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Akira Kokado

Publications and source records attributed to Akira Kokado.

At least 19 recordsLinked to original sources
arXiv2018

Gravity in a warped 6D world with an extra 2D sphere

Corrections to Newton's inverse law have been so far considered, but not clear in warped higher dimensional worlds, because of complexity of the Einstein equation. Here we give a model of a warped 6D world with an extra 2D sphere. We take a general energy-momentum tensor, which does not depend on a special choice of bulk matter fields. The 6D Einstein equation reduces to the spheroidal differential equation, which can be easily solved. The gravitational potential in our 4D universe is calculated to be composed of infinite series of massive Yukawa potentials coming from the KK mode, together with Newton's inverse law. The series of Yukawa type potentials converges well to behave as $1/r^3$ near $r=0$.

hep-th↗
arXiv2017

Weak gravitation from a small extra 2D sphere

In order to explain weak gravitation in our 4-dimensional universe, a 6-dimensional model with a small extra 2D sphere is proposed. The traceless energy-momentum tensor is quite naturally appeared in our 6-dimensional model. The warp factor is given by $ϕ(θ) = ε+ \sin{θ}$, where $ε$ plays a role of killing the singular point $ϕ(θ)=0$, and is assumed $0 < ε\ll 1$. Any massive particle is rolling down into points along this geodesic line. The light ray can be shown to stay in our 4-dimensional universe. This suggest us that our 4-dimensional world can be located at $θ=0 $ and/or $θ= π$, its background metric being $ε^2 η_{μν}$. As a result, we have the 4-dimensional Newton constant, which is given by $G_N \simeq G_6 ε^{10}$ and the fifth force coefficients appeared here are $α_i\simeq ε^{2(i-4)}$, $i=1, 2, 3$. Here $G_6$ is the gravitational constant in 6-dimensional spacetime. If we take $ε= 10^{-3.8}$ against $G_6\sim 1($GeV$)^{-2}$, we get $G_N\sim 10^{-38}($Gev$)^{-2}$, the present time gravitational constant.

hep-th↗
arXiv2015

New Mixing Angles in the Left-Right Symmetric Model

In the left-right symmetric model neutral gauge fields are characterized by three mixing angles $θ_{12}, θ_{23}, θ_{13}$ between three gauge fields $B_μ, W^3_{Lμ}, W^3_{Rμ}$, which produce mass eigenstates $A_{μ}, Z_{μ}, Z'_{μ}$, when $G = SU(2)_L\times SU(2)_R\times U(1)_{B-L} \times D$ is spontaneously broken down until $U(1)_{em}$. We find a new mixing angle $θ'$, which corresponds to the Weinberg angle $θ_{W}$ in the standard model with the $SU(2)_{L}\times U(1)_{Y}$ gauge symmetry, from these mixing angles. It is then shown that any mixing angle $θ_{ij}$ can be expressed by $\varepsilon $ and $θ'$, where $\varepsilon = g_L/g_R$ is a ratio of running left-right gauge coupling strengths. We observe that light gauge bosons are described by $θ'$ only, whereas heavy gauge bosons are described by two parameters $\varepsilon$ and $θ'$.

hep-ph↗
arXiv2015

Fermion masses on a warped 6D world with the extra 2D sphere

In a warped 6-dimensional world with an extra 2-dimensional surface of a sphere, we find a 4-dimensional fermion mass formula with a zero mode. The warp factor is given by $ϕ(θ,φ)=\sin{θ}\cos{φ}$, which is a solution to the 6-dimensional Einstein equation with the bulk cosmological constant $Λ$ and the energy-momentum tensor of the bulk matter fields.

hep-th↗
arXiv2015

A Solvable Model for Fermion Masses on a Warped 6D World with the Extra 2D Sphere

In a warped 6D world with an extra 2-dimensional sphere, we propose an exactly solvable model for fermion masses with zero mode. The warp factor is given by $ϕ(θ,φ)=\sin{θ}\cos{φ}$, which is a solution to the 6D Einstein equation with the bulk cosmological constant $Λ$ and the energy-momentum tensor of the bulk matter fields. Our model provides another possibility of obtaining fermion zero mode, rather than traditional model based on Dirac's monopole.

hep-th↗
arXiv2012

A Confinement Potential for Leptons and Their Tunneling Effects into Extra Dimensions

Considering the five-dimensional warped spacetime AdS_5 with the D3-brane, we derive a potential in the fifth dimension, according to which ordinary particles are initially confined on the D3-brane. It is estimated, however, that the lightest neutrino with mass m_1 is tunneling away into the extra dimension. Hence there is a possibility that no neutrinos with mass m_1 exist in cosmicbackground neutrinos, but surviving neutrinos are those with heavier masses m_2 and m_3. The other possibilities are also discussed.

