天文現象及活動 | 香港天文學會

以暗物質與暗輻射的交互作用來協調宇宙模型間差異

Seminar:- Cosmic Discordance and Interacting Dark Matter and Radiation

Precision cosmological measurements, especially measurements of the CMB from Planck, have allowed a determination of the basic ingredients (energy densities) of the universe at per-cent level precision. The overall picture strongly supports the so-called concordance model with cold dark matter and dark energy. However, with the increase in precision also came some tension in the data. Direct measurements of the expansion rate of the universe today, H_0, and measurements of the matter power spectrum, sigma_8, each disagree with predictions of the concordance model at 2-3 standard deviations. The speaker reviews the experimental situation and proposes and describes a model in which dark matter interacts with dark radiation which can resolve both discrepancies.　
　
時間：2017.06.13(二) 14:00
地點：香港科技大學李兆基校園盧家驄薈萃樓4樓高研院4042室
講者：Prof Martin Schmaltz (Boston University)
語言：英語

免費會議，歡迎參加

#127

此活動由香港科技大學賽馬會高等研究院主辦。

2017-06-13

Low frequency array (LOFAR) 低頻陣列簡介

時間：2017.06.13(二) 19:00 ~ 20:15
地點：香港理工大學 R502
講者：梁振聲博士（香港天文學會理論组组長）

簡介:
本講座會簡介這套荷蘭射電天文台的低頻射電陣。這套前沿的射電接收系统是非常有創意，也許適合香港安装。2018年中國嫦娥四號將會携帶此LOFAR系统到月球背面。嘗試應用。本講座適合任何人士。

此活動由香港天文學會理論天文組主辦。

2017-06-13

BMS對稱陪集 – 重力子作為南-戈玻色子的一種

Seminar:- Coset for BMS: Graviton as a Nambu-Goldstone Boson

It has been known that graviton can be thought of as a Nambu-Goldstone (NG) boson for spontaneously broken GL(4) symmetry, which is a part of large gauge transformations associated to general covariance. In this interpretation, all the components of the metric are identified with NG bosons, so that these NG modes include gauge degrees of freedom in addition to the two physical helicity modes of graviton. In this talk, the speaker will revisit such property of graviton based on the Bondi-Metzner-Sachs (BMS) symmetry, an infinite dimensional symmetry of asymptotically flat spacetimes. In particular, he will illustrate that the viewpoint of asympotics resolves the mismatch between the number of broken symmetries and physical helicity modes. 　
　
時間：2017.06.13(二) 14:00
地點：香港科技大學李兆基校園盧家驄薈萃樓4樓高研院4042室
講者：野海俊文教授 Prof. Toshifumi Noumi (日本神戶大學)
語言：英語

免費講座，歡迎參加

#145

此活動由香港科技大學賽馬會高等研究院主辦。

2017-06-13

從宇宙膨漲-規範場交互作用來的原初重力波

Seminar:- Primordial Gravitational Waves from an Inflaton-Gauge Interaction

In this talk, the speaker will focus on a gauge field interacting with the inflaton through an exponential type coupling function. It is known that such a coupling is ubiquitous from higher dimensional fundamental theory. He will show that the gauge field grows at the later stage of inflaton due to the interaction. Consequently, high-frequency gravitational waves are induced by such gauge field production. 　
　
時間：2017.06.13(二) 15:00
地點：香港科技大學李兆基校園盧家驄薈萃樓4樓高研院4042室
講者：伊藤飛鳥博士 Dr. Asuka Ito (日本神戶大學)
語言：英語

免費講座，歡迎參加

#145

此活動由香港科技大學賽馬會高等研究院主辦。

2017-06-13