Date 
Speaker 
Title ( Abstract : Click the title ) 
4/12 
Yoshihiko Abe
(Kobe Univ.)

Origin of pseudoNambuGoldstone dark matter
A pseudoNambuGoldstone boson (pNGB) is an attractive dark matter (DM) candidate avoiding the severe constraints from the direct detection experiments naturally.
However, it is assumed to introduce the softbreaking mass term in order to give a nonvanishing mass to the pNGB.
We proposed the gauged U(1)_{BL} pNGB DM model as the UV completion of the simple pNGB DM model, where the softbreaking mass is produced by the additional scalar vacuum expectation value.
We discuss that the DM candidate in this model is a decaying dark matter and show the allowed parameter space.
Then, we consider embedding this model into the SO(10) grand unification and discuss the relation between the origin of the pNGB and grand unification.
We show that the unification determines the free parameters of the gauged U(1)_{BL} model, the BL breaking scale, the gauge coupling, and the gauge kinetic mixing.
In particular, we find that the breaking scale is lower than that in the gauged U(1)_{BL} model, which implies O(100) GeV pNGB DM mass to realize the current DM relic abundance.
This talk is based on the collaborations with Takashi Toma, Koji Tsumura, and Naoki Yamatsu,
JHEP05(2020)057
and
Phys. Rev. D 104, 035011 (2021).

4/26 
Ziwei Wang
(Kobe Univ.)

A New Realization of the Ekpyrotic Scenario
We explores an alternative early universe scenario rather than inflation named Ekpyrotic Scenario.
It suggests by adding an Sbrane located after the Ekpyrotic contraction phase, puzzles of the standard Hot Big Bang cosmology can be resolved in this new model.
Besides, using the methodology of cosmological perturbation theory connecting between the primordial universe and latetime cosmological observations, predictions of the model are well consistent with the current constraints.
Furthermore, to bridge Ekpyrotic contraction in the very early universe and Standard Hot Big Bang, a natural process of reheating is well studied for Sbrane Ekpyrotic Scenario. The result shows that the Sbrane efficiently decays into radiation so that the emergent scenario can be smoothly connected to Hot Big Bang cosmology.

5/10 
Jiro Soda
(Kobe Univ.)

A puzzle in cosmology?
Many years ago, we found anisotropic inflation which can be interpreted as the cosmological symmetry breaking.
There, a constant of integration played an important role.
Interestingly, the constant appears as a consequence of quantum fluctuations.
The same mechanism can be applicable to multiscalar field system which has been discussed in the context of inflation.
In this talk, I will extend the analysis to late time universe.
In particular, I will focus on the axion system and discuss the consequence of the constant of integration.
It seems that the conventional cosmological scenario has a puzzle.
I will conclude my talk with a suggestion of a possible direction of cosmology.

5/24 
Kohei Fujikura
(Kobe Univ.)

A NelsonBarr model
Several solutions to the strong CP problem including QCD axion have been proposed so far. One possible solution to the strong CP problem is that CP is an exact symmetry, spontaneously broken at some scale. Nelson and Barr constructed the simple phenomenologically viable models in this framework called NelsonBarr models. In this talk, I will review the general features of a NelsonBarr model and show that a supersymmetric NelsonBarr model in gauge mediation is a plausible solution to the strong CP problem.

5/31 
Toshifumi Noumi
(Kobe Univ.)

Phenomenological Motivation for Gravitational Positivity Bounds: A Case Study of Dark Sector Physics
Positivity bounds on scattering amplitudes provide a necessary condition for a lowenergy effective field theory to have a consistent ultraviolet completion.
Their extension to gravity theories has been studied in the past years aiming at application to the swampland program, showing that positivity bounds hold at least approximately even in the presence of gravity.
An issue in this context is how much negativity is allowed for a given scattering process.
In this talk, we address importance of this rather technical issue by demonstrating that it is relevant to physics within the scope of ongoing experiments, especially in the context of dark sector physics.
In particular, we provide detailed analysis of dark photon scenarios as an illustrative example.
This motivates further studies on gravitational positivity bounds.

6/7 
Pak Hang Chris Lau
(Kobe Univ.)

