2020/7/16 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Yusuke Yamada

Title: Quantum tunneling and related phenomena

Abstract:
Quantum tunneling is a hallmark of nonclassical physics. Such a phenomenon is relevant to microscopic physics to cosmology. In this talk, I will briefly review examples of tunneling phenomena mostly in cosmology. In tunneling phenomena, the notion of decay rate of a state is one of the most important quantities. I will review how the decay rate is precisely defined and computed in a modern way. For simplicity, I will discuss it in quantum mechanics, but the formulation is straightforwardly applied to quantum field theory as well.

I will discuss several topics, but the topic discussed in detail is based on the following paper : A. Andreassen, D. Farhi, W. Frost, M. D. Schwartz, Phys.Rev.D 95 (2017) 8, 085011

※Notice: This is scheduled to be the last seminar in this semester.

2020/7/9 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Kotaro Fujisawa

Title: How to use a quantum computer

Abstract:
Quantum computing is one of the most exciting fields in computer science and physics. Quantum computers must be powerful tools in cosmology and astrophysics in the future. Of course, I and you are not experts on quantum computing, but we can enjoy the quantum computer and quantum computing easily. In this talk, I will introduce basic quantum programmings and how to use IBM quantum computers. I will also talk about recent hot topics of quantum computers, such as quantum machine learning if I can.

Web Reference
IBM Quantum Experience
https://quantum-computing.ibm.com/
Quantum Native dojo (Japanese)
https://dojo.qulacs.org/ja/latest/
TensorFlow Quantum
https://www.tensorflow.org/quantum

2020/7/2 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Kazuhiro Kanagawa

Title: Theory and observation of planet formation in protoplanetary disks

Abstract:
A planet is born in a protoplanetary disk that is formed around a young star. The planet is formed from the dust grains which is only typically 1% of the mass of gas. The mass and orbital radius of the planet are changed due to interaction with the surrounding gas. After disk gas dissipation, a planetary system like our solar system is formed. At the present, over 4000 exoplanets have been confirmed. Moreover, a planet-forming region in protoplanetary disks has been directly observed by e.g., Atacama Large Millimeter/submillimeter Array (ALMA). In this talk, I will review theory and recent observations of planets formation in protoplanetary disks.

2020/6/25 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Kohei Kamada

Title: An Introduction to Chiral Kinetic Theory

Abstract:
It has recently been recognized that the chiral anomaly in the quantum field theory
can cause a macroscopic and non-negligible phenomena such as the chiral magnetic effect.
In this talk, I will introduce the chiral kinetic theory, which implements the effect of chiral anomaly.
In this theory, the kinetic equations or the Boltzmann equations for fermions are modified
with the so-called Berry curvature, and it reconstructs the anomaly equation.
I will also explain that this leads to the chiral magnetic effect, where the electric current
parallel to the magnetic field in the presence of the chiral asymmetry in the system,
at the hydrodynamic limit.
This talk is done with the whiteboard on the ipad.

Note available here

2020/6/18 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Atsushi Nishizawa

Title: Test of gravity with gravitational wave polarizations

Abstract:
Gravitational waves (GWs) bring forth new opportunities to test theories of gravity in strong and dynamical regimes. One of such tests is the polarizations test of GWs. GWs have only two polarization modes in general relativity, while there are at most six possible modes of polarizations in a metric theory of gravity. Therefore, GW polarizations enable us to search for anomalous deviations from general relativity in a model-independent way and provides a powerful tool to probe the strong regime of gravity. In this talk, I review the tests of gravity with GW polarizations from a basic concept to recent progresses, particularly showing how a mixture of polarization signals is separated in data analysis and how KAGRA as a fourth detector contributes to the joint observation with a global detector network.

2020/6/11 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Kenta Hotokezaka

Title: Progress in Kilonova Science

Abstract:
Kilonova science has been rapidly developed in the past decade (in fact this year is 10 yr anniversary of "kilonova").
I'll overview several works that played important roles and will discuss the lessons that we can learn from the progress in kilonova science.
I'll also briefly discuss a few topics which remain as mysteries after the discovery of the kilonova in GW170817.

