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INPAC-Seminar 14: Halo Shape and Relic Density Constraints of Sommerfeld-Enhanced Dark Matter Explan |
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作者：Saturnman
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周三, 2010年 01月 06日 10:13 |
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INPAC-Seminar 14 Title: "Halo Shape and Relic Density Constraints of Sommerfeld-Enhanced Dark Matter Explanations of Cosmic Ray Excesses" Speaker: Hai-Bo Yu (Department of Physics and Astronomy, University of California-Irvine, USA) Time and place: 12:30, Jan. 8 (Friday), 2010, Lecture Hall/INPAC (上海交通大学粒子物理宇宙学研究所，包玉刚图书馆东楼四楼(从北门进)) Abstract Dark matter with Sommerfeld-enhanced annihilation has been proposed to explain observed cosmic ray positron excesses in the 10 GeV to TeV energy range. We show that the required enhancement implies thermal relic densities that are too small to be all of dark matter. We also show that the dark matter is sufficiently self-interacting that observations of elliptical galactic dark matter halos exclude large Sommerfeld enhancement for light force carriers. Resonant Sommerfeld enhancement does not modify these conclusions, and the astrophysical boosts required to resolve these discrepancies are disfavored, especially when significant self-interactions suppress halo substructure. I will also discuss about the halo shape constraints on Breit-Wigner enhancement scenario. Main references: arXiv:0911.0422 and arXiv:0912.5425
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最后更新 ( 周三, 2010年 01月 06日 10:16 )
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INPAC-Seminar 13: J/psi nuclear modification factor in nucleus-nucleus collisions |
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作者：Saturnman
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周四, 2009年 12月 24日 08:42 |
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INPAC-Seminar 13 Title: "J/psi nuclear modification factor in nucleus-nucleus collisions" Speaker: Professor Xiao-Ming Xu (Department of Physics, Shanghai University) Time and place: 12:30, Dec. 25 (Friday), 2009, Lecture Hall/INPAC (上海交通大学粒子物理宇宙学研究所，包玉刚图书馆东楼四楼(从北门进)) Abstract Various mechanisms for J/psi suppression and the recombination mechanism of charm quark and charm antiquark are reviewed. STAR collaboration has offered eminent nuclear modification factor of J/psi at high p_T and at midrapidity produced in Cu-Cu collisions at the center-of-mass energy 200 GeV. Recalling a prediction of the speaker we can understand that the feature of high-p_T nuclear modification factor is related to charm quark-antiquark pairs produced by 2-to-1 and 2-to-2 partonic processes in deconfined matter particularly in the prethermal stage and to the recombination of charm quark and charm antiquark in deconfined matter. The nuclear modification factor at high p_T is sensitive to the earliest form of deconfined matter that does not have a temperature. |
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最后更新 ( 周四, 2009年 12月 24日 08:45 )
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INPAC-Seminar 11: Cluster-gas-like states in nuclei |
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作者：Saturnman
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周二, 2009年 12月 08日 12:04 |
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INPAC-Seminar 11 Title:"Cluster-gas-like states in nuclei" Speaker: Professor Hisashi Horiuchi (Research Center for Nuclear Physics (RCNP), Osaka University, Japan) Time and place: 12:30, Dec. 11 (Friday), 2009, Lecture Hall/INPAC (上海交通大学粒子物理宇宙学研究所，包玉刚图书馆东楼四楼(从北门进)) Abstract The second 0+ state of 12C is located near the 3-alpha breakup threshold. It is called the Hoyle state in honor of astrophysicist Fred Hoyle who predicted the existence of this state which plays a crucial role for the synthesis of 12C in the universe. From the side of the nuclear structure theory, this state is well known as one of the mysterious 0+ states in light nuclei. The understanding of its structure has been actually one of the most difficult and challenging problems of nuclear structure. Its small excitation energy of 7.66 MeV has been regarded to be difficult to explain by the shell model. The no-core shell model which is the most advanced modern shell model approach at present has so far not succeeded to reproduce it. Recently we have proposed to explain this state as a Bose-condensate-like state of 3 alpha clusters. The alpha-cluster condensate-like