In the first part of this talk, I will discuss sterile neutrino production in modified cosmologies. Although the standard assumption is a radiation dominated universe up to the era of reheating, there are motivated models in which the Hubble rate-temperature relation changes. The abundance of sterile neutrinos produced both resonantly and non-resonantly can be drastically altered with interesting implications for experimental searches. In the second part of my talk, I will present a set of bounds on the primordial black hole (PBH) mass density. By considering stable gas clouds in thermal equilibrium, we can calculate the cooling rate and impose constraints on possible heating processes. Intermediate mass black holes, which can form efficient accretion disks, and light black holes, which emit Hawking radiation, would generate significant amounts of thermal energy. We set limits on the dark matter fraction of PBH as a result and briefly explore the possible contributions from jets. In the final section of the talk, I will discuss two PBH formation models from first order phase transitions. During a first order phase transition, compact remnants in the form of thermal balls and Fermi balls can be formed from particles trapped within the false vacuum. Eventually, after significant cooling, these remnants can collapse into primordial black holes. We consider a delayed formation scenario in which PBH formation occurs after the CMB era. This evades a strong constraint on intermediate mass black holes derived from Planck observations, and opens parameter space for two astrophysically significant populations: BBH progenitors and SMBH seeds. Another PBH formation scenario relies on the decreased pressure forces during a high temperature QCD transition. This produces a peak in the PBH mass distribution at sub-solar mass and even asteroid mass scales, within the PBH mass window.

Twenty years ago, in an experiment at Brookhaven National Laboratory, physicists detected what seemed to be a discrepancy between measurements of the muon’s magnetic moment and theoretical calculations of what that measurement should be, raising the tantalizing possibility of physical particles or forces as yet undiscovered. The Fermilab team has announced that their precise measurement supports this possibility. The reported significance for new physics is 4.2 sigma just slightly below the discovory level of 5 sigma. However, an extensive new calculation of the muon’s magnetic moment using lattice QCD by the BMW-collaboration reduces the gap between theory and experimental measurements. In this talk both the theoretical and experimental aspects are summarized with two possible narratives:
a) almost discovery or b) Standard Model re-inforced. Some details of the lattice caluculation are also shown.

Gravitational lensing (GL) has been a powerful method to probe matter inhomogeneities in the Universe. GL of gravitational waves, which will be detected in the near future, will enable us to gain more information of the nature of dark matter and further boost the significance of GL. In light of this situation, it is important to have understanding of basic properties of GL. In my talk, I show that gravitational lensing obeys the causality in the sense that (electromagnetic/gravitational) waves emitted from the source arrive at an observer only after the arrival of the signal in geometrical optics. This leads to the Kramers-Kronig relation, a well-known relation in the field of optics, in GL, as the relation between real and imaginary parts of the amplification factor. I will also show some relations which hold as consequence of the Kramers-Kronig relation. Finally, I argue that examining the violation of the Kramers-Kronig relation may be used for correctly extracting the lensing signal in the gravitational wave observations.

Bosonization, in which a fermionic model in 1 + 1 dimensions is transformed to an equivalent bosonic model, has been a powerful technique for the analytical study of many models. However, although the bosonized model is usually much simpler than the original model, obtaining the analytical exact solution is still very hard in some cases.
In this seminar, I present the lattice formulation of the bosonized Schwinger model, which enables us to study the model using the Monte Carlo method. This approach has several distinct advantages over the conventional one based on the original fermionic Lagrangian. First, the approach is unambiguously free from the fermion doubling problem.
Second, it is also free from the sign problem. Moreover, much more efficient configuration generation is possible. I demonstrate the validity of my formulation by showing my numerical results and discuss possible applications to other models.

Ref: H. Ohata, Monte Carlo study of Schwinger model without the sign
problem, arXiv:2303.05481 [hep-lat].

https://www-conf.kek.jp/kincha/

The chiral kinetic theory is a pivotal theoretical tool for the transport theory of massless degrees of freedom. Despite various developments, the usual framework contains only linear-order quantum corrections. In this talk, I will explain the formulation of the chiral kinetic theory with the nonlinear-order corrections. Also I will show several findings from this nonlinear chiral kinetic theory, such as nondissipative transport phenomena, a consistency with the Euler-Heisenberg effective theory and a potential issue on regularization.

Scattering amplitudes are key ingredients for cross sections relevant to collider physics. In the last decade, novel geometric ideas have emerged that hint at a completely different formulation of quantum field theory. For example, the Amplituhedron provides, via geometric means, the all-loop integrand of planar scattering amplitudes in maximally supersymmetric Yang-Mills theory. Unfortunately, dimensional regularization, used conventionally for integration, breaks the beautiful geometric picture. This motivates us in this talk to propose a ‘deformed’ Amplituhedron, which is well-defined in four dimensions. Leveraging four-dimensional integration techniques based on differential equations, we compute the four-particle amplitude up to two loops, as a function of the two deformation parameters. The latter can be interpreted as certain mass and energy variables. We observe simple behaviour in various physical limits of the parameters.

Electroweak baryogenesis is a promising scenario to solve baryon asymmetry of the Universe, which is one of big mysteries of particle physics. I will discuss a scenario of electroweak baryogenesis in the two Higgs doublet model with quark flavor mixing. In general, off-diagonal components of quark Yukawa interactions with additional Higgs bosons are strongly constrained by the data for flavor changing neutral currents. However, top-charm quark mixing is not the case, so that a large off-diagonal element can be taken, which can contribute to generating baryon asymmetry of the universe. I will also discuss characteristic predictions for Kaon rare decays in the scenario of top-charm electroweak baryogenesis.

最近 ChatGPT に代表される大規模言語モデル (Large Language Model; LLM）が大きな話題となっている。LLM以前の自動対話システムでは、宅配便の配達問い合わせのようにあらかじめ決められた話題と目的のために応答を生成するのがやっとであり、しかもその応答も定型文の域を出ないものが多かった。それにたいしLLMは一見人間が応答しているのと区別がつかないやりとりを広範な話題について行うことができるため、様々な応用が期待されるとともに、その発展についていろいろな懸念も生じている。本講演では、LLMとは実際のところどういうものなのかその仕組みを解説するとともに、単なる印象論を越えてLLMについて冷静に議論をするための視点を提供する。

Majorons are (pseudo-)Nambu-Goldstone bosons associated with lepton number symmetry breaking due to the Majorana mass term of neutrinos introduced in the seesaw mechanism. They are good dark matter candidates since their lifetime is suppressed by the lepton number breaking scale. We update constraints and discuss future prospects on majoron dark matter in the singlet majoron models based on neutrino, gamma-ray, and cosmic-ray telescopes in the mass region of MeV-10 TeV.