Mitsutoshi Fujita

Fractional quantum Hall effect via holography: Chern-Simons, edge states and hierarchy

We present three holographic constructions of fractional quantum Hall effect (FQHE) via string theory. The first model studies edge states in FQHE using supersymmetric domain walls in = 6 Chern-Simons theory. We show that D4-branes wrapped on 1 or D8-branes wrapped on 3 create edge states that shift the rank or the level of the gauge group, respectively. These holographic edge states correctly reproduce the Hall conductivity. The second model presents a holographic dual to the pure U(N)k (Yang-Mills-)Chern-Simons theory based on a D3-D7 system. Its holography is equivalent to the level-rank duality, which enables us to compute the Hall conductivity and the topological entanglement entropy. The third model introduces the first string theory embedding of hierarchical FQHEs, using IIA string on 2/Zn.

Aspects of AdS/BCFT

A bstractWe expand the results of arXiv:1105.5165, where a holographic description of a conformal field theory defined on a manifold with boundaries (so called BCFT) was proposed, based on AdS/CFT. We construct gravity duals of conformal field theories on strips, balls and also time-dependent boundaries. We show a holographic g-theorem in any dimension. As a special example, we can define a ‘boundary central charge’ in three dimensional conformal field theories and our holographic g-theorem argues that it decreases under RG flows. We also computed holographic one-point functions and confirmed that their scaling property agrees with field theory calculations. Finally, we give an example of string theory embedding of this holography by inserting orientifold 8-planes in AdS4 × CP3.

Competition between charge- and spin-density-wave order and superconductivity in La1.875Ba0.125-xSrxCuO4

We have performed a series of elastic neutron scattering measurements on 1/8-hole doped La(1.875)-Ba(0.125-x)Sr(x)CuO(4) single crystals with x = 0.05, 0.06, 0.075, and 0.085. Both charge-density-wave (CDW) and spin-density-wave orders are found to develop simultaneously below the structural transition temperature between the low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) or low-temperature less-orthorhombic (LTLO) phases. In the ground state the CDW order is observed only in the LTT/LTLO phase and drastically degrades towards the LTO boundary. The x dependence of T(c) strongly suggests a direct effect of the CDW order on the suppression of superconductivity.

Disordered Systems and the Replica Method in AdS/CFT

We formulate a holographic description of effects of disorder in conformal field theories based on the replica method and the AdS/CFT correspondence. Starting with n copies of conformal field theories, randomness with a gaussian distribution is described by a deformation of double trace operators. After computing physical quantities, we take the n → 0 limit at the final step. We compute correlation functions in the disordered systems by using the holographic replica method as well as the formulation in the conformal field theory. We find examples where disorder changes drastically the scaling of two point functions. The renormalization group flow of the effective central charge in our disordered systems is also discussed.

Genus-one correction to asymptotically free Seiberg-Witten prepotential from Dijkgraaf-Vafa matrix model

We find perfect agreements on the genus-one correction to the prepotential of SU(2) Seiberg-Witten theory with Nf = 2, 3 between field theoretical and Dijkgraaf-Vafa-Penner type matrix model results.

Finite-temperature spectral function of the vector mesons in a holographic QCD model

We use the soft-wall anti-de Sitter/QCD model to investigate the finite-temperature effects on the spectral function in the vector channel. The dissociation of the vector meson tower onto the anti-de Sitter black hole leads to the in-medium mass shift and the width broadening in a way similar to the lattice QCD results for the heavy quarkonium at finite temperature. We also show the momentum dependence of the spectral function and find it consistent with screening in a hot wind.

Geometric entropy and hagedorn/deconfinement transition

It has recently been proposed that the entanglement entropy can be an order parameter of confinement/deconfinement transitions. To find a clear evidence, we introduce a new quantity called the geometric entropy, which is related to the entanglement entropy via a double Wick rotation. We analyze the geometric entropy and manifestly show that its value becomes discontinuous at the Hagedorn temperature both in the free = 4 super Yang-Mills and in its supergravity dual.

Fermi-liquid ground state in the n-type Pr0.91LaCe0.09CuO4-y copper-oxide superconductor

We report nuclear magnetic resonance studies on the low-doped n-type copper-oxide Pr_{0.91}LaCe_{0.09}CuO_{4-y} (T_c=24 K) in the superconducting state and in the normal state uncovered by the application of a strong magnetic field. We find that when the superconductivity is removed, the underlying ground state is the Fermi liquid state. This result is at variance with that inferred from previous thermal conductivity measurement and contrast with that in p-type copper-oxides with a similar doping level where high-T_c superconductivity sets in within the pseudogap phase. The data in the superconducting state are consistent with the line-nodes gap model.

Melting spectral functions of the scalar and vector mesons in a holographic QCD model

We investigate the finite-temperature spectral functions of heavy quarkonia by using the soft-wall anti-de Sitter/QCD model. We discuss the scalar, the pseudoscalar, the vector, and the axial-vector mesons and compare their qualitative features of the melting temperature and growing width. We find that the axial-vector meson melts earlier than the vector meson, while there appears only a slight difference between the scalar and pseudoscalar mesons, which also melt earlier than the vector meson.

Eschenburg space as gravity dual of flavored = 4 Chern-Simons-matter theory

We find a 3D flavored = 4 Chern-Simons-matter theory, a kind of = 3 SCFT, has a gravity dual AdS4 × 7(t1, t2, t3) where three coprime parameters can be read off according to the number and charge of 5-branes in the dual Type IIB string setup. Because 7(t1, t2, t3) has been known in literature as Eschenburg space, we exploit some of its properties to examine the correspondence between two sides.