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Osamu Yasuda

Publications and source records attributed to Osamu Yasuda.

At least 19 recordsLinked to original sources
arXiv2025

Analytic formulae for T violation in neutrino oscillations

Recently, a concept known as $μ$TRISTAN, which involves the acceleration of $μ^+$, has been proposed. This initiative has led to considerations of a new design for a neutrino factory. Additionally, leveraging the polarization of $μ^+$, measurements of T violation in neutrino oscillations are also being explored. In this paper, we present analytical expressions for T violation in neutrino oscillations within the framework of standard three flavor neutrino oscillations, a scenario involving nonstandard interactions, and a case of unitarity violation. We point out that examining the energy spectrum of T violation may be useful for probing new physics effects.

hep-ph↗
arXiv2024

Octant Degeneracy and Plots of Parameter Degeneracy in Neutrino Oscillations Revisited

The three kinds of parameter degeneracy in neutrino oscillation, the intrinsic, sign and octant degeneracy, form an eight-fold degeneracy. The nature of this eight-fold degeneracy can be visualized on the ($\sin^22θ_{13}$, $1/\sin^2θ_{23}$)-plane, through quadratic curves defined by $P(ν_μ\toν_e)=$ const. and $P(\barν_μ\to\barν_e)=$ const., along with a straight line $P(ν_μ\toν_μ)=$ const. After $θ_{13}$ was determined by reactor neutrino experiments, the intrinsic degeneracy in $θ_{13}$ transforms into an alternative octant degeneracy in $θ_{23}$, which can potentially be resolved by incorporating the value of $P(ν_μ\toν_μ)$. In this paper, we analytically discuss whether this octant parameter degeneracy is resolved or persists in the future long baseline accelerator neutrino experiments, such as T2HK, DUNE, T2HKK and ESS$ν$SB. It is found that the energy spectra near the first oscillation maximum are effective in resolving the octant degeneracy, whereas those near the second oscillation maximum are not.

hep-ph↗
arXiv2023

Effect of Matter Density in T2HK and DUNE

CP phase determination for the near future long baseline experiments, T2HK and DUNE, will require precise measurements of the oscillation probabilities. However, the uncertainty in the Earth's density must be considered in determining these oscillation probabilities. Therefore, in this study, we update the individual sensitivities of these experiments for determining the current unknowns in the standard three flavor scenario considering the latest configuration and also the complementarity between them while considering the uncertainty in the density. Our study showed that this uncertainty has a non-negligible impact on the precision of the CP phase determination particularly for DUNE.

hep-ph↗
arXiv2022

Search for sterile neutrinos by shower events at a future neutrino telescope

It is pointed out that searching for sterile neutrinos at high energy regions at a future IceCube-like facility has advantages compared with that of reactor or short baseline accelerator neutrino experiments, in which the size of the detector and energy resolution make it difficult to gain good sensitivity for a large mass-squared difference. In this study we show that it is possible to improve constraints on sterile neutrino mixing $θ_{14}$ for 1 eV$^2~\lesssim Δm_{41}^2\lesssim$ 100 eV$^2$ by looking for a dip in the shower events at an IceCube-like neutrino telescope whose volume is at least 10 times as large as that of IceCube and duration is 10 years. We also give an analytic expression for the oscillation probabilities in two cases where the condition of one mass scale dominance is satisfied.

hep-ph↗
arXiv2020

Neutrino Oscillations at low energy long baseline experiments in the presence of nonstandard interactions and parameter degeneracy

We discuss the analytical expression of the oscillation probabilities at low energy long baseline experiments, such as T2HK and T2HKK in the presence of nonstandard interactions (NSIs). We show that these experiments are advantageous to explore the NSI parameters ($ε_D$, $ε_N$), which were suggested to be nonvanishing to account for the discrepancy between the solar neutrino and KamLAND data. We also show that, when the NSI parameters are small, parameter degeneracy in the CP phase $δ$, $ε_D$ and $ε_N$ can be resolved by combining data of the T2HK and T2HKK experiments.

