Motohiko Yoshimura

Catastrophic particle production under periodic perturbation

We develop a formalism to investigate the behavior of quantum field and quantum ground state when the field is coupled to perturbation that periodically oscillates. Working in the Schroedinger picture of quantum field theory, we confirm that the phenomenon of parametric resonance in the classical theory implies an instability of quantum vacuum, and correspondingly it gives rise to catastrophic particle production if the oscillation lasts indefinitely; the produced number of particles exponentially increases without bound as time proceeds. The density matrix describing the limiting stage of the quantum state is determined by a small set of parameters. Moreover, the energy spectrum and the intensity of produced particles are worked out in greatest detail in the limit of weak coupling or small amplitude perturbation. In the case of strong coupling or large amplitude perturbation the leading adiabatic formula is derived. Application to cosmological fate of weakly interacting spinless fields (WISF) such as the invisible axion, the Polonyi, and the modular fields is discussed. Although very little effect is expected on the invisible axion, the Polonyi type field has a chance that it catastrophically decays at an early epoch without much production of entropy, provided that an intrinsic coupling is large enough.We develop a formalism to investigate the behavior of quantum field and quantum ground state when the field is coupled to perturbation that periodically oscillates. Working in the Schroedinger picture of quantum field theory, we confirm that the phenomenon of parametric resonance in the classical theory implies an instability of quantum vacuum, and correspondingly it gives rise to catastrophic particle production if the oscillation lasts indefinitely; the produced number of particles exponentially increases without bound as time proceeds. The density matrix describing the limiting stage of the quantum state is determined by a small set of parameters. Moreover, the energy spectrum and the intensity of produced particles are worked out in greatest detail in the limit of weak coupling or small amplitude perturbation. In the case of strong coupling or large amplitude perturbation the leading adiabatic formula is derived. Application to cosmological fate of weakly interacting spinless fields (WISF) such as the invisible axion, the Polonyi, and the modular fields is discussed. Although very little effect is expected on the invisible axion, the Polonyi type field has a chance that it catastrophically decays at an early epoch without much production of entropy, provided that an intrinsic coupling is large enough.

Origin of Cosmological Baryon Asymmetry

Abstract A new version of cosmological baryon generation is examined. In this scheme the baryon asymmetry is caused by the nonequilibrium decay of an X(leptoquark) and X† boson of ∼1016 GeV, which takes place after an equilibrium period of baryon nonconserving two-body reactions. This mechanism imposes a severe constraint on grand unified theories; both upper and lower limits to the unification mass are derived.

Cosmological amount of baryons

Abstract The grand unified SU(5) model is analyzed as to whether it can give a sizable, cosmological baryon asymmetry consistent with the observation, N B / N γ = O(10 −8 −10 −10 ). Assuming a recently suggested decay mechanism of the heavy X-boson, we find that a numerical agreement is possible only if the minimal Higgs system is extended to allow a general class of CP violation and if interesting constraints on parameters of the SU(5) model are satisfied.

Neutrino mixing in a class of grand unified theories

Abstract A remarkably simple formula of neutrino oscillation is derived by minimizing the number of Yukawa couplings in SO(10) models; spectrum of neutrino masses precisely follow tthe hierarchy of quark masses, m t ⪢ m c ⪢ m u , and the neutrino mixing matrix coincides with that in the quark sector. Even in a larger class of models transition probabilities of v e are also suppressed by the known Cabibbo factor.

An Effective Lower Bound of the Solar Neutrino Flux

Abstract If the deficit of the solar neutrino ( ν e ) flux is caused by the neutrino oscillation, there exists a lower bound of an effective neutrino flux detectable by electron scattering experiment, since the converted neutrino can also interact with atomic electron via neutral current effect. The effective reduction factor and day-night asymmetry for the 8 B flux is calculated and plotted in the mixing parameter space, when matter oscillation effects both in the sun and in the earth are included, yielding a lower flux bound, ∼ 14% of the standard value.

Quantum Dissipation in Open Harmonic Systems —Operator Solution and Application to Decay Process—

A finite number of harmonic oscillators coupled to infinitely many environment oscillators is fundamental to the problem of understanding quantum dissipation of a small system immersed in a large environment. Exact operator solution as a function of time is given to this problem, by using diagonalized dynamical variable of the entire system, the small system plus the environment. The decay law of prepared initial configuration is worked out in greatest detail. A clear separation of the exponential- and the power-law decay period is made possible by our method. Behavior of physical quantities at asymptotically late times can be understood in terms of the overlap probability of the system variable with the diagonal variable of the entire system.

Higgs boson production by high-energy lepton-nucleon interactions

The production rate of Higgs bosons in high-energy lepton-nucleon collisions is calculated. In the case in which a Higgs boson is produced off an internal line of a weak boson, a complete formula is given in terms of Q2 dependent structure functions together with a numerical estimate in the TeV region. An estimate of the cross section is also attempted when a Higgs boson is emitted from a heavy quark.

Moving Mirror Model of Hawking Evaporation

The moving mirror model is designed to extract essential features of the black hole formation and the subsequent Hawking radiation by neglecting complication due to a finite curvature. We extend this approach to dynamically treat back reaction against the mirror motion due to Hawking radiation. It is found that a unique model in two spacetime dimensions exists in which Hawking radiation completely stops and the end point of evaporation contains a disconnected remnant. When viewed from asymptotic observers at one side of the spacetime, quantum mechanical correlation is recovered in the end. Although the thermal stage accompanying short range correlation may last for an arbitrarily long period, at a much longer time scale a long tail of non-thermal correlation is clearly detected.

Wormhole and Hawking Radiation

It is shown in a variant of two dimensional dilaton gravity theories that an arbitrary, localized massive source put in an initially regular spacetime gives rise to formation of the wormhole classically, without accompanying the curvature singularity. The semiclassical quantum correction under this wormhole spacetime yields Hawking radiation. It is expected, with the quantum back reaction added to the classical equation, that the information loss paradox may be resolved in this model.

Heavy muon as a possible cause of two anomalies

Abstract We propose to explain two observed anomalies that suggest extension of the minimal gauge scheme, the eμ production in the e+e− reaction and the anomalous y-distribution in ν μ reactions, as being caused by a single object, a heavy muon. With more accurate neutrino data this explanation can readily be distinguished from that of a new quark production.