A pseudo-Nambu-Goldstone 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 soft-breaking mass term in order to give a non-vanishing mass to the pNGB.
We proposed the gauged U(1)_{B-L} pNGB DM model as the UV completion of the simple pNGB DM model, where the soft-breaking 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)_{B-L} model, the B-L 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)_{B-L} 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).

We explores an alternative early universe scenario rather than inflation named Ekpyrotic Scenario. It suggests by adding an S-brane 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 late-time 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 S-brane Ekpyrotic Scenario. The result shows that the S-brane efficiently decays into radiation so that the emergent scenario can be smoothly connected to Hot Big Bang 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 multi-scalar 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.

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 Nelson-Barr models. In this talk, I will review the general features of a Nelson-Barr model and show that a supersymmetric Nelson-Barr model in gauge mediation is a plausible solution to the strong CP problem.

Positivity bounds on scattering amplitudes provide a necessary condition for a low-energy 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.

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.

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.

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 non-perturbative 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 state-of-the-art lattice simulations. We then predict the location of the critical endpoint and the first-order phase transition line. Moreover, we present the energy spectrum of the stochastic gravitational-wave background associated with the QCD first-order 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.

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