Searcharxiv⌕ Search

arXiv subjects

Hiroshi Ohki

Publications and source records attributed to Hiroshi Ohki.

At least 73 records · Page 4Linked to original sources
arXiv2010

Study of the scaling properties in SU(2) gauge theory with eight flavors

We present our preliminary study of the SU(2) gauge theory with 8 flavors of fermions in fundamental representation. This theory could be a candidate of the gauge theory with conformal fixed point. By using Wilson/Polyakov loop in a finite volume with twisted boundary conditions, we study the renormalization group flow of the gauge coupling constant. Our calculation gives consistent result with the perturbative prediction of the running coupling in the weak coupling region. We investigate a possible signal for conformal behavior in the strong coupling region.

hep-lat↗
arXiv2010

Non-Abelian Discrete Flavor Symmetries on Orbifolds

We study non-Abelian flavor symmetries on orbifolds, $S^1/Z_2$ and $T^2/Z_3$. Our extra dimensional models realize $D_N$, $Σ(2N^2)$, $Δ(3N^2)$ and $Δ(6N^2)$ including $A_4$ and $S_4$. In addition, one can also realize their subgroups such as $Q_N$, $T_7$, etc. The $S_3$ flavor symmetry can be realized on both $S^1/Z_2$ and $T^2/Z_3$ orbifolds.

hep-th↗
arXiv2010

Geometric entropy and third order phase transition in d=4 N=2 SYM with flavor

We analyze the phase structure of $d=4$ $\mathcal{N}=2$ large $N$ SYM theory with flavor on $S^1\times S^3$ by using geometric entropy as an order parameter. We introduce chemical potential conjugate to global U(1) symmetry and find the third order phase transition at finite density by using the geometric entropy as the order parameter. We also find that the geometric entropy at the finite density has an interesting behavior at low temperature and for large $N_f$.

hep-th↗
arXiv2010

Non-Abelian Discrete Symmetries in Particle Physics

We review pedagogically non-Abelian discrete groups, which play an important role in the particle physics. We show group-theoretical aspects for many concrete groups, such as representations, their tensor products. We explain how to derive, conjugacy classes, characters, representations, and tensor products for these groups (with a finite number). We discussed them explicitly for $S_N$, $A_N$, $T'$, $D_N$, $Q_N$, $Σ(2N^2)$, $Δ(3N^2)$, $T_7$, $Σ(3N^3)$ and $Δ(6N^2)$, which have been applied for model building in the particle physics. We also present typical flavor models by using $A_4$, $S_4$, and $Δ(54)$ groups. Breaking patterns of discrete groups and decompositions of multiplets are important for applications of the non-Abelian discrete symmetry. We discuss these breaking patterns of the non-Abelian discrete group, which are a powerful tool for model buildings. We also review briefly about anomalies of non-Abelian discrete symmetries by using the path integral approach.

hep-th↗
arXiv2010

Chiral four dimensional field theory from superstring and higher dimensional super Yang-Mills theory

We study four dimensional field theory from the low-energy effective theory of Type I, II or heterotic string theories. Chiral fermions in four dimensions are obtained by several mechanisms. Especially, the background flux is one of the most interesting mechanisms for obtaining four dimensional chiral theories. Chiral matter fields have localized wavefunctions on extra dimensions. We discuss about the relations between background flux and low-energy spectra which are counted by their zero-modes. Yukawa couplings are free parameters in the standard model and may be related to the underlying physics. In the string theory or its low-energy limit, they are determined by overlap integral of wavefunctions on extra dimensions. We also study the higher order couplings based on the field theoretical approach. From the analysis of generic n-point couplings, we can discuss about flavor structures. We find that in such a construction some discrete flavor symmetries appear in the four dimensional effective theory. Their phenomenological implications are discussed. Furthermore we extend these constructions to orbifold background. Magnetic flux still plays an important role and leads to various types of low-energy spectra different from that of toroidal compactifications. The orbifold models with heterotic string are also investigated.

hep-th↗
arXiv2010

E6,7,8 Magnetized Extra Dimensional Models

We study 10D super Yang-Mills theory with the gauge groups $E_6$, $E_7$ and $E_8$. We consider the torus/orbifold compacfitication with magnetic fluxes and Wilson lines. They lead to 4D interesting models with three families of quarks and leptons, whose profiles in extra dimensions are quasi-localized because of magnetic fluxes.

hep-ph↗
arXiv2010

A new scheme for the running coupling constant in gauge theories using Wilson loops

