Various plants and fungi have evolved ingenious devices to disperse their spores. One such mechanism is the cavitation-triggered catapult of fern sporangia. The spherical sporangia enclosing the spores are equipped with a row of 12 to 13 specialized cells, the annulus. When dehydrating, these cells induce a dramatic change of curvature in the sporangium, which is released abruptly after the cavitation of the annulus cells. The entire ejection process is reminiscent of human-made catapults with one notable exception: The sporangia lack the crossbar that arrests the catapult arm in its returning motion. We show that much of the sophistication and efficiency of the ejection mechanism lies in the two very different time scales associated with the annulus closure.

Abstract:The minimal seesaw extension of the Standard SU(3) c ⊗ SU(2) L ⊗ U(1) Y Model requires two electroweak singlet fermions in order to accommodate the neutrino oscillation parameters at tree level. Here we consider a next to minimal extension where light neutrino masses are generated radiatively by two electroweak fermions: one singlet and one triplet under SU(2) L . These should be odd under a parity symmetry and their mixing gives rise to a stable weakly interactive massive particle (WIMP) dark matter candidate. For mass in the GeV-TeV range, it reproduces the correct relic density, and provides an observable signal in nuclear recoil direct detection experiments. The fermion triplet component of the dark matter has gauge interactions, making it also detectable at present and near future collider experiments.ArXiv ePrint: 1307.8134 IFIC/13-53 arXiv:1307.8134v2 [hep-ph]

By combining the simplest (3,1) version of the seesaw mechanism containing a single heavy "righthanded" neutrino with the minimal scotogenic approach to dark matter, we propose a theory for neutrino oscillations. The "atmospheric" mass scale arises at tree level from the seesaw, while the "solar" oscillation scale emerges radiatively, through a loop involving the "dark sector" exchange. Such simple setup gives a clear interpretation of the neutrino oscillation lengths, has a viable WIMP dark matter candidate, and implies a lower bound on the neutrinoless double beta decay rate. PACS numbers: 13.15.+g, 14.60.Pq, 14.60.St, 95.35.+d * nicolas.rojasro@usm.cl † rahulsri@ific.uv.es ‡ valle@ific.uv.es, URL: http://astroparticles.es 1 Since singlet fermions, such as "right-handed" neutrinos, carry no anomaly, their multiplicity is not fixed [7]. Note that in two-component form all fermions are "left-handed". Our N corresponds to what people normally call "right-handed" neutrino in 4-component form.

Abstract:The scotogenic scenario provides an attractive approach to both Dark Matter and neutrino mass generation, in which the same symmetry that stabilises Dark Matter also ensures the radiative seesaw origin of neutrino mass. However the simplest scenario may suffer from inconsistencies arising from the spontaneous breaking of the underlying Z 2 symmetry. Here we show that the singlet-triplet extension of the simplest model naturally avoids this problem due to the presence of scalar triplets neutral under the Z 2 which affect the evolution of the couplings in the scalar sector. The scenario offers good prospects for direct WIMP Dark Matter detection through the nuclear recoil method.