6,194 research outputs found
Origin of the Mott Gap
We show exactly that the only charged excitations that exist in the
strong-coupling limit of the half-filled Hubbard model are gapped composite
excitations generated by the dynamics of the charge boson that appears
upon explicit integration of the high-energy scale. At every momentum, such
excitations have non-zero spectral weight at two distinct energy scales
separated by the on-site repulsion . The result is a gap in the spectrum for
the composite excitations accompanied by a discontinuous vanishing of the
density of states at the chemical potential when exceeds the bandwidth.
Consequently, we resolve the long-standing problem of the cause of the charge
gap in a half-filled band in the absence of symmetry breaking.Comment: 6 pages, 2 figures: Expanded Published versio
Multi-Boundary Entanglement in Chern-Simons Theory and Link Invariants
We consider Chern-Simons theory for gauge group at level on
3-manifolds with boundary consisting of topologically linked tori.
The Euclidean path integral on defines a quantum state on the boundary,
in the -fold tensor product of the torus Hilbert space. We focus on the case
where is the link-complement of some -component link inside the
three-sphere . The entanglement entropies of the resulting states define
framing-independent link invariants which are sensitive to the topology of the
chosen link. For the Abelian theory at level () we give a
general formula for the entanglement entropy associated to an arbitrary
partition of a generic -component link into sub-links. The formula
involves the number of solutions to certain Diophantine equations with
coefficients related to the Gauss linking numbers (mod ) between the two
sublinks. This formula connects simple concepts in quantum information theory,
knot theory, and number theory, and shows that entanglement entropy between
sublinks vanishes if and only if they have zero Gauss linking (mod ). For , we study various two and three component links. We show that the
2-component Hopf link is maximally entangled, and hence analogous to a Bell
pair, and that the Whitehead link, which has zero Gauss linking, nevertheless
has entanglement entropy. Finally, we show that the Borromean rings have a
"W-like" entanglement structure (i.e., tracing out one torus does not lead to a
separable state), and give examples of other 3-component links which have
"GHZ-like" entanglement (i.e., tracing out one torus does lead to a separable
state).Comment: 37 pages, 19 figure
The effects of a background potential in star cluster evolution: a delay in the relaxation time-scale and runaway collision processes
Runaway stellar collisions in dense star clusters are invoked to explain the
presence of very massive stars or blue stragglers in the center of those
systems. This process has also been explored for the first star clusters in the
Universe and shown to yield stars that may collapse at some points into an
intermediate mass black hole. Although the early evolution of star clusters
requires the explicit modeling of the gas out of which the stars form, these
calculations would be extremely time-consuming and often the effects of the gas
can be accurately treated by including a background potential to account for
the extra gravitational force. We apply this approximation to model the early
evolution of the first dense star clusters formed in the Universe by performing
-body simulations, our goal is to understand how the additional
gravitational force affects the growth of a very massive star through stellar
mergers in the central parts of the star cluster. Our results show that the
background potential increases the velocities of the stars, causing an overall
delay in the evolution of the clusters and in the runaway growth of a massive
star at the center. The population of binary stars is lower due to the
increased kinetic energy of the stars, initially reducing the number of stellar
collisions, and we show that relaxation processes are also affected. Despite
these effects, the external potential enhances the mass of the merger product
by a factor 2 if the collisions are maintained for long times.Comment: 16 pages. Accepted for publication in Astronomy and Astrophysic
Interfaces and the extended Hilbert space of Chern-Simons theory
The low energy effective field theories of dimensional topological
phases of matter provide powerful avenues for investigating entanglement in
their ground states. In \cite{Fliss:2017wop} the entanglement between distinct
Abelian topological phases was investigated through Abelian Chern-Simons
theories equipped with a set of topological boundary conditions (TBCs). In the
present paper we extend the notion of a TBC to non-Abelian Chern-Simons
theories, providing an effective description for a class of gapped interfaces
across non-Abelian topological phases. These boundary conditions furnish a
defining relation for the extended Hilbert space of the quantum theory and
allow the calculation of entanglement directly in the gauge theory. Because we
allow for trivial interfaces, this includes a generic construction of the
extended Hilbert space in any (compact) Chern-Simons theory quantized on a
Riemann surface. Additionally, this provides a constructive and principled
definition for the Hilbert space of effective ground states of gapped phases of
matter glued along gapped interfaces. Lastly, we describe a generalized notion
of surgery, adding a powerful tool from topological field theory to the gapped
interface toolbox.Comment: 46 pages, many figures, 1 appendix; v2: fixed affiliations, minor
revisions, added reference
Dynamics of the DBI Spike Soliton
We compare oscillations of a fundamental string ending on a D3-brane in two
different settings: (1) a test-string radially threading the horizon of an
extremal black D3-brane and (2) the spike soliton of the DBI effective action
for a D3-brane. Previous work has shown that overall transverse modes of the
test-string appear as l=0 modes of the transverse scalar fields of the DBI
system. We identify DBI world-volume degrees of freedom that have dynamics
matching those of the test-string relative transverse modes. We show that there
is a map, resembling T-duality, between relative and overall transverse modes
for the test-string that interchanges Neumann and Dirichlet boundary conditions
and implies equality of the absorption coefficients for both modes. We give
general solutions to the overall and relative transverse parts of the DBI
coupled gauge and scalar system and calculate absorption coefficients for the
higher angular momentum modes in the low frequency limit. We find that there is
a nonzero amplitude for l>0 modes to travel out to infinity along the spike,
demonstrating that the spike remains effectively 3+1-dimensional.Comment: 15 pages, 1 figur
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