The classical double copy for Taub-NUT spacetime

The double copy is a much-studied relationship between gauge theory and gravity amplitudes. Recently, this was generalised to an infinite family of classical solutions to Einstein's equations, namely stationary Kerr-Schild geometries. In this paper, we extend this to the Taub-NUT solution in gravity, which has a double Kerr-Schild form. The single copy of this solution is a dyon, whose electric and magnetic charges are related to the mass and NUT charge in the gravity theory. Finally, we find hints that the classical double copy extends to curved background geometries.Comment: 13 pages, no figures. Minor edits to match journal versio

Black holes and the double copy

Recently, a perturbative duality between gauge and gravity theories (the double copy) has been discovered, that is believed to hold to all loop orders. In this paper, we examine the relationship between classical solutions of non-Abelian gauge theory and gravity. We propose a general class of gauge theory solutions that double copy to gravity, namely those involving stationary Kerr-Schild metrics. The Schwarzschild and Kerr black holes (plus their higher-dimensional equivalents) emerge as special cases. We also discuss plane wave solutions. Furthermore, a recently examined double copy between the self-dual sectors of Yang-Mills theory and gravity can be reinterpreted using a momentum-space generalisation of the Kerr-Schild framework.Comment: 22 pages; typos corrected and references adde

Inevitability of Plate Tectonics on Super-Earths

The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.Comment: 13 pages, 2 figures and 1 table; in press in ApJ

Zitterbewegung is not an observable

It has recently been claimed that Zitterbewegung has been observed. However, we argue that it is not an observable and that the authors' observations must be reinterpreted

Local Industrial Structures and Female Entrepreneurship in India

We analyze the spatial determinants of female entrepreneurship in India in the manufacturing and services sectors. We focus on the presence of incumbent female-owned businesses and their role in promoting higher subsequent female entrepreneurship relative to male entrepreneurship. We find evidence of agglomeration economies in both sectors, where higher female ownership among incumbent businesses within a district-industry predicts a greater share of subsequent entrepreneurs will be female. Moreover, higher female ownership of local businesses in related industries (e.g., those sharing similar labor needs, industries related via input-output markets) predict greater relative female entry rates even after controlling for the focal district-industry’s conditions. The core patterns hold when using local industrial conditions in 1994 to instrument for incumbent conditions in 2000-2005. The results highlight that the traits of business owners in incumbent industrial structures influence the types of entrepreneurs supported.

WRIST POSITION AFFECTS HAND-GRIP STRENGTH IN TENNIS PLAYERS

In tennis the wrist is required to be in different degrees of orientation at ball impact depending on the stroke and type of shot being hit. To date, little is known about the interplay between wrist position and grip strength, despite the fact that hitting the ball and firmly holding the racket when the wrist is flexed has been suggested as factor predisposing tennis players to lateral epicondylitis. The aim of this study was to investigate the effect of different wrist positions on isometric grip strength at self-selected grip size. Thirty-seven tennis players performed three isometric contractions at each of the following wrist positions: neutral, extension, flexion, ulnar deviation and radial deviation. Maximal isometric grip force was measured at each wrist position with the use of a hand-held grip dynamometer and then the highest value at each position selected for analysis. Our results are as follows: at neutral the force exerted was 80.2 ± 22.07 (mean ± sd) kg, at wrist extension 56.99 ± 18.40 kg, at wrist flexion 33.96 ± 9.47 kg, at radial deviation 56.26 ± 19.39 kg and at ulnar deviation 56.64 ± 17.60 kg. Our findings show that, compare to the position defined as neutral, the maximum isometric force exerted by the fingers’ flexor muscles is significantly affected (lowered) by wrist position (

Competition and innovation-driven inclusive growth

The paper investigates the strength of innovation-driven employment growth, the role of competition in stimulating and facilitating it, and whether it is inclusive. In a sample of more than 26,000 manufacturing establishments across 71 countries (both OECD and developing), the authors find that firms that innovate in products or processes, or that have attained higher total factor productivity, exhibit higher employment growth than non-innovative firms. The strength of firms'innovation-driven employment growth is significantly positively associated with the share of the firms'workforce that is unskilled, debunking the conventional wisdom that innovation-driven growth is not inclusive in that it is focused on jobs characterized by higher levels of qualification. They also find that young firms have higher propensities for product or process innovation in countries with better Doing Business ranks (both overall and ranks for constituent components focused on credit availability and property registration). Firms generally innovate more and show greater employment growth if they are exposed to more information (through internet use and membership in business organizations) and are exporters. The empirical results support the policy propositions that innovation is a powerful driver of employment growth, that innovation-driven growth is inclusive in its creation of unskilled jobs, and that the underlying innovations are fostered by a pro-competitive business environment providing ready access to information, financing, export opportunities, and other essential business services that facilitate the entry and expansion of young firms.Environmental Economics&Policies,Labor Policies,Labor Markets,E-Business,Microfinance