Natio et gens: Venice biennale 2009

The following is an informal reflection on the changing place of nationality and national consciousness in cultural life with reference to last year’s Biennale. Having drawn tentative inferences regarding the roles of these, we offer a selective review of what appear to us to be the most memorable national representations. These in turn suggest a paradoxical benefit which an awareness of localised histories may bring to artistic production

Perturbations of near-horizon geometries and instabilities of Myers-Perry black holes

It is shown that the equations governing linearized gravitational (or electromagnetic) perturbations of the near-horizon geometry of any known extreme vacuum black hole (allowing for a cosmological constant) can be Kaluza-Klein reduced to give the equation of motion of a charged scalar field in AdS_2 with an electric field. One can define an effective Breitenlohner-Freedman bound for such a field. We conjecture that if a perturbation preserves certain symmetries then a violation of this bound should imply an instability of the full black hole solution. Evidence in favour of this conjecture is provided by the extreme Kerr solution and extreme cohomogeneity-1 Myers-Perry solution. In the latter case, we predict an instability in seven or more dimensions and, in 5d, we present results for operator conformal weights assuming the existence of a CFT dual. We sketch a proof of our conjecture for scalar field perturbations.Comment: 24 pages (+ 16 pages appendices), 2 figures. v2: Corrected error in CFT operator dimensions (they are all integers). v3: Various improvements and corrections, in particular for electromagnetic perturbations. Accepted by Physical Review

On the smoothness of static multi-black hole solutions of higher-dimensional Einstein-Maxwell theory

Previous work has shown that static multi-black hole solutions of higher-dimensional Einstein-Maxwell theory do not possess smooth horizons. We show that the lack of smoothness is worse than previously demonstrated. We consider solutions describing multiple black holes on a common axis. In five dimensions, the metric is generically twice, but not three times, continuously differentiable at the horizon. The Maxwell field is generically continuous, but not differentiable, at the horizon. In more than five dimensions, the metric is once, but not twice, continuously differentiable, and there is a parallely-propagated curvature singularity at the horizon. The Maxwell field strength is again continuous, but not differentiable, at the horizon.Comment: 19 pages; minor correction

Trend Damping: Under-Adjustment, Experimental Artifact, or Adaptation to Features of the Natural Environment?

People’s forecasts from time series underestimate future values for upward trends and overestimate them for downward ones. This trend damping may occur because 1) people anchor on the last data point and make insufficient adjustment to take the trend into account, 2) they adjust towards the average of the trends they have encountered within the experiment, or 3) they are adapted to an environment in which natural trends tend to be damped. Two experiments eliminated the first account: for series that are negatively accelerated or have shallow slopes, people showed anti-damping (the opposite of damping), a phenomenon that cannot be interpreted in terms of under-adjustment. These experiments also produced results consistent with the second account: forecasts for a given function clearly depended on the other functions that were forecast within the same experiment. However, this second account was itself eliminated by a third experiment demonstrating both damping and, to a lesser degree, anti-damping when people forecast from a single series. We conclude that people have adapted to degrees of growth and decay that are representative of their environment: damping occurs when trends in presented series are steeper than this and anti-damping occurs when they are shallower

Bars, lines and points: The effect of graph format on judgmental forecasting

Time series are often presented graphically, and forecasters often judgmentally extrapolate graphically presented data. However, graphs come in many different formats: here, we examine the effect of format when non-experts make forecasts from data presented as bar charts, line graphs, and point graphs. In four web-based experiments with over 4000 participants, we elicited judgmental forecasts for eight points that followed a trended time series containing 50 points. Forecasts were lower for bar charts relative to either line or point graphs. Factors potentially affecting these format effects were investigated: We found that the intensity of shading had no effect on forecasts and that using horizontal stepped lines led to higher forecasts than bars. We also found that participants added more noise to their forecasts for bars than for points, leading to worse performance overall. These findings suggest that format significantly influences judgmental time series forecasts

The Coase Theorem, or the Coasian Lens? An Application to GMO Regulation

We develop a property rights-transaction costs framework called the Coasian Lens (CL). We argue the CL captures Coase's seminal ideas (1937; 1960) more closely than the Coase Theorem. We use the CL to examine how regulation of genetically modified organisms (GMOs) may affect contract structures in the global agri-food chain.Research and Development/Tech Change/Emerging Technologies,

Noncommutative Solitons and Intersecting D-Branes

We construct intersecting D-branes as noncommutative solitons in bosonic and type II string theory. ``Defect'' branes which are D-branes containing bubbles of the closed string vacuum play an important role in the construction.Comment: 17 pages, harvmac; published version with added clarification

‘Fixing’ the climate crisis: capital, states, and carbon offsetting in India

The paper analyzes dynamics of accumulation and displacement in the Clean Development Mechanism (CDM). It combines the theoretical work of David Harvey and James O’Connor with a case study of the Gujarat Fluorochemicals Limited HFC-23 destruction project in Gujarat, India. The framework is used to connect the factors driving opportunities for capital accumulation in the CDM market with the causes of social and ecological dislocation at the local project level. We argue that the CDM is a spatial fix to the ecological crisis of climate change which secures conditions of production for fossil fuel industries and promotes new sites of accumulation for other companies. The political–economic ‘fix’ is dependent on ‘fixing’ a global sociospatial divide between developed and developing countries down to ‘fixed’ projects at the local level. This spatial fix facilitates a displacement of the costs of responding to the climate crisis from North to South. </jats:p

General Scheme for Perfect Quantum Network Coding with Free Classical Communication

This paper considers the problem of efficiently transmitting quantum states through a network. It has been known for some time that without additional assumptions it is impossible to achieve this task perfectly in general -- indeed, it is impossible even for the simple butterfly network. As additional resource we allow free classical communication between any pair of network nodes. It is shown that perfect quantum network coding is achievable in this model whenever classical network coding is possible over the same network when replacing all quantum capacities by classical capacities. More precisely, it is proved that perfect quantum network coding using free classical communication is possible over a network with $k$ source-target pairs if there exists a classical linear (or even vector linear) coding scheme over a finite ring. Our proof is constructive in that we give explicit quantum coding operations for each network node. This paper also gives an upper bound on the number of classical communication required in terms of $k$, the maximal fan-in of any network node, and the size of the network.Comment: 12 pages, 2 figures, generalizes some of the results in arXiv:0902.1299 to the k-pair problem and codes over rings. Appeared in the Proceedings of the 36th International Colloquium on Automata, Languages and Programming (ICALP'09), LNCS 5555, pp. 622-633, 200

Non-Commutative Instantons and the Seiberg-Witten Map

We present several results concerning non-commutative instantons and the Seiberg-Witten map. Using a simple ansatz we find a large new class of instanton solutions in arbitrary even dimensional non-commutative Yang-Mills theory. These include the two dimensional ``shift operator'' solutions and the four dimensional Nekrasov-Schwarz instantons as special cases. We also study how the Seiberg-Witten map acts on these instanton solutions. The infinitesimal Seiberg-Witten map is shown to take a very simple form in operator language, and this result is used to give a commutative description of non-commutative instantons. The instanton is found to be singular in commutative variables.Comment: 26 pages, AMS-LaTeX. v2: the formula for the commutative description of the Nekrasov-Schwarz instanton corrected (sec. 4). v3: minor correction