We propose a new renormalization scheme of the running coupling constant in general gauge theories using the Wilson loops. The renormalized coupling constant is obtained from the Creutz ratio in lattice simulations and the corresponding perturbative coefficient at the leading order. The latter can be calculated by adopting the zeta-function resummation techniques. We perform a benchmark test of our scheme in quenched QCD with the plaquette gauge action. The running of the coupling constant is determined by applying the step-scaling procedure. Using several methods to improve the statistical accuracy, we show that the running coupling constant can be determined in a wide range of energy scales with relatively small number of gauge configurations.

hep-lat↗
arXiv2010

Flavor structure from magnetic fluxes and non-Abelian Wilson lines

We study the flavor structure of 4D effective theories, which are derived from extra dimensional theories with magnetic fluxes and non-Abelian Wilson lines. We study zero-mode wavefunctions and compute Yukawa couplings as well as four-point couplings. In our models, we also discuss non-Abelian discrete flavor symmetries such as $D_4$, $Δ(27)$ and $Δ(54)$.

hep-th↗
arXiv2009

Search for the IR fixed point in the twisted Polyakov loop scheme

We present a non-perturbative study of the running coupling constant in the Twisted Polyakov Loop (TPL) scheme. We investigate how the systematic and statistical errors can be controlled {\it via} a feasibility study in SU(3) pure Yang-Mills theory. We show that our method reproduces the perturbative determination of the running coupling in the UV. In addition, our numerical result agrees with the theoretical prediction of this coupling constant in the IR. We also present our preliminary results for $N_f=12$ QCD, where an IR fixed point may be present.

hep-lat↗
arXiv2009

Higher Order Couplings in Magnetized Brane Models

We compute three-point and higher order couplings in magnetized brane models. We show that higher order couplings are written as products of three-point couplings. This behavior is the same as higher order amplitudes by conformal field theory calculations e.g. in intersecting D-brane models.

hep-th↗
arXiv2009

Magnetic flux, Wilson line and orbifold

We study torus/orbifold models with magnetic flux and Wilson line background. The number of zero-modes and their profiles depend on those backgrounds. That has interesting implications from the viewpoint of particle phenomenology.

hep-th↗
arXiv2008

Three generation magnetized orbifold models

We study three generation models in the four-dimensional spacetime, which can be derived from the ten-dimensional N=1 super Yang-Mills theory on the orbifold background with a non-vanishing magnetic flux. We classify the flavor structures and show possible patterns of Yukawa matrices. Some examples of numerical studies are also shown.

hep-th↗
arXiv2008

A New Method of Calculating the Running Coupling Constant

We propose a new method to compute the running coupling constant of gauge theories on the lattice. We first give the definition of the running coupling in the new scheme using the Wilson loops in a finite volume, and explain how the running of the coupling constant is extracted from the measurement of the volume dependence. The perturbative calculation of the renormalization constant to define the scheme is also given at the leading order. As a benchmark test of the new scheme we apply the method the case of the quenched QCD. We show the preliminary result from our numerical simulations which are carried out with plaquette gauge action for various lattice sizes and bare lattice couplings. With techniques to improve the statistical accuracy, we show that we can determine the non-perturbative running of the coupling constant in a wide range of the energy scale with relatively small number of gauge configurations in our scheme. We compare our lattice data of the running coupling constant with perturbative renormalization group evolution at one- and two-loop order, and confirm the consistency between them at high energy.

hep-lat↗
arXiv2008

Magnetized orbifold models

We study (4+2n)-dimensional N=1 super Yang-Mills theory on the orbifold background with non-vanishing magnetic flux. In particular, we study zero-modes of spinor fields. The flavor structure of our models is different from one in magnetized torus models, and would be interesting in realistic model building.

hep-th↗
arXiv2008

Soft supersymmetry breaking terms from D4 x Z2 lepton flavor symmetry

We study the supersymmetric model with $D_4 \times Z_2$ lepton flavor symmetry. We evaluate soft supersymmetry breaking terms, i.e. soft slepton masses and A-terms, which are predicted in the $D_4$ flavor model. We consider constraints due to experiments of flavor changing neutral current processes.

hep-ph↗
arXiv2008

D4 Flavor Symmetry for Neutrino Masses and Mixing

We present the $D_4\times Z_2$ flavor symmetry, which is different from the previous work by Grimus and Lavoura. Our model reduces to the standard model in the low energy and there is no FCNC at the tree level. Putting the experimental data, parameters are fixed, and then the implication of our model is discussed. The condition to realize the tri-bimaximal mixing is presented. The possibility for stringy realization of our model is also discussed.

hep-ph↗