arXiv subjects

Shohei Takada

Publications and source records attributed to Shohei Takada.

11 recordsLinked to original sources

arXiv2025

Generation structures and Yukawa couplings in magnetized $T^{2g}/\mathbb{Z}_N$ models

We study fermion zero-mode wave functions with various chiralities in magnetized $T^{2g}$, $(g=2,3)$ torus. First, we consider the wave functions satisfying the Dirac equation and the boundary conditions on the magnetized torus. Second, we introduce the $SO(3)$ (or parity) transformations and derive the wave functions under the modular transformation. Additionally, we calculate the Yukawa couplings with consideration for the chirality. Lastly, we briefly review how to construct $T^{4}/\mathbb{Z}_N$ ($N=2,3,4,6$) and $T^6/\mathbb{Z}_{12}$ twisted orbifold. Also, we explicitly analyze the number of the wave functions in $\mathbb{Z}_N$ sectors.

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arXiv2025

Modular symmetry of localized modes

We study the modular symmetry of localized modes on fixed points of $T^2/\mathbb{Z}_2$ orbifold. First, we find that the localized modes with even (odd) modular weight generally have $Δ(6n^2)$ ($Δ'(6n^2)$) modular flavor symmetry. Moreover, when we consider an additional Ansatz, the localized modes with even (odd) modular weight generally enjoy $S_3$ ($S'_4$) modular flavor symmetry, and we show the concrete wave functions of the localized modes.

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arXiv2024

Flavor symmetries from modular subgroups in magnetized compactifications

We study the flavor structures of zero-modes, which are originated from the modular symmetry on $T^2_1\times T^2_2$ and its orbifold with magnetic fluxes. We introduce the constraint on the moduli parameters by $τ_2=Nτ_1$, where $τ_i$ denotes the complex structure moduli on $T^2_i$. Such a constraint can be derived from the moduli stabilization. The modular symmetry of $T^2_1 \times T^2_2$ is $SL(2,\mathbb{Z})_{τ_1} \times SL(2,\mathbb{Z})_{τ_2} \subset Sp(4,\mathbb{Z})$ and it is broken to $Γ_0(N) \times Γ^0(N)$ by the moduli constraint. The wave functions represent their covering groups. We obtain various flavor groups in these models.

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arXiv2023

$Sp(6,Z)$ modular symmetry in flavor structures: quark flavor models and Siegel modular forms for $\widetildeΔ(96)$

We study an approach to construct Siegel modular forms from $Sp(6,Z)$. Zero-mode wave functions on $T^6$ with magnetic flux background behave Siegel modular forms at the origin. Then $T$-symmetries partially break depending on the form of background magnetic flux. We study the background such that three $T$-symmetries $T_I$, $T_{II}$ and $T_{III}$ as well as the $S$-symmetry remain.Consequently, we obtain Siegel modular forms with three moduli parameters $(ω_1,ω_2,ω_3)$, which are multiplets of finite modular groups. We show several examples. As one of examples, we study Siegel modular forms for $\widetildeΔ(96)$ in detail. Then, as a phenomenological applicantion, we study quark flavor models using Siegel modular forms for $\widetildeΔ(96)$. Around the cusp, $ω_1=i\infty$, the Siegel modular forms have hierarchical values depending on their $T_I$-charges. We show the deviation of $ω_1$ from the cusp can generate large quark mass hierarchies without fine-tuning. Furthermore CP violation is induced by deviation of $ω_2$ from imaginary axis.

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arXiv2023

Modular symmetry in magnetized $T^{2g}$ torus and orbifold models

We study the modular symmetry in magnetized $T^{2g}$ torus and orbifold models. The $T^{2g}$ torus has the modular symmetry $Γ_{g}=Sp(2g,\mathbb{Z})$. Magnetic flux background breaks the modular symmetry to a certain normalizer $N_{g}(H)$. We classify remaining modular symmetries by magnetic flux matrix types. Furthermore, we study the modular symmetry for wave functions on the magnetized $T^{2g}$ and certain orbifolds. It is found that wave functions on magnetized $T^{2g}$ as well as its orbifolds behave as the Siegel modular forms of weight $1/2$ and $\widetilde{N}_{g}(H,h)$, which is the metapletic congruence subgroup of the double covering group of $N_{g}(H)$, $\widetilde{N}_{g}(H)$. Then, wave functions transform non-trivially under the quotient group, $\widetilde{N}_{g,h}=\widetilde{N}_{g}(H)/\widetilde{N}_{g}(H,h)$, where the level $h$ is related to the determinant of the magnetic flux matrix. Accordingly, the corresponding four-dimensional (4D) chiral fields also transform non-trivially under $\widetilde{N}_{g,h}$ modular flavor transformation with modular weight $-1/2$. We also study concrete modular flavor symmetries of wave functions on magnetized $T^{2g}$ orbifolds.

