arXiv subjects

Naohiro Osamura

Publications and source records attributed to Naohiro Osamura.

7 recordsLinked to original sources

arXiv2026

Full Three-Loop Electroweak Multiplet Contributions to the Electron Electric Dipole Moment

Experimental sensitivity to the electric dipole moment (EDM) of the electron has improved remarkably in recent years. Consequently, future prospects could probe new physics whose contribution to the electron EDM first arises at three-loop order. Additional SU(2)$_L$ multiplets with CP-violating Yukawa interactions, which contribute to the electron EDM at three-loop level, is one such testable new physics scenario. In this scenario, the electron EDM is radiatively induced from two contributions: the CP-odd trilinear $W$-boson coupling, called the electroweak-Weinberg operator, and the CP-odd dipole operator of electron. The former and the latter operators are generated at two-loop and three-loop levels, respectively, after integrating out the SU(2)$_L$ multiplets. Within the same models, according to an analysis based on the Standard Model Effective Field Theory (SMEFT), we previously found that the contribution to the electron EDM from the electroweak-Weinberg operator can be probed in future experiments. However, the one-loop matching condition between the electron EDM and the electroweak-Weinberg operator does not receive a large logarithmic enhancement because the associated anomalous dimension is zero. The CP-odd dipole operator of the electron would contribute to the electron EDM at the same three-loop order as the contribution through the electroweak-Weinberg operator. In this paper, we directly calculate the electron EDM induced by the CP-violating Yukawa interactions of the SU(2)$_L$ multiplets at full three-loop level. A central result is that the full three-loop calculation is a factor of three larger than that of the electroweak-Weinberg operator alone.

hep-ph↗

arXiv2025

Two-loop corrections to QCD $θ$ angle from evanescent operator in the BMHV scheme

We study the renormalization of the QCD $θ$ angle at the two-loop level focusing on divergent and finite $CP$-violating contributions from evanescent operators, using dimensional regularization with the BMHV scheme. When one considers the Lagrangian in $d$-dimensional space-time instead of four dimensions in dimensional regularization, evanescent operators that break the chiral symmetry are induced. Consequently, $T$-odd and $P$-odd fermion loops in the BMHV scheme generate evanescent contributions to the QCD $θ$ angle. We carefully classify the evanescent contributions into two types: one originating from the evanescent operators at the one-loop level and the other directly produced by two-loop calculations. We show that renormalization of the parameters in the BMHV scheme keeps removing those unphysical contributions to the QCD $θ$ angle at any scale at the two-loop level. We also discuss how the rephasing invariance of the radiative correction to the QCD $θ$ angle is realized in the BMHV scheme.

hep-ph↗

arXiv2025

Impact of the Electroweak Weinberg Operator on the Electric Dipole Moment of Electron

Recent progresses in the measurements of the electric dipole moment (EDM) of the electron using the paramagnetic atom or molecule are remarkable. In this paper, we calculate a contribution to the electron EDM at three-loop level, introducing the CP-violating Yukawa couplings of new SU(2)$_L$ multiplets. At two-loop level, the Yukawa interactions generate a CP-violating dimension-six operator, composed of three SU(2)$_L$ field strengths, called the electroweak Weinberg operator. Another one-loop diagram with the operator inserted induces the electron EDM. We find that even if new SU(2)$_L$ particles have masses around TeV-scale, the electron EDM may be larger than the Standard Model contribution to the paramagnetic atom or molecule EDMs. We also discuss the relation between the Barr-Zee diagram contribution at two-loop level and the three-loop one, assuming that the SM Higgs has new Yukawa interactions with the SU(2)$_L$ multiplets.

