Dark radiation in cosmology
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Transcript of Dark radiation in cosmology
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Dark radiation in cosmology
张益重庆邮电大学
2011.4.3
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• Dark Energy! • Dark Matter!
• What is dark radiation ? Observations! Theory!
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宇宙中的组分
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不同组分的演化规律
Friedmann Equation
Radiation
Matter
Cosmological constant
Curvature term
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集中讨论两个加速膨胀阶段
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Radiation
通常 : 辐射是指静止质量为零的粒子组成的气体
在温度为 T 的早期宇宙中: 当温度 T 显著超过粒子静质量 m ,这种粒子会作
为辐射的组分存在; 辐射气体是一切满足 m<T 的粒子组成的混合气
体。
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辐射物质
光子,正反中微子,正反电子,质子和中子
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BBN ( Big Bang Nucleosynthesis )
温度降到 0.1MeV :
热碰撞(1MeV)
Next
电子俘获
碰撞
温度降到0.01MeV, 热核反应结束
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The radiation dominating universe
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辐射项对 BBN 的影响辐射项对 BBN 的影响
有效中微子数目大
宇宙的膨胀率大
弱退耦发生的时间得更早
冻结下来的中子数密度更多
氦的产额更大
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CMBR (微波背景辐射) CMBR 各向异性可分为: 宇宙早期产生的初级各向异性 从光子退耦到现在产生的二级各向异性
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ISW 效应( Integrated Sachs-Wolfe effect )
• 宇宙不是完全均匀的,所以到处存在着引力势阱。当微波背景辐射的光子掉进引力势阱的时候就会获得能量,爬出这个势阱的时候就会损失能量。
• 该效应是光子路径上所有引力势变化的累加效应,称为积分 Sachs-Wolfe 效应 .
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1, 对于一个固定的能量密度
辐射能量密度增加物质 - 辐射相等的时刻延迟
ISW 效应加强
2, 没有和光子 - 重子流体耦合的相对论性粒子,可以比声速更快地逃出势阱。
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Motivation from Observations
• WMAP shows:• BBN Observations limit ( 68% CL) (astro-
ph:0408033 )
• CMBR ( 68% CL) ( arxiv:1001.4538 , 1009.0866
)
ATACAMA COSMOLOGY TELESCOPE: ACT measures fluctuations at scale 500<l<3000
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Possibilities! ( astro-ph:0612150,1103.4132 )
• Motivated by the LSND(Liquid Scintillator Neutrino Detector) oscillation claim , assume a (light) massive sterile neutrino (1006.5276);
• The neutrinos acquire a mass from a broken lepton flavor symmetry(astroph:0312267,1009.4666,1011.0911);
• Allow for a violation of the spin-statistics theorem;• A Brans-Dicke field with non trivial potential which could mimic the effect
of adding extra radiation between the BBN and CMB epochs ( astro-ph:0510359 ) ;
• An extra interaction between the dark energy and radiation (or dark matter);
• A quintessence with a tracking potential behavior;• Decaying matter(1011.3501);• Nonstandard thermal history; • ……
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Theories
• Brane Cosmology• Hovara-Lifshitz cosmology• Electroweak phase transition• EDE ( Early Dark Energy )• ………..
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Brane Cosmology ( astro-ph:0211285 )
Dark radiation term arises from the projection of Weyl curvature of the bulk black hole on the brane and behaves like an additional collisionless and isotropic massless component.
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• 其中 BBN 的限制是
• CMB 的限制:把 CMB 的峰移到高 l 处 对于
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Electroweak phase transition(0902.4699)
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Triple coincidence problem
• Coincidence problem: why the cosmological constant and the matter have comparable energy density today even through their time evolution is so different
• Triple coincidence problem: why the radiation energy density today is only three orders of magnitude smaller than the dark-matter and dark-energy ones, although it also scales very differently
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Scalar field dark energy
Interaction 1
Interaction 2
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Phase-space analysis
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Quintessence
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Phantom
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点
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Conclusion
• “Triple coincidence problem”still need fine-tunning 。
• This model can recover the history of our universe.
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The Future
• Data : Planck, BAO, new result on primordial nuclei abundance?
• Models: based on string theory, particle physics or others?
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THANKS ALL !