UHE 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.

💡 Analysis

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.

📄 Content

arXiv:0901.0527v2 [astro-ph.HE] 4 Nov 2010 UHE neutrinos from superconducting cosmic strings Veniamin Berezinsky,1, ∗Ken D. Olum,2, † Eray Sabancilar,2, ‡ and Alexander Vilenkin2, § 1INFN, Laboratori Nazionali del Gran Sasso, I–67010 Assergi (AQ), Italy 2Institute of Cosmology, Department of Physics and Astronomy, Tufts University, Medford, MA 02155, USA. 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 narrow jets with opening angle θ ∼1/γc, where γc 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 ∼10−6 G and a filling factor fB ∼10−3. Two string parameters determine the emission of the particles: the symmetry breaking scale η, which for successful applications should be of order 109–1012 GeV, and the dimensionless parameter ic, which determines the maximum induced current as Jmax = iceη and the energy of emitted charge carriers as ǫX ∼icγcη, where e is the electric charge of a particle. For the parameters η and B mentioned above, the Lorentz factor reaches γc ∼1012 and the maximum particle energy can be as high as γcη ∼1022 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 1020 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. PACS numbers: 98.70.Sa 98.80.Cq 11.27.+d ∗Electronic address: venya.berezinsky@lngs.infn.it †Electronic address: kdo@cosmos.phy.tufts.edu ‡Electronic address: eray.sabancilar@tufts.edu §Electronic address: vilenkin@cosmos.phy.tufts.edu 1 I. INTRODUCTION A. Neutrino astronomy Ultra-high-energy (UHE) neutrino astronomy at energies above 1017 eV is based on new, very efficient methods of neutrino detection and on exciting theories for neutrino produc- tion. The most interesting range of this astronomy covers tremendously high energies above 1019 −1020 eV. In fact, this energy scale gives only the low-energy threshold, where the new observational methods, such as space-based observations of fluorescent light and radio and acoustic methods, start to operate. These methods allow observation of very large areas and so detection of tiny fluxes of neutrinos. For example the exposure of the space detector JEM-EUSO [1] is planned to reach ∼106 km2yr sr. The upper limits obtained by radio observations are presented in Fig. 1. The basic idea of detection by EUSO is similar to the fluorescence technique for obser- vations of extensive air showers (EAS) from the surface of the Earth. The UHE neutrino entering the Earth’s atmosphere produces an EAS. A known fraction of its energy, which reaches 90%, is radiated in the form of isotropic fluorescent light, which can be detected by an optical telescope in space. There is little absorption of up-going photons, so the fraction of flux detected is known, and thus EUSO provides a calorimetric measurement of the pri- mary energy. In the JEM-EUSO project [1] a telescope with diameter 2.5 m will observe an area ∼105 km2 and will have a threshold for EAS detection Eth ∼1 × 1019 eV. The observations are planned to start in 2012–2013. UHE neutrinos may also be very efficiently detected by observations of radio emission by neutrino-induced showers in ice or lunar regolith. This method was originally suggested by G. Askaryan in the 1960s [2]. Propagating in matter the shower acquires excess negative electric charge due to scattering of the matter electrons. The coherent Cerenkov radiation of these electrons produces a radio pulse. Recently this method has been confirmed by laboratory measurements [3]. Experiments have searched for such radiation from neutrino- induced showers in the Greenland and Antarctic ice and in the lunar regolith. In all cases the radio emission can be observed only for neutrinos of extremely high energies. Upper limits on the flux of these neutrinos have been obtained in the GLUE experiment [4] by radiation from the moon, in the FORTE experiment [5] by radiation from the Greenland ice, and in the ANITA [6] and RICE [7] experiments from the Antarctic ice. Probably the first proposal for detection of UHE neutrinos with energies higher than 1017 eV was made in [8]. It was proposed there to use the horizontal Extensive Air Showers (EAS) for neutrino detection. Later this idea was transformed into the Earth-skimming effect [9] for τ

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