# Seminar Report

## Special DMWG seminar : The latest results from the XENON1T experiment

2020-07-27

XENON1T collaboration has reported interesting results in June, which could be the signature of the physics beyond the standard model. We held a special DMWG seminar on July 22, inviting Prof. Yamashita, who is a specialist in the XENON1T data analysis, from Nagoya University. Many people from various research fields have registered and participated in this online seminar. The number of registrants is more than 180 while the participants than 100. We first would like to apologize to our guests, especially to whom could not attend the seminar although they have registered due to our trouble with the webinar system.

XENON1T is an experiment aiming to detect the scattering between dark matter (DM) and a xenon nucleus. Xenon is one of the best targets material for WIMP (Weakly Interacting Massive Particle) because of its stability and the large atomic number. By setting the detector deep underground, the cosmic-ray scattering event, which is the main source of the background, is efficiently removed. The original experiment was started in 2005 (XENON10) and after several upgrades, XENON1T has completed its first observing run in 2018.

The signature of the so-called nuclear recoil event is searched to detect WIMP. There is another type of event referred to as the electronic recoil event, which is also useful to detect other DM signatures, and this seminar focuses on such a kind of event. The target region of the DM parameter space is different between these two event types. The 285 electronic recoil events over the expected 217-247 from the background are observed in the recoil energy range of 1-7keV during the 1st observing run of the XENON1T experiment.

In this talk, Prof. Yamashita has explained the details of the analysis and the possible interpretation of the signature. Starting from the introductions about the possible background considered in the traditional analysis, the statistical treatments, and also the model fitting results are provided. There are several possibilities for explaining the excess: (i) tritium background, (ii) solar axion, (iii) anomalous neutrino magnetic moment, and (iv) bosonic DM. If the excess is explained by tritium (i), it means that we have detected the first tritium background events while others indicate the detection of the signatures of the new physics. Solar axion (ii) could fit the recoil spectrum beautifully, however, there may not be consistent with the results from astrophysical observations. The neutrino scenario (iii) is another possibility with less significance, and the significance of the bosonic DM scenario (iv) could not over the 3.0 sigma.

The excess itself is convincing while it is difficult to conclude its origin. Abobe-mentioned possibilities are planned to be tested with further upgrades of the XENON1T experiment, XENONnT. We should be excited about the results in the near future. Stay tuned!

DMWG special seminar : “The result of the XENON1T experiment and its implications”

July 22 at 15:30 - 17:00, 2020

# Seminar Report

## Math seminar by Dr. Yuichi Ike on July 15, 2020

2020-07-20

We have all heard that "data is the new oil". But just like any fossil resource, data also has to be worked with to use it effectively. In his talk, titled "Topological data analysis from a practical and mathematical perspective", Dr. Yuichi Ike from Fujitsu highlighted several mathematical aspects of data processing as well as relevant applications in the health sector.

In the first part of the talk, the audience was introduced to basic concepts of topological data analysis. The goal of this technique is to infer the shape of data - i.e. topological quantities such as the number of connected components, loops, cavities, etc. - from the input data points. While the shape is represented by the homology group in the continuous case, the discrete case calls for different methodology. One possible technique is the creation of persistence diagrams to identify critical components.

In a general application workflow, these approaches appear as follows. From the input data, its persistent homology is computed, visualized via a persistence diagram, and finally passed on to experts for evaluation. This has applications in material sciences and time series analysis as well as medical settings. Here, a recent work of the speaker was able to reduce misclassifications in a diagnosis setting by up to 70%.

The second part of the talk was devoted to the mathematical foundations of the presented work, namely on persistence-like distance on the sheaf category and displacement energy. Starting from elements in symplectic geometry, via a Morse theory for sheaves, the speaker integrated several mathematical fields. Finally, after introducing the non-displacement theorem, the audience learned about several proofs in the field. Thus, the talk nicely tied current relevant applications to deep results in theoretical mathematics.

Topological data analysis from a practical and mathematical perspective

July 15 at 16:00 - 18:10, 2020

# Hot Topic

## iTHEMS Science Outreach Workshop 2020 was held on July 3 and 4

2020-07-27

On July 3 and 4, we had Journalist in Residence Workshop 2020 on Zoom. It had been planned to be held at Tambara Institute of Mathematical Sciences of the University of Tokyo as in a same way as May 31 - June 3 of the last year 2019. This year, Tambara Institute is closed because of COVID-19 but we organized it on Zoom. There were in fact much more participants than last year and those living in US also participated in the meeting. The participants included 14 journalists and 17 participants from RIKEN, 9 from universities and 2 from others. 7 iTHEMS members mainly explained their working field and recent important achievements to the nonspecialists. There were 24 talks in total in a variety of fields. The discussion among the participants continued with joy in the evening of July 3 even in ZOOM. If we organize next year, it will be necessary to include online participants.

