409 research outputs found
Motion of influential players can support cooperation in Prisoner's Dilemma
We study a spatial Prisoner's dilemma game with two types (A and B) of
players located on a square lattice. Players following either cooperator or
defector strategies play Prisoner's Dilemma games with their 24 nearest
neighbors. The players are allowed to adopt one of their neighbor's strategy
with a probability dependent on the payoff difference and type of the given
neighbor. Players A and B have different efficiency in the transfer of their
own strategy therefore the strategy adoption probability is reduced by a
multiplicative factor (w < 1) from the players of type B. We report that the
motion of the influential payers (type A) can improve remarkably the
maintenance of cooperation even for their low densities.Comment: 7 pages, 7 figure
Cooperation and its evolution in growing systems with cultural reproduction
We explore the evolution of cooperation in the framework of the evolutionary
game theory using the prisoner's dilemma as metaphor of the problem. We present
a minimal model taking into account the growing process of the systems and
individuals with imitation capacity. We consider the topological structure and
the evolution of strategies decoupled instead of a coevolutionary dynamic. We
show conditions to build up a cooperative system with real topological
structures for any natural selection intensity. When the system starts to grow,
cooperation is unstable but becomes stable as soon as the system reaches a
small core of cooperators whose size increase when the intensity of natural
selection decreases. Thus, we reduce the emergence of cooperative systems with
cultural reproduction to justify a small initial cooperative structure that we
call cooperative seed. Otherwise, given that the system grows principally as
cooperator whose cooperators inhabit the most linked parts of the system, the
benefit-cost ratio required for cooperation evolve is drastically reduced
compared to the found in static networks. In this way, we show that in systems
whose individuals have imitation capacity the growing process is essential for
the evolution of cooperation.Comment: 16 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1111.247
Analytical Results for Individual and Group Selection of Any Intensity
The idea of evolutionary game theory is to relate the payoff of a game to reproductive success (= fitness). An underlying assumption in most models is that fitness is a linear function of the payoff. For stochastic evolutionary dynamics in finite populations, this leads to analytical results in the limit of weak selection, where the game has a small effect on overall fitness. But this linear function makes the analysis of strong selection difficult. Here, we show that analytical results can be obtained for any intensity of selection, if fitness is defined as an exponential function of payoff. This approach also works for group selection (= multi-level selection). We discuss the difference between our approach and that of inclusive fitness theory
The -dependence of the generalised Gerasimov-Drell-Hearn integral for the deuteron, proton and neutron
The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution
to the magnetic moment of the target nucleus with an energy-weighted integral
of the difference of the helicity-dependent photoabsorption cross sections. The
data collected by HERMES with a deuterium target are presented together with a
re-analysis of previous measurements on the proton. This provides a measurement
of the generalised GDH integral covering simultaneously the nucleon-resonance
and the deep inelastic scattering regions. The contribution of the
nucleon-resonance region is seen to decrease rapidly with increasing . The
DIS contribution is sizeable over the full measured range, even down to the
lowest measured . As expected, at higher the data are found to be in
agreement with previous measurements of the first moment of . From data on
the deuteron and proton, the GDH integral for the neutron has been derived and
the proton--neutron difference evaluated. This difference is found to satisfy
the fundamental Bjorken sum rule at GeV.Comment: 12 pages, 10 figure
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