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arXiv2023

Quark mass hierarchies and CP violation in $A_4\times A_4\times A_4$ modular symmetric flavor models

We study $A_4 \times A_4 \times A_4$ modular symmetric flavor models to realize quark mass hierarchies and mixing angles without fine-tuning. Mass matrices are written in terms of modular forms. At modular fixed points $τ= i\infty$ and $ω$, $A_4$ is broken to $Z_3$ residual symmetry. When the modulus $τ$ is deviated from the fixed points, modular forms show hierarchies depending on their residual charges. Thus, we obtain hierarchical structures in mass matrices. Since we begin with $A_4\times A_4 \times A_4$, the residual symmetry is $Z_3 \times Z_3 \times Z_3$ which can generate sufficient hierarchies to realize quark mass ratios and absolute values of the CKM matrix $|V_{\textrm{CKM}}|$ without fine-tuning. Furthermore, CP violation is studied. We present necessary conditions for CP violation caused by the value of $τ$. We also show possibilities to realize observed values of the Jarlskog invariant $J_{\textrm{CP}}$, quark mass ratios and CKM matrix $|V_{\textrm{CKM}}|$ simultaneously, if $\mathcal{O}(10)$ adjustments in coefficients of Yukawa couplings are allowed.

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arXiv2023

Number of zero-modes on magnetized $T^4/Z_N$ orbifolds analyzed by modular transformation

We study fermion zero-mode wavefunctions on $T^4/Z_N$ orbifold with background magnetic fluxes. The number of zero-modes is analyzed by use of $Sp(4,\mathbb{Z})$ modular transformation. Conditions needed to realize three generation models are clarified. We also study parity transformation in the compact space which leads to better understanding of relationship between positive and negative chirality wavefunctions.

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arXiv2023

Zero-modes in magnetized $T^6/\mathbb{Z}_N$ orbifold models through $Sp(6,\mathbb{Z})$ modular symmetry

We study of fermion zero-modes on magnetized $T^6/\mathbb{Z}_N$ orbifolds. In particular, we focus on non-factorizable orbifolds, i.e. $T^6/\mathbb{Z}_7$ and $T^6/\mathbb{Z}_{12}$ corresponding to $SU(7)$ and $E_6$ Lie lattices respectively. The number of degenerated zero-modes corresponds to the generation number of low energy effective theory in four dimensional space-time. We find that three-generation models preserving 4D $\mathcal{N}=1$ supersymmetry can be realized by magnetized $T^6/\mathbb{Z}_{12}$, but not by $T^6/\mathbb{Z}_7$. We use $Sp(6,\mathbb{Z})$ modular transformation for the analyses.

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arXiv2023

Remark on modular weights in low-energy effective field theory from type II string theory

We revisit the modular weights in type IIB magnetized D-brane models. The simple analysis of wave function shows that the four-dimensional matter fields have the modular weight -1/2, but it may shift as one in type IIA intersecting D-brane models. For example, the localized gauge flux as well as the localized curvature can shift the modular weight in the magnetized D-brane models. Such corrections do not affect physical couplings such as physical Yukawa couplings. However, it leads to differences in supersymmetry breaking sfermion masses, which depend on the modular weights, although the $A$-term coefficients and the sum of sfermion masses squared seem to be the same between two models.

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arXiv2023

Quark hierarchical structures in modular symmetric flavor models at level 6

We study modular symmetric quark flavor models without fine-tuning. Mass matrices are written in terms of modular forms, and modular forms in the vicinity of the modular fixed points become hierarchical depending on their residual charges. Thus modular symmetric flavor models in the vicinity of the modular fixed points have a possibility to describe mass hierarchies without fine-tuning. Since describing quark hierarchies without fine-tuning requires $Z_n$ residual symmetry with $n\geq 6$, we focus on $Γ_6$ modular symmetry in the vicinity of the cusp $τ=i\infty$ where $Z_6$ residual symmetry remains. We use only modular forms belonging to singlet representations of $Γ_6$ to make our analysis simple. Consequently, viable quark flavor models are obtained without fine-tuning.

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arXiv2022

Modular symmetry of soft supersymmetry breaking terms

We study the modular symmetry of soft supersymmetry breaking terms. Soft scalar masses and $A$-term coefficients are invariant under the modular symmetry when we regard $F$-term as a spurion with the modular weight $-2$. Their flavor structure is determined by the same symmetry as Yukawa couplings, i.e., fermion masses. The modular symmetric behavior of $μ$-term and $B$-term depends on how the $μ$-term is generated.

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