Particle theory

Abstract:

We present a search for a light sterile neutrino using three years of atmospheric neutrino data from the DeepCore detector in the energy range of approximately 10-60 GeV. DeepCore is the low-energy subarray of the IceCube Neutrino Observatory. The standard three-neutrino paradigm can be probed by adding an additional light (Δm412∼1 eV2) sterile neutrino. Sterile neutrinos do not interact through the standard weak interaction and, therefore, cannot be directly detected. However, their mixing with the three active neutrino states leaves an imprint on the standard atmospheric neutrino oscillations for energies below 100 GeV. A search for such mixing via muon neutrino disappearance is presented here. The data are found to be consistent with the standard three-neutrino hypothesis. Therefore, we derive limits on the mixing matrix elements at the level of |Uμ4|2 < 0.11 and |Uτ4|2 < 0.15 (90% C.L.) for the sterile neutrino mass splitting Δm412=1.0 eV2.

Abstract:

There is numerical evidence that the world sheet action of the confining flux tube in D =3 +1SU(N)gauge theories contains a massive excitation with 0−quantum numbers whose mass shows some decrease as one goes from SU(3)to SU(5). Moreover it has been shown that the natural coupling of this pseudoscalar has a topological interpretation making it natural to call it the world-sheet ‘axion’. Recently it has been pointed out that if the mass of this ‘axion’ vanishes as N→∞then it becomes possible for the world sheet theory to be integrable in the planar limit. In this paper we perform lattice calculations of this ‘axion’ mass from SU(2)to SU(12), which allows us to make a controlled extrapolation to N=∞and so test this interesting possibility. We find that the ‘axion’ does not in fact become massless as N→∞. So if the theory is to possess planar integrability then it must be some other world sheet excitation that becomes massless in the planar limit.