Self-interacting dark matter with a stable vector mediator

Light vector mediators can naturally induce velocity-dependent dark matter self-interactions while at the same time allowing for the correct dark matter relic abundance via thermal freeze-out. If these mediators subsequently decay into Standard Model states such as electrons or photons however, this is robustly excluded by constraints from the Cosmic Microwave Background. We study to what extent this conclusion can be circumvented if the vector mediator is stable and hence contributes to the dark matter density while annihilating into lighter degrees of freedom. We find viable parts of parameter space which lead to the desired self-interaction cross section of dark matter to address the small-scale problems of the collisionless cold dark matter paradigm while being compatible with bounds from the Cosmic Microwave Background and Big Bang Nucleosynthesis observations.Comment: 25 pages, 6 figures. Matches published versio

Scale and cost efficiency in the Swiss electricity distribution industry: evidence from a frontier cost approach

The deregulation of the electricity industry is currently on the political agenda in many countries. In most countries, the deregulation of the sector is combined with a (re-) regulation of the electricity networks in most of the countries. In this paper, we analyze the costs structure of 59 Swiss electricity distribution network operators with respect to cost and scale efficiency of the industry. A stochastic frontier model is applied to estimate the average costs of efficient network operators as a benchmark for the industry. Moreover, the heterogeneity of service areas is taken into account. The Swiss authorities might use our results to regulate the prices for the access to the distribution networks.stochastic frontier analysis; electricity distribution; efficiency measurement; regulation; benchmarking; returns to scale; returns to density

Does lowering dividend tax rates increase dividends repatriated?: evidence of intra-firm cross-border dividend repatriation policies by German Multinational Enterprises

This paper explores the impact dividend taxes exert on the dividends repatriated from foreign affiliates to their German parent company. Based on an augmented Lintner model of firms' dividend payout decisions, the paper focusses on cross-border intra-firm dividend payments of wholly-owned foreign affiliates in the manufacturing sector. Firm-level data from the Microdatabase Direct Investment (MiDi) of the Deutsche Bundesbank is used. Results firstly signal the validity of the original Lintner model for cross-border intra-firm dividend payments of German affiliates abroad, although the target payout ratio and the degree of dividend smoothing drops substantially once timeinvariant unobserved heterogeneity is controlled for. Secondly, results from an augmented Lintner model imply that increases in dividend taxes indeed have a statistically significant negative impact on the expected value of dividends repatriated: Evaluated at the overall mean dividend payment a one percentage point increase in the dividend tax rate would decrease dividends repatriated by about 3.5 percent. Evaluated at the mean of positive dividend payments a semi-elasticity of -1.6 is derived. --Dividend policy,taxes,lintner model,multinational enterprise

Globalisation: trends and issues for government

Globalisation has many faces, and they do not always align neatly with the organisation of government. For example, some aspects of globalisation - trade, foreign investment, merger policy - fall clearly within the remit of the UK Department of Trade & Industry (DTI). But as well as these economic and commercial globalisations, Anthony Giddens and others have drawn attention to others - social, environmental, cultural, and political. These are interrelated in ways we do not yet understand, still less control - yet they have clear impact on policy areas which are of great interest to DTI. In particular, issues of ethics and sustainability, and the way in which they will interact with personal value systems, are probably the single largest imponderable for all parts of government over the next 20 years. Multi-faceted, rapidly changing globalisation will profoundly affect the way corporations and other institutions operate. These changes will challenge the existing ways of government, extending into and beyond all areas of DTI’s work. Government more than other actors has power to shape the future by arranging itself to deal with a range of possible futures; but incremental changes to structures designed for an earlier age may not achieve this. Scenario planning techniques make it possible to "think aloud" about the co-evolution of governmental institutions with the environment in which they operate, and open up the possibility of steering that process better by thinking about different possible futures. When other actors adopt new global ways to organise, co-ordinate, and achieve agility at scale, what should be the response of government

Adiabatic Quantum Search in Open Systems

Adiabatic quantum algorithms represent a promising approach to universal quantum computation. Whilst in a closed system these algorithms are limited by avoided level crossings, where the gap becomes exponentially small in the system size, their robustness in open systems remains unresolved. We study the dynamics in the proximity of such an avoided level crossing associated with the adiabatic quantum search algorithm in a quantum system that is coupled to a generic environment. At zero temperature, we find that the algorithm remains scalable provided the noise spectral density of the environment decays sufficiently fast at low frequencies. At finite temperature, however, scattering processes render the algorithm inefficient and no quantum speedup can be achieved. Owing to the generic nature of our model, we expect our results to be widely applicable to other adiabatic quantum algorithms.Comment: Accepted version. 6 pages, 2 figures, 10 pages supplemental material

Evidence of a Nondiffusive Transport in a Monodisperse Screened Coulomb System by a Molecular-Dynamics Simulation

A molecular-dynamics simulation is carried out for particles (tracers) interacting with a screened Coulomb potential in three dimensions. A phase transition is observed from a liquid to an fcc solid on reducing the temperature at a fixed density, consistent with previous studies. In the liquid phase, the variation of the rms displacement Rtr of the charged particles with time seems to depend on the density and the temperature. In the short-time regime, the effective exponent k for the subdiffusive power-law behavior, i.e., Rtr∼tk, decreases on increasing the density and lowering the temperature. A crossover from subdiffusive to a diffusive behavior is observed for a wide density regime in the liquid phase. At high temperatures and large densities, a single power law does not seem to describe the variation of Rtr with t