Bubbles in the Self-Accelerating Universe

We revisit the issue of the stability in the Dvali-Gabadadze-Porrati model, by considering the nucleation of bubbles of the conventional branch within the self-accelerating branch. We construct an instanton describing this process in the thin wall approximation. On one side of the bubble wall, the bulk consists of the exterior of the brane while on the other side it is the interior. The solution requires the presence of a 2-brane (the bubble wall) which induces the transition. However, we show that this instanton cannot be realized as the thin wall limit of any smooth solution. Once the bubble thickness is resolved, the equations of motion do not allow O(4) symmetric solutions joining the two branches. We conclude that the thin wall instanton is unphysical, and that one cannot have processes connecting the two branches, unless negative tension bubble walls are introduced. This also suggests that the self-accelerating branch does not decay into the conventional branch nucleating bubbles. We comment on other kinds of bubbles that could interpolate between the two branches.Comment: 8 pages, 5 figure

Realization of Berezinskii's superconductivity in quasi-one-dimensional systems

We revisit the pairing symmetry competition in quasi-one-dimensional systems. We show that spin-triplet s-wave pairing, where the pair is formed by electrons with different times and has an odd-frequency symmetry, can be realized in systems with strong one-dimensionality when the strength of charge fluctuation dominates over spin fluctuation. The present study provides a novel microscopic mechanism for this exotic pairing originally proposed by Berezinskii in 1974.Comment: 4 pages, 4 figure

Understanding and utilizing students’ attitudes toward participation in discussions by using emotion analysis

We propose a method that uses an emotion analysis for PBL education. The emotion analysis is a method of analyzing a person's emotions from the person's remarks or facial expressions. In this method, teachers understand the situation of students from the results of the emotion analysis and give accurate advice. PBL education often involves group activities. The students conducted groups discuss, propose ideas, select ideas, and make the products. However, not all students are able to participate in discussions and express their opinions. It is the teacher's duty to provide guidance to such students. Therefore, we propose the use of the emotion analysis techniques to identify and guide students who have problems, such as those who cannot participate in discussions. The method is possible for one teacher to grasp multiple groups at the same time and to help developing the students' ability to learn. Under COVID-19, face-to-face classes were restricted. Online classes using Zoom etc. have also been introduced in PBL education. In online classes, it is difficult to grasp the situation of students. This was a big difference from face-to-face classes. So we looked at ways to keep track of the situation for all students. This is because the gap between students who are willing to take classes and those who are reluctant to take classes has widened due to the shift to online classes. As a result of the adaption to the classes, the number of students who actively participate in the classes has increased. The effectiveness of the proposed method was confirmed