iTHEMS Science Outreach Workshop 2020

July 3 - 4, 2020

# Upcoming Events

## Seminar

### Stability of ferromagnetism in many-electron systems

July 31 at 16:00 - 18:10, 2020

Prof. Tadahiro Miyao (Associate Professor, Department of Mathematics, Faculty of Science, Hokkaido University)

First part

Title: Stability of ferromagnetism in many-electron systems

Abstract:

I construct a model-independent framework describing stabilities of ferromagnetism in strongly correlated electron systems. Within the new framework, I reinterpret the Marshall-Lieb-Mattis theorem and Lieb’s theorem; in addition, from the new perspective, I prove that Lieb’s theorem still holds true even if the electron-phonon and electron-photon interactions are taken into account. I also examine the NagaokaThouless theorem and its stability. These examples verify the effectiveness of the new viewpoint.

Second part

Title: Order preserving operator inequalities in many-electron systems

Abstract:

In this talk, I will introduce order preserving operator inequalities and explain how these inequalities are applied to the mathematical study of ferromagnetism. As examples of applications, Lieb's theorem of the Hubbard model and its stabilities will be discussed in terms of the inequalities.

Venue: via Zoom

Event Official Language: English

## Seminar

### Nambu-Goldstone fermion in a Bose-Fermi mixture with an explicitly broken supersymmetry

August 7 at 13:00 - 14:30, 2020

Dr. Hiroyuki Tajima (PhD, Department of Natural Science, Kochi University)

Supersymmetry, which is a symmetry associated with interchange between bosons and fermions, is one of the most important symmetries in high-energy physics but its evidence has never been observed yet. Apart from whether supersymmetric partners such as squark exist or not in our world, it is an interesting problem to explore the consequences of the supersymmetry in an ultracold atomic gas. In this study, we address the Nambu-Goldstone mode called Goldstino associated with the spontaneous supersymmetry breaking in a Bose-Fermi mixture. While the explicit supersymmetry breaking is unavoidable even in cold atomic systems, the energy gap in Goldstino spectra can be measured in such atomic systems. By comparing the energy gaps obtained from the Gell-Mann-Oakes-Renner relation and the random phase approximation, we elucidate how the Goldstino acquires the energy gap due to the explicit breakings. We also show effects of Goldstino pole on the fermionic single-particle spectral functions, which can be measured in the recent experiments.

Venue: via Zoom

Event Official Language: English

# Paper of the Week

## Week 4 & 5 of July

2020-07-30

Title: Community analysis of inter-firm networks with graph convolutional networks

Author: Shunsuke Ohkoda, Yasuhiro Yamaguchi, Takeru Nitta, Yoshimasa Hidaka, Takahiro Doi, Masaki Yanaoka, Atsushi Takemasa

doi: 10.11517/pjsai.JSAI2020.0_1N5GS1301

Title: Performance correlation analysis of business-to-business transactions and its application to corporate growth forecast

Author: Takahiro Doi, Shunsuke Ohkoda, Takeru Nitta, Yoshimasa Hidaka, Yasuhiro Yamaguchi, Masaki Yanaoka, Atsushi Takemasa

doi: 10.11517/pjsai.JSAI2020.0_1N4GS1305

Title: Dynamics of interfirm trading network based on multi-agents based model

Author: oshimasa Hidaka, Shunsuke Ohkoda, Takeru Nitta, Takahiro Doi, Yasuhiro Yamaguchi, Masaki Yanaoka, Atsushi Takemasa

doi: 10.11517/pjsai.JSAI2020.0_4G3GS701

Title: X-ray Hotspots in the Northwest Shell of the Supernova Remnant RX J1713.7−3946

Author: Ryota Higurashi, Naomi Tsuji, Yasunobu Uchiyama

arXiv: 2006.15796

Title: Resolving acceleration to very high energies along the Jet of Centaurus A

Author: The H.E.S.S. Collaboration, Tsuji, N

doi: 10.1038/s41586-020-2354-1

arXiv: 2007.04823

Title: Improved thermal area law and quasi-linear time algorithm for quantum Gibbs states

Author: Tomotaka Kuwahara, Álvaro M. Alhambra, Anurag Anshu

arXiv: http://arxiv.org/abs/2007.11174v1

Title: Dirichlet Series with Periodic Coefficients and their Value-Distribution Near the Critical Line

Author: Athanasios Sourmelidis, Jörn Steuding, Ade Irma Suriajaya

arXiv: http://arxiv.org/abs/2007.14008v1

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