Papers by Hisakazu Minakata
Physical Review D, 2012
We study distances of propagation and the group velocities of the muon neutrinos in the presence ... more We study distances of propagation and the group velocities of the muon neutrinos in the presence of mixing and oscillations assuming that Lorentz invariance holds. Oscillations lead to distortion of the ν µ wave packet which, in turn, changes the group velocity and the distance ν µ travels. We find that the change of the distance, d osc , is proportional to the length of the wave packet, σ x , and the oscillation phase, φ p , acquired by neutrinos in the π− and K− meson decay tunnel where neutrino wave packet is formed: d osc ∝ σφ p. Although the distance d osc may effectively correspond to the superluminal motion, the effect is too tiny (∼ 10 −5 cm) to be reconciled with the OPERA result. We analyze various possibilities to increase d osc and discuss experimental setups in which d osc (corresponding to the superluminal motion) can reach an observable value ∼ 1 m.
Journal of High Energy Physics, 2014
We discuss how the lepton CP phase can be constrained by accelerator and reactor measurements in ... more We discuss how the lepton CP phase can be constrained by accelerator and reactor measurements in an era without dedicated experiments for CP violation search. To characterize globally the sensitivity to the CP phase δ CP , we use the CP exclusion fraction, which quantifies what fraction of the δ CP space can be excluded at given input values of θ 23 and δ CP. Using the measure we study the CP sensitivity which may be possessed by the accelerator experiments T2K and NOνA. We show that, if the mass hierarchy is known, T2K and NOνA alone may exclude, respectively, about 50% − 60% and 40% − 50% of the δ CP space at 90% CL by 10 years running, provided that a considerable fraction of beam time is devoted to the antineutrino run. The synergy between T2K and NOνA is remarkable, leading to the determination of the mass hierarchy through CP sensitivity at the same CL.
Physical Review D
Symmetry in neutrino oscillation serves for a better understanding of the physical properties of ... more Symmetry in neutrino oscillation serves for a better understanding of the physical properties of the phenomenon. We present a systematic way of finding symmetry in neutrino oscillation, which we call symmetry finder (SF). By extending the known framework in vacuum into a matter environment, we derive the SF equation, a powerful machinery for identifying symmetry in the system. After learning lessons on symmetry in the Zaglauer-Schwarzer system with matter equivalent to the vacuum symmetry, we apply the SF method to the [P. B. Denton et al., Compact perturbative expressions for neutrino oscillations in matter, J. High Energy Phys. 06 (2016) 051.] (DMP) perturbation theory to first order. We show that the method is so powerful that we uncover the eight reparametrization symmetries with the 1 ↔ 2 state exchange in DMP, denoted as IA, IB, …, IVB, all new except for IA. The transformations consist of both fundamental and dynamical variables, indicating their equal importance. It is also shown that all the symmetries discussed in this paper can be understood as the Hamiltonian symmetries, which ensures their all-order validity and applicability to varying density matter.
Physical Review D
Observation of the interference between the atmospheric-scale and solar-scale oscillations is one... more Observation of the interference between the atmospheric-scale and solar-scale oscillations is one of the challenging and tantalizing goals of the ongoing and upcoming neutrino experiments. An inevitable first step required for such analyses is to establish the way the oscillation S matrix can be decomposed into the atmospheric and solar waves, the procedure dubbed as the amplitude decomposition. In this paper, with the use of the perturbative framework proposed by Denton et al. (DMP), we establish the prescription for amplitude decomposition which covers the whole kinematical region of the terrestrial neutrino experiments. We analyze the limits to the atmospheric-and solar-resonance regions to argue that the dynamical two modes of the DMP decomposition can be interpreted as the matter-dressed atmospheric and solar oscillations. The expressions of the oscillation probability, which are decomposed into the noninterference and interference terms, are derived for all the relevant flavor oscillation channels. Through construction of the DMP decomposition, we reveal the nature of ψ (θ 12 in matter) symmetry as due to the S matrix rephasing invariance. A new picture of the DMP perturbation theory emerged, a unified perturbative framework for neutrino oscillation in earth matter.
