arXiv subjects

Yuhsuke Yoshida

Publications and source records attributed to Yuhsuke Yoshida.

14 recordsLinked to original sources

arXiv2010

Invariance of the bit error rate in the ancilla-assisted homodyne detection

We investigated the minimum achievable bit error rate of discriminating binary coherent states by homodyne measurements with the help of arbitrary ancilla states coupled via beam splitters. We took into account arbitrary pure ancillary states those were updated in real-time by those partial measurements and classical feedforward operations where the partial measurements were made by homodyne detections with a common fixed phase. It was shown that the minimum bit error rate of the system was invariant under these operations. We also discussed how generalize the homodyne detection beyond the scheme which made the bit error rate invariant.

quant-ph↗

arXiv2000

Nonperturbative Aspect In N=2 Supersymmetric Noncommutative Yang-Mills Theory

We investigate asymptotic behaviors of the strong coupling limit in the N=2 supersymmetric non-commutative Yang-Mills theory. The strong coupling behavior is quite different from the commutative one since the non-commutative dual U(1) theory is asymptotic free, although the monodoromy is the same as that of the ordinary theory. Singularities are produced by infinitely heavy monopoles and dyons. Nonperturbative corrections may be determined by holomorphy.

hep-th↗

arXiv1999

Black Hole Entropy from BPS Closed String

By using BPS closed string, the entropy is calculated of the extremal five dimensional black hole consisting of Dirichlet onebranes, Dirichlet fivebranes and Kaluza-Klein momentum in the flat background approximation. In our formulations we consider two kinds of BPS closed strings with or without a winding number. In the former case heavy excitation modes of closed strings are used to derive the entropy. In the latter case we have no oscillator modes and consider collective motion of such massless closed strings. The entropy is given by the number of the ways how we divide the Kaluza-Klein momentum among the massless closed strings. In both cases the black hole entropy is the same as the Bekenstein-Hawking entropy. We argue that the collective modes of closed strings without winding is equivalent to a single closed string with winding. We propose that the two closed string pictures are connected with the open string pictures by the modular transformation.

hep-th↗

arXiv1999

Asymptotic Symmetry and the General Black Hole Solution in Ads_3 Gravity

We describe the Brown-Henneaux asymptotic symmetry of the general black holes in the Chern-Simons gauge theory of the gauge group $SL(2;{\bf R})_L\times SL(2;{\bf R})_R$. We make it clear that the vector-like subgroup $SL(2; {\bf R})_{L+R}$ plays an essential role in describing the asymptotic symmetry consistently. We find a quite general black hole solution in the $AdS_3$ gravity theory. The solution is specified by an infinite number of conserved quantities which constitute a family of mapping from $S^1$ to the gauge group. The BTZ black hole is one of the simplest case.

hep-th↗

arXiv1997

A Proof of Brane Creation via M theory

We study configurations of a single $M$ fivebrane in the geometry ${\bf R}^7 \times Q$ where $Q$ is the Taub-NUT space. Taking the IIA limit at each value of their modulus, two possibilities of the IIA configuration are revealed. One consists of a NS fivebrane and a D sixbrane while the other consists of a NS fivebrane, a D sixbrane and a D fourbrane. In the latter case the fourbrane is shown to be suspended by the fivebrane and the sixbrane. This appearance of fourbrane can be interpreted in Type IIA picture as the result of the crossing of the fivebrane and the sixbrane

hep-th↗

arXiv1997

Geometrical Analysis of Brane Creation via M-Theory

A geometrical analysis is given of Dirichlet fourbrane creation, when sixbrane crosses fivebrane in M-theory. A special property of the Taub-NUT space leads to the consequence. When brane configurations are considered for four dimensional N=2 field theories, sixbrane contributes to the beta-function through the Dirac string of the Taub-NUT space.

hep-th↗

arXiv1997

Higgs Branch of N=2 SQCD and M theory Branes

Higgs branch of N=2 SQCD is studied from the M theory viewpoint. With a differential geometrical proof of the s-rule besides an investigation on the global symmetry of M theory brane configurations, an exact description of the baryonic and non-baryonic branches in terms of M theory is presented. The baryonic branch root is also studied. The ``electric'' and ``magnetic'' descriptions of the root are shown to be related with each other by the brane exchange in M theory.

