arXiv subjects

Hajime Otsuka

Publications and source records attributed to Hajime Otsuka.

At least 73 records · Page 4Linked to original sources

arXiv2023

Generalized Matter Parities from Finite Modular Symmetries

We classify a supersymmetric extension of the Standard Model by discrete symmetries originating from finite modular symmetries $Γ_N$. Since all the couplings in supersymmetric theories of finite modular symmetries $Γ_N$ are described by holomorphic modular forms with even modular weights, renormalizable and non-renormalizable operators such as baryon- and/or lepton-number violating operators are severely constrained. From the modular transformation of matter multiplets with modular weight $1/M$, we find $\mathbb{Z}_{2M}$ symmetries, including the generalized baryon and lepton parities, $R$-parity, $\mathbb{Z}_3$ baryon triality and $\mathbb{Z}_6$ proton hexality. Such $\mathbb{Z}_{2M}$ symmetries are enlarged to $\mathbb{Z}_{2M} \rtimes \mathbb{Z}_2^{\text{CP}}$ symmetries together with the CP transformation.

hep-ph↗

arXiv2022

Full higher-dimensional analysis of moduli oscillation and radiation in expanding universe

We investigate effects of the radiation and the moduli oscillation around the stabilized values on the evolution of a 6-dimensional spacetime compactified on $S^2$. In order to see the transition from the 5-dimensional space to the 3-dimensional one, we develop a procedure to pursue the spacetime evolution with appropriate approximations, which is valid until the spacetime behaves like 4-dimensional. In the case that the moduli stabilization process cannot be described in the context of the 4-dimensional effective theory, it takes quite a long time for the moduli oscillation to dominate the total energy density, in contrast to the conventional result obtained by the 4-dimensional effective theory approach. We also found that even if the moduli are set at the stabilized values, they start to oscillate due to the pressure in the extra space $S^2$ in some cases.

hep-th↗

arXiv2022

Phenomenological implications on a hidden sector from the Festina Lente bound

We apply the Festina Lente (FL) bound on a hidden sector with $U(1)$ gauge symmetries. Since the FL bound puts a lower bound on masses of particles charged under the $U(1)$ gauge symmetries, it is possible to constrain the hidden sector even with a tiny coupling to the Standard Model. In particular, we focus on the phenomenological implications of the FL bound on milli-charged particles, which naturally arise when kinetic mixing between the photon and the hidden photon is allowed. It turns out that the milli-charged particle with the mass $M\lesssim 5$ meV is prohibited by the FL bound in the case of a single hidden $U(1)$, independent of the value of kinetic mixing. This bound is crucial when bosonic dark matter is taken in consideration in this framework: the fuzzy bosonic dark matter models requesting minuscule masses are ruled out by the FL bound if the longevity of dark matter is protected by the hidden gauge symmetry.

hep-ph↗

arXiv2022

Pseudo-Nambu-Goldstone Dark Matter from Non-Abelian Gauge Symmetry

We propose a pseudo-Nambu-Goldstone boson (pNGB) dark matter (DM) model based on an additional non-Abelian gauge symmetry $SU(2)_D$. The gauge symmetry $SU(2)_D$ is spontaneously broken to a global custodial symmetry $U(1)_V$ via the nonvanishing vacuum expectation values of $SU(2)_D$ doublet and triplet scalar fields. Due to the exact global symmetry $U(1)_V$, the lightest $U(1)_V$ charged particle becomes stable. We assume that the lightest charged particle in the model is the charged complex pNGB, which we regard as DM. It avoids the strong constraints from current DM direct detection experiments due to the property of NGB. We find that the measured energy density of DM can be reproduced when the DM mass is larger than the half of the Higgs mass, where the lower limit generally comes from the constraint of DM invisible decay and the upper limit from DM direct detection experiments depends on the model parameters.