The European Physical Journal C
We study visible neutrino decay at the reactor neutrino experiments KamLAND and, JUNO. Assuming t... more We study visible neutrino decay at the reactor neutrino experiments KamLAND and, JUNO. Assuming the Majoron model of neutrino decay, we obtain constraints on the couplings between Majoron and neutrino as well as on the lifetime/mass of the most massive neutrino state i.e., $$\tau _{3} / m_{3}$$ τ 3 / m 3 or $$\tau _{2} / m_{2}$$ τ 2 / m 2 , respectively, for the normal or the inverted mass orderings. We obtain the constraints on the lifetime $$\tau _{2} / m_{2} \ge 1.4 \times 10^{-9}~{\mathrm{s/eV}}$$ τ 2 / m 2 ≥ 1.4 × 10 - 9 s / eV in the inverted mass ordering for both KamLAND and JUNO at 90% CL. In the normal ordering in which the bound can be obtained for JUNO only, the constraint is milder than the inverted ordering case, $$\tau _{3} / m_{3} \ge 1.0 \times 10^{-10}$$ τ 3 / m 3 ≥ 1.0 × 10 - 10 s/eV at 90% CL. We find that the dependence of lightest neutrino mass ($$=m_{{{\mathrm{lightest}}}}$$ = m lightest ), $$m_1 (m_3)$$ m 1 ( m 3 ) for the normal (inverted) mass ordering, on...
Physical Review D
We propose to detect the interference effect between the atmospheric-scale and solar-scale waves ... more We propose to detect the interference effect between the atmospheric-scale and solar-scale waves of neutrino oscillation, one of the key consequences of the three-generation structure of leptons. In vacuum, we show that there is a natural and general way of decomposing the oscillation amplitude into these two oscillation modes. The nature of the interference is cleanest in theν e disappearance channel, since it is free from the CP phase δ. We find that the upcoming JUNO experiment offers an ideal setting to observe this interference with more than 4σ significance, even under conservative assumptions about the systematic uncertainties. Finally, we discuss the relationship between the mass-ordering resolution and the interference effect.
Progress of Theoretical and Experimental Physics
We discuss physics of the three neutrino flavor transformation with non-unitary mixing matrix, wi... more We discuss physics of the three neutrino flavor transformation with non-unitary mixing matrix, with particular attention to the correlation between the νSM- and the α parameters which represent effect of unitarity violating (UV) new physics. Toward the goal, a new perturbative framework is created to illuminate the effect of non-unitarity in region of the solar-scale enhanced oscillations. We refute the skepticism about the physical reality of the νSM CP δ - α parameter phase correlation by analysis with the SOL convention of UMNS in which $$e^{ \pm i \delta}$$ is attached to s12. Then, a comparative study between the solar- and atmospheric-scale oscillation regions allowed by the framework reveals a dynamical δ- (blobs of the α parameters) correlation in the solar oscillation region, in sharp contrast to the “chiral” type phase correlation $$[e^{- i \delta } \bar{\alpha}_{\mu e}, e^{ - i \delta} \bar{\alpha}_{\tau e}, \bar{\alpha}_{\tau \mu}]$$ in the PDG convention seen in the atm...
Proceedings of The 21st international workshop on neutrinos from accelerators — PoS(NuFact2019)
Progress of Theoretical and Experimental Physics
We formulate a perturbative framework for the flavor transformation of the standard active three ... more We formulate a perturbative framework for the flavor transformation of the standard active three neutrinos but with a non-unitary flavor mixing matrix, a system which may be relevant for the leptonic unitarity test. We use the $\alpha$ parametrization of the non-unitary matrix and take its elements $\alpha_{\beta \gamma}$ ($\beta,\gamma = e,\mu,\tau$) and the ratio $\epsilon \simeq \Delta m^2_{21} / \Delta m^2_{31}$ as the small expansion parameters. Two qualitatively new features that hold in all the oscillation channels are uncovered in the probability formula obtained to first order in the expansion: (1) The phases of the complex $\alpha$ elements always come into the observable in the particular combination with the $\nu$SM CP phase $\delta$ in the form $[e^{- i \delta } \bar{\alpha}_{\mu e}, ~e^{ - i \delta} \bar{\alpha}_{\tau e}, ~\bar{\alpha}_{\tau \mu}]$ under the Particle Data Group convention of a unitary $\nu$SM mixing matrix. (2) The diagonal $\alpha$ parameters appear i...
