Hiroki Wada, Tohoku U
Anomalies in family unification models from bordism classification
Hybrid On-site: Kenkyu Honkan meeting room321 322 Online: Zoom
Anomaly cancellation is one of the most fundamental consistency conditions in quantum field theory. In constructing models beyond the Standard Model, one must ensure the absence of anomalies that would render the theory inconsistent. Consequently, anomaly cancellation conditions impose strong constraints on the allowed matter content. Recent developments have made it possible to systematically study not only perturbative anomalies but also the more subtle global anomalies via bordism theory. This perspective has led to a deeper understanding of anomalies and their implications for model building. In this talk, I will discuss anomalies in family unification models, which provide a natural explanation for the three generations of quarks and leptons. We identify the relevant bordism groups that classify possible anomalies in these models and show that no global anomalies arise. We also revisit earlier studies of perturbative anomalies in these models dating back to the 1980s. This talk is based on joint work with Tsubasa Sugeno (Tohoku University), arXiv:2604.04393.
Hiroki Takahashi, Univ. of Tokyo
Asymmetric Dark Matter from Spontaneous Leptogenesis
Hybrid On-site: Kenkyu Honkan Semiar room321 322 Online: Zoom
We investigate a novel type of asymmetric dark matter (ADM) model in which the dark matter asymmetry and the baryon asymmetry in our universe (BAU) are produced simultaneously via low-scale spontaneous leptogenesis, where the mass scale of the right-handed neutrino is much lower than the Davidson–Ibarra bound. In our scenario, both asymmetries are predominantly sourced by a dynamical CP phase, namely the majoron. Its kinetic misalignment provides a sufficiently large, time-dependent effective CP phase, allowing efficient asymmetry production even for low-mass right-handed neutrinos. In our framework, the sources of CP violation responsible for the BAU and ADM are correlated with each other, leading to a predictive relation for the dark matter mass. In particular, when the dark matter asymmetry reaches its equilibrium value before freeze-out, the dark matter mass is typically predicted to be of order GeV, which lies within the sensitivity of direct detection experiments. On the other hand, if the dark matter asymmetry does not reach its equilibrium value due to weak coupling, the allowed mass range extends over a broader interval, from GeV up to 10 TeV.
福山寛, 東大低温科学研究センター/KEK QUP
[金茶会] 超低エネルギー物理学の魅力 −量子凝縮系を中心に−
研究本館1階会議室1（リモート会場：JRB2階会議室, 仁科記念棟106号会議室）
https://www-conf.kek.jp/kincha/
Sotaro Sugishita, Hokkaido University
Celestial holography meets dS/CFT
Online (Zoom)
Celestial holography reformulates scattering amplitudes in (D+2)-dimensional flat spacetime as correlation functions on the D-dimensional celestial sphere, while in (D+1)-dimensional de Sitter spacetime cosmological correlators are also viewed as correlation functions on the D-dimensional sphere at late times. Thus, both frameworks naturally lead to correlators on spheres with the same dimension. We provide a concrete map between celestial amplitudes and cosmological correlators through the dS foliation of (D+2)-dimensional flat spacetime. This gives a cosmological-celestial dictionary relating celestial operators to operators at future and past infinity in dS. In the dictionary, massless fields in Minkowski spacetime are mapped to fields with continuous mass spectra in dS. In particular, the modes associated with asymptotic symmetries in flat spacetime have precise counterparts on the de Sitter side. For U(1) gauge theory, the counterpart is the massless sector within the continuous Proca spectrum. For linearized gravity, supertranslations and superrotations are encoded, respectively, in partially massless and strictly massless sectors of a spin-2 field with continuous spectrum. Using these identifications, we find that the Ward-Takahashi identities of cosmological correlators reproduce the conformally soft photon and graviton theorems through the cosmological-celestial dictionary.
Yukihiro Kanda, ICRR
Particle emission from semilocal string networks
Hybrid On-site: Kenkyu Honkan meeting room 321 322 Online: Zoom
Topological defects can arise as remnants of symmetry-breaking phase transitions in the early universe and are usually classified according to the homotopy groups of the vacuum manifold. However, field theories can admit stable localized configurations whose stability is ensured not only by topology but also by energetic considerations. Semilocal strings provide such an example: they are string-like defects that arise even when the fundamental group of the vacuum manifold is trivial. We present results from numerical lattice simulations of semilocal string networks, focusing for the first time on their particle-emission properties. We find that semilocal string networks efficiently emit Nambu-Goldstone bosons, with emission properties similar to axion radiation from global string networks. Motivated by this result, we discuss a scenario in which the Nambu-Goldstone bosons acquire a soft-breaking mass, and their non-thermal production from the string network accounts for the observed dark matter abundance.
Keisuke Harigaya, Univ. of Chicago
Kinetic isocurvature perturbations
hybrid On-site: Kenkyu Honkan meeting room 321 322 Online: Zoom
We formulate a new class of primordial perturbations called kinetic isocurvature perturbations, where the mass density of dark matter is constant relative to the photon number density while the kinetic energy of dark matter fluctuates in space. Such perturbations naturally arise in scenarios where a nonrelativistic heavy field decays into relativistic dark matter particles with a spatially modulated rate. As dark matter cools and becomes nonrelativistic, these fluctuations in kinetic energy leave large-scale density perturbations essentially unaffected and therefore evade the Cosmic Microwave Background bounds on isocurvature perturbations, yet survive as spatial variations in the free-streaming scale, resulting in patch-by-patch variation of the matter power spectrum.