hep-th↗

arXiv1996

On Instanton Calculations of N=2 Supersymmetric Yang-Mills Theory

Instanton calculations are demonstrated from a viewpoint of twisted topological field theory. Various properties become manifest such that perturbative corrections are terminated at one-loop, and norm cancellations occur between bosonic and fermionic excitations in any instanton background. We can easily observe that for a suitable choice of Green functions the infinite dimensional path integration reduces to a finite dimensional integration over a supersymmetric instanton moduli space.

hep-th↗

arXiv1995

Chiral Symmetry Restoration at Finite Temperature and Chemical Potential in the Improved Ladder Approximation

The chiral symmetry of QCD is studied at finite temperature and chemical potential using the Schwinger-Dyson equation in the improved ladder approximation. We calculate three order parameters; the vacuum expectation value of the quark bilinear operator, the pion decay constant and the quark mass gap. We have a second order phase transition at the temperature $T_c=169$ MeV along the zero chemical potential line, and a first order phase transition at the chemical potential $μ_c=598$ MeV along the zero temperature line. We also calculate the critical exponents of the three order parameters.

hep-ph↗

arXiv1995

Dynamical Symmetry Breaking with Large Anomalous Dimension in Gauge Theories

An analysis is given of the dynamical symmetry breaking of semi-simple gauge groups. We construct a class of renormalizable gauge theories for the dynamically broken topcolor and technicolor interactions. It is shown that a four-Fermi interaction in the strong coupling phase emerges by the tumbling of semi-simple gauge groups in the low energy region. In our models the topcolor interaction provides the top quark with a large anomalous dimension.

hep-ph↗

arXiv1995

Chiral Symmetry, Heavy Quark Symmetry and Bound States

I investigate the bound state problems of lowest-lying mesons and heavy mesons. Chiral symmetry is essential when one consider lowest-lying mesons. Heavy quark symmetry plays an central role in considering the semi-leptonic form factors of heavy mesons. Various properties based on the symmetries are revealed using Bethe-Salpeter equations.

hep-ph↗

arXiv1995

Solving the Homogeneous Bethe-Salpeter Equation

We study a method for solving the homogeneous Bethe-Salpeter equation. By introducing a `fictitious' eigenvalue $λ$ the homogeneous Bethe-Salpeter equation is interpreted as a linear eigenvalue equation, where the bound state mass is treated as an input parameter. Using the improved ladder approximation with the constant fermion mass, we extensively study the spectrum of the fictitious eigenvalue $λ$ for the vector bound states and find the discrete spectrum for vanishing bound state mass. We also evaluate the bound state masses by tuning appropriate eigenvalues $λ$ to be unity, and find massless vector bound states for specific values of the constant fermion masses.

hep-ph↗

arXiv1994

QCD S Parameter from Inhomogeneous Bethe-Salpeter Equation

We calculate the low-energy parameter S in QCD, which is also known as L_{10}, and the pion decay constant f_πusing inhomogeneous Bethe-Salpeter equation in improved ladder approximation. To extract these quantities we calculate the ``V-A'' two-point function, Π_{VV}(q^2) - Π_{AA}(q^2), in space-like region. We obtain S = 0.43 \sim 0.48, which is about 30% larger than the experimental value. The calculated f_πis well consistent with the result by solving the homogeneous Bethe-Salpeter equation for pion. We also evaluate $S$ parameter in SU(3) gauge theory with N_D doublets of fermions in connection with walking technicolor model, and find that the value of S/N_D hardly depends on N_D.

hep-ph↗

arXiv1993

Isgur-Wise Function from Bethe-Salpeter Amplitude

We develop the improved ladder approximation to QCD in order to apply it to the heavy quark mesons. The resulting Bethe-Salpeter equation is expanded in powers of the inverse heavy quark mass 1/M, and is shown to be consistent with the heavy quark spin symmetry. We calculate numerically the universal leading order BS amplitude for heavy pseudoscalar and vector mesons, and use this to evaluate the Isgur-Wise function and the decay constant F_B. The resulting Isgur-Wise function predicts a large charge radius, rho^2 = 1.8 - 2.0, which when fitted to the ARGUS data corresponds to the value Vcb = .044 - .050 for the Kobayashi-Maskawa matrix element.

hep-ph↗