Effects of Neutrino Oscillation on the Supernova Relic Neutrino Background

We investigate to what extent the oscillation or conversion of neutrinos enhances the expected event rate of the supernova relic neutrino background (SRN) at the Super-Kamiokande detector (SK). The SRN \bar\nu_e's can be almost completely exchanged with \nu_\mu-like neutrinos by the MSW oscillation under the inverse mass hierarchy with \Delta m^2 ~ 10^{-8}--10^5 [eV^2], or by the magnetic moment of Majorana neutrinos with \mu_\nu >~ 10^{-12} \mu_B and \Delta m^2 ~ 10^{-4}--10^0 [eV^2]. In the standard calculation of the SRN flux, the event rate of the SRN \bar\nu_e's at the SK in the observable energy range of 15--40 MeV can be enhanced from 1.2 yr^{-1} to 2.4 yr^{-1} if all \bar\nu_e's are exchanged with \nu_\mu-like neutrinos. The enhancement is prominent especially in the high energy range (\gtilde 25 MeV). In the astrophysically optimistic calculation, the event rate becomes as high as 9.4 yr^{-1}. Because the theoretical upper bound of the SRN events without oscillation is about 5 yr^{-1} taking account of the various astrophysical uncertainties, we might have to resort to the neutrino oscillation if more than 5 events in a year, as well as a significantly harder spectrum, were observed in the SK.Comment: 10 pages, 3 postscript figures include

マイクロマグネティックシミュレーションによる磁気渦コアに関する研究

Recently, a memory cell using the direction of a magnetic vortex core in a magnetic disk was proposed. In the magnetic disk, the curling magnetization structure(magnetic vortex) appears to reduce the demagnetizing energy. In the center of the structure, the magnetization directs up or down to the disk plane to reduce the exchange energy(vortex core). Since the vortex structure is stable magnetization structure, the vortex core switching requires several thousands Oersted of the perpendicular field to the plane. Some researchers reported that the vortex core can be switched efficiently by using spin current. For the realization of the memory using the vortex core, the fundamental and applied studies of the vortex core has been reported frequently. However, the detail of the vortex core motion by spin current is still not clear. This research reports the following studies, (1) fast simulation by GPU, (2) effect of the Oersted field induced by spin current, (3) stability of vortex structure on core switching, (4) reduction of switching current density by using Pac-man shaped disk.(1) The 3-dimensional model is required for the detailed investigation of the vortex core motion. However, it consumes a lot of time for the simulation. To reduce the simulation time, we speed up the micromagnetic simulator by using GPU in this research. By using GPU, the simulation is 172 times faster than the simulation by the conventional CPU micromagnetic simulator. The simulator is used for the following researches.(2) To indicate possibility of integration of the vortex memory, the effect of the Oersted field is investigated. In case of the vortex core manipulation by spin current, both the spin torque and the Oersted field induced by the spin current affect the vortex core motion. The Oersted field decreases with miniaturization of the magnetic disk. If the effect of the Oersted field is large, the vortex core cannot be manipulated with the miniaturization. To establish the vortex core manipulation by spin current, the detailed investigation of the effect of the Oersted field is required. This research investigates the effect by the 3-dimensional simulation. It clarifies that the effect of the Oersted field is just 8 % of the whole driving force at a maximum. The estimated effect is much smaller than that of the experimental work.(3) The stability of the vortex structure has an important role to define the device size. To reveal the relation between the stability of the structure and the geometry of the magnetic disk, the stability of the vortex structure in a remnant state was reported. However, the relation between the stability and the geometry on the core switching has not been reported yet.This research investigates the stability varying the diameter and the thickness of the disk by the micromagnetic simulation. The result shows that the disk diameter has to be increased 20!80 nm than the reported disk diameter to manipulate the vortex core without collapsing the vortex structure, and the minimum disk diameter is 40 nm.(4) However some researchers reported that the vortex core can be switched efficiently by spin current, further reduction of the switching current density for the realization of the memory using vortex core. The reported studies relating to the vortex core switching, a vortexantivortex pair appears during the switching process. However, the nucleation of the vortexantivortex pair requires high current density, and it is a strong factor in preventing reduction of the switching current density. For the reduction of the current density, this reasearch proposes to use a Pac-man shaped disk which does not use the vortex-antivortex pair in the switching process. The simulation result hows that the switching current density can be reduced 75 % compared with the conventional switching method.電気通信大学201

Correspondence of topological classification between quantum graph extra dimension and topological matter

In this paper, we study a classification of boundary conditions with symmetries for a five-dimensional Dirac fermion on a quantum graph. We find that there is a nontrivial correspondence between the classification of boundary conditions at the vertex on the quantum graph and that of the symmetry-protected topological phases of gapped free-fermion systems, which are classified into ten symmetry classes by the time-reversal symmetry, particle-hole symmetry and chiral symmetry. A Hermitian matrix which specifies the boundary conditions in our model corresponds to a zero-dimensional Hamiltonian in the gapped free-fermion systems. Furthermore, symmetries in our model give the condition that restricts the parameter space of the boundary conditions. These conditions are identical to the ones in the gapped free-fermion systems that the Hamiltonian with the symmetries should satisfy. We also show that the topological number for each symmetry class in our model implies the presence of 4d massless fields localized at the vertex of the quantum graph, like gapless boundary states for the free-fermion systems from the bulk-boundary correspondence.Comment: 39 pages, 7 figures, 5 table

Generating Shuttling Procedures for Constrained Silicon Quantum Dot Array

In silicon quantum computers, a single electron is trapped in a microstructure called a quantum dot, and its spin is used as a qubit. For large-scale integration of qubits, we previously proposed an approach of arranging the quantum dots in a two-dimensional array and sharing a control gate in a row or column of the array. In our array, the shuttling of electrons is a useful technique to operate the target qubit independently and avoid crosstalk. However, since the shuttling is also conducted using shared control gates, the movement of qubits is complexly constrained. We therefore propose a formal model on the basis of state transition systems to describe those constraints and operation procedures on the array. We also present an approach to generate operation procedures under the constraints. Utilizing this approach, we present a concrete method for our 16 $\times$ 8 quantum dot array. By implementing the proposed method as a quantum compiler, we confirmed that it is possible to generate operation procedures in a practical amount of time for arbitrary quantum circuits. We also demonstrated that crosstalk can be avoided by shuttling and that the fidelity in that case is higher than when crosstalk is not avoided

Observed behaviours of precipitable water vapour and precipitation intensity in response to upper air profiles estimated from surface air temperature

Extremely heavy precipitation affects human society and the natural environment, and its behaviour under a warming climate needs to be elucidated. Recent studies have demonstrated that observed extreme precipitation increases with surface air temperature (SAT) at approximately the Clausius-Clapeyron (CC) rate, suggesting that atmospheric water vapour content can explain the relationship between extreme precipitation and SAT. However, the relationship between atmospheric water vapour content and SAT is poorly understood due to the lack of reliable observations with sufficient spatial and temporal coverage for statistical analyses. Here, we analyse the relationship between atmospheric water vapour content and SAT using precipitable water vapour (PWV) derived from global positioning system satellites. A super-CC rate appears in hourly PWV when the SAT is below 16°C, whereas the rate decreases at high SAT, which is different from the precipitation-SAT relationship. The effects of upper air temperature and water vapour can consistently explain the super-CC rate of PWV relative to SAT. The difference between moist and dry adiabatic lapse rates increases with SAT, in consequence of more ability to hold water vapour in the free atmosphere under higher SAT conditions; therefore, attainable PWV increases more rapidly than the CC rate as SAT increases.CC-BY 4.