16,256 research outputs found
Heavy Hadrons and QCD Instantons
Heavy hadrons are analyzed in a random and dilute gas of instantons. We
derive the instanton-induced interactions between heavy and light quarks at
next to leading order in the heavy quark mass and in the planar approximation,
and discuss their effects on the hadronic spectrum. The role of these
interactions in the formation of exotic hadrons is also discussed.Comment: 26 pages, REVTeX, 2 tables, 5 figures, uses FEYNMAN.st
The dynamics of Machiavellian intelligence
The "Machiavellian intelligence" hypothesis (or the "social brain"
hypothesis) posits that large brains and distinctive cognitive abilities of
humans have evolved via intense social competition in which social competitors
developed increasingly sophisticated "Machiavellian" strategies as a means to
achieve higher social and reproductive success. Here we build a mathematical
model aiming to explore this hypothesis. In the model, genes control brains
which invent and learn strategies (memes) which are used by males to gain
advantage in competition for mates. We show that the dynamics of intelligence
has three distinct phases. During the dormant phase only newly invented memes
are present in the population. During the cognitive explosion phase the
population's meme count and the learning ability, cerebral capacity
(controlling the number of different memes that the brain can learn and use),
and Machiavellian fitness of individuals increase in a runaway fashion. During
the saturation phase natural selection resulting from the costs of having large
brains checks further increases in cognitive abilities. Overall, our results
suggest that the mechanisms underlying the "Machiavellian intelligence"
hypothesis can indeed result in the evolution of significant cognitive
abilities on the time scale of 10 to 20 thousand generations. We show that
cerebral capacity evolves faster and to a larger degree than learning ability.
Our model suggests that there may be a tendency toward a reduction in cognitive
abilities (driven by the costs of having a large brain) as the reproductive
advantage of having a large brain decreases and the exposure to memes increases
in modern societies.Comment: A revised version has been published by PNA
Dynamics and Decay of Heavy-Light Hadrons
Recent signals for narrow hadrons containing heavy and light flavours are
compared with quark model predictions for spectroscopy, strong decays, and
radiative transitions. In particular, the production and identification of
excited charmed and cs states are examined with emphasis on elucidating the
nature of and states. Roughly 200 strong decay amplitudes of
and states up to 3.3 GeV are presented. Applications include determining
flavour content in mesons and the mixing angle in and wave
states and probes of putative molecular states. We advocate searching for
radially excited states in B decays.Comment: 19 pages, 7 figures, revtex. A numerical error is corrected. Some
strong decay rates have change
Impact of generalized benefit functions on the evolution of cooperation in spatial public goods games with continuous strategies
Cooperation and defection may be considered as two extreme responses to a
social dilemma. Yet the reality is much less clear-cut. Between the two
extremes lies an interval of ambivalent choices, which may be captured
theoretically by means of continuous strategies defining the extent of the
contributions of each individual player to the common pool. If strategies are
chosen from the unit interval, where 0 corresponds to pure defection and 1
corresponds to the maximal contribution, the question is what is the
characteristic level of individual investments to the common pool that emerges
if the evolution is guided by different benefit functions. Here we consider the
steepness and the threshold as two parameters defining an array of generalized
benefit functions, and we show that in a structured population there exist
intermediate values of both at which the collective contributions are maximal.
However, as the cost-to-benefit ratio of cooperation increases the
characteristic threshold decreases, while the corresponding steepness
increases. Our observations remain valid if more complex sigmoid functions are
used, thus reenforcing the importance of carefully adjusted benefits for high
levels of public cooperation.Comment: 8 two-column pages, 8 figures; accepted for publication in Physical
Review
Anomalous Chiral Fermi Surface
We provide a geometrical argument for the emergence of a Wess-Zumino-Witten
(WZW) term for a Fermi surface threaded by a Berry curvature. In the presence
of external fields, the gauged WZW term yields a chiral (triangle) anomaly for
the fermionic current at the edge of the Fermi surface. Fermion number is
conserved though since the Berry curvatures occur always in pairs with opposite
(monopole) charge. The anomalous vector and axial currents for a a fermionic
fluid at low temperature threaded by pairs of Berry curvatures are discussed.
The leading temperature correction to the chiral vortical effect in a slowly
rotating Fermi surface threaded by a Berry curvature maybe tied to the
gravitational anomaly.Comment: 4 pages; version to appear in PR
The pace of evolution across fitness valleys
How fast does a population evolve from one fitness peak to another? We study
the dynamics of evolving, asexually reproducing populations in which a certain
number of mutations jointly confer a fitness advantage. We consider the time
until a population has evolved from one fitness peak to another one with a
higher fitness. The order of mutations can either be fixed or random. If the
order of mutations is fixed, then the population follows a metaphorical ridge,
a single path. If the order of mutations is arbitrary, then there are many ways
to evolve to the higher fitness state. We address the time required for
fixation in such scenarios and study how it is affected by the order of
mutations, the population size, the fitness values and the mutation rate
- …