state is the lowest energy state of the alpha-cluster gas-like state. In nuclear physics, gas-like state of nucleons has been an important subject of study for a long time. Such a state has a very high excitation energy and therefore has been a subject of nuclear matter and nuclear reaction rather than nuclear structure. On the other hand, the gas-like state of clusters is not a so highly excited state, and can be a discrete state accessible spectroscopically. We will discuss that in 16O we have a candidate of Bose-condensate-like state of 4 alpha clusters near the 4-alpha breakup threshold. Gas-like state of clusters is a new concept of nuclear structure and is now studied in many nuclei both theoretically and experimentally. As another example we will discuss a state in 11B wich has a gas-like structure of 2-alpha + triton. |
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INPAC-Seminar 12: Explorations of the Top Quark Forward-Backward Asymmetry at the Tevatron |
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作者：Saturnman
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周二, 2009年 12月 15日 16:02 |
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INPAC-Seminar 12 Title: "Explorations of the Top Quark Forward-Backward Asymmetry at the Tevatron" Speaker: Kai Wang (Institute for the Physics and Mathematics of the Universe (IPMU), The University of Tokyo, Japan) Time and place: 12:30, Dec. 18 (Friday), 2009, Lecture Hall/INPAC (上海交通大学粒子物理宇宙学研究所，包玉刚图书馆东楼四楼(从北门进)) Abstract Motivated by recent measurements of the top quark forward-backward asymmetry at the Tevatron, we study two models that can contribute to a large asymmetry in ttbar production. One example is to introduce a fermion number violating scalar with maximal flavor violation in t-channel. The second model is a variation of chiral color model with s-channel axigluon. We will discuss implications at the LHC as well. Main references: [1] Jing Shu, Tim M.P. Tait, Kai Wang, arXiv:0911.3237 [hep-ph] [2] Paul H. Frampton, Jing Shu, Kai Wang, arXiv:0911.2955 [hep-ph] |
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最后更新 ( 周二, 2009年 12月 15日 16:06 )
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INPAC-Seminar 10: Bright Lights, Dark Energy, and a Quite Curious Coefficient: Thermonuclear Supernovae and the Equation of State for the Universe |
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作者：Saturnman
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周三, 2009年 12月 02日 11:30 |
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INPAC-Seminar 10 Title: "Bright Lights, Dark Energy, and a Quite Curious Coefficient: Thermonuclear Supernovae and the Equation of State for the Universe" Speaker: Professor Mike Guidry (Department of Physics and Astronomy, University of Tennessee, andPhysics Division, Oak Ridge National Laboratory) Time and place: 13:00, Dec. 4 (Friday), 2009, Lecture Hall/INPAC (上海交通大学粒子物理宇宙学研究所，包玉刚图书馆东楼四楼(从北门进)) Abstract An equation of state is a relationship among thermodynamic variables that typically goes beyond the information supplied by thermodynamics alone. What then is the equation of state for the Universe as a whole? We believe that this most profound of questions has a conceptually simple answer: the pressure of the Universe is proportional to its energy density. Causality arguments require that the coefficient of proportionality be less than or equal to 1, but it is only within the past decade that observations have begun to close in on the actual value of this elusive coefficient. These observations indicate that the Universe is permeated by a mysterious "dark energy" causing the expansion of the Universe to accelerate. This requires the coefficient to have a value less than -1/3 (which is most curious, since this means that the Universe on large scales has an equation of state fundamentally different from any ever measured in a local laboratory within that Universe!). To constrain it further requires parallel improvements in observational technology and the theoretical understanding of those observations. The key tool is comparison of observed brightness with expected brightness for some of the most luminous objects in the sky, Type Ia (thermonuclear) supernovae. I will provide an overview of these issues and describe our own efforts to contribute through a more fundamental understanding of the Type Ia mechanism. |
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最后更新 ( 周三, 2009年 12月 02日 11:35 )
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