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arXiv2020

Testing NSI suggested by the solar neutrino tension in T2HKK and DUNE

It was shown that the tension between the mass-squared differences obtained from solar neutrinos and those acquired through KamLAND experiments may be solved by the introduction of a non-standard flavor-dependent interaction (NSI) in neutrino propagation. In this study, we discuss the possibility of testing such a hypothesis using the future long-baseline neutrino experiments T2HKK and DUNE. Assuming that the NSI does not exist, we provide the excluded region within the ($ε_D$, $ε_N$) plane, where $ε_D$ and $ε_N$ are the parameters appearing in the solar neutrino analysis conducted with the NSI. We find that the best-fit value from the solar neutrino and KamLAND data (global analysis of a particular coupling to quarks) can be tested at more than 10$σ$ (3$σ$) by these two experiments for most of the parameter space.

hep-ph↗
arXiv2017

The T2HKK Experiment and Non-Standard Interaction

In this work we study the the sensitivity of the T2HKK experiment to probe non-standard interaction in neutrino propagation. As this experiment will be statistically dominated due to its large detector volume and high beam-power, it is expected that the sensitivity will be affected by systematics. This motivates us to study the effect of systematics in probing the non-standard interaction. We also compare our results with the other future proposed experiments i.e., T2HK, HK and DUNE.

hep-ph↗
arXiv2017

Effect of systematics in the T2HK, T2HKK, and DUNE experiments

T2HK and T2HKK are the proposed extensions of the of T2K experiments in Japan and DUNE is the future long-baseline program of Fermilab. All these three experiments will use extremely high beam power and large detector volumes to observe neutrino oscillation. Because of the large statistics, these experiments will be highly sensitive to systematics. Thus a small change in the systematics can cause a significant change in their sensitivities. To understand this, we do a comparative study of T2HK, T2HKK and DUNE with respect to their systematic errors. Specifically we study the effect of the systematics in the determination of neutrino mass hierarchy, octant of the mixing angle $θ_{23}$ and $δ_{CP}$ in the standard three flavor scenario and also analyze the role of systematic uncertainties in constraining the parameters of the nonstandard interactions in neutrino propagation. Taking the overall systematics for signal and background normalization, we quantify how the sensitivities of these experiments change if the systematics are varied from $1\%$ to $7\%$.

hep-ph↗
arXiv2017

Sensitivity of the T2HKK experiment to the non-standard interaction

If the flavor dependent non-standard interactions (NSI) in neutrino propagation exist, then the matter effect is modified and the modification is parametrized by the dimensionless parameter $ε_{αβ}~(α,β=e, μ, τ)$. In this paper we discuss the sensitivity of the T2HKK experiment, whose possibility is now seriously discussed as a future extension of the T2K experiment, to such NSI. On the assumption that $ε_{αμ}=0~(α=e, μτ)$ and $ε_{ττ}=|ε_{eτ}|/(1+ε_{ee})$, which are satisfied by other experiments to a good approximation, we find that, among the possible off-axis flux configurations of $1.3^\circ$, $1.5^\circ$, $2.0^\circ$ and $2.5^\circ$, the case of the off-axis angle $1.3^\circ$ gives the highest sensitivity to $ε_{ee}$ and $|ε_{eτ}|$. Our results show that the $1.3^\circ$ off-axis configuration can exclude NSI for $|ε_{ee}|\gtrsim 1$ or $|ε_{eτ}|\gtrsim 0.2$ at 3$σ$. We also find that in the presence of NSI, T2HKK (for the off-axis angle $1.3^\circ$) has better sensitivity to the two CP phases ($δ_{CP}$ and arg($ε_{e τ}$)) than DUNE. This is because of the synergy between the two detectors i.e., one at Kamioka and one at Korea. T2HKK has better sensitivity to the CP phases than the atmospheric neutrino experiment at Hyperkamiokande in inverted hierarchy, but in normal hierarchy the atmospheric neutrino experiment has the best sensitivity to the CP phases.

hep-ph↗
arXiv2017

Complementarity Between Hyperkamiokande and DUNE in Determining Neutrino Oscillation Parameters

In this work we investigate the sensitivity to the neutrino mass hierarchy, the octant of the mixing angle $θ_{23}$ and the CP phase $δ_{CP}$ in the future long-baseline experiments T2HK and DUNE as well as in the atmospheric neutrino observation at Hyperkamiokande (HK). We show for the first time that the sensitivity is enhanced greatly if we combine these three experiments. Our results show that the hierarchy sensitivity of both T2HK and HK are limited due to the presence of parameter degeneracy. But this degeneracy is removed when T2HK and HK are added together. With T2HK+HK (DUNE), the neutrino mass hierarchy can be determined at least at $ 5 σ$ (8 $σ$) C.L. for any value of true $δ_{CP}$. With T2HK+HK+DUNE the significance of the mass hierarchy increases to almost 15 $σ$ for the unfavorable value of $δ_{CP}$. For these combined setup, octant can be resolved except $43.5^\circ < θ_{23} < 48^\circ$ at $5σ$ C.L for both the hierarchies irrespective of the value of $δ_{CP}$. The significance of CP violation is around 10 $σ$ C.L. for $δ_{CP} \sim \pm 90^\circ$. Apart from that these combined facility has the capability to discover CP violation for at least $68\%$ fraction of the true $δ_{CP}$ values at $5 σ$ for any value of true $θ_{23}$. We also find that, with combination of all these three, the precision of $Δm^2_{\rm eff}$, $\sin^2θ_{23}$ and $δ_{CP}$ becomes 0.3%, 2% and 20% respectively. We also clarify how the octant degeneracy occurs in the HK atmospheric neutrino experiment.

