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 \sim 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 , \pm 1 , \pm 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 \gamma _ { 0 } can thus be significantly constrained .
In the “ Lorentz-invariant ” case n = -1 , we obtain the upper limit \gamma _ { 0 } < 0.78 \times 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 \sim 2 with respect to previous analyses .