In this talk, I will discuss perturbative quantum gravity at the 1-loop level by reviewing and systematizing old results on UV divergences and presenting new findings along with new methods for their calculation. The traditional approach to this problem employs the Schwinger-DeWitt heat kernel method. We extend this approach by incorporating worldline path integrals to compute the perturbative expansion at small proper time. In addition, we explore a more principled approach that utilizes the BRST path integral quantization of the N=4 spinning particle, which describes the graviton in first quantization. Using these methods, we calculate the one-loop divergences in quantum gravity with a cosmological constant in arbitrary dimensions. When evaluated on-shell, these calculations yield a set of gauge-invariant coefficients that characterize pure quantum gravity with a cosmological constant. These coefficients may serve as benchmarks for comparing various approaches to quantum gravity.

The presence of hyperons in the neutron star interior have been investigated by many researchers using both phenomenological and microscopic approaches for the equation of state (EOS) of neutron star matter with hyperons. However, hyperon fractions in nuclear matter are still far from being understood, since there are relatively large uncertainties in hyperon interactions due to the small amount of the experimental data. Furthermore, recently observed masses of massive pulsars impose severe constraints on the hyperon EOS.
In this seminar, I will review the recent results of microscopic nuclear EOS including hyperons and its applications to astrophysical compact objects to discuss the possible signatures of the presence of hyperons in compact star interiors. In particular, I will discuss the effect of three-body forces including hyperons on the structure and particle composition of (proto) neutron stars.

I will start my talk with a brief overview of the standard reheating scenario. Then, I will discuss reheating through the evaporation of primordial black holes (PBHs) if one assumes PBHs are formed during the phase of reheating. Depending on their initial mass, abundance, and inflaton coupling with the radiation, I discuss two physically distinct possibilities of reheating the universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs, while inflaton plays the role of the dominant energy component in the entire process. In the other possibility, PBHs dominate the total energy budget of the universe during evolution, and then their subsequent evaporation leads to a radiation-dominated universe. Furthermore, I will discuss the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized. The evaporation of PBHs is also responsible for the production of DM. I will show its parameters in the background of reheating obtained from two chief systems in the early universe: the inflaton and the primordial black holes (PBHs). Then, I will move my discussion towards stable PBHs and discuss the effects of the parameters describing the epoch of reheating on the abundance of PBHs and the fraction of cold dark matter that can be composed of PBHs. If PBHs are produced due to the enhancement of the primordial scalar power spectrum on small scales, such primordial spectra also inevitably lead to strong amplification of the scalar-induced secondary gravitational waves (GWs) at higher frequencies. I will show how the recent detection of the stochastic gravitational wave background (SGWB) by the pulsar timing arrays (PTAs) has opened up the possibility of directly probing the very early universe through the scalar-induced secondary gravitational waves. Finally, I will conclude my talk by elaborating on the effect of quantum correction on the Hawking radiation for ultra-light PBHs and its observational signature through dark matter and gravitational waves.

14:45-15:00 Teatime discussion
15:00-16:00 Talk by Prof. Satoshi Taguchi (Professor, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University)
16:15-17:15 Talk by Prof. Yoshihiro Morishita (Professor, Division of Biological Sciences, Graduate School of Science, Kyoto University)
17:15-18:00 Discussion

The evolution of spiteful and altruistic behaviour remains a fascinating and somewhat puzzling phenomenon. In recent years there has been interest in examining how stochasticity arising from a finite population size might affect the evolution of these traits. Some results suggest that such stochasticity can reverse the direction of selection and promote the evolution of traits like altruism and spitefulness that are selected against in very large (deterministic) populations. However, other results seem to call this finding into question. In this talk I will consider a simple but quite general model of spite and of altruistic behaviour and examine how demographic stochasticity affects the evolution of these traits. I will show that stochasticity can indeed affect the direction of evolution but not in the way that previous studies have suggested. The results also help to clarify the broader issue of how and why stochasticity can sometimes reverse the direction of evolution.

The problem of embedding abstract Riemannian manifolds isometrically (i.e. preserving the lengths) into Euclidean space stems from the conceptually fundamental question of whether abstract Riemannian manifolds and submanifolds of Euclidean space are the same. As it turns out, such embeddings have a drastically different behaviour at low regularity (i.e. C¹) than at high regularity (i.e. C²). For example, by the famous Nash--Kuiper theorem it is possible to find C1 isometric embeddings of the standard 2-sphere into arbitrarily small balls in R³, and yet, in the C² category there is (up to translation and rotation) just one isometric embedding, namely the standard inclusion. Analoguous to the Onsager conjecture in fluid dynamics, one might ask if there is a sharp regularity threshold in the Holder scale which distinguishes these flexible and rigid behaviours. In my talk I will review some known results and argue why the Holder exponent 1/2 can be seen as a critical exponent in the problem.