hep-ph↗
arXiv2010

Closed Superstrings in a Constant Magnetic Field and Regularization Criterion

We propose a new type of interaction of closed superstrings with the electromagnetic field, other than the usual Kaluza-Klein type or a gauge field with internal gauge group origin. This model with a constant magnetic field is also shown to have an exact solution. We consider a regularization criterion. Some models will be excluded according to this criterion. The spectrum-generating algebra is also constructed in our interacting model.

hep-th↗
arXiv2009

Heterotic String in a Constant Magnetic Field

When a charged heterotic string is placed in a constant magnetic field B, we show that this system can be solved exactly by using the cyclotron frequency. We then calculate anomalies of the super Virasoro algebra, and give the corresponding spectrum-generating algebra for this system. They differ from the free case by the cyclotron frequency. It is remarkable that our system is equivalent to the completely free system when B takes integral values.

hep-th↗
arXiv2008

Spectrum-Generating Algebra for Charged Superstrings in Background Gauge Fields

The spectrum-generating algebra (SGA) for charged superstrings placed in constant background magnetic fields is constructed. Contrary to the neutral string this algebra is characteristic of including the cyclotron frequency. The Regge intercept and superconformal anomalies are calculated to be shifted by the cyclotron frequency and D-brane parameters from the conventional values.

hep-th↗
arXiv2006

Spectrum-Generating Algebra for Charged Strings

When an open string ends with charges on a D2-brane, which involves constant background magnetic field perpendicular to the brane, we construct the spectrum-generating algebra for this charged string, which assures that our system is ghost-free under some conditions. The application to the Hall effect for charged strings is also shortly remarked.

hep-th↗
arXiv2006

Charged Strings and Spectrum-Generating Algebra

We consider a system that both ends of a charged open string are attached on the D$p$-brane with constant electromagnetic fields. Contrary to neutral strings, the quantization of charged strings has not been so far considered well. For this system we construct the spectrum-generating algebra (SGA), which involves the cyclotron frequency. When the cyclotron frequency is set to be zero, the SGA is reduced to the ordinary SGA for neutral strings. The new SGA for charged strings guarantees that this system is ghost-free if certain conditions are satisfied. We also consider its application to the Hall effect for charged strings.

hep-th↗
arXiv2006

Hall Conductivity for Charged Strings and Modified Spectrum-Generating Algebra

When open strings end with a charge q on a D2-brane, which involves constant background magnetic field B perpendicular to the brane, we calculate the Hall conductivity for these charged strings. We also construct the corresponding spectrum-generating algebra, which assures that our system is ghost-free under some conditions.

hep-th↗
arXiv2004

Noncommutative Quantum Mechanics and Seiberg-Witten Map

In order to overcome ambiguity problem on identification of mathematical objects in noncommutative theory with physical observables, quantum mechanical system coupled to the NC U(1) gauge field in the noncommutative space is reformulated by making use of the unitarized Seiberg-Witten map, and applied to the Aharonov-Bohm and Hall effects of the NC U(1) gauge field. Retaining terms only up to linear order in the NC parameter θ, we find that the AB topological phase and the Hall conductivity have both the same formulas as those of the ordinary commutative space with no θ-dependence.

hep-th↗
arXiv2003

Hall effect in Noncommutative spaces

In order to investigate whether space coordinates are intrinsically noncommutative, we make use of the Hall effect on the two-dimensional plane. We calculate the Hall conductivity in such a way that the noncommutative U(1) gauge invariance is manifest. We find that the noncommutativity parameter theta does not appear in the Hall conductivity itself, but the particle number density of electron depends on theta. We point out that the peak of particle number density differs from that of the charge density.

hep-th↗
arXiv2002

Hall Effect on Noncommutative Phase Space

When phase space coordinates are noncommutative, especially including arbitrarily noncommutative momenta, the Hall effect is reinvestigated. A minimally gauge-invariant coupling of electromagnetic field is introduced by making use of Faddeev-Jackiw formulation for unconstrained and constrained systems. We find that the parameter of noncommutative momenta makes an important contribution to the Hall conductivity.

hep-th↗
arXiv2002

Noncommutative Hall Effect

When coordinates are noncommutative, the Hall effect is reinvestigated. The Hall conductivity is expressed with noncommutative parameters, so that in the commutative limit it tends to the conventional result.

hep-th↗
arXiv2002

Wigner's Formulation of Noncommutative Quantum Mechanics

When we have noncommutativity among coordinates (or conjugate momenta), we consider Wigner's formulation of quantum mechanics, including a new derivation of path integral formula. We also propose the Moyal star product based on the Dirac bracket in constrained systems.

hep-th↗