arXiv subjects

Akio Sugamoto

Publications and source records attributed to Akio Sugamoto.

At least 55 records · Page 3Linked to original sources

arXiv2004

'TeV Gamma-ray Crisis' and an Anisotropic Space Model

To solve the `TeV gamma crisis', we examine a model whose one spatial direction is discretized at a high energy scale. Assuming the standard extra-galactic IR photon distribution, we evaluate the mean free-path of a energetic photon which acquires an effective mass in the model. For a wide range of the value of the lattice energy scale between a few TeV and around $10^{10}$ GeV, the mean free-path of a TeV energy photon can be enlarged enough to solve the `crisis'. Taking into account the effects of the universe expansion, we find bounds of the lattice constant.

astro-ph↗

arXiv2004

Accelerating cosmology in modified gravity with scalar field

The modified gravity with 1/R term (R being scalar curvature) and the Einstein-Hilbert term is studied by incorporating the phantom scalar field. A number of cosmological solutions are derived in the presence of the phantom field in the perfect fluid background. It is shown the current inflation obtained in the modified gravity is affected by the existence the phantom field.

gr-qc↗

arXiv2004

Freedom in electroweak symmetry breaking and mass matrix of fermions in dimensional deconstruction model

There exists a freedom in a class of four-dimensional electroweak theories proposed by Arkani-Hamed et al. relying on deconstruction and Coleman-Weinberg mechanism. The freedom comes from the winding modes of the link variable (Wilson operator) connecting non-nearest neighbours in the discrete fifth dimension. Using this freedom, dynamical breaking of SU(2) gauge symmetry, mass hierarchy patterns of fermions and Cabbibo-Kobayashi-Maskawa matrix may be obtained.

hep-th↗

arXiv2003

Exciton in Matrix Formulation of Quantum Hall Effect

The quantum Hall effect is studied by introducing two different matrix variables for electrons and holes, having Chern-Simons type interactions. By generalizing the constraint condition proposed by Susskind to realize the Pauli's exclusion principle in this two component matrix model, the classical exciton solution having excitation of both quasi-electron and quasi-hole is obtained. The constraint condition is also solved quantum mechanically in the infinite-sized matrix case, giving the examples of the physical states. Using these quantum states, the corrections of the exciton energy, coming from the noncommutativity of space (Pauli principle) and from the quantum effects of the background state, are estimated in the lowest order perturbation expansion. As a result, the dispersion relation of exciton is obtained.

hep-th↗

arXiv2002

CERN LEP2 constraint on 4D QED having dynamically generated spatial dimension

We study 4D QED in which one spatial dimension is dynamically generated from 3D action, following the mechanism proposed by Arkani-Hamed, Cohen and Georgi. In this model, the generated fourth dimension is discretized by an interval parameter $a$. We examine the phenomenological constraint on the parameter $a$ coming from the collider experiments on the QED process $e^+ e^- \to γγ$. It is found that the LEP2 experiments give the constraint of $1/a \simgt 461\gev$. Expected bound on the same parameter $a$ at the future $e^+ e^-$ linear collider is briefly discussed.

hep-ph↗

arXiv2002

Stabilization and radion in de Sitter brane-world

We consider the stabilization of de Sitter brane-world. The scalar field bulk-brane theory produces the non-trivial minimum of modulus potential where temporal radion is realized. The hierarchy problem (between Planck and electroweak scales) may be solved. However, the interpretation of radion is not so clear as in AdS brane-world. In particulary, the introduction of two times physics or pair-creation of bulk spaces or identification of one of spatial coordinates with imaginary time (non-zero temperature) may be required.

hep-th↗

arXiv2001

Mixing Matrix of Quarks Having Natural Twisting in E_6 Grand Unified Model

Mass matrix of quarks is studied in the Supersymmetric $E_6$ Grand Unified Theory (GUT). The fundamental representation $\textbf{27}$ in $E_6$ which corresponds to one generation contains two sets of $\textbf{5}^{*}$'s in SU(5), so that there are six flavors of lepton doublets and right-handed down-quark triplets. It is known that the twisting (interchange) among the $\textbf{5}^{*}$ representations may reproduce the observed quark and lepton mixing matrices. If $E_6$ is directly broken down to $SU(3)_C \times SU(2)_L \times U(1)_Y$ and two extra U(1)'s, the extra 3 sets of down-type quarks do not necessarily decouple from the quark mass matrix, under the appropriate choice of the U(1) flavor charges on the quark and Higgs fields. Then, by diagonalizing the 6 $\times$ 6 down-quark mass matrix, we find a certain set of parameters, in which the twisting between a pair of the right-handed down-quarks occurs naturally, reproducing the reasonable values for the $d$-, $s$- and $b$-quark masses, and for $V_{ud}$, $V_{us}$, $V_{cd}$, $V_{cs}$ and $V_{tb}$ of the CKM matrix elements. As a by-product, one vector-like down-quark appears at the experimentally accessible TeV scale.

