engleski

Spacetime noncommutativity and ultra-high energy cosmic ray experiments

If new physics were capable of pushing the neutrino-nucleon inelastic cross section 3 orders of magnitude beyond the standard model prediction, then ultrahigh energy (UHE) neutrinos would have already been observed at neutrino observatories. We use such a constraint to reveal information on the scale of noncommutativity (NC)
NC in noncommutative gauge field theories where neutrinos possess a tree-level coupling to photons in a generation-independent manner. In the energy range of interest (1010 to 1011 GeV), the
expansion (j
j
1=
2 NC) and, therefore, the perturbative expansion, in terms of
NC, retains no longer its meaningful character, forcing us to resort to those NC field theoretical frameworks involving the full
resummation. Our numerical analysis of the contribution to the process coming from the photon exchange impeccably pins down a lower bound on
NC to be as high as 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result that occurred in Pierre Auger Observatory data, that UHE cosmic rays are mainly composed of highly ionized Fe nuclei, then our bounds get weaker, due to the diminished cosmic neutrino flux. Nevertheless, we show that, even for the very high fraction of heavy nuclei in primary UHE cosmic rays, our method may still yield remarkable bounds on
NC, typically always above 200 TeV. Albeit, in this case, one encounters a maximal value for the Fe fraction, from which any useful information on
NC can be drawn, delimiting thus the applicability of our method.

noncommutativity; ultrahigh energy

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