arXiv subjects

Y. Kato

Publications and source records attributed to Y. Kato.

150 records · Page 9Linked to original sources

arXiv2001

Spin-1/2 Kagome Like Lattice in Volborthite Cu3V2O7(OH)2-H2O

A novel cuprate Volborthite, Cu3V2O7(OH)2-2H2O, containing an S-1/2 (Cu 2+ spin) kagome-like lattice is studied by magnetic susceptibility, specific heat, and 51 V NMR measurements. Signs for neither long-range order nor spin-gapped singlet ground states are detected down to 1.8 K, in spite of large antiferromagnetic couplings of ~100 K between Cu spins forming a two-dimensional kagome-like network. It is suggested that Volborthite represents a system close to a quantum critical point between classical long-range ordered and quantum disordered phases.

cond-mat.str-el↗

arXiv2001

Magnetohydrodynamic Simulations of Accretion Disks around a Weakly Magnetized Neutron Star in Strong Gravity

We carried out two dimensional high-resolution magnetohydrodynamic (MHD) simulations of an accretion disk around a weakly magnetized neutron star. General relativistic effects are taken into account by using pseudo-Newtonian potential of Paczýnski, B., P. J. Witta (1980). When magnetic loops connect the neutron star and the accretion disk, the twist injection from the disk or from the rotating neutron star triggers expansion of the loops. Since the expanding magnetic loops prevent inflow toward the magnetic poles of the neutron star, disk matter accumulates on the boundary between the magnetosphere and the disk. Magnetic reconnection taking place in the loops creates a channel along which the disk matter can accrete and unloads the magnetosphere. This process produces quasi-periodic variation of the accretion flow in the innermost region of the disk. We found two kinds of oscillations. One is the magnetospheric oscillation regulated by magnetic reconnection. The other is the radial disk oscillation. The typical frequency of the oscillations is 100 Hz to 2 kHz. Furthermore, we predict that QPO sources inevitably accompany X-ray flares by magnetic reconnection and bipolar outflows of hot X-ray emitting plasma similar to the optical jets in protostars.

astro-ph↗

arXiv2001

Low Energy Quasiparticle Excitation in the Vortex State of Borocarbide Superconductor YNi_2B_2C

We have measured the low temperature heat capacity Cp and microwave surface impedance Zs in the vortex state of YNi_2B_2C. In contrast to conventional s-wave superconductors, Cp shows a nearly \sqrt H-dependence. This \sqrt H-dependence persists even after the introduction of the columnar defects which change the electronic structure of the vortex core regime dramatically and strongly disturb the regular vortex lattice. On the other hand, flux flow resistivity obtained from Zs is nearly proportional to H. Taken together, these results indicate that the vortex state of YNi_2B_2C is fundamentally different from the conventional s-wave counterparts, in that the delocalized quasiparticle states around the vortex core play a much more important role, similar to d-wave superconductors.

cond-mat.supr-con↗

arXiv2000

Lorentz Angle Measurement for CO2/Isobutane Gas Mixtures

We have developed a Lorentz angle measurement system for cool gas mixtures in the course of our R&D for a proposed JLC central drift chamber (JLC-CDC). The measurement system is characterized by the use of two laser beams to produce primary electrons and flash ADCs to read their signals simultaneously. With this new system, we have measured Lorentz angles for CO2/isobutane gas mixtures with different proportions (95:5, 90:10, and 85:15), varying drift field from 0.6 to 2.0 kV/cm and magnetic field up to 1.5 T. The results of the measurement are in good agreement with GARFIELD/MAGBOLTZ simulations.

hep-ex↗

arXiv2000

The QCD and Standard Model Working Group: Summary Report from Les Houches

The Les Houches Workshop on Physics at TeV Colliders took place from June 8-18, 1999. One of the three working groups at Les Houches concentrated on QCD issues, both at the Tevatron Collider and at the LHC. Besides the interest in QCD in its own right, QCD dynamics plays an important role in the production mechanisms for any new physics process that might be observed at either collider, as well as any processes that may form backgrounds to the new physics. This writeup serves both as a pedagogical overview of QCD as well as an update on the current status of the field.

hep-ph↗

arXiv1999

Study of e^{+}e^{-} --> \tildeχ^{+}_{1} \tildeχ^{-}_{1} --> \tildeτ^{+}_{1}ν_τ + \tildeτ^{-}_{1}\barν_τ

In Supersymmetry with large $\tanβ$ values, the lighter stau ($\tildeτ_{1}$) may be lighter than the lightest chargino ($\tildeχ^{\pm}_{1}$). The decay $\tildeχ^{\pm}_{1} \to \tildeτ^{\pm}_{1} ν_τ$, followed by $\tildeτ^{\pm}_{1} \to \tildeχ^{0}_{1} τ$, alters a phenomenology of the chargino production. We study the chargino pair production at future $e^{+}e^{-}$ linear colliders.

hep-ph↗