hep-ph↗

arXiv2001

4d Gauge Theory and Gravity Generated from 3d Ones at High Energy

Dynamical generation of 4d gauge theories and gravity at low energy from the 3d ones at high energy is studied, based on the fermion condensation mechanism recently proposed by Arkani-Hamed, Cohen and Georgi. For gravity, 4d Einstein gravity is generated from the multiple copy of the 3d ones, by referring to the two form gravity. Since the 3d Einstein action without matter coupling is topological, ultraviolet divergences are less singular in our model. In the gauge model, matter fermions are introduced on the discrete lattice following Wilson. Then, the 4d gauge interactions are correctly generated from the 3d theories even in the left-right asymmetric theories of the standard model. In order for this to occur, the Higgs fields as well as the gauge fields of the extra dimension should be generated by the fermion condensates. Therefore, the generation of the 4d standard model from the multiple copy of the 3d ones is quite promising. To solve the doubling problem in the weak interaction sector, two kinds of discrete lattices have to be introduced separately for L- and R-handed sectors, and the two types of Higgs fields should be generated.

hep-th↗

arXiv2001

Old Fashioned Duality for D-brane and String

Old fashioned duality used to derive the closed string field theory for magnetic vortex from the gauge theory with Higgs scalar, is applied to the string theories. The bosonic sring theory coupled to the Kalb-Ramond 2-form field is dually transformed to the 6-brane theory coupled to the 7-form field. The old fashioned dual transformation is also examined for the Type IIA and IIB superstrings. For this study, the string field theoretical treatment of the bosonic and fermionic strings is developped based on the reparametrization invariant formulation of strings by Marshall and Ramond. In order for the self-duality of the Type IIB superstring to appear, the following dual correspondence may happen: the dual transformation of the NS-NS field functional is the bosonization of the R-R one.

hep-th↗

arXiv2001

Inclusive dileptonic rare B decays with an extra generation of vector-like quarks

We investigate the leading effects of extending the Standard Model of electroweak interactions by an extra iso-singlet up- and down- type quark pair on various distributions and total branching ratio of the inclusive B-> X_s l^+ l^- (l =e,μ) rare B decays. The presence of the extra vector-like down quark $D$ results in the non-unitarity of the extended quark mixing matrix V, which in turn leads to b-> s FCNC at the tree level proportional to (V^\dagger V)_{sb}. On the other hand, the effective penguin and box vertex functions are sensitive to the mass of the extra iso-singlet up quark m_U. The experimental upper bound on BR(B-> X_s μ^+ μ^-) is used to constrain the parameters of the model. It is shown that the shapes of the differential branching ratio and forward-backward asymmetry distribution are very sensitive to the value of the model parameters. We also calculate the CP aymmetry distribution of the dileptonic decay in the vector-like quark model. It is shown that, for a typical choice of the model parameters, asymmetries up to around 10% can be achieved for certain values of the dilepton invariant mass.

hep-ph↗

arXiv2000

$B\to ππ, K π$ Decays in QCD Improved Factorization Approach

Motivated by recent measurements, we investigate $B\to ππ, K π$ decay modes in the framework of QCD improved factorization, which was recently proposed by Beneke $et al$. We find that all the measured branching ratios are well accommodated in the reasonable parameter space except for $B\to K^0 π^0 $. We also discuss in detail the strong penguin contributions and the ${\cal O}(α_s)$ corrections to the chirally enhanced terms. We find that the weak phase $γ$ lies in the region $120^{\circ}<γ<240^{\circ}$, which is mainly constrained by $B\to π^- π^+ $.

