arXiv subjects

Ryusei Nishida

Publications and source records attributed to Ryusei Nishida.

7 recordsLinked to original sources

arXiv2026

Note on arithmetic structure of modulus vacua in flux compactifications

We study modulus stabilization by background fluxes. The supersymmetric minima satisfy a holomorphic quadratic equation. As concrete examples, we consider $T^6/(\mathbb{Z}_2\times\mathbb{Z}_2')$ orientifold model and a simple Calabi-Yau compactification. The modulus values show specific patterns. For example, they show the Farey sequence. The void structure appears around modulus vacua with high degeneracies. We find a correlation between the degeneracy and the void area. The modulus vacua are related by discrete Abelian symmetries generated by the Gauss composition law, which includes the CP symmetry. Spontaneous CP violation is also discussed.

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arXiv2026

More about modular symmetries and non-invertible properties in magnetized compactifications

We study the modular symmetry in magnetized compactifications. The zero-modes with different Scherk-Schwarz phases transform each other. A generic model does not include modes with all the Scherk-Schwarz phases. Incomplete multiplet representations appear. Thus, the modular symmetry is violated as group-like symmetry. However, the modular symmetry still controls coupling terms in those models. Modular forms of the full symmetry appear as coupling constants.

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arXiv2026

Residual group-like symmetries in selection rules without group actions

We analyze loop-induced group-like symmetries in theories where fields are labeled by basis elements of a fusion algebra constructed from the conjugacy classes of finite groups. Although the fusion rules for conjugacy classes are in general violated at loop level, residual group-like symmetries, including both Abelian and non-Abelian ones, remain exact through a procedure referred to as ``groupification''. By examining various conjugacy classes of finite groups realized in heterotic string theory on non-Abelian orbifolds, we identify an approximate discrete symmetry that controls the magnitude of loop-induced couplings. As a result, most parameters appearing in non-invertible selection rules are natural in the sense of 't Hooft. Furthermore, we discuss anomalies of the groupification symmetry, which can impose additional constraints on models with non-invertible fusion rules.

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arXiv2025

Non-Invertible Selection Rules on Heterotic Non-Abelian Orbifolds

We investigate coupling selection rules in heterotic string theory on non-Abelian orbifolds. Since boundary conditions on the orbifolds are classified by conjugacy classes of space group elements, non-Abelian orbifolds give rise to non-invertible selection rules on couplings among twisted sectors as well as ones including untwisted sectors. Furthermore, we find that non-invertible selection rules lead to characteristic patterns of Yukawa matrices.

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arXiv2025

On discrete gauging and non-invertible selection rules

We clarify selection rules of conjugacy classes of several finite discrete groups where we deal with both gauged and ungauged cases. We find that the selection rules enjoy finite Abelian or non-Abelian discrete symmetries originating from the inner and/or outer automorphism of underlying discrete groups. Since the selection rules of conjugacy classes do not obey conventional group-like selection rules, they open up new coupling selection rules of fields which are labeled by the conjugacy classes.

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arXiv2025

Coupling Selection Rules in Heterotic Calabi-Yau Compactifications

We study coupling selection rules of chiral matter fields in heterotic string theory with standard embedding. These selection rules are determined by topological properties of Calabi-Yau threefolds. We classify coupling selection rules on complete intersection Calabi-Yau threefolds for $h^{1,1}\leq 5$. It is found that all of these selection rules for $h^{1,1}\leq 5$ are understood by combinations of only five types of fusion rules.

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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 $\tau_2=N\tau_1$, where $\tau_i$ 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 $SL(2,\mathbb{Z})_{\tau_1} \times SL(2,\mathbb{Z})_{\tau_2} \subset Sp(4,\mathbb{Z})$ and it is broken to $\Gamma_0(N) \times \Gamma^0(N)$ by the moduli constraint. The wave functions represent their covering groups. We obtain various flavor groups in these models.

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