The Decoherence Time in High Energy Heavy Ion Collisions

We calculate the decoherence time of the ground state wave function of a nucleus in a high energy heavy ion collision. We define this time as the decay time of the ratio Tr D^2 / (Tr D)^2 of traces of the density matrix D. We find that this time is smaller or equal to 1/Q_s, where the saturation scale Q_s is defined within the color glass condensate model of parton saturation. Our result supports the notion that the extremely rapid entropy production deduced for the early stage of heavy ion collisions at collider energies is to a large extent caused by the decoherence of the initial-state wave functions.Comment: Final, slightly modified version as it will be published in Phys. Rev.

Approximate Message Passing under Finite Alphabet Constraints

In this paper we consider Basis Pursuit De-Noising (BPDN) problems in which the sparse original signal is drawn from a finite alphabet. To solve this problem we propose an iterative message passing algorithm, which capitalises not only on the sparsity but by means of a prior distribution also on the discrete nature of the original signal. In our numerical experiments we test this algorithm in combination with a Rademacher measurement matrix and a measurement matrix derived from the random demodulator, which enables compressive sampling of analogue signals. Our results show in both cases significant performance gains over a linear programming based approach to the considered BPDN problem. We also compare the proposed algorithm to a similar message passing based algorithm without prior knowledge and observe an even larger performance improvement.Comment: 4 pages, 2 figures, to appear in IEEE International Conference on Acoustics, Speech, and Signal Processing ICASSP 201

Mitigating Greenhouse Gases in Agriculture

Climate change has severe adverse effects on the livelihood of millions of the world’s poorest people. Increasing temperatures, water scarcity and droughts, flooding and storms affect food security. Thus, mitigation actions are needed to pave the way for a sustainable future for all. Currently, agriculture directly contributes about 10-15 percent to global greenhouse gas (GHG) emissions. Adding emissions from deforestation and land use change for animal feed production, this rises to about 30 percent. Scenarios predict a significant rise in agricultural emissions without effective mitigation actions. Given all the efforts undertaken in other sectors, agriculture would then become the single largest emitter within some decades, and without mitigation in agriculture, ambitious goals, such as keeping global warming below two degrees may become impossible to reach. The main agricultural emission sources are nitrous oxide from soils and methane from enteric fermentation in ruminants. In addition, conversion of native vegetation and grasslands to arable agriculture releases large amounts of CO2 from the vegetation and from soil organic matter. The main mitigation potential lies in soil carbon sequestration and preserving the existing soil carbon in arable soils. Nitrous oxide emissions can be reduced by reduced nitrogen application, but much still remains unclear about the effect different fertilizer types and management practices have on these emissions. Methane emissions from ruminants can only be reduced significantly by a reduction in animal numbers. Sequestration, finally, can be enhanced by conservative management practices, crop rotation with legumes (grass-clover) leys and application of organic fertilizers. An additional issue of importance are storage losses of food in developing and food wastage in developed countries (each about 30-40 percent of end products). Thus, there are basically five broad categories of mitigation actions in agriculture and its broader context: zz reducing direct and indirect emissions from agriculture; zz increasing carbon sequestration in agricultural soils; zz changing human dietary patterns towards more climate friendly food consumption, in particular less animal products; zz reducing storage losses and food wastage; zz the option of bioenergy needs to be mentioned, but depending on the type of bioenergy several negative side-effects may occur, including effects on food security, biodiversity and net GHG emissions. Although there are many difficulties in the details of mitigation actions in agriculture, a paradigm of climate friendly agriculture based on five principles can be derived from the knowledge about agricultural emissions and carbon sequestration: zz Climate friendly agriculture has to account for tradeoffs and choose system boundaries adequately; zz it has to account for synergies and adopt a systemic approach; zz aspects besides mitigation such as adaptation and food security are of crucial importance; zz it has to account for uncertainties and knowledge gaps, and zz the context beyond the agricultural sector has to be taken into account, in particular food consumption and waste patterns. Regarding policies to implement such a climate friendly agriculture, not much is yet around. In climate policy, agriculture only plays a minor role and negotiations proceed only very slowly on this topic. In agricultural policy climate change mitigation currently plays an insignificant role. In both contexts, some changes towards combined approaches can be expected over the next decade. Its 13 is essential that climate policy adequately captures the special characteristics of the agricultural sector. Policies with outcomes that endanger other aspects of agriculture such as food security or ecology have to be avoided. Agriculture delivers much more than options for mitigating greenhouse gas emissions and serving as a CO2 sink. We close this report with recommendations for the five most important goals to be realized in the context of mitigation and agriculture and proposals for concrete actions. First, soil organic carbon levels have to be preserved and, if possible, increased. Governments should include soil carbon sequestration in their mitigation and adaptation strategies and the climate funds should take a strong position on supporting such practices. Second, the implementation of closed nutrient cycles and optimal use of biomass has to be supported. Again, governments and funds should act on this. Policy instruments for nitrate regulation are a good starting point for this. As a third and most effective goal, we propose changes in food consumption and waste patterns. Without a switch to attitudes characterized by sufficiency, there is a danger that all attempts for mitigation remain futile. Finally, there are two goals for research, namely to develop improved knowledge on nitrous oxide dynamics, and on methods for assessment of multi-functional farming systems. Without this, adequate policy instruments for climate friendly agriculture and an optimal further development of it are not possible

Lobbying and the Power of Multinational Firms

Are national or multinational firms better lobbyists? This paper analyzes the extent of national environmental regulation when policy is determined in a lobbying game between a government and firm. We compare the resulting regulation levels for national and multinational firms. We identify three countervailing forces, the easier-to-shut-down effect, the easier-to-curb-exports effect and the multiple-plant effect. The interplay of these three forces determines whether national or multinational firms produce more, depending on such parameters as the potential environmental damages, transportation costs and the in uence of the firm. We also show that welfare levels are higher with multinational firms than with national firms when there is no lobbying, but that lobbying can reverse the welfare ordering.Multinational enterprises, regulation, policy formation, lobbying, interest groups, foreign direct investment

Towards a Theory of Entropy Production in the Little and Big Bang

We propose a broadly applicable formalism for the description of coarse grained entropy production in quantum mechanical processes. Our formalism is based on the Husimi transform of the quantum state, which encodes the notion that information about any quantum state is limited by the experimental resolution. We show in two analytically tractable cases (the decay of an unstable vacuum state and reheating after cosmic inflation) that the growth rate of the Wehrl entropy associated with the Husimi function approaches the classical Kolmogorov-Sinai entropy. We also discuss various possible applications of our formalism, including the production of entropy in the early stages of a relativistic heavy ion collision.Comment: 21 pages, 6 figures. One section is added in v