2020/6/4 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Kazumi Kashiyama

Title: Fast radio bursts and related phenomena

Abstract:
Fast radio bursts (FRBs) are an enigmatic phenomenon; trains of
coherent radio waves are arriving from a cosmological distance for a
millisecond. In this talk I will first review the evolution of FRB
research since its discovery in 2007. The most promising source of FRB
is neutron star (NS). In fact, very recently a low-luminosity FRB has
been detected from a strongly magnetized NS, SGR 1935+2154,
simultaneously with an X-ray flare. Focusing on the NS model, I will
describe the theoretical insights and challenges that such
observational achievements have implied : “What is the emission
mechanism of FRB?”, “What type of NSs can be the source of FRB?”, and
“How such NSs are formed with what type of explosive transients?”.
Finally I will discuss prospects and strategies to provide a
comprehensive answer to these questions.

2020/5/28 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Masamune Oguri

Title: Compartmental models in epidemiology

Abstract:
I will review the basics of compartmental models in epidemiology, focusing on understanding of their qualitative behaviors. I will then discuss some implications for COVID-19.

2020/5/21 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Toshikazu Shigeyama

Title: Eruptive mass loss in the late evolutionary stage of massive stars

Abstract:
Recent high cadence observations for transient events have captured outbursts from massive stars prior to the final supernova explosions. The luminosity seemingly exceeding the Eddington limit suggests that the outburst results in eruptive mass loss from the progenitor star. Furthermore, the following supernova exhibits narrow emission lines in the spectrum, which are thought to originate from the dense circum-stellar matter. Some observations indicated very high mass loss rates of ~0.1 Msun/yr. I will review some examples of such observations and possible mechanisms to account for these eruptive mass loss events.

2020/5/14 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Naoki Yoshida

Title: The Distribution of Cosmic Relic Neutrinos in Six-Dimensional Phase Space

Abstract:
We present the state-of-the-art computer simulations of structure formation
in the Universe. The phase-space distribution of the cosmic relic neutrinos
is followed, for the first time, by directly integrating the six-dimensional collisionless
Boltzmann equation. Our novel approach allows us to reproduce free streaming and
clustering of neutrinos, and their gravitational interaction with cold dark matter
accurately. We perform a suite of hybrid Vlasov/N-body simulations with various
neutrino masses, and systematically examine the dynamical effects of massive
neutrinos on large-scale structure formation. Our simulations show characteristic
large-scale clustering of the neutrinos and their coherent streaming motions
relative to dark matter. The effective local neutrino ”temperature” around massive
galaxy clusters varies by several percent with respect the cosmic mean;
the neutrinos in clusters can be hotter or colder depending on the neutrino mass.
We study a number of statistics of the large- scale structure and of dark matter
halos in comparison with those obtained by conventional N-body simulations
and/or by perturbation theory.

2020/5/7 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Jun'ichi Yokoyama

Title: Toward removing nonlinearly coupled noises in gravitational-wave detection:
machine learning? manual learning??

Abstract: Recently we have found an optimal method to remove linearly coupled
noises in gravitational wave strain data using physical environmental channels.
The next task is to remove nonlinearly coupled ones. I will introduce previous
attempts in LIGO and Virgo, some of which use machine learning, as well as
future attempts in KAGRA.

2020/4/30 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Yasushi Suto

Title: The Planet Nine Hypothesis

Abstract:
The possible existence of the Planet Nine has attracted significant
attention in the planetary science and astronomy. I will begin with
the historical account of the exploration of the Solar planets beyond
Saturn, describe possible intriguing puzzles in the Trans-Neptunian
Objects, and introduce the Planet Nine hypothesis to account for their
anomalous architecture. This talk is based on a recent excellent
review by Konstantin Batygin, Fred C. Adams, Michael E. Brown, and
Juliette C. Becker

"The planet nine hypothesis"

Physics Report 805(2019)1-53,  arXiv:1902.10103

https://www.sciencedirect.com/science/article/abs/pii/S037015731930047X

https://www.dropbox.com/s/qb754s8saucdwgq/Planet-Nine-2020April30s.pdf?dl=0

2020/4/23 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Yuji Chinone

Title: The results and achievements of the POLARBEAR experiment in 2010's and its future

