Tsutomu T. Yanagida

A bstract: The internal structure of the Standard Model implies a natural ℤ ₄ × ℤ ₃ discrete gauge symmetry. Cancellation of the corresponding Dai-Freed anomalies requires the introduction of three right-handed neutrinos and three additional Majorana fermions χ _i . This gauge symmetry forbids the decay of the lightest fermion χ ₁ into Standard Model particles, rendering it automatically stable and providing a dark matter candidate without introducing an ad hoc stabilizing symmetry and domain-wall problem. The mass of χ ₁ is generated by the vacuum expectation value of a singlet scalar near the electroweak scale, naturally realizing a weakly interacting massive particle (WIMP) freeze-out scenario. Dark matter annihilation proceeds through scalar mediation, allowing the observed relic abundance to be reproduced while remaining consistent with current direct-detection constraints. It naturally realizes the secluded dark matter scenario and can be further tested in the next generation of experiments.

A bstract: The QCD axion remains one of the most compelling solutions to the strong CP problem. Meanwhile, the type-I seesaw mechanism offers an elegant explanation for the lightness of the observed neutrino masses; however, its extremely heavy Majorana states place it far beyond experimental reach. Low-scale alternatives such as the inverse seesaw improve testability but typically lack a strong theoretical motivation. In this paper we bridge this gap by showing that gauging the discrete symmetry ℤ ₄ × ℤ ₃ — motivated by the internal structure of the Standard Model — naturally yields a QCD axion with a high-quality Peccei-Quinn symmetry solving the strong CP problem, while simultaneously enforcing the field content and hierarchy required for a natural inverse seesaw. The resulting model is highly predictive and has the potential to be fully tested by future experiments. Beyond addressing the strong CP problem and the origin of neutrino masses, our scenario also contains a viable dark-matter candidate and offers potential mechanisms for generating the baryon asymmetry of the Universe.

In light of the latest Planck and Atacama Cosmology Telescope (P-ACT) joint results on the primordial scalar power spectrum, we show that the R ² inflation model extended with a non-minimally coupled scalar field χ — namely the χ-extended R ² inflation model — can naturally accommodate a larger spectral index n _s and a small positive running α _s at cosmic microwave background (CMB) scales, both of which are consistent with the latest P-ACT constraints. This is because the χ field contributes a blue-tilted component to the primordial power spectrum, which both modifies the large-scale power and, as a result, significantly enhances power on small scales. The deviation of the n _s and α _s from the single field R ² inflation is related to the non-minimal coupling constant ξ . The consequent enhancement in the primordial power spectrum can be large enough to lead to the formation of primordial black holes (PBHs) of mass ≲10 ²⁰ g as dark matter candidates. Furthermore, future observations of the small-scale power spectrum, CMB spectral distortions, and stochastic gravitational waves will provide decisive tests of this model and its predictions for PBHs. We stress its strong connection to the seesaw mechanism for the generation of the observed small masses.

The QCD axion remains one of the most compelling solutions to the strong CP problem. Meanwhile, the type-I seesaw mechanism offers an elegant explanation for the lightness of the observed neutrino masses; however, its extremely heavy Majorana states place it far beyond experimental reach. Low-scale alternatives such as the inverse seesaw improve testability but typically lack a strong theoretical motivation. In this paper we bridge this gap by showing that gauging the discrete symmetry $\mathbb Z_4 \times \mathbb Z_3$-motivated by the internal structure of the Standard Model-naturally yields a QCD axion with a high-quality Peccei-Quinn symmetry solving the strong CP problem, while simultaneously enforcing the field content and hierarchy required for a natural inverse seesaw. The resulting model is highly predictive and has the potential to be fully tested by future experiments. Beyond addressing the strong CP problem and the origin of neutrino masses, our scenario also contains a viable dark-matter candidate and offers potential mechanisms for generating the baryon asymmetry of the Universe.

The electromagnetic memory is a theoretically predicted effect of great conceptual importance. In this Letter, we show that gravitation acceleration can serve as a source to print memory phases in superconducting states, through the electric field and vector potential it induces inside a conductor. This physical picture offers a novel perspective on the control of quantum phases and the test of gravitational effects in conductors.

It is very much intriguing if the Planck scale M _Pl is not a fundamental parameter. The Brans-Dicke gravity is nothing but the theory where the Planck scale M _Pl is indeed an illusional parameter. The theory predicts a massless scalar boson whose exchanges between matters induce unwanted long range forces. We solve this problem imposing there is no dimensionful parameter in the theory, even at the quantum level. We further extend the theory by including a R ² term and a non-minimal coupling of the Standard Model Higgs to gravity, as their coefficients are dimensionless. This extension provides a heavy inflaton field that is consistent with all cosmological observations, with a potential very similar to that of the Starobinsky model. The inflaton necessarily decays into the massless scalar bosons, resulting in a non-negligible amount of dark radiation in the present universe. We demonstrate that the inflation model yields a sufficiently high reheating temperature for successful leptogenesis, and we also discuss a possible candidate for dark matter.