arXiv subjects

Hisakazu Minakata

Publications and source records attributed to Hisakazu Minakata.

At least 109 records · Page 6Linked to original sources

arXiv1999

Model Independent Analysis of the Solar Neutrino Data

We perform an updated model-independent analysis using all the latest solar neutrino data, including the one coming from remarkably high statistics SuperKamiokande experiment. We confirm that the astrophysical solutions to the solar neutrino problem are extremely disfavored. We also present a new way of illuminating the suppression pattern of various solar neutrino flux, which indicates that the strong suppression of $^{7}$Be neutrinos is no more true once the neutrino flavor conversion is taken into account.

hep-ph↗

arXiv1998

Cooper pairing at large N in a 2-dimensional model

We study a 2-dimensional model of Fermi fields that is closely related to the Gross-Neveu model, and show that to leading order in 1/N a condensate forms. This effect is independent of the chemical potential, a peculiarity that we expect to be specific to 2 dimensions. We also expect the condensate to be unstable against corrections at higher orders in 1/N. We compute the Green's functions associated with the composite psi-psi, and show that the Fermion acquires a Majorana mass proportional to the gap, and that a massless Goldstone pole appears.

hep-ph↗

arXiv1998

Current Status of the Solar Neutrino Problem with Super-Kamiokande

We perform an updated model-independent analysis using the latest solar neutrino data obtained by $^{37}$Cl and $^{71}$Ga radiochemical experiments, and most notably by a large water-Cherenkov detector SuperKamiokande with their 504 days of data taking. We confirm that the astrophysical solutions to the solar neutrino problem are extremely disfavored by the data and a low-temperature modification of the standard solar model is excluded by more than 5 $σ$. We also propose a new way of illuminating the suppression pattern of various solar neutrino flux without invoking detailed flavor conversion mechanisms. It indicates that the strong suppression of $^7$Be neutrinos is no more true when the neutrino flavor conversion is taken into account.

hep-ph↗

arXiv1998

Unitarity of the Aharonov-Bohm Scattering Amplitudes

We discuss the unitarity relation of the Aharonov-Bohm scattering amplitude with the hope that it distinguishes between the differing treatments which employ different incident waves. We find that the original Aharonov-Bohm scattering amplitude satisfies the unitarity relation under the regularization prescription whose theoretical foundation does not appear to be understood. On the other hand, the amplitude obtained by Ruijsenaars who uses plane wave as incident wave also satisfies the unitarity relation but in an unusual way.

hep-th↗

arXiv1998

Dark Matter Neutrinos Must Come with Degenerate Masses

It has been known that there are two schemes in the framework of three flavor neutrinos to accommodate the global features of the hot dark matter neutrinos, the solar neutrino deficit and the atmospheric neutrino anomaly in a manner consistent with terrestrial neutrino experiments, i.e., hierarchical mass neutrinos and almost degenerate neutrinos. We demonstrate that the recent result by the CHOOZ experiment excludes the scheme of hierarchical neutrinos. We also point out in the scheme of almost degenerate neutrinos that if neutrinos are Majorana particles then the double $β$ decay experiments must see positive signals on their way to reach a limit more stringent than the present one by a factor of 5.

hep-ph↗

arXiv1998

Two Pion Correlations as a Possible Experimental Probe for Disoriented Chiral Condensates

We discuss two-pion correlations as a possible experimental probe into disoriented chiral condensates. In particular, we point out that the iso-singlet squeezed states of the BCS type have peculiar two-particle correlations in the back-to-back and the identical momentum configurations which should be detectable experimentally. We motivate the examination of the squeezed state by showing that such state naturally appears in a final stage of nonequilibrium phase transitions via the parametric resonance mechanism proposed by Mrówczyński and Müller.

