucially, we emphasize that these Wilson loops
cannot change without closing a gap to the nontrivial bands. By studying the
entanglement spectrum for the fragile bands, we comment on the relationship
between fragile topology and the "obstructed atomic limit" of B. Bradlyn et
al., Nature 547, 298--305 (2017). We conclude with some perspectives on
topological matter beyond the K-theory classification.Comment: 13 pages, 10 figures v2. accepted versio
Effective action approach to the filling anomaly in crystalline topological matter
In two dimensions, magnetic higher-order topological insulators (HOTIs) are
characterized by excess boundary charge and a compensating bulk ``filling
anomaly.'' At the same time, without additional noncrystalline symmetries, the
boundaries of two-dimensional HOTIs are gapped and featureless at low energies,
while the bulk of the system is predicted to have a topological response to the
insertion of lattice (particularly disclination) defects. Until recently, a
precise connection between these effects has remained elusive. In this work, we
point the direction towards a unifying field-theoretic description for the bulk
and boundary response of magnetic HOTIs. By focusing on the low-energy
description of the gapped boundary of a two-dimensional magnetic HOTI with no
time-reversing symmetries, we show that the boundary charge and filling anomaly
arise from the gravitational ``Gromov-Jensen-Abanov'' (GJA) response action
first introduced in [Phys. Rev. Lett. 116, 126802 (2016)] in the context of the
quantum Hall effect. As in quantum Hall systems the GJA action cancels apparent
anomalies associated with bulk response to disclinations, allowing us to derive
a concrete connection between the bulk and boundary theories of HOTIs. We show
how our results elucidate the connection between higher order topology and
geometric response both in band insulators, and point towards a new route to
understanding interacting higher order topological phases beyond the simple
cases considered here.Comment: v2: accepted version v1: 14+epsilon page
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