hep-ph↗

arXiv2022

Zero-mode wave functions by localized gauge fluxes

We study chiral zero-mode wave functions on blow-up manifolds of $T^2/Z_N$ orbifolds with both bulk and localized magnetic flux backgrounds. We introduce a singular gauge transformation in order to remove $Z_N$ phases for $Z_N$ twisted boundary condition of matter fields. We compute wave functions of not only bulk zero modes but also localized modes at the orbifold singular points, which correspond to new zero modes induced by localized flux. By studying their Yukawa couplings, it turns out that only three patterns of Yukawa couplings are allowed. Our theory has a specific coupling selection rule.

hep-th↗

arXiv2022

Index theorem on magnetized blow-up manifold of $T^2/\mathbb{Z}_N$

We investigate blow-up manifolds of $T^2/{\mathbb{Z}}_N\,(N=2,3,4,6)$ orbifolds with magnetic flux $M$. Since the blow-up manifolds have no singularities, we can apply the Atiyah-Singer index theorem to them. Then, we establish the zero-mode counting formula $n_{+}-n_{-}=(M-V_{+})/N+1$, where $V_{+}$ denotes the sum of winding numbers at fixed points on the $T^2/{\mathbb{Z}}_N$ orbifolds, as the Atiyah-Singer index theorem on the orbifolds, and clarify physical and geometrical meanings of the formula.

hep-th↗

arXiv2022

Spacetime evolution during moduli stabilization in radiation dominated era beyond 4D effective theory

We investigate the time evolution of the background spacetime during the moduli stabilization process, which is assumed to occur in the radiation dominated era. The setup is basically the Salam-Sezgin model, but we add a potential term for the dilaton in order to stabilize the moduli completely. We numerically solve the higher-dimensional background field equations, including a case that the stabilization process cannot be described within the 4D effective theory. In contrast to the conventional 4D effective theory analysis, we find that when the mass scale of the stabilization is larger than the compactification scale, the radiation contribution to the total energy density remains to be non-negligible for a much longer time than the stabilization time scale. As a result, the non-compact 3D space expands slower than the matter dominated universe. We also find the equation of state for the radiation $w_{\rm rad}$ remains to be smaller than 1/3 for a long time, which indicates that the radiation still feels the extra dimensions for a while even after the moduli are stabilized.

hep-th↗

arXiv2022

Residual flavor symmetry breaking in the landscape of modular flavor models

We study a symmetry breaking of residual flavor symmetries realized at fixed points of the moduli space. In the supersymmetric modular invariant theories, a small departure of the modulus from fixed points is required to realize fermion mass hierarchies and sizable CP-breaking effects. We investigate whether one can dynamically fix the moduli values in the vicinity of the fixed points in the context of Type IIB string theory. It is found that the string landscape prefers $|δτ| \simeq 10^{-5}$ for the deviation of the complex structure modulus from all fixed points and the CP-breaking vacuum is statistically favored. To illustrate phenomenological implications of distributions of moduli values around fixed points, we analyze the lepton sector on a concrete $A_4$ modular flavor model.

hep-ph↗

arXiv2022

4D modular flavor symmetric models inspired by higher dimensional theory

We study a scenario to derive four-dimensional modular flavor symmetric models from higher dimensional theory by assuming the compactification consistent with the modular symmetry. In our scenario, wavefunctions in extra dimensional compact space are modular forms. That leads to constraints on combinations between modular weights and $Γ_N$ ($Γ_N')$ representations of matter fields. We also present illustrating examples.

hep-ph↗

arXiv2022

Lepton flavor violation, lepton $(g-2)_{μ,\,e}$ and electron EDM in the modular symmetry

