2021-04-15
(木) 宇宙物理学セミナーUTAPwiki/セミナー/宇宙物理学セミナー
Speaker:Daisuke Toyouchi
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.
2021-04-19
(月) 観測的宇宙論速報
内容：添付ファイル [添付] 参照
Author(s)TitleYear, Journal,Number(,Link)Y. SutoJinsei Ippan ni Sotairon2010, ISBN978-4-13-063354-3
2021-04-19
(月) 初期宇宙・相対論速報UTAPwiki/セミナー/初期宇宙・相対論速報
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Title: Dark Matter and Inflation in Einstein-Cartan Gravity †
↑Speaker: Inar Timiryasov †
Abstract: It is known that the gravitational force can be obtained by gauging the Poincaré group. Once the resulting theory – Einstein-Cartan gravity – is coupled to matter, its action contains more terms of mass dimension at most 4 than metric gravity. In this talk, I will discuss them and explore two phenomenological consequences. First, Einstein-Cartan theory generalizes inflationary scenarios driven by the Higgs field. As in the known metric and Palatini models, the resulting predictions agree with observations. Secondly, we obtain a new mechanism for producing singlet fermions in the Early Universe. In a large range of masses, these fermions can constitute all of the dark matter.
The seminar will be preceded by three short (one hour) lectures introducing Einstein-Cartan theory and other required tools.
References:
https://arxiv.org/abs/2007.14978
https://arxiv.org/abs/2007.16158
https://arxiv.org/abs/2008.11686
2021-04-26
(月) 観測的宇宙論速報
内容：添付ファイル [添付] 参照
Author(s)TitleYear, Journal,Number(,Link)Y. SutoJinsei Ippan ni Sotairon2010, ISBN978-4-13-063354-3
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