8,989 research outputs found
Topological spin liquids: Robustness under perturbations
We study the robustness of the paradigmatic kagome Resonating Valence Bond
(RVB) spin liquid and its orthogonal version, the quantum dimer model. The
non-orthogonality of singlets in the RVB model and the induced finite length
scale not only makes it difficult to analyze, but can also significantly affect
its physics, such as how much noise resilience it exhibits. Surprisingly, we
find that this is not the case: The amount of perturbations which the RVB spin
liquid can tolerate is not affected by the finite correlation length, making
the dimer model a viable model for studying RVB physics under perturbations.
Remarkably, we find that this is a universal phenomenon protected by
symmetries: First, the dominant correlations in the RVB are spinon
correlations, making the state robust against doping with visons. Second,
reflection symmetry stabilizes the spin liquid against doping with spinons, by
forbidding mixing of the initially dominant correlations with those which lead
to the breakdown of topological order.Comment: v2: accepted versio
Efficient algorithms for a class of partitioning problems
The problem of optimally partitioning the modules of chain- or tree-like tasks over chain-structured or host-satellite multiple computer systems is addressed. This important class of problems includes many signal processing and industrial control applications. Prior research has resulted in a succession of faster exact and approximate algorithms for these problems. Polynomial exact and approximate algorithms are described for this class that are better than any of the previously reported algorithms. The approach is based on a preprocessing step that condenses the given chain or tree structured task into a monotonic chain or tree. The partitioning of this monotonic take can then be carried out using fast search techniques
Performance tradeoffs in static and dynamic load balancing strategies
The problem of uniformly distributing the load of a parallel program over a multiprocessor system was considered. A program was analyzed whose structure permits the computation of the optimal static solution. Then four strategies for load balancing were described and their performance compared. The strategies are: (1) the optimal static assignment algorithm which is guaranteed to yield the best static solution, (2) the static binary dissection method which is very fast but sub-optimal, (3) the greedy algorithm, a static fully polynomial time approximation scheme, which estimates the optimal solution to arbitrary accuracy, and (4) the predictive dynamic load balancing heuristic which uses information on the precedence relationships within the program and outperforms any of the static methods. It is also shown that the overhead incurred by the dynamic heuristic is reduced considerably if it is started off with a static assignment provided by either of the other three strategies
The Refined Topological Vertex
We define a refined topological vertex which depends in addition on a
parameter, which physically corresponds to extending the self-dual graviphoton
field strength to a more general configuration. Using this refined topological
vertex we compute, using geometric engineering, a two-parameter (equivariant)
instanton expansion of gauge theories which reproduce the results of Nekrasov.
The refined vertex is also expected to be related to Khovanov knot invariants.Comment: 70 Pages, 23 Figure
Wall-crossing, free fermions and crystal melting
We describe wall-crossing for local, toric Calabi-Yau manifolds without
compact four-cycles, in terms of free fermions, vertex operators, and crystal
melting. Firstly, to each such manifold we associate two states in the free
fermion Hilbert space. The overlap of these states reproduces the BPS partition
function corresponding to the non-commutative Donaldson-Thomas invariants,
given by the modulus square of the topological string partition function.
Secondly, we introduce the wall-crossing operators which represent crossing the
walls of marginal stability associated to changes of the B-field through each
two-cycle in the manifold. BPS partition functions in non-trivial chambers are
given by the expectation values of these operators. Thirdly, we discuss crystal
interpretation of such correlators for this whole class of manifolds. We
describe evolution of these crystals upon a change of the moduli, and find
crystal interpretation of the flop transition and the DT/PT transition. The
crystals which we find generalize and unify various other Calabi-Yau crystal
models which appeared in literature in recent years.Comment: 61 pages, 14 figures, published versio
Channel Impulse Response-based Distributed Physical Layer Authentication
In this preliminary work, we study the problem of {\it distributed}
authentication in wireless networks. Specifically, we consider a system where
multiple Bob (sensor) nodes listen to a channel and report their {\it
correlated} measurements to a Fusion Center (FC) which makes the ultimate
authentication decision. For the feature-based authentication at the FC,
channel impulse response has been utilized as the device fingerprint.
Additionally, the {\it correlated} measurements by the Bob nodes allow us to
invoke Compressed sensing to significantly reduce the reporting overhead to the
FC. Numerical results show that: i) the detection performance of the FC is
superior to that of a single Bob-node, ii) compressed sensing leads to at least
overhead reduction on the reporting channel at the expense of a small
( dB) SNR margin to achieve the same detection performance.Comment: 6 pages, 5 figures, accepted for presentation at IEEE VTC 2017 Sprin
- …