60 research outputs found
The Semi-Chiral Quotient, Hyperkahler Manifolds and T-duality
We study the construction of generalized Kahler manifolds, described purely
in terms of N=(2,2) semichiral superfields, by a quotient using the semichiral
vector multiplet. Despite the presence of a b-field in these models, we show
that the quotient of a hyperkahler manifold is hyperkahler, as in the usual
hyperkahler quotient. Thus, quotient manifolds with torsion cannot be
constructed by this method. Nonetheless, this method does give a new
description of hyperkahler manifolds in terms of two-dimensional N=(2,2) gauged
non-linear sigma models involving semichiral superfields and the semichiral
vector multiplet. We give two examples: Eguchi-Hanson and Taub-NUT. By
T-duality, this gives new gauged linear sigma models describing the T-dual of
Eguchi-Hanson and NS5-branes. We also clarify some aspects of T-duality
relating these models to N=(4,4) models for chiral/twisted-chiral fields and
comment briefly on more general quotients that can give rise to torsion and
give an example.Comment: 31 page
A simulated annealing based genetic local search algorithm for multi-objective multicast routing problems
This paper presents a new hybrid evolutionary algorithm to solve multi-objective multicast routing problems in telecommunication networks. The algorithm combines simulated annealing based strategies and a genetic local search, aiming at a more flexible and effective exploration and exploitation in the search space of the complex problem to find more non-dominated solutions in the Pareto Front. Due to the complex structure of the multicast tree, crossover and mutation operators have been specifically devised concerning the features and constraints in the problem. A new adaptive mutation probability based on simulated annealing is proposed in the hybrid algorithm to adaptively adjust the mutation rate according to the fitness of the new solution against the average quality of the current population during the evolution procedure. Two simulated annealing based search direction tuning strategies are applied to improve the efficiency and effectiveness of the hybrid evolutionary algorithm. Simulations have been carried out on some benchmark multi-objective multicast routing instances and a large amount of random networks with five real world objectives including cost, delay, link utilisations, average delay and delay variation in telecommunication networks. Experimental results demonstrate that both the simulated annealing based strategies and the genetic local search within the proposed multi-objective algorithm, compared with other multi-objective evolutionary algorithms, can efficiently identify high quality non-dominated solution set for multi-objective multicast routing problems and outperform other conventional multi-objective evolutionary algorithms in the literature
Semichiral fields on S^2 and generalized Kahler geometry
Abstract: We study a class of two-dimensional N=(2,2) supersymmetric gauge theories, given by semichiral multiplets coupled to the usual vector multiplet. In the UV, these theories are traditional gauge theories deformed by a gauged Wess-Zumino term. In the IR, they give rise to nonlinear sigma models on noncompact generalized K\ue4hler manifolds, which contain a three-form field H and whose metric is not K\ue4hler. We place these theories on S2 and compute their partition function exactly with localization techniques. We find that the contribution of instantons to the partition function that we define is insensitive to the deformation, and discuss our results from the point of view of the generalized K\ue4hler target space. \ua9 2016, The Author(s)
Supersymmetric black hole non-uniqueness in five dimensions
We present a systematic study of the moduli space of asymptotically flat,
supersymmetric and biaxisymmetric black hole solutions to five-dimensional
minimal supergravity. Previously, it has been shown that such solutions must be
multi-centred solutions with a Gibbons-Hawking base. In this paper we perform a
full analysis of three-centred solutions with a single black hole, for which
there are seven regular black hole solutions. We find that four of these can
have the same conserved charges as the BMPV black hole. These consist of a
black lens with L(3,1) horizon topology and three distinct families of
spherical black holes with nontrivial topology outside the horizon. The former
provides the first example of a nonspherical black hole with the same conserved
charges as the BMPV black hole. Moreover, of these four solutions, three can
have a greater entropy than the BMPV black hole near the BMPV upper spin bound.
One of these is a previously known spherical black hole with nontrivial
topology and the other two are new examples of a spherical black hole with
nontrivial topology and an L(3,1) black lens.Comment: version 2: typos corrected, minor clarifications added; 26 pages, 10
figure
Rotating black hole entropy from M5-branes
We compute the superconformal index of 3d N = 2 superconformal field theories obtained from N M5-branes wrapped on a hyperbolic 3-manifold. Exploiting the 3d-3d correspondence, we use perturbative invariants of SL(N, \u2102) Chern-Simons theory to determine the superconformal index in the large N limit, including corrections logarithmic in N. The leading order partition function provides a microscopic foundation for the entropy function of the dual rotating asymptotically AdS4 black holes. We also verify that the supergravity one-loop contribution to the log N term coincides with the field theoretic result. We propose a 3d-3d formulation for the refined topologically twisted index, and provide strong evidence in support of its vanishing \u2014 which agrees with the fact that the expected dual rotating magnetically-charged black hole does not exist. This provides an interesting link between gravity and a tantalizing mathematical result
Quantum Spacetime Phenomenology
I review the current status of phenomenological programs inspired by
quantum-spacetime research. I stress in particular the significance of results
establishing that certain data analyses provide sensitivity to effects
introduced genuinely at the Planck scale. And my main focus is on
phenomenological programs that managed to affect the directions taken by
studies of quantum-spacetime theories.Comment: 125 pages, LaTex. This V2 is updated and more detailed than the V1,
particularly for quantum-spacetime phenomenology. The main text of this V2 is
about 25% more than the main text of the V1. Reference list roughly double
Comments on black holes in bubbling spacetimes
In five-dimensional minimal supergravity, there are spherical black holes
with nontrivial topology outside the horizon which have the same conserved
charges at infinity as the BMPV solution. We show that some of these black
holes have greater entropy than the BMPV solution. These spacetimes are all
asymptotically flat, stationary, and supersymmetric. We also show that there is
a limit in which the black hole shrinks to zero size and the solution becomes a
nonsingular "bubbling" geometry. Thus, these solutions provide explicit
analytic examples of placing black holes inside solitons.Comment: 17 pages, 5 figures; v2: references adde
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