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The 121-130th REM talks

The 130th REM: Apr. 3rd, 2025

• Time: 11:00-12:00
• Speaker: Ignacio Magaña Hernandez (Carnegie Mellon University)

  • Title: "Binary black hole populations and cosmology with gravitational-wave observations"

    • Abstract:

      Since the first detection of gravitational waves (GWs) from the merger of two stellar-mass black holes in 2015, the LIGO-Virgo-KAGRA (LVK) Collaboration has accumulated over 90 observations of mergers involving neutron stars and black holes. With upcoming observing runs for the LVK network of GW detectors, many more binary mergers are expected to be detected. The increasing size of gravitational wave catalogs has enabled the study of their population and its cosmic expansion history. In this talk, I will discuss the latest constraints on the BBH population, focusing on models that search for astrophysical subpopulations driven by various formation channels with both parametric and fully data-driven methods. Then, I will explain how the BBH mass spectrum can be used as a calibrating scale to measure cosmology—providing a GW data-only way to do cosmology. Lastly, I will demonstrate how using galaxy survey information as a prior on potential galaxy hosts for BBH mergers can improve our cosmological measurements.

The 129th REM: Mar. 4th, 2025

• Time: 14:00-15:00
• Speaker: Yusuke Okuma (JAXA ISAS/UTokyo)

  • Title: "Development of Back-Linked Fabry-Perot Interferometer for Space Gravitational Wave Telescopes"

    • Abstract:

      Currently, space-based gravitational wave telescopes are being planned to observe low-frequency gravitational waves. Among them, DECIGO and B-DECIGO, which aim to observe gravitational waves in the 0.1 Hz band, propose a method using Fabry-Pérot cavities. One of the topologies for space-based gravitational wave detectors using cavities is the Back-Linked Fabry-Perot Interferometer (BLFPI).
      A BLFPI equips two lasers for each space craft and controls the frequencies of six lasers to satisfy six resonance conditions. This eliminates the need for precise control of the spacecraft's orbit. However, since the gravitational wave signal is obtained by interfering two independent lasers, the signal is contaminated by laser frequency noise.
      In a BLFPI, post-processing is performed using the beat signal and the error signal used for frequency control. Through post-processing, laser frequency noise is reduced, and gravitational wave signals distorted by finite control accuracy are restored.
      In this study, we constructed a BLFPI setup in the laboratory and conducted experiments to demonstrate the ability to recover gravitational wave signals through post-processing. To achieve this, a method was used to inject simulated gravitational wave signals into the experimental setup using an auxiliary laser. The simulated-gravitational wave signals were then injected into the system, and post-processing was applied to test whether the injected signals could be recovered.

The 128th REM: Feb. 6th, 2025

• Time: 11:00-12:00
• Speaker: Anarya Ray (Northwestern University)

  • Title: "Population Properties of Merging Compact Binaries: Astrophysical Implications and Source Classification"

    • Abstract:

      In the era of growing gravitational wave (GW) catalogs and multi-messenger astronomy, understanding the ensemble properties of merging compact binaries is of fundamental importance. Constraining phenomenologically parametrized and flexible models for the population-level distributions of compact object parameters from GW data will reveal key insights into the uncertain astrophysical mechanisms of compact binary formation. Moreover, specific classes of systems—such as binary neutron stars (BNSs), binary black holes (BBHs), and neutron star–black hole (NSBH) binaries—are expected to exhibit distinct population properties. Constraining these properties can, in turn, facilitate source classification, a crucial step in optimizing the search for multi-messenger counterparts to GW signals from BNSs and NSBHs.
      In this talk, I will discuss GW population inference and its astrophysical implications, with a focus on data-driven methods and findings from the third GW transient catalog. Additionally, I will explore how knowledge of population distributions can be leveraged to classify compact binary merger systems in real-time, thereby optimizing the search for multi-messenger counterparts, which are expected predominantly from neutron star-containing mergers. I will conclude with a discussion on the future prospects of these investigations, including a self-consistent approach to population inference and source classification, in the context of upcoming observing runs of ground-based GW detectors.

The 127th REM: Dec 10th, 2024

• Time: 11:00-12:00
• Speaker: Kazuhiro Agatsuma (EX-Fusion Inc.)

  • Title: "A career path from gazing star to making star"

    • Abstract:

      I show my career path from the field of gravitational waves (GWs) to the field of laser inertial fusion energy (IFE). I have worked on several projects in the GW community for 16 years, for example, TAMA300, CLIO, KAGRA, Ad-Virgo, and Ad-LIGO. The study subjects were broad; seismic attenuation system, pendulum thermal noise, radiation pressure noise, phase camera, and the expansion of the universe. The pandemic caused serious damage in my career, but gave me a chance to challenge another field (IFE). 
      In addition, I show my recent work in EX-Fusion Inc. that is a startup company in Japan. Our goal is to realize a commercial laser fusion reactor. In the future reactor a highly repetitive operation is essential to generate sufficient energy. The fuel targets must be illuminated by the laser spot continuously. However, the target injection system has a limited precision, which causes the target trajectories to fluctuate. The fusion rate can be degraded by a mismatch at the engagement point. We have demonstrated a laser target tracking system to solve this issue. A continuous illumination of targets by 10-Hz operation has been achieved by a controlled mirror. Recently, we have upgraded this system by a new steering mirror, which has a local control system with techniques of GW detectors. 

