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2023/4/10 (月)Speaker: Hyun Jeong Title: Higher-derivative Quantum Gravity and Its Application to Cosmology Abstract: I briefly review the renormalizability of the four-derivative quantum gravity and compare its proof with that of the non-abelian gauge theory. Further, I show the close relationship between renormalizability and the anomaly. These are very essential concepts for building the consistent quantum field theory. Based on these theoretical considerations, I will review the paper [4] and discuss the further theoretical implications. References: 2023/2/6 (月)Speaker: Katsuki Aoki Title: Gravitational positivity bounds Abstract: 2023/1/30 (月)Title: TBA †Speaker: Valerie Domcke †TBA 2023/1/23 (月)Speaker: Kohei Kamada Title: Particle interaction induced CMB polarization Abstract: References: 2023/1/16 (月)Title: TBA †Speaker: Jun'ichi Yokoyama †On January 17 (=today) I will introduce stochastic inflation 2022/12/19 (月)Title: Introduction of machine learning and its application to physics of the universe. (Sequel of his talk on 11/28) †Speaker: Takumi Hayashi †With the improvement of knowledge of information science and computation power of machine, the role of machine learning(ML) is growing in various field, also in physics. In my last talk, I reviewed the basics of ML and the models widely used. In this talk, I will complete the remaining part, introduction of the application of ML to the physics familiar to us. Especially I focus on the estimation of the quasi-normal modes of a blackhole ringdown, and show the comparison between ML and other traditional methods such as matched filtering, HHT, AR-model. [1] Giuseppe Carleo, Rev. Mod. Phys. 91, 045002 (2019), [arXiv:1903.10563]. 2022/12/12 (月)Title: Cancellation of the VIA source in Electroweak Baryogenesis †Speaker: Jorinde van de Vis (Universiteit Utrecht) †In electroweak baryogenesis, the asymmetry between matter and antimatter is generated during the electroweak phase transition. Predicting the amount of matter requires a derivation of transport equations for the CP-violating particles. For a long time, two different formalisms were used in the literature: the semi-classical method and the vev-insertion approximation. The latter typically yielded a much larger value for the asymmetry, such that certain models for electroweak baryogenesis were only consistent with observations if the vev-insertion approximation was correct. In this talk, I will argue that the CP-violating source derived in the vev-insertion approximation is a mere artefact, and in fact vanishes completely. 2022/12/5 (月)Title: Apperance of fixed singularities and modified normalization in the Borel-summed WKB method †Speaker: Ryo Namba †The Borel sum applied to the (Jeffreys-)Wentzel-Kramers-Brillouin (WKB) method, often called exact WKB, is a powerful tool for a systematic treatment of Schrodinger-type second-order differential equations and gives a mathematical interpretation of particle production in physics as the crossing of Stokes curves, as Koki Tokeshi showed at the RESCEU seminar on Nov. 14. However, interestingly, caution is needed in the cases where multiple turning points of a differential equation are connected by Stokes curves. This is due to the fact that a new type of singularities, called "fixed singularities", appear in the Borel-transformed space. A careful analysis can show that these singularities do not make the final result divergent but do change the asymptotic behavior of the Borel-summed solution. In this talk, I will show that the exact WKB method can reproduce the result of Koffman-Linde Starobinsky 1997 only after taking into account this modification. 2022/11/28 (月)Title: Introduction of machine learning and its application to physics of the universe. †Speaker: Takumi Hayashi †With the improvement of knowledge of information science and computation power of machine, the role of machine learning(ML) is growing in various field, also in physics. I review the basics of ML and the models widely used, and introduce its application to the problems of the physics familiar to us. Especially I focus on the estimation of the quasinormal modes of a blackhole ringdown, and show the comparison between ML and other traditional methods such as matched filtering, HHT, AR-model. [1] Giuseppe Carleo, Rev. Mod. Phys. 91, 045002 (2019), [arXiv:1903.10563]. 2022/11/21 (月)Title: Evaluating Witten Diagram †Speaker: Jason Kristiano †Witten diagram describes correlation of scalar fields at the boundary of Anti-de Sitter (AdS) space. In this talk, I will explain how to evaluate the simplest Witten diagram that is generated by three-point interaction. I will also introduce correspondence with conformal field theory (CFT) and definition of Mellin amplitude. [1] J. Penedones, TASI Lectures on AdS/CFT, arXiv:1608.04948. 2022/11/14 (月)Title: Exact WKB analysis †Speaker: Koki Tokeshi †The Wentzel-Kramers-Brillouin (WKB) method is known to give an approximate solution for Schroedinger equation. However, such an asymptotic series diverges in general. In this talk, I will introduce the Borel resummation method and see that it gives the corresponding regular and converging expression. I will also discuss Stokes phenomena, from which we have the connection formula of the regular solutions between different regions. [1] C. M. Bender and T. T. Wu, Phys. Rev., 184 (1969) 1231-1260. 2022/11/7 (月)Title: Charge teleportation †Speaker: Fumio Uchida †Magnetic monopoles could have electric charges at the same time as their magnetic charges, and they are called dyons when their electric charges are non-zero. As a generalization of Dirac’s quantization condition [1], Witten showed that electric charges of dyons are related to the CP-violating theta term (Witten effect) [2]. Its consequences in the presence of axion-photon coupling are discussed in, e.g., [3]. Among them, I will introduce charge teleportation between a dyon and an axion string [4]. [1] Dirac 1931 (https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1931.0130) 2022/10/31 (月)Title: Coleman-Weinberg Abrikosov-Nielsen-Olesen strings †Speaker: Ryusuke Jinno †We study properties of Abrikosov-Nielsen-Olesen (ANO) strings with the Coleman-Weinberg (CW) potential, which we call CW-ANO strings. While the scale-invariant scalar potential has a topologically trivial vacuum admitting no strings at the classical level, quantum correction allows topologically nontrivial vacua and stable string solutions. We find that the system of the CW potential exhibits significant difference from that of the conventional Abelian-Higgs model with the quadratic-quartic potential. While a single-winding string is qualitatively similar in both systems, and the static intervortex force between two strings at large distance is attractive/repulsive in the type-I/II regime for both, that between two CW-ANO strings exhibits a nontrivial structure. It develops an energy barrier between them at intermediate distance, implying that the string with winding number n > 1 can constitute a metastable bound state even in the type-II regime. We also discuss implications to high-energy physics and cosmology. 2022/10/24 (月)No seminar (JGRG31) 2022/10/17 (月)Canceled 2022/9/26 (月)Title: On the origin of primordial gravitational waves †Speaker: Paolo Campeti †An almost scale-invariant, Gaussian and parity-conserving stochastic gravitational 2022/8/29 (月)Title: Cosmology and the AB transition in superfluid helium 3 †Speaker: Mark Hindmarsh †The extreme purity and precise control of pressure and temperature achievable in the laboratory All calculations of the gravitational wave power spectrum rely on a relativistic version I discuss how the nucleation rate influences gravitational wave production 2022/8/8 (月)Title: The sunset glow of CMB †Speaker: Fumihiro Naokawa †The physics of CMB is mainly explained by Thomson scattering during the recombination epoch. We can also take Rayleigh scattering into consideration, but we have not detected that yet. Observing this effect corresponds to watching neutral hydrogen atoms right after the recombination, or in the beginning of the dark age. [1] B. Beringue et al., JCAP, 01 (2021) 060 2022/8/2 (火)Title: Magnetic Monopoles in the Early Universe †Speaker: Takeshi Kobayashi (SISSA) †13:30-15:00, onsite only, at room 1723 †2022/7/25 (月)Postponed to 8/8 |