Quantum-gravity decoherence effects in neutrino oscillations: Expected constraints from CNGS and J-PARC

Quantum decoherence, the evolution of pure states into mixed states, may be a feature of quantum-gravity models. In most cases, such models lead to fewer neutrinos of all active flavors being detected in a long-baseline experiment as compared to three-flavor standard neutrino oscillations. We discuss the potential of the CNGS and J-PARC beams in constraining models of quantum-gravity induced decoherence using neutrino oscillations as a probe. We use as much as possible model-independent parametrizations, even though they are motivated by specific microscopic models, for fits to the expected experimental data which yield bounds on quantum-gravity decoherence parameters.

Figure 1

Left: Ratio of the observed ${\overline{\nu }}_e$ spectrum to the expectation versus $L_0/E$ for our decoherence model. The dots correspond to KamLand data. Right: Decoherence fit. The dots correspond to Super-Kamiokande data.

Figure 2

The number of reconstructed ${\nu }_{\mu }$ CC events in OPERA as a function of the neutrino energy with (blue line) and without (red line with error bars) QG decoherence effect included in case of inversely proportional dependence on neutrino energy. $3\sigma$ difference between the expected and QG disturbed spectra is shown.

Figure 3

The expected CNGS sensitivity contour at $3\sigma$ C.L., with two decoherence parameters contributing to the combined time evolution of the gravitational MSW effect (with stochastic metric fluctuations), calculated for damping with no energy dependence (left panel) and damping proportional to the neutrino energy (right panel).

Figure 4

The number of reconstructed ${\nu }_{\mu }$ CC events in T2K as a function of the neutrino energy with (blue line) and without (red line with error bars) QG decoherence effect included in the case of inversely proportional dependence on neutrino energy. $3\sigma$ difference between the expected and QG disturbed spectra is shown.

Figure 5

The expected T2K sensitivity contour at $3\sigma$ C.L., with two decoherence parameters contributing to the combined time evolution of the gravitational MSW effect (with stochastic metric fluctuations), calculated for damping with no energy dependence (left panel) and damping proportional to the neutrino energy (right panel).

Figure 6

The sensitivity of CNGS to probabilities corrected for one-parametric decoherence effects as functions of the true values of ${\theta }_{23}$ (left panels) and $\Delta m_{23}$ (right panels). The input value for the mass difference in the left panels is $\Delta m^2=2.5\times {10}^{-3}{\mathrm{eV}}^2$, while for the right panels ${\theta }_{23}=45°$. Three cases of damping exponents are considered with no energy dependence (top), inverse-energy dependence (middle), and quadratic energy dependence (bottom).

Figure 7

The same as in Fig. 6 calculated for the sensitivity of T2K.