Cosmic strings as emitters of extremely high energy neutrinos

We study massive particle radiation from cosmic string kinks, and its observability in extremely high energy neutrinos. In particular, we consider the emission of moduli—weakly coupled scalar particles predicted in supersymmetric theories—from the kinks of cosmic string loops. Since kinks move at the speed of light on strings, moduli are emitted with large Lorentz factors, and eventually decay into many pions and neutrinos via hadronic cascades. The produced neutrino flux has energy $E\gtrsim {10}^{11}\mathrm{GeV}$, and is affected by oscillations and absorption (resonant and nonresonant). It is observable at upcoming neutrino telescopes such as JEM-EUSO, and the radio telescopes LOFAR and SKA, for a range of values of the string tension, and of the mass and coupling constant of the moduli.

Figure 1

Graphical representation of the interval of observed energy, Eq. (54), where suppression of the flux due to resonant $\nu -\overline{\nu }$ annihilation is expected (region between the diagonal lines). The dashing indicates the region where Eq. (54) is only indicative, due to thermal effects influencing the resonance. The horizontal shaded area refers to the interval of neutrino masses where the neutrino mass spectrum is strongly degenerate. We also mark the value $m_{\nu }\simeq 0.05\mathrm{eV}$, which is the highest mass expected for a nondegenerate (hierarchical) mass spectrum.

Figure 2

Examples of neutrino flux from cosmic string kinks, via moduli decay. We took $G\mu ={10}^{-17}$. The dashed curves, (a), (c) and (d) refer to $m_{\nu }=0$ and $\overline{\alpha }=1$, ${10}^2$, ${10}^3$ respectively. The dot-dashed line, (b), is the same as (a) but for $m_{\nu }=0.3\mathrm{eV}$, with resonant absorption effects included. Cases (c) and (d) are not affected by the $Z^0$ resonance for this value of the neutrino mass. The figure also shows existing limits from ANITA, FORTE, NuMoon and RICE [20, 21, 22, 23], and expected sensitivities of the future detectors JEM-EUSO, LOFAR and SKA [25, 26, 27].