Quantum information and abstract algebra
In this seminar, I will motivate the study of von Neumann algebra as a unified framework to understand quantum mechanics and quantum field theory.
I will review some of the interesting and surprising results in the algebra and its consequence in a general quantum system.
Many familiar quantum informatics quantities appears naturally in this algebraic framework.
I will demonstrate a few applications of this algebraic framework to quantum information.

6/14 
Siyi Zhou
(Kobe Univ.)

Inflation with extra dimension
I will first introduce some background on the historical development of the idea of extra dimension.
Then I will introduce a toy model of inflation with extra dimension.
We see that steep potentials usually appear in such kind of model and make the model inconsistent with observation.
We then introduce several possible ideas where inflation with steep potentials can be consistent with observations.
The ideas include assisted inflation, trapped inflation and DBI inflation.
I will also introduce Stokes line method, a tool to calculate particle production rate.
I will apply this method to simple cosmology settings such as production rate of massive particle in de Sitter space and also the case of changing mass such as trapped inflation.

6/28 
Song He
(Jilin U.)

QCD phase diagram V.S. Holographic QCD
The Quantum Chromodynamics (QCD) phase diagram involves the behaviors of strongly interacting matter under extreme conditions and remains an important open problem.
Based on the nonperturbative approach from the gauge/gravity duality, we construct a family of black holes that provide a dual description of the QCD phase diagram at finite chemical potential and temperature.
The thermodynamic properties of the model are in good agreement with the stateoftheart lattice simulations.
We then predict the location of the critical endpoint and the firstorder phase transition line.
Moreover, we present the energy spectrum of the stochastic gravitationalwave background associated with the QCD firstorder transition, which is found to be detected by IPTA and SKA, while by NANOGrav with less possibility.
If the time is allowed, we will present how to construct a holographic model for a pure gluon system.

7/12 
WeiMing Chen
(Kobe Univ.)

Onshell Scattering Amplitudes and Classical Gravity
In this talk, I will review the application of onshell scattering amplitudes to two classical systems: classical systems like binary black holes and the system of a massless particle accompanied by a massive object.
The connection between scattering amplitudes and relevant observables (potential, spin kick, and so on) from scattering amplitudes will also be established.
This is based on the recent paper 2111.13639 and 2205.07305.

7/19 
Junsei Tokuda
(Kobe Univ.)

Regge theory and its success: a biased review
In models with tower of higherspin resonances, scattering amplitudes often exhibit the interesting behavior, socalled the Regge behavior.
Examples of such models are QCD and String Theory.
Therefore, it is important to understand how such higherspin particles contribute to the scattering processes.
Regge theory is a framework to handle them.
In this talk, I will briefly review basics of the Regge theory and its success in the context of hadron physics.
I will then explain the socalled DHS duality and how it leads to the finding of Veneziano amplitude.
If time permitted, I may also briefly explain my own work.

9/26 
D3 students
(Kobe Univ.)

Mock thesis defense of three D3 students
Mock thesis defense of three D3 students

10/5 
Kimihiro Nomura
(Kobe Univ.)

Photonaxion conversion in photon spheres of black holes
The axion is a pseudoscalar particle expected to exist from highenergy theory.
It is characterized by a small mass and a feeble coupling to the photon.
Although the coupling is weak, it is known that photons propagating over long distances in a strong magnetic field can be converted to axions.
Such an environment can be provided by magnetospheres of black holes.
In this talk, I will review the photonaxion conversion phenomenon, and then discuss its application to black hole magnetospheres and implications for observations.

10/12 
Taiga Miyachi
(Kobe Univ.)

Tunneling in de Sitter spacetime via stochastic approach
Usually, the tunneling rate of the false vacuum is calculated in the Euclidean spacetime.
It is the same in the case of curved spacetime.
In de Sitter spacetime, however, there is another way to compute the rate by using stochastic approach.
Interestingly, the rate can be represented as a path integral and we can see a nontrivial configuration as a flow in phase space.
In this seminar, I will review the formalism of a stochastic approach and its path integral representation, and reproduce the result of the HawkingMoss instanton.

11/2 
ChongBin Chen
(Kobe Univ.)

Introduction of CMB physics
Cosmic Microwave Background(CMB) is one of the most accurate observation in the modern cosmology.
The features of power spectrum of photon reveal the history and large scale structure of our universe (for example, the recombination, the abundance of dark matter...).
In this serminar, I will introduce some basic knowledges of CMB physics and explain some key physical effects on the power spectrum.
I also introduce the axion particles as dark matter candidates and see how they effect the CMB power spectrum.

