We argue that the small fraction of neutrinos that undergo direction-changing scattering outside of the neutrinosphere could have significant influence on neutrino flavor transformation in core-collapse supernova environments. We show that the standard treatment for collective neutrino flavor transformation is adequate at late times, but could be inadequate in the crucial shock revival/explosion epoch of core-collapse supernovae, where the potentials that govern neutrino flavor evolution are affected by the scattered neutrinos. Taking account of this effect, and the way it couples to entropy and composition, will require a new paradigm in supernova modeling.PACS numbers: 05.60. Gg,13.15.+g,14.60.Pq,26.30Hj,26.30Jk,26.50+x,97.60.Bw In this letter we point out a surprising feature of neutrino flavor transformation in core-collapse supernovae. These supernovae have massive star progenitors which form cores which collapse to nuclear density and produce proto-neutron stars. The gravitational binding energy released, eventually some ∼ 10 % of the rest mass of the neutron star, is emitted as neutrinos of all flavors in a time window of a few seconds. Diverting a small fraction of this neutrino energy into heating can drive revival of the stalled core bounce shock [1][2][3][4][5][6][7] creating a supernova explosion and setting the conditions for the synthesis of heavy elements [4,[6][7][8][9]. However, the way neutrinos interact in this environment depends on their flavors, necessitating calculations of neutrino flavor transformation. These calculations show that neutrino flavor transformation has a rich phenomenology, including collective oscillations , which can affect important aspects of supernova physics [15, 16, 19-23, 27-29, 31, 32, 39-43]. For example, neutrino-heated heavy element r-process nucleosynthesis [44][45][46][47][48] and potentially supernova energy transport above the core and the explosion itself [11,37,49] could be affected.All collective neutrino flavor transformation calculations employ the "Neutrino Bulb" model, where neutrino emission is sourced from a "neutrinosphere", taken to be a hard spherical shell from which neutrinos freely stream. This seems like a reasonable approximation because well above the neutrinosphere scattered neutrinos comprise only a relatively small fraction of the overall neutrino number density. However, this optically thin "halo" of scattered neutrinos nonetheless may influence the way flavor transformation proceeds. This result stems from a combination of the geometry of supernova neutrino emission, as depicted in Fig. 1, and the neutrino intersection angle dependence of neutrino-neutrino coupling.Neutrinos are emitted in all directions from a neutrinosphere of radius R ν , but those that arrive at a location at radius r, and suffer only forward scattering, will be confined to a narrow cone of directions (dashed lines in Fig. 1) when r R ν . In contrast, a neutrino which suffers one or more direction-changing scattering events

It has been suggested that the baseline scenario of collisionless cold dark matter over-predicts the numbers of satellite galaxies, as well as the dark matter (DM) densities in galactic centers. This apparent lack of structure at small scales can be accounted for if one postulates neutrino-DM and DM-DM interactions mediated by light O(MeV) force carriers. In this letter, we consider a simple, consistent model of neutrinophilic DM with these features where DM and a "secluded" SMsinglet neutrino species are charged under a new U (1) gauge symmetry. An important ingredient of this model is that the secluded sector couples to the Standard Model fields only through neutrino mixing. We observe that the secluded and active neutrinos recouple, leading to a large relic secluded neutrino population. This relic population can prevent small-scale halos from collapsing, while at same time significantly modifying the optical depth of ultra-high-energy neutrinos recently observed at Icecube. We find that the bulk of the parameter space accommodating an (a)symmetric thermal relic has potentially observable consequences for the IceCube high energy signal, with some of the parameter ranges already ruled out by the existing data. Future data may confirm this mechanism if either spectral absorption features or correlations with nearby sources are observed.

When and how were the Mediterranean islands first settled? Has insularity itself—the special characteristics of islands everywhere—acted as a constraint on the manner and rate of their colonization by man? If so, is it possible for archaeologists to make use of ecological and biogeographical models which have been developed to account for the abundance and diversity of animals and plants on islands of varying size and remoteness? This paper offers a brief review of the available data on the first of these important questions, seen in the light of the second and third, and it proposes some modifications to the scenarios of colonization to be found in most current accounts of early island prehistory in the Mediterranean. As a reflection of personal research interests, I emphasize the east Mediterranean evidence, but there are useful insights to be gleaned, I believe, by comparing what we find there with the pattern for the islands of the west.

We perform an exhaustive scan of the allowed resonant production regime for sterile neutrino dark matter in order to improve constraints for dark matter structures which arise from the nonthermal sterile neutrino energy spectra. Small-scale structure constraints are particularly sensitive to large lepton asymmetries/small mixing angles which result in relatively warmer sterile neutrino momentum distributions. We revisit Milky Way galaxy subhalo count constraints and combine them with recent searches for X-ray emission from sterile neutrino decays. Together they rule out models outside the mass range 7.0 keV ≤ mν s ≤ 36 keV and lepton asymmetries smaller than 15 × 10 −6 per unit entropy density at 95% CI or greater. We also find that while a portion of the parameter space remains unconstrained, the combination of subhalo counts and X-ray data indicate the candidate 3.55 keV X-ray line signal potentially originating from a 7.1 keV sterile neutrino decay to be disfavored at 93% CI.