Ultrahigh energy neutrinos from superconducting cosmic strings

Abstract

Superconducting cosmic strings naturally emit highly boosted charge carriers from cusps. This occurs when a cosmic string or a loop moves through a magnetic field and develops an electric current. The charge carriers and the products of their decay, including protons, photons and neutrinos, are emitted as a narrow jets with opening angle $\theta \sim 1/\gamma_c$, where $\gamma_c$ is the Lorentz factor of the cusp. The excitation of electric currents in strings occurs mostly in clusters of galaxies, which are characterized by magnetic fields $B \sim 10^{-6}$ G and a filling factor $f_B \sim 10^{-3}$. Two string parameters determine the emission of the particles: the symmetry breaking scale $\eta$, which for successful applications should be of order $10^9$--$10^{12}$ GeV, and the dimensionless parameter $i_c$, which determines the maximum induced current as $J_{max} =i_c e \eta$ and the energy of emitted charge carriers as $\epsilon_x \sim i_c \gamma_c \eta$, where $e$ is the electric charge of a particle. For the parameters $\eta $ and $B$ mentioned above, the Lorentz factor reaches $\gamma_c \sim 10^{12}$ and the maximum particle energy can be as high as $\gamma_c\eta \sim 10^{22}$ GeV. The diffuse fluxes of UHE neutrinos are close to the cascade upper limit, and can be detected by future neutrino observatories. The signatures of this model are: very high energies of neutrinos, in excess of $10^{20}$ eV, correlation of neutrinos with clusters of galaxies, simultaneous appearance of several neutrino-produced showers in the field of view of very large detectors, such as JEM-EUSO, and 10 TeV gamma radiation from the Virgo cluster. The flux of UHE protons from cusps may account for a large fraction of the observed events at the highest energies.