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arXiv1997

CP Violation vs. Matter Effect in Long-Baseline Neutrino Oscillation Experiments

We investigate, within the framework of three generations of neutrinos, the effects of CP violation in long-baseline neutrino oscillation experiments. We aim at illuminating the global feature of the interplay between genuine effect due to the CP violating phase and a fake one due to the earth matter effect. To this goal, we develop a formalism based on the adiabatic approximation and perturbative treatment of the matter effect which allows us to obtain approximate analytic expressions of the oscillation probabilities. We present an order-of-magnitude estimation and a detailed numerical computation of the absolute and the relative magnitudes of the CP violations under the mass hierarchy suggested by the atmospheric neutrino anomaly and the cosmological dark matter. We find that the genuine CP violating effect is at most \sim 1%, and the matter effect dominates over the intrinsic CP violation only in a region of parameters where the oscillation probability of $ν_μ\toν_e$ is large.

hep-ph↗

arXiv1997

The Gross-Neveu Model with Chemical Potential; An Effective Theory for Solitonic-Metallic Phase Transition in Polyacetylene?

The Gross-Neveu model with chemical potential is investigated as a low-energy effective theory of polyacetylene. In particular, we focus on the abrupt change in the features of electric conductivity such as sharp rise in the Pauli paramagnetism at dopant concentration of about 6%. We will try to explain it by the finite density phase transition in the Gross-Neveu model. The thermodynamic Bethe ansatz is combined with the large-N expansion to construct thermodynamics of the Gross-Neveu model. A first-order phase transition is found in leading order in the 1/N expansion and it appears to be stable against the 1/N correction. The next to leading order correction to the critical dopant concentration is explicitly calculated.

hep-th↗

arXiv1997

How to Measure CP Violation in Neutrino Oscillation Experiments?

We propose a new method for measuring CP violation in neutrino oscillation experiments. The idea is to isolate the term due to the CP-violating phase out of the oscillation probability by taking difference between yields of two (or three) detectors at path-lengths $L = 250 (\frac{E}{1.35 {GeV}}) (\frac{Δm^2}{10^{-2}{eV}^2})^{-1} {km}$ and at $L/3$ (and also at $2L/3$ in the case of three detectors). We use possible hierarchies in neutrino masses suggested by the astrophysical and the cosmological observations to motivate the idea and to examine how the method works.

hep-ph↗

arXiv1997

Can Long-Baseline Neutrino Oscillation Experiments Tell Us about Neutrino Dark Matter?

We define the ratio R = (No. of observed electron events)/ (No. of expected muon events - No. of observed muon events) as a measure for relative importance of $ν_μ\to ν_e$ and $ν_μ\to ν_τ$ oscillations which will be measurable in coming long-baseline neutrino experiments. We then argue that if neutrino oscillation is observed with 0.02 < R < 0.87 it implies the rejection of the neutrino dark matter hypothesis. Our argument is valid if neutrinos come with only three flavors without steriles and if they have a hierarchical mass pattern.

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arXiv1996

Three-Flavor Analysis of Neutrino Mixing with and without Mass Hierarchy

I summarize the results of barely model-dependent phenomenological analyses of the structure of the neutrino flavor mixing. The analyses are based on the three-flavor mixing framework without sterile neutrinos and utilize the hints from solar and atmospheric neutrino observations as well as that from mixed dark matter cosmology. It will be demonstrated that the features of the analysis is sharply distinguished by the two cases (I) with and (II) without dark matter mass scale, and by whether one (or two) mass is dominant (OMD) or the three states are almost degenerate (ADN). The global features of the neutrino mixing is illuminated for these different mass patterns.

hep-ph↗

arXiv1996

The Thermodynamic Bethe Ansatz and the 1/N Correction to the Density Phase Transition in the Gross-Neveu Model

We compute the $1/N$ correction to the location of the previously found first-order phase transition in the Gross-Neveu model at a chemical potential $μ= μ_c = {1 \over \sqrt{2}} m$, where $m$ is the fermion mass. We employ an expression for the free energy $f(μ)$ given by the thermodynamic Bethe ansatz under the approximation that the fundamental fermions dominate the ground state, and combine it with the effective potential evaluated at zero chemical potential. Our result is $μ_c = {m \over \sqrt{2}} [1 - {0.47 \over N}]$.

