MeasuringtheDensityParametersoftheUniverse(WITHEMPHASISONBARYONICACOUSTICOSCILLATIONS)ANDREWYIDEPARTMENTOFPHYSICS, KAIST
TableofContentsTheObjective
TheOtherTwoMethods◦ CosmicMicrowaveBackground(CMB)◦ TypeIa Supernova(SNIa)
BaryonicAcousticOscillations(BAO)◦ Whattheyare◦ Whatwecanlearnfromthem
PuttingEverythingTogether
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TheObjective
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Howdoestheuniversework?
Weneedausefulcosmologicalmodel!
TheΛCDMCosmologicalModelBigBang+Inflation+GravitationalInstability+ColdDarkMatter+CosmologicalConstant
Fourcomponentsmakeuptheuniverse:matter,darkenergy,radiation,curvature
Wecanrelatetheexpansionratewithredshift
Ourquestion:Howmuchofeachcomponentisthereintheuniverse?
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Ω",Ω#
TheDensityParametersandMethods
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CosmicMicrowaveBackgroundTheBasis
TypeIa SupernovaeTheStandardCandle
BaryonicAcousticOscillationsTheStandardRuler
CosmicMicrowaveBackground(CMB)
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http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2013/03/planck_cmb/12583930-4-eng-GB/Planck_CMB.jpg
AnisotropiesinCMBAnisotropiesinCMBcanbestudiedusingthepowerspectrum
Duetothelocationofthefirstpeak,theuniverseisflat.
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P.Ade,etal.,(PlanckCollaboration),A&A594,A13(2016).arXiv:1502.01589.
𝑙% =220Ω)
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CosmicMicrowaveBackgroundTheuniverseisflatΩ" + Ω# ≈ 1
Ω"
Ω#0
0.2
0.4
0.6
1.0
0.8
1.2
1.4
00.2 0.4
0.6
0.8 1.0
NoBigBang
TypeIa Supernovae(SNIa)
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http://sci.esa.int/science-e-media/img/68/Gaia_SNIa_Artist_Impression.jpg
SNIa asstandardcandlesAftersufficientcorrection,theluminositycurveofallSNIa arethesame
Validtobeusedasstandardcandles
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http://burro.astr.cwru.edu/Academics/Astr328/Notes/Tests/stretch_hamuy1.gif http://burro.astr.cwru.edu/Academics/Astr328/Notes/Tests/stretch_hamuy2.gif
DarkEnergyBecomesNecessaryItturnsoutthatsupernovaexplosionsarefainterthanweexpectedinveryfarregions
Anacceleratinguniverseneedsdarkenergy
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A.Riess,etal.,AJ,116,1009(1998)
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TypeIa SupernovaeThereshouldbemoredark
energythanmatter
Ω"
Ω#0
0.2
0.4
0.6
1.0
0.8
1.2
1.4
00.2 0.4
0.6
0.8 1.0
NoBigBang
SNIa
BaryonicAcousticOscillationsBeforerecombination:Freeelectronspreventphotonsfrompropagatinginonedirection(Thomsonscattering)
Pressureandgravitytrytobalanceeachother,producingacousticwavesintheprocess
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Pressure:Expansion
Gravity:Collapsehttp://background.uchicago.edu/~whu/intermediate/gravity.html
BAO:AfterrecombinationNeutralatomsareformed.Photonspropagatefreelyandpressureisrelieved
Baryonsanddarkmatter formseparateoverdensity regions
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http://galaxies-cosmology-2015.wikidot.com/baryon-acoustic-oscillations D.J.Eisenstein,H.J.Seo,andM.White,ApJ.664,660(2007)
TheSoundHorizonBaryonicacousticwaveswillpropagateatthespeedofsound,whichisrelatedtothedensityofbaryonsandphotons
Thiswillformasoundhorizonwherematterisdistributedsphericallyaroundonedensepoint
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GalaxyFormationfromBAOsBaryonswillendupforminggalaxiesalongthecircumferenceofthesoundhorizon
BAObecomesa“statistical”standardruler
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http://galaxies-cosmology-2015.wikidot.com/baryon-acoustic-oscillations B.A.BassettandR.Hlozek,DarkEnergy,Ed.P.Ruiz-Lapuente.(2010)
TheCorrelationFunctionA preferredscaleforgalaxyformationcanbefoundusingthecorrelationfunction
Thereisapeakat100h-1 Mpc ~150Mpc,whichisinterpretedasthescaleofthesoundhorizon
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D.J.Eisenstein,etal.,ApJ,633,560(2005)
MatchingObservationsWiththeModelThesizeofthesoundhorizoncanbecalculatedusingtheangulardiameterdistance 𝑑/
Meanwhile,𝑑/ and𝐻(𝑧) canbeobserveddirectly
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1 + 𝑧 𝑑/ 𝑧 𝜃
𝑐𝑑𝑧𝐻(𝑧)
𝜃
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Ω"
Ω#0
0.2
0.4
0.6
1.0
0.8
1.2
1.4
00.2 0.4
0.6
0.8 1.0
NoBigBang
BAO
BaryonicAcousticOscillationsTheremustbeacertainamount
ofmatterintheuniverse
SUMMARY
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BaryonicAcousticOscillationsTheremustbeacertainamount
ofmatterintheuniverse
CosmicMicrowaveBackgroundTheuniverseisflatΩ" + Ω# ≈ 1
TypeIa SupernovaeThereshouldbemoredark
energythanmatter
R.Amanullah,etal.,ApJ,716,712,2010
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SummaryPuttingEverythingTogether
http://planck.cf.ac.uk/files/Planck-only_Cosmic%20recipe%20pie%20chart.jpg
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Q&ASession
AdditionalSlide1:ThewCDMModelThedarkenergydoesnotnecessarilyneedtobeconstant,andmaydependonredshift.
Currentobservationresultspointtoa𝑤) = −1,𝑤8 = 0 solution,meaningthatdarkenergyisindeedthecosmologicalconstant.
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Forsomespecificpointontheprojected(𝜃, 𝜑) planeforCMB,wecandefinetheanisotropyas
Sphericalharmonicsanddefiningthepowerspectrum
AdditionalSlide2:SpecificsofCMB
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AdditionalSlide3:SpecificsofCMB2Fordarkenergydominantuniverses,thelocationofthefirstmultipolepeakisaffected.
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A.MelchiorriandL.M.Griths,NewAstron.Rev.45,321(2001)
AdditionalSlide4:SpecificsofSNIaSNIa measurementsusetheluminositydistance.
Byusingthedistancemodulusrelationship,wecancalculatetheluminositydistanceanduseittofindthechangeinluminositydistanceasafunctionofredshift.
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