Program
https://sci.nao.ac.jp/MEMBER/kohri/programKEK-NAOJ2025Fall.html
Abstract
- School Year: D3 (KEK)
- Name: Haruki Takahashi (髙橋 晴輝)
- Title:Model uncertainty of axion search using ultra-high energy gamma-ray
observation
- Abstract:
Axions are one of the candidates for dark matter in the Universe. One
way to search for axions is through gamma-ray observation. If there
exist axions in the Universe, gamma rays emitted from some sources can
be converted into axions, vice versa, by magnetic fields in several
astrophysical environments. Constraints on axion mass and its coupling
to photons have been given by looking for its signal in observed gamma
ray spectra. Not only extra-galactic sources but also galactic sources
have been recently used for this kind of analysis, but model
uncertainties were not taken into account well. In this work, we
investigate their impacts on axion search and give conservative
constraints on axion parameters using ultra-high energy gamma-ray
observations.
- School Year: D2 (UTokyo)
- Name: Kanako Narita（成田 佳奈香）
- Title: Probing Axion-like Dark Matter via Time-Variable Polarization
in Protoplanetary Disks
- Abstract:
Among the various dark matter candidates, axion-like dark
matter—particularly in the ultralight regime around 10^−22 eV—has
attracted significant attention in recent years, as it has been
proposed as a potential solution to the small-scale structure problems
in the standard cosmological model. In this talk, we present a new
observational constraint on ALP dark matter based on archival data
from the Very Large Telescope (VLT). Specifically, we analyze
time-series polarimetric data of HD 163296 and place limits on the
coupling between ALP dark matter and photons. Furthermore, we show
that if the uncertainty in the polarization angle can be reduced to
0.01° and high-cadence monitoring is achieved, the existing upper
bounds can be significantly improved. This demonstrates the potential
of time-domain polarimetry of nearby young stellar objects as a novel
probe of ultralight dark matter.
- School Year: D2 (NAOJ)
- Name: Kuria Watanabe（渡辺 くりあ）
- Title:
The Chemical Enrichment and Origin of Nitrogen-Rich Galaxies at High
Redshift
- Abstract:
Observations with the James Webb Space Telescope (JWST) have revealed
galaxies at z > 6 with unusually high nitrogen-to-oxygen ratios ([N/O]
> 0.4). The origin is debated, with potential sources including
Wolf-Rayet stars, supermassive stars, or Tidal Disruption Events
(TDEs). As these scenarios are hard to distinguish using only N/O and
C/O ratios, we constructed chemical evolution models for each and
compared them with JWST/NIRSpec data from 8 high-redshift galaxies. By
analyzing the emission lines of additional elements like Ne, S, Ar,
and Fe, we found that Neon (Ne) is a particularly effective indicator
for differentiating between the models. This comparison between models
and observational data helps clarify the origin of elements in these
early, nitrogen-rich galaxies.
- School Year: D2 (NAOJ)
- Name: Gabriel Teixeira Guimarães
- Title: From planets to particles: chaos all around.
- Abstract:
Chaotic phenomena in higher dimension dynamical systems are the norm
rather than the exception. A central challenge is to determine which
initial conditions lead to stable, periodic motion and which give rise
to chaos. For planetary systems, the question is whether planets can
remain in stable orbits throughout their lifetimes. For particle
accelerators, it is whether beams of particles can remain stably
confined over many turns.
There is no single way to answer these questions, but a variety of
tools can reveal the underlying dynamical structures and different
regimes of motion. In this talk, I will briefly discuss chaotic
phenomena in dynamical systems, highlight their characteristic
features, and show how Frequency Analysis can be used to identify
dynamical regimes. This method reduces complex systems to their
fundamental frequencies, bridging insights from celestial mechanics to
those relevant for particle accelerators and for any other
conservative dynamical system.
- School Year: D1 (KEK)
- Name: Hidenaga Watanabe (渡邉 秀長)
- Title: A new mechanism for leptogenesis in three Higgs-doublet model
- Abstract:
In standard leptogenesis, several conditions must be satisfied to
produce the observed baryon asymmetry: weak wash-out, CP violation in
the neutrino Yukawa couplings, and a heavy Majorana mass. We propose
a new mechanism for leptogenesis that relaxes these conditions by
employing three-Higgs-doublet models. The non-thermal decay of an
additional heavy Higgs generates a charge asymmetry, which remains
conserved in the early universe. This asymmetry is subsequently
converted into a lepton asymmetry through thermal processes involving
neutrino Yukawa interactions. Our results indicate that the Majorana
mass scale can be reduced to as low as 10^5GeV.
- School Year: D1 (KEK)
- Name: Ruau Watanabe (渡辺 瑠合)
- Title: Optimizing NEG Film Deposition with a Compact NEG-Coating Device
- Abstract:
Non‑evaporable getter (NEG) coating enables ultra‑high vacuum by
turning chamber walls into efficient pumps. We have developed a
compact NEG‑ coating device and optimized TiZrV deposition
parameters. Controlling sputtering gas flow, stabilized by an orifice
gasket, further improved film performance, achieving pressures in the
10⁻¹⁰ Pa range solely by the film’s pumping effect.
