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Neutrino Astrophysics and Fundamental Properties (INT-15-2a)
(INT Program June 1 - 26, 2015)

Reported by K. Abazajian, W. Haxton, C. Lundardini, I. Sarcevic
  Date posted July 27, 2015

The INT Program Neutrino Astrophysics and Fundamental Properties was held at the INT in Seattle, Washington from June 1-26, 2015. The program was organized by Kevork Abazajian (University of California, Irvine), Wick Haxton (University of California at Berkeley), Cecilia Lunardini (Arizona State University), and Ina Sarcevic (University of Arizona). The purpose of the four-week program was to address several topics:

  • The extent to which astrophysical neutrinos can help us address open questions in fundamental neutrino physics, such as the absolute scale of neutrino mass and the hierarchy, on a timescale comparable to that envisioned for major terrestrial experiments, such as LBNF and LBNO.

  • The new opportunities that arise for using neutrinos to probe astrophysical objects - such as the Sun, supernovae, and high-energy astrophysical accelerators - given that we now know enough about their properties to interpret neutrino signals.

  • The role of neutrinos in controlling the conditions important for nucleosynthesis in astrophysical environments such as the Big Bang, supernovae, and accretion disks.

  • The prospect for constraints or signals of neutrino mass and number from cosmological data, including the cosmic microwave background and large-scale structure.

These themes were timely in view of recent experimental progress in neutrino physics, such as the results from IceCube, Planck and GERDA. The participants were roughly equally split between expertise in solar neutrinos, supernovae and correspondent neutrino physics, high-energy astrophysical neutrinos, and cosmological neutrino probes. Overall, the participants received the program very well and excellent progress was made on these topical areas, from members of the program that do not typically interact in detail. The purpose of stimulating the interactions between the different communities was well served.

The program included a five-day workshop entitled Neutrino Astrophysics and Fundamental Properties during the third week of the program, from June 15-19. The organizers of the workshop were also the main program organizers.

During the non-workshop weeks, the number of talks was limited to two morning talks, happening three or four days a week. We asked speakers to limit their formal presentations to 30 minutes, and we provided an additional 15 minutes for discussion. This format worked very well, and helped conserve time for collaborative discussions among smaller groups of participants as well as individual research. The talks were generally very interactive. Daily afternoon discussion sessions, about one hour long, provided an additional opportunity for questions and other follow-up, on topics directly related to the morning's talks or on other related topics of interest. The presence of a moderator ensured that these meetings were sufficiently focused and productive.

There were a number of key advances during the workshop:

  • The analyses of the IceCube high energy neutrino spectrum. Various models for diffuse neutrino emission by astrophysical objects were compared to the latest neutrino data, with the conclusion that the proton-proton scattering is favored over proton-photon processes. The effect of new physics on the IceCube data was analyzed as well, especially in connection with the lack of data above ~1 PeV, and the non-observation of the Glashow resonance, which should have produced a significant boost of flux at higher energies.

  • The comparison of neutrino heating induced supernovae explosions among supernova numerical modeling groups, including standing accretion shock instability (SASI) compared to neutrino-driven convection, and lepton-number emission self-sustained asymmetry (LESA). The presence of the latter mechanism was actively explored between the Garching and Oak Ridge supernova modeling groups during the workshop.

  • The nature and robustness of cosmological and laboratory constraints on neutrino mass and number were explored between several groups working on these constraints. The discussions on this topic included open questions on the existence of sterile neutrinos at eV or KeV mass scale, and the possibility to directly detect the cosmological neutrino background.

  • The physics of neutrino flavor evolution in supernovae and accretion disks was presented and studied by a number of independent groups working on the problem, including its connection to nucleosynthesis sites, as well as the r-process.

Several new collaborations were discussed during the program, and we expect a number of publications in the next few months to result from discussions during the program. The field remains very active, with the expectation of new discoveries in the near future.