37,186 research outputs found
Neutrino masses and baryogenesis in SO(10) unified theories
We report on some phenomenological implications of a class of unified models
based on SO(10) gauge group, with intermediate symmetry group containing
SU(2)_R. Interesting predictions for neutrino masses are discussed, which are
relevant both for solar neutrino and dark matter problems, as well as a model
for the formation of the baryon asymmetry of the universe required by
primordial nucleosynthesis.Comment: Latex 16 pages, 1 ps figure. Appeared in Proceedings of seventh
International Workshop on Neutrino Telescopes, Venezia February 27 - March 1
1996, Editor M. Baldo Ceoli
Gravitino cosmology in supersymmetric warm inflation
In supersymmetric models of warm inflation, the large temperature of the
radiation bath produced by the dissipative motion of the inflaton field may
induce a significant thermal abundance of potentially dangerous gravitinos.
While previous discussions of this problem focused on gravitino production only
at the end of warm inflation, similarly to conventional reheating scenarios, we
study the full evolution of the gravitino abundance during and after inflation
for simple monomial potentials, taking into account the enhanced gravitino and
possibly gaugino masses due to supersymmetry breaking during inflation and the
smooth transition into a radiation-dominated era. We find, on one hand, that
the continuous thermal production increases the gravitino yield, although, on
the other hand, `freeze-out' occurs at temperatures much lower than previously
estimated. Moreover, for sufficiently strong dissipation, which allows for
sub-planckian inflaton values, the lower radiation temperature significantly
alleviates and possibly solves the gravitino problem, with a baryon asymmetry
being nevertheless produced through dissipative effects. Our analysis may also
be relevant to standard reheating as an oscillating inflaton will also change
the gravitino mass, potentially modifying the produced gravitino yield.Comment: 18 pages, 12 figures. Published version Phys.Rev.
Colour reverse learning and animal personalities: the advantage of behavioural diversity assessed with agent-based simulations
Foraging bees use colour cues to help identify rewarding from unrewarding flowers, but as conditions change, bees may require behavioural flexibility to reverse their learnt preferences. Perceptually similar colours are learnt slowly by honeybees and thus potentially pose a difficult task to reverse-learn. Free-flying honeybees (N = 32) were trained to learn a fine colour discrimination task that could be resolved at ca. 70% accuracy following extended differential conditioning, and were then tested for their ability to reverse-learn this visual problem multiple times. Subsequent analyses identified three different strategies: ‘Deliberative-decisive’ bees that could, after several flower visits, decisively make a large change to learnt preferences; ‘Fickle- circumspect’ bees that changed their preferences by a small amount every time they encountered evidence in their environment; and ‘Stay’ bees that did not change from their initially learnt preference. The next aim was to determine if there was any advantage to a colony in maintaining bees with a variety of decision-making strategies. To understand the potential benefits of the observed behavioural diversity agent-based computer simulations were conducted by systematically varying parameters for flower reward switch oscillation frequency, flower handling time, and fraction of defective ‘target’ stimuli. These simulations revealed that when there is a relatively high frequency of reward reversals, fickle-circumspect bees are more efficient at nectar collection. However, as the reward reversal frequency decreases the performance of deliberative-decisive bees becomes most efficient. These findings show there to be an evolutionary benefit for honeybee colonies with individuals exhibiting these different strategies for managing resource change. The strategies have similarities to some complex decision-making processes observed in humans, and algorithms implemented in artificial intelligence systems
Bounds on Cubic Lorentz-Violating Terms in the Fermionic Dispersion Relation
We study the recently proposed Lorentz-violating dispersion relation for
fermions and show that it leads to two distinct cubic operators in the
momentum. We compute the leading order terms that modify the non-relativistic
equations of motion and use experimental results for the hyperfine transition
in the ground state of the ion to bound the values of the
Lorentz-violating parameters and for neutrons. The resulting
bounds depend on the value of the Lorenz-violating background four-vector in
the laboratory frame.Comment: Revtex 4, four pages. Version to match the one to appear in Physical
Review
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