81 research outputs found
On 2-form gauge models of topological phases
We explore various aspects of 2-form topological gauge theories in (3+1)d.
These theories can be constructed as sigma models with target space the second
classifying space of the symmetry group , and they are classified by
cohomology classes of . Discrete topological gauge theories can typically
be embedded into continuous quantum field theories. In the 2-form case, the
continuous theory is shown to be a strict 2-group gauge theory. This embedding
is studied by carefully constructing the space of -form connections using
the technology of Deligne-Beilinson cohomology. The same techniques can then be
used to study more general models built from Postnikov towers. For finite
symmetry groups, 2-form topological theories have a natural lattice
interpretation, which we use to construct a lattice Hamiltonian model in (3+1)d
that is exactly solvable. This construction relies on the introduction of a
cohomology, dubbed 2-form cohomology, of algebraic cocycles that are identified
with the simplicial cocycles of as provided by the so-called
-construction of Eilenberg-MacLane spaces. We show algebraically and
geometrically how a 2-form 4-cocycle reduces to the associator and the braiding
isomorphisms of a premodular category of -graded vector spaces. This is used
to show the correspondence between our 2-form gauge model and the Walker-Wang
model.Comment: 78 page
From gauge to higher gauge models of topological phases
We consider exactly solvable models in (3+1)d whose ground states are
described by topological lattice gauge theories. Using simplicial arguments, we
emphasize how the consistency condition of the unitary map performing a local
change of triangulation is equivalent to the coherence relation of the
pentagonator 2-morphism of a monoidal 2-category. By weakening some axioms of
such 2-category, we obtain a cohomological model whose underlying 1-category is
a 2-group. Topological models from 2-groups together with their lattice
realization are then studied from a higher gauge theory point of view. Symmetry
protected topological phases protected by higher symmetry structures are
explicitly constructed, and the gauging procedure which yields the
corresponding topological gauge theories is discussed in detail. We finally
study the correspondence between symmetry protected topological phases and 't
Hooft anomalies in the context of these higher group symmetries.Comment: 38 pages, v2: minor revisio
Entanglement entropy of (3+1)D topological orders with excitations
Excitations in (3+1)D topologically ordered phases have very rich structures.
(3+1)D topological phases support both point-like and string-like excitations,
and in particular the loop (closed string) excitations may admit knotted and
linked structures. In this work, we ask the question how different types of
topological excitations contribute to the entanglement entropy, or
alternatively, can we use the entanglement entropy to detect the structure of
excitations, and further obtain the information of the underlying topological
orders? We are mainly interested in (3+1)D topological orders that can be
realized in Dijkgraaf-Witten gauge theories, which are labeled by a finite
group and its group 4-cocycle up to group
automorphisms. We find that each topological excitation contributes a universal
constant to the entanglement entropy, where is the quantum
dimension that depends on both the structure of the excitation and the data
. The entanglement entropy of the excitations of the
linked/unlinked topology can capture different information of the DW theory
. In particular, the entanglement entropy introduced by Hopf-link
loop excitations can distinguish certain group 4-cocycles from the
others.Comment: 12 pages, 4 figures; v2: minor changes, published versio
Intertwined symmetry and topology in 3 + 1 dimensional gapped quantum phases of matter
This thesis is an investigation of various topological properties of 3 + 1 dimensional Bosonic gapped phases of matter. We divide our study into two main themes, the first involving short-range entangled phases with global symmetries also known as symmetry protected topological phases and the second involving phases with long range entanglement also known as topologically ordered phases
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