TeV string state excitation via high energy cosmic neutrinos

Abstract

We construct the open-string scattering amplitudes for neutrino-gluon collisions and evaluate the high energy neutrino-nucleon scattering cross section via string state excitations in the TeV stringscale scenario. We find that the neutrino-gluon scattering is the dominant contribution, 5 − 10 times larger than neutrino-quark processes, though black hole production may be larger than the string contribution at higher energies. We illustrate the observability of the string signal at the Auger Observatory and the IceCube neutrino telescope for the string scale M S 1 TeV. 04.50.+h, 95.55.Vj, 95.85.Ry

Bounds on four-fermion contact interactions induced by string resonances

“…The neutral current case involves 4-fermion amplitudes as well as 2-lepton plus 2-gluon external line amplitudes [6]. We find that in the low energy realm the gluon amplitudes contribute negligibly to the constraints.…”

“…These expressions are the analogs of those written down for the NC neutrino case in [5] and [6], which we expand for the full range of NC cases in the next subsection.…”

“…On the other hand, one could take a more phenomenological approach, from the "bottom up". One of the recent endeavors is to obtain the SM tree-level amplitudes at low energies [4,5,6] based on open-string amplitudes [7,8]. This approach assures the correct low energy phenomenology as given by the SM, yet captures one of the essential features of string theory, namely the string resonances, in a relatively model-independent way.…”

“…The basic assumptions in this approach are that the fundamental string scale M S is at the order of one TeV, and that the dominant contributions to the low energy processes are due to the exchange of string resonances. Earlier work on phenomenological studies dealt with QED from the M Z scale to the first few string resonances [4], or neutrino inclusive processes far above the string scale to explore the effects from cosmic neutrinos [5,6]. Phenomenologically, this string-amplitude approach complements the low-scale gravity calculations based on expansions in Kaluza-Klein modes [9], which are argued to be higher orders in string-coupling expansion [3,4].…”

“…For example, leptoquark states are one such effect, and perturbative string resonances can carry the same quantum numbers as the lepto-quarks in some channels [5,6]. At the parton level, much of the kinematical range is low enough to justify keeping the lowest order terms in an expansion in inverse string scale.…”