Hiroki Matsui, Osaka Metropolitan University
Perturbative and Non-Perturbative Aspects of Lorentzian Quantum Cosmology
Hybrid On-site: Kenkyu Honkan meeting room 321 322 Online: Zoom One of the fundamental issues in quantum gravity is how to describe the initial state of the Universe. In quantum cosmology, the quantum state of the entire Universe is formulated as the “wave function of the Universe,” and its origin has been investigated using the path integral approach. However, conventional formulations based on the Euclidean path integral suffer from intrinsic problems.
One of the fundamental issues in quantum gravity is how to describe the initial state of the Universe. In quantum cosmology, the quantum state of the entire Universe is formulated as the “wave function of the Universe,” and its origin has been investigated using the path integral approach. However, conventional formulations based on the Euclidean path integral suffer from intrinsic problems.
In this talk, I will review recent developments in quantum cosmology based on the Lorentzian path integral and introduce our work applying Picard-Lefschetz theory and resurgence theory to this framework. First, I will explain how introducing an infinitesimal deformation in the parameter space fixes the Lefschetz thimble structure, naturally selecting the tunneling wave function. Second, I will demonstrate that the Borel resummation ambiguity of the perturbative series around the saddle is exactly canceled by the non-perturbative contribution from the other saddle. These results illustrate how non-perturbative aspects of quantum gravity offer new perspectives on the origin of the Universe. If time permits, I will also discuss the perturbation issues in quantum cosmology.
Jianing Wang, Kavli IPMU
PBH Formation and Its Origin in Inflation
Hybrid On-site: Kenkyu Honkan meeting room 321 322 Online: Zoom Primordial black holes (PBHs) are believed to form through the gravitational collapse of overdense regions in the early Universe. They may serve as seeds for galaxy formation and are also considered one of the important candidates for cold dark matter (DM).
Primordial black holes (PBHs) are believed to form through the gravitational collapse of overdense regions in the early Universe. They may serve as seeds for galaxy formation and are also considered one of the important candidates for cold dark matter (DM).
In particular, I will focus on several representative toy models of single-field inflation. The enhanced primordial perturbations in these models can not only produce PBHs, but also generate gravitational waves through higher-order effects. I will further extend the discussion to the possibility of a PBH-dominated era, which could leave observable signatures if PBH evaporation produces stable relics.
These studies demonstrate the significant potential of PBHs as probes of the early Universe, naturally leading to the important question of how to accurately estimate the PBH abundance. In the latter part of the talk, I will introduce a method based on peaks theory for estimating the abundance of primordial black holes. Our approach works well for arbitrary forms of the power spectrum, and by incorporating more systematic statistical methods, we expect it to provide useful cross-checks in combination with future gravitational-wave observations and related cosmological probes.
Fukutaro Miya, Osaka University
Generalizations and UV completions of Cho–Maison monopole
Hybrid On-site: Kenkyu Honkan meeting room 321 322 Online: Zoom Magnetic monopoles are important topological solitons predicted in gauge theories with spontaneous symmetry breaking. In the electroweak theory, Cho and Maison constructed a monopole configuration by allowing a singular behavior at the origin. Since its essential structure is tied to electroweak-type symmetry breaking, analogous monopoles are expected to arise in a wider class of gauge theories.
Magnetic monopoles are important topological solitons predicted in gauge theories with spontaneous symmetry breaking. In the electroweak theory, Cho and Maison constructed a monopole configuration by allowing a singular behavior at the origin. Since its essential structure is tied to electroweak-type symmetry breaking, analogous monopoles are expected to arise in a wider class of gauge theories.
In this talk, I will show that Cho-Maison-like monopole configurations can indeed be constructed in broad classes of models. I will also discuss how the electroweak Cho-Maison monopole can be embedded into a regular ‘t Hooft-Polyakov monopole as its low-energy effective description. In particular, I will show that a monopole in the Pati-Salam model reduces to the electroweak Cho-Maison monopole after heavy degrees of freedom are integrated out. This provides a possible ultraviolet origin of the Cho-Maison monopole and clarifies its generality beyond the Standard Model.
Sunao Sugiyama, Kavli IPMU
[IPNS Joint Experimental-Theoretical Cosmology Seminar] Probing Primordial Black Hole Dark Matter with Subaru HSC Microlensing Observations of M31
Hybrid On-site: Bldg 4 Seminar Hall Online: Zoom Primordial black holes (PBHs) are a well-motivated dark-matter candidate that may have formed in the early Universe from the collapse of primordial density fluctuations. If PBHs constitute even a fraction of dark matter, they can be probed through gravitational microlensing. To test this possibility, we have been conducting microlensing observations of stars in the Andromeda galaxy (M31) with the Subaru Hyper Suprime-Cam (HSC).