hep-ph↗

arXiv2024

Closer look at the matching condition for radiative QCD $θ$ parameter

In this paper, we scrutinize a radiatively generated QCD $θ$ parameter at the two-loop level based on both full analytical loop functions with the Fock-Schwinger gauge method and the effective field theory approach, using simplified models. We observe that the radiatively generated $θ$ parameters at the low energy scale precisely match between them. It provides validity to perturbative loop calculations of the QCD $θ$ parameter with the Fock-Schwinger gauge method. Furthermore, it is also shown that the ordinary Fujikawa method for the radiative $θ$ parameter by using $\barθ= - arg det M_q^{loop}$ does not cover all contributions in the simplified models. But, we also find that when there is a scale hierarchy in $CP$-violating sector, evaluation of the Fujikawa method is numerically sufficient. As an application, we calculate the radiative $θ$ parameter at the two-loop level in a slightly extended Nelson-Barr model, where the spontaneous $CP$ violation occurs to solve the strong $CP$ problem. It is found a part of the radiative $θ$ parameters cannot be described by the Fujikawa method.

hep-ph↗

arXiv2023

Novel loop-diagrammatic approach to QCD $θ$ parameter and application to the left-right model

When the QCD axion is absent in full theory, the strong $CP$ problem has to be explained by an additional mechanism, e.g., the left-right symmetry. Even though tree-level QCD $\barθ$ parameter is restricted by the mechanism, radiative corrections to $\barθ$ are mostly generated, which leads to a dangerous neutron electric dipole moment (EDM). The ordinary method for calculating the radiative $\barθ$ utilizes an equation $\bar θ= - \text{arg}\, \text{det}\, m_q^{\rm loop}$ based on the chiral rotations of complex quark masses. In this paper, we point out that when full theory includes extra heavy quarks, the ordinary method is unsettled for the extra quark contributions and does not contain its full radiative corrections. We formulate a novel method to calculate the radiative corrections to $\barθ$ through a direct loop-diagrammatic approach, which should be more robust than the ordinary one. As an application, we investigate the radiative $\barθ$ in the minimal left-right symmetric model. We first confirm a seminal result that two-loop level radiative $\barθ$ completely vanishes (corresponding to one-loop corrections to the quark mass matrices). Furthermore, we estimate the size of a non-vanishing radiative $\barθ$ at three-loop level. It is found that the resultant induced neutron EDM is comparable to the current experimental bound, and the expected size is restricted by the perturbative unitarity bound in the minimal left-right model.

hep-ph↗

arXiv2022

Contribution of the Weinberg-type operator to atomic electric dipole moments

We report the calculation of the isovector CP-odd $πN$ interaction generated by the Weinberg operator, the CP violating three-gluon operator. This enables to restrict models which induce the operator by using experimental data of atomic electric dipole moment. The QCD sum rules are used to determine the matrix element required to assess the CP-odd $πN$ interactions. The relation between the Weinberg operator and the Hg and Xe EDMs is clarified, and the constraint on the Weinberg operator is obtained using the experimental data for the Hg EDM.

hep-ph↗

arXiv2022

Contribution of the Weinberg-type Operator to atomic and nuclear electric dipole moments

The contribution of the CP violating three-gluon Weinberg operator, $\frac{1}{3!} w f^{abc} ε^{νραβ} G^a_{μν} G^b_{αβ} G^{c μ}_ρ$, to the atomic and nuclear EDMs is estimated using QCD sum rules. After calculating the transition matrix element between the pion and the vacuum through the Weinberg operator, we obtain the long-range CP-odd nuclear force by determining the isovector CP-odd pion-nucleon vertex, using chiral perturbation theory at NLO. The EDMs of $^{199}$Hg, $^{129}$Xe, $^{225}$Ra, $^2$H, and $^3$He are finally given including comprehensive uncertainty analysis. While the leading contribution of the $^{199}$Hg EDM is given by the intrinsic nucleon EDM, that of $^{129}$Xe atom may be dominated by the one-pion exchange CP-odd nuclear force generated by the Weinberg operator. From current experimental data of the $^{199}$Hg atomic EDM, we obtain an upper limit on the Weinberg operator magnitude of $\left|w \right| < 4 \times 10^{-10} {\rm GeV}^{-2}$ if we assume that it is the only source of CP violation at the scale $μ=1$ TeV.

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