hep-th↗

arXiv1996

Constraining Almost Degenerate Three-Flavor Neutrinos

We discuss constraints on a scenario of almost degenerate three-flavor neutrinos imposed by the solar and the atmospheric neutrino anomalies, hot dark matter, and neutrinoless double $β$ decays. It is found that in the Majorana version of the model the region with relatively large $θ_{13}$ is favored and a constraint on the CP violating phases is obtained.

hep-ph↗

arXiv1996

High Energy Cosmic Neutrinos and the Equivalence Principle

Observation of the ultra-high energy neutrinos, in particular, detection of $ν_τ$ from cosmologically distant sources like active galactic nuclei (AGN) opens new possibilities to search for neutrino flavor conversion. We consider effects of violation of the equivalence principle (VEP) on propagation of these cosmic neutrinos. Two effects are studied: (1) the oscillations of neutrinos due to the VEP in the gravitational field of our Galaxy and in the intergalactic space, (2) the resonance flavor conversion driven by the gravitational potential of the AGN. We show that the ultra-high energies of the neutrinos as well as cosmological distances to the AGN, or strong AGN gravitational potential will allow one to improve the accuracy of test of the equivalence principle by 21 orders of magnitude for massless or degenerate neutrinos ($Δf \sim 10^{-41}$) and at least by 12 orders of magnitude for massive neutrinos ($Δf \sim 10^{-28} \times (Δm^2/1 {\rm eV}^2)$). Experimental signatures of the transitions induced by the VEP are discussed.

hep-ph↗

arXiv1996

Three flavor neutrino oscillation constraints from accelerator, reactor, atmospheric and solar neutrino experiments

We discuss constraints on three flavor neutrino mixings from the accelerator and reactor experiments, the Kamiokande multi-GeV data, and the solar neutrino observations. The LSND result is excluded at 90\%CL by the constraints imposed by all the data of reactor and accelerator experiments and the Kamiokande multi-GeV data if the mass scale required for the solution to the solar neutrino problem is hierarchically small. The region of a set of the effective two-flavor mixing parameters ($Δm^2$, $\sin^22θ$) is given for the channel $ν_μ\rightarrowν_e$ which is allowed at 90\%CL by the multi-GeV Kamiokande data alone.

hep-ph↗

arXiv1996

Disoriented Chiral Condensate and Strong Electromagnetic Fields

We discuss the effect of strong electromagnetic fields on chiral orientation in the framework of the linear $σ$ model. Based on lessons we learn from computation of the effective potential at one loop, we argue that the chiral U(1) anomaly dominates chiral disorientation driven by electromagnetism. We show that the anomaly effect induces a quasi-instantaneous ``kick'' to field configurations along the $π^0$ direction in relativistic heavy ion collisions. We discuss the possibility that a ``kick'', even though small in magnitude, can have a substantial effect on the formation of chirally misaligned domains.

hep-ph↗

arXiv1995

Neutrino Flavor Mixing Constrained by Accelerator and Reactor Experiments and Solar Neutrino Observation

We derive the constraints imposed on neutrino masses and mixing angles by performing a combined analysis of the data from the Los Alamos and the other terrestrial neutrino oscillation experiments with the assumption of the flavor-mixing solutions to the solar neutrino problem. In a three-flavor mixing scheme which ignores the possibility of sterile neutrinos, we obtain severe constraints on the pattern of masses and flavor mixing of neutrinos. For example, we show that in the standard Kobayashi-Maskawa type mixing matrix $s_{13}^2 \lsim 10^{-2}$ independent of the choice of the solar neutrino solutions. The constraint from the double $β$ decay is also discussed.

hep-ph↗

arXiv1995

Possible Implications of the Atmospheric, the Bugey, and the Los Alamos Neutrino Experiments

A combined analysis of the terrestrial neutrino experiments and the Kamiokande observation of atmospheric neutrino anomaly is performed under the assumption of the existence of dark-matter-mass neutrinos, as suggested by the recent Los Alamos experiment. In the three-flavor mixing scheme of neutrinos it is shown that the constraints from these experiments are so strong that the patterns of mass hierarchy and flavor mixing of neutrinos are determined almost uniquely depending upon the interpretation of the atmospheric neutrino anomaly.

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