Abstract:
POLARBEAR is a ground-based experiment designed to measure polarization of the Cosmic Microwave Background (CMB) at 150 GHz at an elevation of 5,190m in the Atacama Desert in Chile. Our main science goals are for searching for the B-mode signal created by primordial gravitational waves (PGWs), as well as for characterizing the B-mode signal from gravitational lensing with high angular resolution.
POLARBEAR has been deployed in 2011 and started science observations in early 2012 focusing on small patches of the sky (deep survey). In 2014, we started to observe a large patch of the sky focusing on search for PGWs (wide survey). We have published a series of results from the deep survey, including the first measurement of a non-zero B-mode auto-power spectrum at sub-degree scales induced by gravitational lensing, constraint of cosmic birefringence and primordial magnetic fields, and demonstration of delensing. We also have achieved the measurement of cross-correlations of gravitational lensing between our CMB data and optical/infrared surveys by the Subaru Hyper Suprime-Cam and Herschel ATLAS. With the wide survey, we have reported the measurement of large angular scale B-mode signal induced by the dust foreground and successfully put an upper limit on PGWs.
In this talk, I summarize the science results and achievements of the POLARBEAR experiment. Finally I show the status of Simons Array, which is upgraded from POLARBEAR and consists of three new receivers. It will have about 20 times better sensitivity than POLARBEAR and observe at 90, 150, 220, and 270 GHz.

2020/4/16 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Keisuke Inomata

Title: Effects of an early matter dominated era on gravitational waves induced by scalar perturbations

Abstract:
Scalar perturbations can induce not only the fluctuations of cosmic microwave background (CMB) and the large scale structures (LSSs), but also gravitational waves (GWs) through their non-linear interactions. Observations of the induced GWs enable us to access small-scale ($k\gtrsim 1$\,Mpc$^{-1}$) scalar perturbations, which are difficult to measure through CMB or LSS observations. For this reason, many authors have focused on the induced GWs recently.
In this seminar, I discuss how the existence of an early matter dominated (eMD) era, preceding the radiation dominated (RD) era, changes the spectrum of the induced GWs. I carefully take into account the evolutions of the scalar perturbations before, during, and after the transition from an eMD era to the RD era. To make the discussion concrete, I consider two scenarios for the transition: the gradual transition and the sudden transition. In the gradual (sudden) transition scenario, the transition from an eMD era to the RD era occurs with the timescale comparable to (much shorter than) the Hubble timescale at that time. As a result, I find that the induced GWs are suppressed in the gradual transition scenario, or on the other hand are much enhanced in the sudden transition scenario. In particular, in the sudden transition scenario, the enhanced GWs could be detected by future observations and be used to determine the reheating temperature.

2020/4/9 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Speaker: Tatsuya Matsumoto

Title: Dynamics of an emission centroid during Sgr A* flares

Abstract:
Sgr A* is a supermassive BH in our Galaxy confirmed by long-term monitoring of stellar orbits.
The luminosity of Sgr A* is usually very small (~10^8 times smaller than its Eddington luminosity), but sometimes it rises up suddenly, so-called flare events. Flares are most noticeable in near-infrared and X-ray bands, where the luminosity increases from a quiescent level of ~10^{33-34} erg/s to a peak level of ~10^{35} erg/s. Although several flare models have been proposed, their origin is still uncertain. Recently, the Gravity collaboration carried out an interferometric observations of NIR flares and detected a motion of an emission centroid with an astrometric accuracy of ~10^{-5} arcsecond. They fit the observed trajectory with a circular Kepler orbit and find the best-fit radius of 7-10 gravitational radius. However, their best-fit orbit lies entirely inside of the trajectory because the small radius is required to reproduce the duration.To resolve this problem, we fit the observed trajectory with different models and I will discuss our results.

2020/2/27 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

no seminar

2020/2/20 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Cannon

2020/2/13 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Chan

2020/2/6 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Park

2020/1/30 (木)

UTAPwiki/セミナー/宇宙物理学セミナー

Tsukada


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Last-modified: 2013-11-20 (水) 11:11:54 (2529d)