Quantum simulation is a novel method of simulation physical systems with quantum computers. Compared to conventional methods, quantum algorithms have various advantages in doing non-perturvative calculations and real-time evolutions, which makes it very promising to apply them in high energy nuclear physics. We propose a systematic quantum algorithm, which integrates both the hadronic state preparation and the evaluation of real-time light-front correlators. This algorithm can be applied to the calculation of a wide range of quantities in high energy nuclear physics. As a demonstration, we calculate the parton distribution functions, the light-cone distribution amplitudes and scattering amplitudes in the 1+1 dimensional NJL model. The results are qualitatively consistent with QCD calculations.

9:30-10:00 Keynote by Lucy Mcneill
10:00-10:30 Keynote by Jose Said Gutierrez Ortega
10:35-11:05 Keynote by Puttarak Jai-akson
11:05-11:35 Keynote by Kannaka Kazuki

11:35-12:30 Lunch Time Session

12:30-13:30 Working Group / Study Group Report

13:30-15:30 Flash Talk & Poster Presentation Part 1

15:30-17:30 Flash Talk & Poster Presentation Part2
17:30 Concluding Remarks by the Director

18:00 reception

Recently, the layered honeycomb material α-RuCl3 exhibits several anomalous features that are consistent with expectations of the Kitaev quantum spin liquid (KQSL) under in-plane magnetic field. Most remarkably, finite planar thermal Hall conductivity has been observed, whose magnitude is close to the half-integer quantization value expected for the chiral edge currents of Majorana fermions[1]. However, it has been reported that the thermal Hall conductivity shows strong sample dependence. Also, there are attempts to offer a different explanation by the bosonic edge excitations due to topological magnons or phonon. A key to distinguishing between fermionic and bosonic origins of unusual features in the high-field state of α-RuCl3 is the difference in the field angle dependence of the excitation gap.

Therefore, we distinguish these origins from combined low-temperature measurements of high-resolution specific heat and thermal Hall conductivity with rotating magnetic fields within the honeycomb plane. A distinct closure of the low-energy bulk gap is observed for the fields in the Ru-Ru bond direction, and the gap opens rapidly when the field is tilted. Notably, this change occurs concomitantly with the sign reversal of the Hall effect. General discussions of topological bands show that this is the hallmark of an angle rotation–induced topological transition of fermions, providing conclusive evidence for the Majorana-fermion origin of the thermal Hall effect in α-RuCl3[2].

Furthermore, to understand the nature of the high-field state, it is crucial to elucidate the effects of disorder, which inevitably exists in real materials. We artificially introduce point defects by electron irradiation and compare the low-energy excitations in the pristine and irradiated sample by high-resolution specific heat measurements. We observed an additional in-gap T-linear term in C/T, whose coefficient shows distinct field-sensitive behaviors suggestive of Majorana physics in the KSL. This can be interpreted by the weak localization of Majorana fermions, which is induced by the disorder[3]. Moreover, recently, we succeed in synthesizing very high-quality crystals of α-RuCl3[4].

Humans and other organisms develop collective behaviors through interactions with diverse environments and various species. These behaviors are significant topics across multiple research fields, including evolutionary biology, behavioral ecology, and animal sociology. Unraveling the decision-making mechanisms of individuals in groups within cooperative and competitive contexts has captured the attention of many researchers but remains a complex challenge. This seminar will present research cases that employ multi-agent reinforcement learning, a machine learning technique, to investigate the decision-making processes underlying collective behavior. Through this approach, we aim to provide deeper insights into the dynamics and mechanisms that drive group behaviors in various biological systems.

In mathematics, contact geometry is a type of geometry describing a variety of dynamical systems. They are the phase spaces of systems arising in geometric optics, semi-classical quantum systems, classical dynamics, and control theory. On the mathematical side, contact geometry relates to a variety of other geometric structures, such as Kahler geometry, smooth topology, and foliation theory. It can be especially interesting to look at contact geometry in 3-dimensional space, because we can explicitly visualize the spaces. Additionally, by connecting contact geometry with our understanding of 3-D topology, mathematicians have the ability to understand the large-scale structure of these spaces like never before.
The talk will introduce the basics of contact geometry and its applications. We'll particularly focus on the 3-dimensional case, while also mentioning some of the unique properties of higher-dimensional spaces which are recently being explored.

Registration required: Register before Wednesday, July 24, 15:00.