A UV theory is required in order to describe the origin of late-time Hawking radiation. In this talk, I will explore Hawking radiation in a non-local model of the radiation field inspired by Witten's open string field theory. An attempt at extracting the correlators of this theory will be discussed, which leads to a space-time uncertainty relation. As a result, the characteristics of trans-Planckian field modes differ significantly from that in the standard low-energy effective theory, and I will argue that this ultimately results in the termination of Hawking radiation around the scrambling time of the black hole.

(The speaker is also a professor at University of Amsterdam & QuSoft. This is a joint seminar with the iTHEMS Quantum Computation Study Group.)

One of the major challenges in computer science is to establish lower bounds on the resources, typically time, that are needed to solve computational problems, especially those encountered in practice. A promising approach to this challenge is the study of fine-grained complexity, which employs special reductions to prove time lower bounds for many diverse problems based on the conjectured hardness of key problems.
For instance, the problem of computing the edit distance between two strings, which is of practical interest for determining the genetic distance between species based on their DNA, has an algorithm that takes O(n^2) time. Through a fine-grained reduction, it can be demonstrated that a faster algorithm for edit distance would imply a faster algorithm for the Boolean Satisfiability (SAT) problem. Since faster algorithms for SAT are generally considered unlikely to exist, this implies that faster algorithms for the edit distance problem are also unlikely to exist. Other problems used for such reductions include the 3SUM problem and the All Pairs Shortest Path (APSP) problem.
The quantum regime presents similar challenges; almost all known lower bounds for quantum algorithms are defined in terms of query complexity, which offers limited insight for problems where the best-known algorithms take super-linear time. Employing fine-grained reductions in the quantum setting, therefore, represents a natural progression. However, directly translating classical fine-grained reductions to the quantum regime poses various challenges.
In this talk, I will present recent results in which we overcome these challenges and prove quantum time lower bounds for certain problems in BQP, conditioned on the conjectured quantum hardness of, for example, SAT (and its variants), the 3SUM problem, and the APSP problem. This presentation is based on joint works with Andris Ambainis, Bruno Loff, Florian Speelman, and Subhasree Patro.

14:45-15:00 Teatime discussion
15:00-16:00 Talk by Dr. Wataru Morita (Researcher, Department of Anthropology, National Museum of Nature and Science / Associate Professor, Department of Biological Sciences, Graduate School of Science, The University of Tokyo)
16:15-17:20 2024 Study Group introduction session
17:30-18:30 Discussion

In this RIKEN DAY, we will introduce various phenomena in the world (all things in the universe) that are understood using "mathematics” and the use of "mathematics", including the latest research, while looking at the annual S&T poster for everyone titlled “Mathematics: One S&T poster for Every Household”.

For details, please see the related links.

We will learn about nuclear fusion and related subjects, such as turbulence in astronomy and astrophysics, from experts and discuss possible interdisciplinary collaborations in the near future. Some researchers will visit RIKEN iTHEMS from the National Institute for Fusion Science (NIFS) and other universities and research institutes for the workshop. We will have the workshop in a hybrid style so that many researchers in Japan can hear the presentations even remotely. This workshop is supported by Moonshot Goal 10 (Program Director Yoshida Zensho (NIFS)).

Program
Session１
9:00-9:35 (25+10: 25 mins for Presentation, 10 mins for Q&A)：Shinya Maeyama
9:35-10:10 (25+10): Naoki Sato
10:10-10:45 (25+10): Yohei Kawazura
10:45-11:15 Coffee Break
Session２
11:15-11:50 (25+10): Takanobu Amano
11:50-12:25 (25+10): Yosuke Matsumoto
12:25-13:00 (25+10): Akira Mizuta
13:00-14:00 Lunch Break
Session３
14:00-14:35 (25+10): Chiho Nonaka
14:35-15:10 (25+10): Takeo Hoshi
15:10-15:45 (25+10): Motoki Nakata
15:45-16:15 Coffee Break
Session ４
16:15-16:50 (25+10): Kumiko Hori
16:50-17:25 (25+10): Yutaka Ohira
17:25-18:00 (25+10): Camilia Demidem (TBC)
18:30-20:30: Dinner in the Main Research Building.

Drawing from a thought experiment that we conduct, we propose that a virtual graviton gives rise to a black hole geometry when its momentum surpasses a certain threshold value on the Planck scale. This hypothesis implies that the propagator of a virtual graviton, that possesses momentum surpassing this threshold, vanishes. Consequently, a Feynman diagram containing this type of graviton propagator does not add to the overall amplitude. This mechanism suggests the feasibility of formulating an ultraviolet-finite four-dimensional quantum gravitational theory. The elementary particles including the gravitons are treated as point particles in this formulation.

Thanks to intensive research efforts, topology has been established as a fundamental concept in physics. For closed quantum systems, the classification of gapped topological phases has matured. Moreover, the importance of topology is not limited to isolated quantum systems. Recently, the topology of non-Hermitian Hamiltonians, which effectively describe systems with dissipation, has attracted much attention worldwide. This fascination is exemplified by topological phases and topological phenomena unique to non-Hermitian systems.

Against this background, the primary purpose of this workshop is to bring together researchers working on topological phases and to discuss (i) open questions in topological phases of closed quantum systems and (ii) the role of topology in open quantum systems and measurements.