Searcharxiv⌕ Search

arXiv subjects

Hikaru Sato

Publications and source records attributed to Hikaru Sato.

26 records · Page 2Linked to original sources
arXiv2013

Supersymmetric Yang-Mills Theory on the Noncommutative Geometry

Recently, we found the supersymmetric counterpart of the spectral triple. When we restrict the representation space to the fermionic functions of matter fields, the counterpart which we name "the triple" reduces to the original spectral triple which defines noncommutative geometry. We see that the fluctuation to the supersymmetric Dirac operator induced by algebra in the triple generates vector supermultiplet which mediates gauge interaction. Following the supersymmetric version of spectral action principle, we calculate the heat kernel expansion of the square of fluctuated Dirac operator and obtain the correct supersymmetric Yang-Mills action with U(N) gauge symmetry.

hep-th↗
arXiv2013

Unusual pressure effects on the superconductivity of indirectly electron-doped (Ba1-xLax)Fe2As2 epitaxial films

Applying an external pressure to indirectly electron-doped 122-type (Ba1-xLax)Fe2As2 epitaxial films enhances the superconducting critical temperature (Tc) up to 30.3 K. Different from the other family compounds, the Tc is enhanced not only in the under-doped region but also in the optimally doped and over-doped regions. Narrowing of the superconducting transition width and an increase in the carrier density take place simultaneously in the whole doping region, except at the heavily over-doped limit. This characteristic is unique to and observed only in (Ba1-xLax)Fe2As2, in which the La doping is stabilized via non-equilibrium growth of the vapor phase epitaxy, among the 122-type iron-based superconductors, AFe2As2 (A = Ba, Sr, and Ca).

cond-mat.supr-con↗
arXiv2013

Anomalous scaling behavior in a mixed-state Hall effect of a cobalt-doped BaFe2As2 epitaxial film with a high critical current density over 1 MA/cm2

The mixed-state Hall effect was examined in a Ba(Fe1-xCox)2As2 epitaxial film with a high critical current density. The transverse resistivity ρxy and the longitudinal resistivity ρxx follow power law scaling ρxy = Aρxxβ. In the temperature-sweep with a fixed field (T sweep), all of the β values are independent of magnetic field up to 9 T, and are lower than 2.0 (around 1.8). In contrast, the β values in the magnetic-field sweep with a fixed temperature (H sweep) change from 1.8 to 2.0 as the temperature increases from 13 to 16 K even in the T/H region that overlaps with the T sweep measurements. These results indicate that the vortices introduced at low temperatures are trapped by strong pinning centers, but a portion of the vortices introduced at high temperatures are not strongly trapped by the pinning centers. The sign of ρxy is negative, and a sign reversal is not detected. These distinct scaling behaviors, which sharply contrast cuprates and MgB2, are explained by high-density c-axis pinning centers in the Ba(Fe1-xCox)2As2 epitaxial film and are consistent with a wider vortex liquid phase.

cond-mat.supr-con↗
arXiv2012

Two-dome structure in electron-doped iron arsenide superconductors

Iron arsenide superconductors based on the material LaFeAsO1-xFx are characterized by a two-dimensional Fermi surface (FS) consisting of hole and electron pockets yielding structural and antiferromagnetic transitions at x = 0. Electron doping by substituting O2- with F- suppresses these transitions and gives rise to superconductivity with a maximum Tc = 26 K at x = 0.1. However, the over-doped region cannot be accessed due to the poor solubility of F- above x = 0.2. Here we overcome this problem by doping LaFeAsO with hydrogen. We report the phase diagram of LaFeAsO1-xHx (x < 0.53) and, in addition to the conventional superconducting dome seen in LaFeAsO1-xFx, we find a second dome in the range 0.21 < x < 0.53, with a maximum Tc of 36 K at x = 0.3. Density functional theory calculations reveal that the three Fe 3d bands (xy, yz, zx) become degenerate at x = 0.36, whereas the FS nesting is weakened monotonically with x. These results imply that the band degeneracy has an important role to induce high Tc.

cond-mat.supr-con↗
arXiv2012

Supersymmetric QCD in the Noncommutative Geometry

Introduction of supersymmetry into the noncommutative geometry is investigated. We propose a new Dirac operator which plays the role of the metric over the extended algebra of chiral and antichiral supermultiplets and is invariant under the supersymmetry transformations. Inner automorphisms for the algebra generate vector supermultiplets as an internal fluctuation of the metric. We show that the supersymmetric QCD action for these supermultiplets is correctly given by the spectral action principle.

hep-th↗
arXiv2002

Crosscap states and Boundary states in D=4,N=1,type-IIB Orientifold Theories

We construct boundary state and crosscap state in D=4,N=1 type-IIB Z_N orientifold and investigate properties of amplitude. We find that the boundary state of a cylinder is different from the boundary state of a Möbius strip. Using these states, we find that amplitudes do not factorize in Z_N(N=even) orientifold. Tadpole divergence remain in Z_4, Z_8, Z'_8 and Z'_{12} model due to volume dependence of boundary and crosscap state. On the other hand the amplitude of Z_3 and Z_7 orientifolds factorize so that we obtain the gauge groups of the model by employing the massless tadpole cancellation condition.

hep-th↗
arXiv1999

D=4, N=1, Type IIA Orientifolds

We study D=4, N=1, type IIA orientifold with orbifold group $Z_N$ and $Z_N \times Z_M$. We calculate one-loop vacuum amplitudes for Klein bottle, cylinder and Mobius strip and extract the tadpole divergences. We find that the tadpole cancellation conditions thus obtained are satisfied by the $Z_4$, $Z_8$, $Z'_8$, $Z'_{12}$ orientifolds while there is no solution for $Z_3$, $Z_7$, $Z_6$, $Z'_6$, $Z_{12}$. The $Z_4 \times Z_4$ type IIA orientifold is also constructed by introducing four different configurations of 6-branes. We argue about perturbative versus non-perturbative orientifold vacua under T- duality between the type IIA and the type IIB $Z_N$ orientifolds in four dimensions.

hep-th↗