hep-ph↗

arXiv2000

Contributions of vector-like quarks to radiative B meson decay

We study the decay B\to X_sγin a minimal extension of the standard model with extra up- and down-type quarks whose left- and right-handed components are both SU(2) singlets. Constraints on the extended Cabibbo-Kobayashi-Maskawa matrix are obtained from the experimental results for the branching ratio. Even if the extra quarks are too heavy to be detected in near-future colliders, the branching ratio could have a value which is non-trivially different from the prediction of the standard model.

hep-ph↗

arXiv2000

Production of CP-even and CP-odd Higgs bosons at Muon colliders

In the $s$-channel Higgs-boson-exchange processes, the interference between the amplitudes for CP-even and CP-odd Higgs bosons is sizable, if the helicities of initial and final particles are properly fixed and if the mass difference between these bosons is not much larger than their decay widths. We discuss this interference effect in the process $μ^+ μ^-$ $\to t\bar{t}$. Examining the effects gives us information on CP-parity for Higgs bosons and on the sign of a product of the coupling constants for $Hμ^-μ^+$, $Ht\bar{t}$, $Aμ^-μ^+$ and $At\bar{t}$ vertices. The feasibility of observing the interference effect in future muon colliders is evaluated in the framework of the minimal supersymmetric extension of the standard model as an example.

hep-ph↗

arXiv2000

Production of Scalar Higgs and Pseudoscalar Higgs in Multi-Higgs Doublet Models at $γγ$ Colliders

We present the effects of heavy CP-even (H) and CP-odd (A) Higgs bosons on the production cross section of the process $γγ$ $\to t\bar{t}$ at the energy around the mass poles of the Higgs bosons. It is found that the interference between H and A with the small mass gap, as well as the ones between Higgs bosons and the continuum, contributes to the cross section, if the photon beams are polarized and if we observe the helicity of the top quarks. It is demonstrated in the framework of the minimal supersymmetric extension of the standard model that the H and A contributions can be sizable at future $γγ$ colliders for small value of $\tanβ$. The methods to measure the CP-parity of the Higgs boson are also presented. The statistical significances of detecting the Higgs signals and measuring the Higgs CP-parity are evaluated.

hep-ph↗

arXiv1999

Genetic Algorithm for Lattice Gauge Theory. on SU(2) and U(1) on 4 dimensional lattice, how to hitchhike to thermal equilibrium state

Applying Genetic Algorithm for the Lattice Gauge Theory is formed to be an effective method to minimize the action of gauge field on a lattice. In 4 dimensions, the critical point and the Wilson loop behaviour of SU(2) lattice gauge theory as well as the phase transition of U(1) theory have been studied. The proper coding methodi has been developed in order to avoid the increase of necessary memory and the overload of calculation for Genetic Algorithm. How hichhikers toward equlibrium appear against kidnappers is clarified.

hep-lat↗

arXiv1999

The annihilation decay B_c \to eta' l ν

We first investigate the semileptonic annihilation decay B_c \to η' lνin QCD. We find that the $η'$ momentum distribution is peaked within its small recoil region due to the loop effects. The branching ratio is estimated to be $ Br(B_c \to η' lν)=1.6\times 10^{-4}$ for $l=μ,e$, which is accessible at CERN LHC.

hep-ph↗

arXiv1999

A Rule of Thumb Derivation of Born-Infeld Action for D-branes

A rule of thumb derivation of the Dirac-Born-Infeld action for D-branes is studied à la Fradkin and Tseytlin, by simply integrating out of the superstring coordinates in a narrow strip attached to the D-branes. In case of superstrings, the coupling of Ramond-Ramond fields as well as the Dirac-Born-Infeld type coupling of the Neveu Schwarz-Neveu Schwarz fields come out in this way.

hep-th↗

arXiv1999

CP-odd WWZ couplings induced by vector-like quarks

A minimal extension of the standard model includes extra quarks with charges 2/3 and/or -1/3, whose left-handed and right-handed components are both SU(2) singlets. This model predicts new interactions of flavor-changing neutral current at the tree level, which also violate CP invariance. We study CP-odd anomalous couplings for the gauge bosons W, W, and Z induced by the new interactions at the one-loop level. These couplings become nonnegligible only if both an up-type and a down-type extra quarks are incorporated. Their form factors are estimated to be maximally of order $10^{-5}$. Such magnitudes are larger than those predicted in the standard model, though smaller than those in certain other models.

hep-ph↗