Proceedings of The 19th International Workshop on Neutrinos from Accelerators NUFACT2017 — PoS(NuFact2017)
|U ↵i | 2 |U ↵j | 2 sin 2 ji. ion is simple: c 2 12 s 2 12 c 4 13 sin 2 21 c 2 12 c 2 13 s 2 13 s... more |U ↵i | 2 |U ↵j | 2 sin 2 ji. ion is simple: c 2 12 s 2 12 c 4 13 sin 2 21 c 2 12 c 2 13 s 2 13 sin 2 31
Lettere Al Nuovo Cimento Series 2
It was proposed by KOBA, NIELSEN and 0LESE~q (KN0) (1) that the semi-inclusive cross-sections asy... more It was proposed by KOBA, NIELSEN and 0LESE~q (KN0) (1) that the semi-inclusive cross-sections asymptotically satisfy a simple scaling law
Lettere Al Nuovo Cimento Series 2
Lettere Al Nuovo Cimento Series 2
In recent years, profound studies of inclusive reaoti0ns have been made both theoretically and ex... more In recent years, profound studies of inclusive reaoti0ns have been made both theoretically and experimentally. It seems that the scaling hypothesis ploposed by
Journal of High Energy Physics
If leptonic unitarity is violated by new physics at an energy scale much lower than the electrowe... more If leptonic unitarity is violated by new physics at an energy scale much lower than the electroweak scale, which we call low-scale unitarity violation, it has different characteristic features from those expected in unitarity violation at high-energy scales. They include maintaining flavor universality and absence of zero-distance flavor transition. We present a framework for testing such unitarity violation at low energies by neutrino oscillation experiments. Starting from the unitary 3 active plus N (arbitrary positive integer) sterile neutrino model we show that by restricting the active-sterile and sterilesterile neutrino mass squared differences to 0.1 eV 2 the oscillation probability in the (3 + N) model becomes insensitive to details of the sterile sector, providing a nearly modelindependent framework for testing low-scale unitarity violation. Yet, the presence of the sterile sector leaves trace as a constant probability leaking term, which distinguishes lowscale unitarity violation from the high-scale one. The non-unitary mixing matrix in the active neutrino subspace is common for the both cases. We analyze how severely the unitarity violation can be constrained in ν e-row by taking a JUNO-like setting to simulate medium baseline reactor experiments. Possible modification of the features of the (3 + N) model due to matter effect is discussed to first order in the matter potential.
I report some progress that occurred since NO-VE 08 in the field of non-standard interactions (NS... more I report some progress that occurred since NO-VE 08 in the field of non-standard interactions (NSI) of neutrinos. After briefly reviewing theoretical developments, I give a summary of the two works in which I was involved. Firstly, we have formulated a perturbative framework to illuminate the global features of neutrino oscillations with NSI, aiming at exploring method for determination of the standard mixing and the NSI parameters. We have recognized that the parameter degeneracy prevails with an extended form which involves the NSI elements. Furthermore, a completely new type of degeneracy is shown to exist. The nature of the former degeneracy is analyzed in detail in the second work. The work is primarily devoted to analyze the problem of discriminating the two CP violation, one due to the lepton Kobayashi-Maskawa phase and the other by phase φ of the NSI elements. We have shown that the near (3000 km)−far (7000 km) two detector setting in neutrino factory does have the discrimination capability and is sensitivities to CP violation due to NSI to |ε eµ | to ≃ several ×10 −4 in most of the region of δ and φ eµ. a Written version of a talk presented at XIII International Workshop on Neutrino Telescopes,
Nucl Phys B Proc Suppl, 2005
We introduce "CP trajectory diagram in bi-probability space" as a powerful tool for pictorial rep... more We introduce "CP trajectory diagram in bi-probability space" as a powerful tool for pictorial representation of the genuine CP and the matter effects in neutrino oscillations. Existence of the correlated ambiguity in a determination of CP violating phase \delta and the sign of \Delta m^2_{13} is uncovered. Principles of tuning beam energy for a given baseline distance are proposed to resolve the ambiguity and to maximize the CP-odd effect. We finally point out, quite contrary to what is usually believed, that the ambiguity may be resolved with 50 % chance in the super-JHF experiment despite its relatively short baseline of 300 km.
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Papers by Hisakazu Minakata