hep-ph↗
arXiv2016

Complementarity Between Hyperkamiokande and DUNE

In this talk we present our results on the sensitivity to the neutrino mass hierarchy, the octant of the mixing angle and the CP phase in the future long baseline experiments T2HK and DUNE as well as in the atmospheric neutrino observation at Hyperkamiokande (HK).

hep-ph↗
arXiv2016

Is nonstandard interaction a solution to the three neutrino tensions?

In this work we present a scenario in which a nonstandard interaction in neutrino propagation can explain the three major tensions in the neutrino oscillation data at present. These tensions are: (i) a non-zero best-fit value of the non-standard oscillation parameters in the the global analysis of the solar and KamLAND data which rules out the standard oscillation scenario at $90\%$ C.L, (ii) the measurement of the non-maximal value of $θ_{23}$ by NO$ν$A which excludes the maximal mixing at $2.5 σ$ C.L. and (iii) a discrepancy in the $θ_{13}$ measurement by T2K which has a tension with the reactor best-fit value of $\sin^2θ_{13}=0.021$ at $90\%$ C.L. Our results show that all these three above mentioned anomalies can be explained if one assumes the existence of the non-standard interactions in neutrino propagation with $θ_{23}=45^\circ$ and $\sin^2θ_{13}=0.021$ in the case of normal hierarchy. In our scenario the phase of $ε_{eτ}$ is zero and the most favorable value of the Dirac CP phase is approximately $255^\circ$.

hep-ph↗
arXiv2016

The possibility to observe the non-standard interaction by the Hyperkamiokande atmospheric neutrino experiment

It was suggested that a tension between the mass-squared differences obtained from the solar neutrino and KamLAND experiments can be solved by introducing the non-standard flavor-dependent interaction in neutrino propagation. In this paper we discuss the possibility to test such a hypothesis by atmospheric neutrino observations at the future Hyper-Kamiokande experiment. Assuming that the mass hierarchy is known, we find that the best-fit value from the solar neutrino and KamLAND data can be tested at more than 8 $σ$, while the one from the global analysis can be examined at 5.0 $σ$ (1.4 $σ$) for the normal (inverted) mass hierarchy.

hep-ph↗
arXiv2016

Constraints on the flavor-dependent non-standard interaction in propagation from atmospheric neutrinos

The sensitivity of the atmospheric neutrino experiments to the non-standard flavor-dependent interaction in neutrino propagation is studied under the assumption that the only nonvanishing components of the non-standard matter effect are the electron and tau neutrino components $ε_{ee}$, $ε_{eτ}$, $ε_{ττ}$ and that the tau-tau component satisfies the constraint $ε_{ττ}=|ε_{eτ}|^2/(1+ε_{ee})$ which is suggested from the high energy behavior for atmospheric neutrino data.

hep-ph↗
arXiv2015

Constraints on the non-standard interaction in propagation from atmospheric neutrinos

The sensitivity of the atmospheric neutrino experiments to the non-standard flavor-dependent interaction in neutrino propagation is studied under the assumption that the only nonvanishing components of the non-standard matter effect are the electron and tau neutrino components $ε_{ee}$, $ε_{eτ}$, $ε_{ττ}$ and that the tau-tau component satisfies the constraint $ε_{ττ}=|ε_{eτ}|^2/(1+ε_{ee})$ which is suggested from the high energy behavior for atmospheric neutrino data. It is shown that the Superkamiokande (SK) data for 4438 days constrains $|\tanβ|\equiv|ε_{eτ}/(1+ε_{ee})|\lesssim 0.8$ at 2.5$σ$ (98.8\%) CL whereas the future Hyperkamiokande experiment for the same period of time as SK will constrain as $|\tanβ|\lesssim 0.3$ at 2.5$σ$CL from the energy rate analysis and the energy spectrum analysis will give even tighter bounds on $ε_{ee}$ and $|ε_{eτ}|$.

hep-ph↗
arXiv2015

Constraints on non-standard flavor-dependent interactions from Superkamiokande and Hyperkamiokande

We investigate the constraint on the flavor-dependent neutral current Non-Standard Interactions in propagation from atmospheric neutrino experiments Superkamiokande and Hyperkamiokande. With the ansatz where the parameters which have strong constraints from other experiments are neglected, we show how these experiments put constraints on the remaining parameters of the Non-Standard Interactions.

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