The Origin Of High-Energy Neutrinos And The Con-Straint On Basic Physical Principles

The IceCube Neutrino observatory has observed neutrinos of energy from?30TeV to several PeV since its mission started.This marks the beginning of high-energy neu-trino astrophysics.Comparing to photons and charged particles,neutrinos can travel through dense matter or radiation fields and experience propagation of cosmology dis-tance without being scattered or absorbed due to its weak interaction.Neutrinos could be used as probe to distinguish between different mechanics of hadron and electron ac-celeration and point to the site of acceleration.Neutrino with cosmology propagation could also test the basic physical principles like Lorentz covariance and equivalence principle.The 1st chapter talks about the motivation of neutrino observation the observato-ries and the observation results.In chapter 2,we try to explain the isotropy result of IceCube observatory with the neutrino produced by cosmic-ray from Gamma-ray bursts(GRBs)propagating in their host galaxies.GRBs are proposed as candidate sources for ultra-high energy cosmic rays(UHECRs).We study the possibility that the PeV neutrinos recently observed by IceCube are produced by GRB cosmic rays interacting with the interstellar gas in the host galaxies.By studying the relation between the X-ray absorption column density NH and the surface star-formation rate of GRB host galaxies,we find that NH is a good indicator of the surface gas density of the host galaxies.Then we are able to calculate the neutrino production efficiency of CRs for GRBs with known NH.We collect a sample of GRBs that have both measurements of NH and accurate gamma-ray fluence,and calcu-late the accumulated neutrino flux with this sample.When the CR intensity produced by GRBs is normalized with the observed UHECR flux above?1019eV,we find that the accumulated neutrino flux at PeV energies is about(0.3±0.2)×10-8GeVcm-2 s-1 sr-1(per flavor)under the assumption that GRB energy production rate follows the cosmic star-formation rate and under the favorable assumption about the CR diffusion coeffi-cient.This flux is insufficient to account for the IceCube observations,but the estimate suffers from some unknowns and uncertainties inherent in the calculation and thus we can not rule out this scenario at present.In chapter 3,we use cosmic neutrino from the blazar to constrain the basic physical principles.It was recently proposed that a giant outburst of the blazar PKS B1424-418 at redshift z = 1.522 occurred in temporal and positional coincidence with a PeV-energy neutrino event detected by IceCube.If the association is real,the flight time difference between the PeV neutrino and low-energy photons can be used to constrain the violations of Einstein equivalence principle(EEP)and the Lorentz invariance.From the calculated Shapiro delay due to clusters or superclusters in the nearby universe,we find that violation of the equivalence principle for neutrinos and photons is constrained to an accuracy of at least 10-5,which is about two orders of magnitude tighter than the constraint placed by MeV neutrinos from supernova 1987A.Lorentz invariance violation(LIV)arises in various quantum-gravity theories,which predict an energy-dependent velocity of propagation in vacuum for photons and neutrinos.We find that the association of the PeV neutrino with the gamma-ray outburst set limits on the energy scale of possible LIV to>0.01Epl for linear LIV models and>6 x 10-8Epl for the quadratic order LIV models,where Epl is the Planck energy scale.These are the most stringent constraints obtained so far for neutrinos for subluminal propagation.The constraint on the quadratic order LIV models is a factor of 6 tighter than the current most stringent constraint obtained with photons.The last chapter is the conclusion and talks about the potential development of multi-messenger astrophysics in the future.