We study the lepton flavor violation (LFV), the leptonic magnetic moments $(g-2)_{μ,\,e} $ and the electric dipole moment (EDM) of the electron in the Standard-Model Effective Field Theory with the $Γ_N$ modular flavor symmetry. We employ the stringy Ansatz on coupling structure that 4-point couplings of matter fields are written by a product of 3-point couplings of matter fields. We take the level 3 finite modular group, $Γ_3$ for the flavor symmetry, and discuss the dipole operators at nearby fixed point $τ=i$, where observed lepton masses and mixing angles are well reproduced. Suppose the anomaly of the anomalous magnetic moment of the muon to be evidence of the new physics (NP), we have related it with $(g-2)_{e}$, LFV decays, and the electron EDM. It is found that the NP contribution to $(g-2)_{e}$ is proportional to the lepton masses squared likewise the naive scaling. We also discuss the correlations among the LFV processes $μ\to eγ$, $τ\to μγ$ and $τ\to eγ$, which are testable in the future. The electron EDM requires the tiny imaginary part of the relevant Wilson coefficient in the basis of real positive charged lepton masses, which is related to the $μ\to eγ$ transition in our framework.

hep-ph↗

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.

hep-ph↗

arXiv2022

Radiative neutrino masses from modular $A_4$ symmetry and supersymmetry breaking

We investigate a modular $A_4$ invariant two-loop neutrino mass model in a supersymmetric framework, where we introduce new fields as minimum as possible, expecting contributions of superpartners to the neutrino masses. We successfully reproduce the neutrino oscillation data thanks to the superpartner contributions in case of normal hierarchy, and predict several observables such as phases and neutrino masses, concentrating on three specific regions at nearby fixed points of modulus $τ=i,ω,i\times \infty$, where $ω\equiv e^{2πi/3}$. These points are statistically favored in flux compactifications of the string theory. We show several results in each the points by performing global $χ^2$ analysis, and demonstrate benchmark points with the minimum $χ^2$.

hep-ph↗

arXiv2022

On Stringy Origin of Minimal Flavor Violation

We study the minimal flavor violation in the context of string effective field theory. Stringy selection rules indicate that $n$-point couplings among fermionic zero-modes and lightest scalar modes in the string effective action are given by a product of Yukawa couplings which are regarded as spurion fields of stringy and geometrical symmetries. Hence, Yukawa couplings determine the dynamics of flavor and CP violations. This observation strongly supports the hypothesis of minimal flavor violation in the Standard Model effective field theory.

hep-ph↗

arXiv2022

Symplectic modular symmetry in heterotic string vacua: flavor, CP, and $R$-symmetries

We examine a common origin of four-dimensional flavor, CP, and $U(1)_R$ symmetries in the context of heterotic string theory with standard embedding. We find that flavor and $U(1)_R$ symmetries are unified into the $Sp(2h+2, \mathbb{C})$ modular symmetries of Calabi-Yau threefolds with $h$ being the number of moduli fields. Together with the $\mathbb{Z}_2^{\rm CP}$ CP symmetry, they are enhanced to $GSp(2h+2, \mathbb{C})\simeq Sp(2h+2, \mathbb{C})\rtimes \mathbb{Z}_2^{\rm CP}$ generalized symplectic modular symmetry. We exemplify the $S_3, S_4, T^\prime, S_9$ non-Abelian flavor symmetries on explicit toroidal orbifolds with and without resolutions and $\mathbb{Z}_2,S_4$ flavor symmetries on three-parameter examples of Calabi-Yau threefolds. Thus, non-trivial flavor symmetries appear in not only the exact orbifold limit but also a certain class of Calabi-Yau threefolds. These flavor symmetries are further enlarged to non-Abelian discrete groups by the CP symmetry.

