The Joker effect: cooperation driven by destructive agents

Understanding the emergence of cooperation is a central issue in evolutionary game theory. The hardest setup for the attainment of cooperation in a population of individuals is the Public Goods game in which cooperative agents generate a common good at their own expenses, while defectors "free-ride" this good. Eventually this causes the exhaustion of the good, a situation which is bad for everybody. Previous results have shown that introducing reputation, allowing for volunteer participation, punishing defectors, rewarding cooperators or structuring agents, can enhance cooperation. Here we present a model which shows how the introduction of rare, malicious agents -that we term jokers- performing just destructive actions on the other agents induce bursts of cooperation. The appearance of jokers promotes a rock-paper-scissors dynamics, where jokers outbeat defectors and cooperators outperform jokers, which are subsequently invaded by defectors. Thus, paradoxically, the existence of destructive agents acting indiscriminately promotes cooperation.Comment: Accepted for publication in the Journal of Theoretical Biology (JTB

Hong-Ou-Mandel interference without beam splitters

We propose a new interferometric setup which displays a completely destructive generalized N-photon Hong-Ou-Mandel interference. The key property of this scheme is that is does not require any optical elements like beam splitters or integrated waveguide structures. The interference is intrinsically produced by the evolution of N photons in free space when emitted by N identical statistically independent single photon sources and measured by N detectors in the far field. In this sense the setup is a most simple and natural implementation of the Hong-Ou-Mandel interference effect, i.e., of a completely destructive multi-photon interference produced by statistically independent incoherent sources.Comment: 8 pages, 7 figure

Hydrodynamics of a new concept of primary containment by energy absorption

Fluid dynamical analysis for idealized reactors system with spherical symmetry determines the effect which the destructive component of a nuclear accident produces on primary containment structures. Steel strands surrounding the reactor cavity in the biological shield exhibit plastic deformation to achieve the energy absorption

Indices that capture creative destruction: questions and implications

The paper argues that micro and macro economists interested in the dynamics of creative destruction can gain important insights by using indices that capture the effect of innovation on the relative position of firms. This is due to the uneven and 'destructive' effect that radical innovation has on firm rankings. One such index is the market share instability index. On the financial side, the excess volatility of stock prices and idiosyncratic risk also appear to capture the uneven dynamics of creative destruction. The paper concludes by considering the implications of these propositions for economy-wide growth during periods of radical innovation (e.g. GPTs)

Fundamental limits for non-destructive measurement of a single spin by Faraday rotation

Faraday rotation being a dispersive effect, is commonly considered as the method of choice for non-destructive detection of spin states. Nevertheless Faraday rotation is inevitably accompanied by spin-flips induced by Raman scattering, which compromises non-destructive detection. Here, we derive an explicit general relation relating the Faraday rotation and the spin-flip Raman scattering cross-sections, from which precise criteria for non-destructive detection are established. It is shown that, even in ideal conditions, non-destructive measurement of a single spin can be achieved only in anisotropic media, or within an optical cavity.Comment: 5 pages, 2 figure