The 126th REM: Oct. 31st, 2024

• Time: 11:00-12:00
• Speaker: Kazuya Kobayashi (ICRR)

  • Title: "Parameter Estimation from Gravitational-wave Data Generated by Compact Binary Coalescences"

    • Abstract:

      Bayesian inference is used to estimate parameters such as masses and spins from gravitational wave data generated by compact binary coalescences.
      This method allows us to calculate the posterior probability distribution of the parameters.
      However, since analytical computation in Bayesian inference is difficult, numerical methods such as MCMC sampling are employed.
      In this talk, I will introduce parameter estimation methods, summarize LIGO-Virgo-KAGRA collaboration results, and present my research on parameter estimation.

The 125th REM: Oct 8th, 2024

• Time: 14:00-15:00
• Speaker: Satoru Takano (AEI)

  • Title: "Torsion pendulum detector towards gravity gradient detection"

    • Abstract:

      Torsion pendulum detector is proposed as a ground-based gravitational wave detector focusing on the 0.1 Hz frequency band [1]. The detector, TOBA (TOrsion-Bar Antenna), consists of two perpendicular torsion pendulums and the small stiffness of the torsion pendulum enables the detector to respond to gravitational waves in low frequencies. The target of TOBA is to observe GWs from IMBH binaries with 10 m bars. To demonstrate the measurement principle and establish necessary techniques, our group has developed small prototypes for more than 10 years. Now we are developing a prototype, Phase-III TOBA.
      Phase-III TOBA is a big milestone towards the final detector. One of the key features is the cryogenic technique for reduction of thermal noises. Recently, we have demonstrated the cryogenic torsion pendulum cooled down to 6 K[2] and the monolithic readout system made of silicon[3]. I will introduce our TOBA experiment and talk about recent progress.
      
      [1] M. Ando et al., PRL, 105, 161101 (2011)
      [2] T. Shimoda, Ph.D Thesis, The University of Tokyo (2020)
      [3] S. Takano, Ph.D Thesis, The University of Tokyo (2024)

The 124th REM: September 5th, 2024

• Time: 11:00-12:00
• Speaker: Ish Gupta (Penn State)

  • Title: "Expectations and Challenges on the Path to the Next-Generation of Gravitational-Wave Discovery"

    • Abstract:

      The current generation of gravitational-wave detectors have detected close to two hundred binary mergers. These detect ions have imposed constraints on astrophysical populations of binaries, alternate theories of general relativity, cosmological parameters, and the equation of state of the neutron star. Notably, these achievements have been realized despite significant challenges, such as limited localization for most events and the rarity of confidently detected neutron star binaries. Thus, to extract the full potential of gravitational-wave astronomy, bigger and more sensitive detectors are needed. This need will be fulfilled with the Cosmic Explorer and the Einstein Telescope observatories, which are intended to be significantly more sensitive than the current generation. Such observatories will not only increase the number of detections by orders of magnitude, they will also allow for precise estimation of parameters, leading to an era of precision cosmology, refined astrophysical inference and optimized targeted electromagnetic follow-up. In this talk, I will highlight some of these science objectives that will be accomplished by next-generation detectors and address the challenges that must be overcome to realize these objectives, underscoring the importance of concerted efforts in advancing gravitational-wave astronomy.

The 123rd REM: Jul 30th, 2024

• Time: 15:00-16:00
• Speaker: Taichi Kawamura (Institut de Physique du Globe de Paris)

  • Title: "Seismic Environment of the Moon"

    • Abstract:

      Abstract: More than 50 years after the first landing on the Moon, lunar exploration has once again become a global trend. In the past decade alone, over eight successful lunar landings have been completed, reflecting a growing scientific interest in the Moon. While lunar science remains a primary focus, the potential to utilize the Moon as a natural laboratory for physics and astrophysics is also being explored. Recently proposed experiments include a lunar-based radio astronomy space telescope and a gravitational wave detector. For such projects to be feasible, it is essential to thoroughly understand the Moon's environment, particularly its seismic activity and associated risks. Observations from the Apollo missions have shown that the Moon remains seismically active, experiencing "moonquakes" almost daily. In this presentation, I will review the seismic data obtained from the Apollo experiments and discuss the Moon's seismic environment. I will conclude by highlighting key considerations for future lunar projects.

The 122nd REM: June 27th, 2024

• Time: 11:00-12:00
• Speaker: Prathamesh Joshi (Penn State)

  • Title: "How are gravitational-wave searches for compact binaries performing, and where are they headed?"

    • Abstract:

      During the fourth observing run of the LVK collaboration, we have already seen large improvements in the results produced by the CBC search pipelines in low-latency. We have reached new levels of sensitivity and reliability. In the quest to detect every gravitational wave out there, we are now more ready than ever to participate in the next multimessenger event. In this presentation, I will talk about how the searches work, and some recent search results we have seen in O4. As we start getting high-latency offline results, we will begin to explore gravitational waves from new parameter spaces. We are seeing advancements in searches for precessing binaries, higher order modes of gravitational waves, as well as unmodeled or burst searches. I will discuss how these improvements will play a crucial role in obtaining a better scientific understanding of some of the biggest mysteries of the universe.

The 121st REM: May 30th, 2024

• Time: 11:00-12:00
• Speaker: Kenta Tanaka (ICRR)

  • Title: "Introduction to laser interferometric GW telescope and Current status of KAGRA"

    • Abstract:

      Gravitational wave astronomy has made remarkable progress since its first detection in 2015. The Japanese gravitational wave telescope, KAGRA, is currently undergoing an upgrade to participate in the 4th International Joint Observations with LIGO (USA) and Virgo (Europe). In this talk, I will introduce gravitational waves and the telescopes used for their detection, and provide an update on the current status of KAGRA for new students.