- School Year: D1 (KEK)
- Name: Mikage Kobayashi (小林 海景)
- Title:
NANOGrav 15-year gravitational-wave signals from binary supermassive
black-holes seeded by primordial black holes
- Abstract:
The nanohertz gravitational wave background (GWB), detectable through
pulsar timing arrays (PTAs), provides a promising window into the
cosmic population of supermassive black hole binaries (SMBHBs). The
NANOGrav 15-year dataset has reported evidence for a GWB in the
nanohertz frequency range. However, several simulations suggest that
the GWB produced by SMBHBs alone may be insufficient to account for
the observed signal.
In this talk, I will introduce a scenario in which primordial black
hole (PBH) seeds grow into SMBHs through accretion, and such SMBHs
contribute to the GWB signal.
School Year : D3 (KEK)
Name : Hayate Kimura (木村 颯)
Title :Quantum Entanglement and the Black Hole Paradox
Abstract :
The question “What is quantum gravity?” can be said to be one of the
greatest questions in modern theoretical physics. An important modern
development is the discovery of the holographic principle-an
equivalence between quantum gravity and gauge field theory-which
emerged from detailed investigations of black holes. Black holes
serve as a crucial testing ground for exploring quantum gravity, and
many fundamental questions about their nature still remain open. In
this talk, I will review the black hole paradox, focusing in
particular on the role of quantum entanglement. I will also discuss
recent progress in the field as well as my own research.
- School Year: M2 (UTokyo)
- Name: YE Yuheng（葉 与衡）
- Title:
Macroscopic Quantum Entanglement with Gravitational-Wave
Interferometers
- Abstract:
Gravitational-wave interferometers also provide a unique platform to
study macroscopic quantum entanglement. Using Wiener filtering and
homodyne detection, we can conditionally prepare quantum states of
test masses and quantify their entanglement via logarithmic
negativity. I will introduce the basic framework, extend it from
two-mode to multi-party correlations, and discuss challenges such as
realistic noise sources and possible routes toward long-distance
entanglement distribution.
- School Year: M2 (KEK)
- Name: Tadashi Kuramoto (倉本 祥至)
- Title:
Analytical study of birefringent cavities for axion-like dark matter
search
- Abstract:
Axions, which are neutral pseudo-scalar particles interacting with
photons, have been searched as one of the dark matter candidates, and
the target mass region becomes wider and wider [1]. Especially in the
lighter mass region where the ALP mass is less than neV, an optical
ring cavity combined with polarized laser light can be utilized and
the ALP signal can be measured as a slight change of the
polarization[2]. However, the birefringence at the cavity mirrors also
rotates the polarization and makes optical path length different
between polarizations. This makes the signal light off-resonant and
results in degradation of sensitivity. In this talk, I will explain
the way to detect ALPs via optical cavity and then introduce
birefringence at the mirror as the waveplate model. Finally, I will
show the effects of birefringence on the sensitivity.
- School Year: M1 (NAOJ)
- Name: Himeka Matsuo（松尾 姫歌）
- Title: The role of major mergers in galaxy evolution
- Abstract:
The role of galaxy major mergers in clumpy starbursts may be more
important than people believe. This is because galaxy merger could
form rotating gas disk that resembles isolated galaxy. In addition, we
need to keep in mind the possibility that merger could be
misidentified as an isolated galaxy. We will investigate the molecular
gas clump properties of post-mergers and compare them to isolated
galaxies in order to understand the role of mergers in galaxy
evolution.
- School Year: M1 (KEK)
- Name: Shirabe Endo (猿渡 調)
- Title: Search of string vacua by quantum computation
- Abstract:
I’ll talk about my research of vacua from string theory by using
quantum computation. Since there are no results yet, I'll mainly talk
about the introduction and direction.
- School Year:M1 (NAOJ)
- Name: Naoto Maki (槇木 直人)
- Title: Dynamical Dark Energy
- Abstract:
Dark energy is an essential component to explain accelerated expansion
of the universe. Observations of Baryon Acoustic Oscillations (BAO) by
DESI (Dark Energy Spectroscopic Instrument) show that equation of
state parameter w is not constant. The latest results of DESI indicate
that w is larger than that of ΛCDM model (w=-1) with a significance
of over two sigma. Such dynamical behavior can be explained by
quintessence model, which attributes the cosmic acceleration to an
unknown scalar field. This presentation reviews the latest results of
DESI and the theory of exponential quintessence model.
- School Year: M1 (KEK)
- Name: Nishiki Tomoya (西木 友哉)
- Title: About Axion
- Abstract:
The strong CP problem is solved by the Pecci-Quinn mechanism. The
particle appearing in this mechanism is axion. This presentation will
outline axion, particularly the QCD axion.
- School Year: M1 (UTokyo)
- Name: Hibiki Obata（小幡 響）
- Title: Design of local sensor and IFI for KAGRA
- Abstract:
To inprove the sensitivity of the gravitational wave telescope KAGRA,
various efforts are being made to reduce the noise. In my
presentation, I will introduce the design of local sesors for
measuring the position of optical components and a plan to reduce the
noise in the Input Faraday Isolator (IFI).
The 6th meeting from
Monday, 6th to
Wednesday, 8th Oct
2025
https://sci.nao.ac.jp/MEMBER/kohri/06-KEK-NAOJ-JointSeminar.html
高エネ研–国立天文台連携セミナートップページ
https://sci.nao.ac.jp/MEMBER/kohri/KEK-NAOJ-JointSeminar.html
問い合わせ先: 郡 和範 (こおり かずのり)
https://sci.nao.ac.jp/MEMBER/kohri/