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Nonlinear chemical amplifiers and the search for animals’ light-dependent magnetic compass sensor

Applied Mathematics,Ìý

Date and time:Ìý

Thursday, March 7, 2013 - 3:15pm

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Much attention has recently developed around chemical reactions that depend on applied magnetic fields as weak as earth’s. This interest is largely motivated by experiments that implicate the role of spin-selective radical pair recombination in biological magnetic compass sensing. Existing literature uses a straightforward calculation to approximate the expected lifetime of coherent radical pairs as a function of the minimum Zeeman-resonant RF amplitude that is observed to disrupt magnetic navigation. Applying the same approach to new behavioral data (by Phillips et al.) indicates a suspiciously long radical pair lifetime, even comparable to the longest quantum coherence lifetimes ever observed at room temperature, and has therefore shed doubt on whether the radical pair hypothesis is valid for newts and rodents. But we argue that chemical nonlinearities can preclude direct computation of coherence lifetime without considering the chemical signalling mechanisms involved, and may explain how some animals compass sense can be disrupted by weak signals like commercial broadcast radio. As an example, we demonstrate how some reactions can introduce threshold effects in the mean-field response to weak applied oscillatory magnetic fields. On the other hand, the mean-field limit is not always a good approximation in biochemical contexts. We therefore discuss some qualitative consequences of chemical fluctuation, and briefly describe some work to understand them better in the Freidlin-Wentzell picture of perturbed dynamical systems.

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