重子声学振荡in cosmology

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1、重子声学振荡Incosmology,baryonacousticoscillations(BAO)referstoanoverdensityorclusteringofbaryonicmatteratcertainlengthscalesduetoacousticwaveswhichpropagatedintheearlyuniverse.[1]Inthesamewaythatsupernovaexperimentsprovidea"standardcandle"forastronomicalobservations,[2]BAOmatterclusteringprovidesa

2、"standardruler"forlengthscaleincosmology.[1]Thelengthofthisstandardruler(~150Mpcintoday'suniverse[3])canbemeasuredbylookingatthelargescalestructureofmatterusingastronomicalsurveys.[3]BAOmeasurementshelpcosmologistsunderstandmoreaboutthenatureofdarkenergy(theaccelerationoftheuniverse)byconstra

3、iningcosmologicalparameters.[1]     宇宙学中,重子声学振荡(BAO)是指由于声波在早期宇宙中传播而在一定尺度上形成的高密度区域或者重子物质的结团.超新星实验为天文学观测提供了一个”标准烛光”,与此相同,BAO造成的物质结团在宇宙学中为长度提供了一个”标准尺度”.这个标准尺度的的长度(在今天的宇宙中大概是1.5亿秒差距)可以通过天文巡天查看物质的大尺度结构来测量.BAO的测量通过限制宇宙学参数的方式来帮助宇宙学家了解更多的暗能量(即宇宙的加速膨胀)的本性.Contents1TheEarlyUniverse2CosmicSound3Standard

4、Ruler4BAOSignalintheSloanDigitalSkySurvey5BAOandDarkEnergyFormalism    5.1GeneralRelativityandDarkEnergy    5.2MeasuredObservablesofDarkEnergy6  References7Externallinks目录1早期宇宙2宇宙的声音3标准尺度4斯隆数字巡天(SloanDigitalSkySurvey)中的BAO信号5BAO与暗能量的公式化形式  5.1广义相对论与暗能量  5.2暗能量的可测量性6参考文献7外部链接TheEarlyUniverse早期

5、宇宙 Theearlyuniverseconsistedofahot,denseplasmaofelectronsandbaryons(protonsandneutrons).Photons(lightparticles)travelinginthisuniversewereessentiallytrapped,unabletotravelforanyconsiderabledistancebeforeinteractingwiththeplasmaviaThomsonscattering.[4]Astheuniverseexpanded,theplasmacooledtobel

6、ow3000K—alowenoughenergysuchthattheelectronsandprotonsintheplasmacouldcombinetoformneutralhydrogenatoms.Thisrecombinationhappenedwhentheuniversewasaround400,000yearsold,orataredshiftofz=1100.[4]Photonsrarelyinteractwithneutralmatter,thereforeatrecombinationtheuniversesuddenlybecametransparent

7、tophotons,allowingthemtodecouplefromthematterandfree-streamthroughtheuniverse.[4]Inother-words,themeanfreepathofthephotonsbecameontheorderofthesizeoftheuniverse.Thecosmicmicrowavebackground(CMB)radiationislightemittedafterrecombinationwhichis