hep-th↗

arXiv2021

Sharpening the Boundaries Between Flux Landscape and Swampland by Tadpole Charge

We investigate the vacuum structure of four-dimensional effective theory arising from Type IIB flux compactifications on a mirror of the rigid Calabi-Yau threefold, corresponding to a T-dual of the DeWolfe-Giryavets-Kachru-Taylor model in Type IIA flux compactifications. By analyzing the vacuum structure of this interesting corner of string landscape, it turns out that there exist perturbatively unstable de Sitter (dS) vacua in addition to supersymmetric and non-supersymmetric anti-de Sitter vacua. On the other hand, the stable dS vacua appearing in the low-energy effective action violate the tadpole cancellation condition, indicating a strong correlation between the existence of dS vacua and the flux-induced D3-brane charge (tadpole charge). We also find analytically that the tadpole charge constrained by the tadpole cancellation condition emerges in the scalar potential in a nontrivial way. Thus, the tadpole charge would restrict the existence of stable dS vacua, and this fact underlies the statement of the dS conjecture. Furthermore, our analytical and numerical results exhibit that distributions of ${\cal O}(1)$ parameters in expressions of several swampland conjectures peak at specific values.

hep-th↗

arXiv2021

Modular symmetry in the SMEFT

We study the modular symmetric standard-model effective field theory. We employ the stringy Ansatz on coupling structure that 4-point couplings $y^{(4)}$ of matter fields are written by a product of 3-point couplings $y^{(3)}$ of matter fields, i.e., $y^{(4)} = y^{(3)}y^{(3)}$. In this framework, we discuss the flavor structure of bilinear fermion operators and 4-fermion operators, where the holomorphic and anti-holomorphic modular forms appear. From the Ansatz, the $A_4$ modular-invariant semileptonic four-fermion operator $[\,\bar E_R ΓE_R][\,\bar D_R ΓD_R\,]$ does not lead to the flavor changing (FC) processes since this operator would be constructed in terms of gauge couplings $g$ as $y^{(3)} \sim g$. The chirality flipped bilinear operator $[\,\bar D_R ΓD_L\,]$ also does not lead FC if the mediated mode corresponds to the Higgs boson $H_d$. In this case, the flavor structure of this operator is the exactly same as the mass matrix. On the other hand, if the flavor structure of the operator is not the exactly same as the mass matrix, the situation would change drastically. Then, we obtain the non-trivial relations of FC transitions at nearby fixed points $τ=i,\,ω\,, i\infty$, which are testable in the future. As an application, we discuss the relations of the lepton flavor violation processes $ μ\to eγ,\, τ\to μγ$ and $τ\to eγ$ at nearby $τ_e=i$, where the successful lepton mass matrix was obtained. We also study the flavor changing 4-quark operators in the $A_4$ modular symmetry of quarks. As a result, the minimal flavor violation could be realized by taking relevant specific parameter sets of order one.

hep-ph↗

arXiv2021

Spontaneous CP violation and symplectic modular symmetry in Calabi-Yau compactifications

We explore the geometrical origin of CP and the spontaneous CP violation in Calabi-Yau compactifications. We find that the CP symmetry is identified with an outer automorphism of the symplectic modular group in the large complex structure regime of Calabi-Yau threefolds, thereby enlarging the symplectic modular group to their semidirect product group. The spontaneous CP violation is realized by the introduction of fluxes, whose effective action is invariant under CP as well as the discrete $\mathbb{Z}_2$ symmetry or $\mathbb{Z}_4$ R-symmetry. We explicitly demonstrate the spontaneous CP violation on a specific Calabi-Yau threefold.

hep-th↗

arXiv2021

Hierarchical structure of physical Yukawa couplings from matter field Kähler metric

We study the impacts of matter field Kähler metric on physical Yukawa couplings in string compactifications. Since the Kähler metric is non-trivial in general, the kinetic mixing of matter fields opens a new avenue for realizing a hierarchical structure of physical Yukawa couplings, even when holomorphic Yukawa couplings have the trivial structure. The hierarchical Yukawa couplings are demonstrated by couplings of pure untwisted modes on toroidal orbifolds and their resolutions in the context of heterotic string theory with standard embedding. Also, we study the hierarchical couplings among untwisted and twisted modes on resolved orbifolds.

hep-th↗