Probing nonstandard decoherence effects with solar and KamLAND neutrinos

Abstract

It has been speculated that quantum gravity might induce a "foamy" space-time structure at small scales, randomly perturbing the propagation phases of free-streaming particles (such as kaons, neutrons, or neutrinos). Particle interferometry might then reveal non-standard decoherence effects, in addition to standard ones (due to, e.g., finite source size and detector resolution.) In this work we discuss the phenomenology of such non-standard effects in the propagation of electron neutrinos in the Sun and in the long-baseline reactor experiment KamLAND, which jointly provide us with the best available probes of decoherence at neutrino energies E ∼ few MeV. In the solar neutrino case, by means of a perturbative approach, decoherence is shown to modify the standard (adiabatic) propagation in matter through a calculable damping factor. By assuming a power-law dependence of decoherence effects in the energy domain (E n with n = 0, ±1, ±2), theoretical predictions for two-family neutrino mixing are compared with the data and discussed. We find that neither solar nor KamLAND data show evidence in favor of non-standard decoherence effects, whose characteristic parameter γ 0 can thus be significantly constrained. In the "Lorentz-invariant" case n = −1, we obtain the upper limit γ 0 < 0.78 × 10 −26 GeV at 95% C.L. In the specific case n = −2, the constraints can also be interpreted as bounds on possible matter density fluctuations in the Sun, which we improve by a factor of ∼ 2 with respect to previous analyses.

Parameter limits for neutrino oscillation with decoherence in KamLAND

“…Therefore, the effect studied here is different from the one studied in [7]. According to [17], the limits found in [7] are combined limits on relaxation and decoherence effects in a modeldependent approach. We use a model-independent approach in this paper to analyze the KamLAND data.…”

“…It is important to explain the difference between the analysis made in this work and the one made in [7], where they use a different set of data from KamLAND (older than the one considered here), but also consider data from solar neutrinos.…”

“…Solar neutrinos cannot be used to bound decoherence, because the fast oscillating terms in∆ ij x average out all the coherence terms [17,18]. Therefore, the effect studied here is different from the one studied in [7]. According to [17], the limits found in [7] are combined limits on relaxation and decoherence effects in a modeldependent approach.…”

“…We will also stress its relevance and the difference between the results found in this work from others such as the one from [7]. In Section I we review the Theory of Open Quantum Systems, and we show how it can be used to study neutrino oscillations.…”

“…We can find in the literature studies of the decoherence effect applied to neutrino oscillations [4][5][6][7].…”