11/9 
Sota Sato
(Kobe Univ.)

Asymptotic symmetry and soft theorem
In this seminar, I will review the connection between Asymptotic symmetries and the soft theorem of gauge theory.
Firstly, I will describe an infinite number of conservation charges of U(1) gauge theory.
Symmetries associated with these charges are gauge symmetries which act nontrivially on the asymptotic data and called asymptotic symmetries.
The soft photon theorem can be derived from Ward identities of these symmetries and can be understood as charge conservation.

11/16 
Kanji Nishii
(Kobe Univ.)

String spectrum in AdS_3
String theory is a strong candidate of quantum gravity.
However, a spectrum of quantum string is wellknown only in flatspace background.
In general, it is difficult to obtain a string spectrum in curvedbackgrounds, since equations of motion become nonlinear.
Under these circumstances, the (physical) string spectrum in AdS_3 background is obtained by using the WZW model.
In this talk, I will review the WZW model with AdS_3 isometry, and briefly introduce the physical string spectrum in AdS_3.

11/30 
Alexandar Ganz
(Jagiellonian U.)

Minimally Modified Gravity and its Phenomenological Properties
Minimally modified gravity models are a class of modified gravity models with only two local degrees of freedom as in general relativity.
In this talk I want to discuss their general properties such as the existence of a preferred foliation and their phenomenology in the case of inflation and the late universe.
Further, I will discuss potential issues arising from trivial constraints.

12/7 
Takuya Takahashi
(Kyoto Univ.)

Evolution of axion clouds in black hole binaries
Ultralight scalar fields such as axions can form clouds around rotating black holes (BHs) by the superradiant instability.
It is important to consider the evolution of clouds associated with BH binaries for the detectability of the presence of clouds through gravitational wave signals and observations of the mass and spin parameters of BHs.
In this talk, I will discuss the effect of the backreaction to the orbital motion and show that axions are radiated away during the inspiral phase, for almost equal binaries.

12/21 
Kohei Kamada
(RESCEU, The Univ. of Tokyo)

Baryon asymmetry of the Universe induced from Axion Inflation
Pseudoscalar inflation or axion inflation is one of the most wellmotivated models of inflation because the approximate shift symmetry guarantees the flatness of the potential against the quantum corrections.
The CP and shift symmetric properties of pseudoscalar inflaton allows it to have a coupling to the ChernPontryagin density of the gauge fields.
In this talk, I will argue that if the inflaton has such a coupling to the hyper U(1) gauge fields in the Standard Model, it can give a significant impact on the baryon asymmetry of the Universe. Namely, through the chiral anomaly, baryon asymmetry is directly produced at the end of inflation together with the helical magnetic fields.
Although this asymmetry suffers from the sphaleron washout, decoupling of relatively light righthanded neutrinos will prevent the asymmetry from being washed out completely through the recently proposed mechanism, dubbed as the "washin" process.
Moreover, the hypermagnetic helicity decay at the electroweak symmetry breaking give additional contributions to the baryon asymmetry of the Universe.
I will explain some details of relevant phenomena in the scenario.

1/11 
Hiroaki Sunagawa
(Kobe Univ.)

Mock master thesis defense
Mock master thesis defense

1/18 
Daiki Ueda
(Theory Center, KEK)

Entropy constraints on effective field theory
Relative entropy quantifies the difference between two probability distribution functions, which is connected with key properties of physics, such as the second law of thermodynamics.
In this talk, one of the most attractive features of relative entropy, nonnegativity, is briefly reviewed.
Then, I consider the relative entropy between two theories with and without interaction between heavy and light degrees of freedom.
I explain connections between the nonnegativity of the relative entropy and various phenomena, e.g., the positive magnetic susceptibility in the Ising model, the spontaneous symmetry breaking in the ColemanWeinberg potential by the quantum effects, the positivity bounds on the SMEFT SU(N) gauge bosonic operators, etc.
I also discuss constraints on higherderivative terms of the EinsteinMaxwell theory and the limitations of the relative entropy consideration in EFTs involving gravitational effects.
