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“Cosmic microwave weak lensing data as a test for the dark Universe”

Università di Roma ‘La Sapienza’. “Cosmic microwave weak lensing data as a test for the dark Universe”. Erminia Calabrese. In collaboration with Alessandro Melchiorri , Anže Slosar , George Smoot and Oliver Zahn , see Calabrese et al, Phys.Rev.D77:123531,2008.

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“Cosmic microwave weak lensing data as a test for the dark Universe”

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  1. Università di Roma ‘La Sapienza’ “Cosmic microwave weak lensing data as a test for the dark Universe” Erminia Calabrese In collaborationwith Alessandro Melchiorri, AnžeSlosar, George Smootand Oliver Zahn, seeCalabrese et al, Phys.Rev.D77:123531,2008 SIGRAV International School in Cosmology Galileo Galilei Institute for Theoretical Physics Firenze, 29th January 2009

  2. The CosmicMicrowave Background Radiation

  3. AnisotropiesAngularPowerSpectrum In the realspace on defines the twopointscorrelationfunctionbetweentwodifferentskydirectionsas : It, under the guassianityassumption, holdsall the CMB statisticalinformations : Ifweexpand the CMB temperature fluctuations in sphericalharmonics : We can define the angularpowerspectrumas : Itdescribes, in the Legendrespace, the contributionofeverymultipole l to the observedsignal

  4. CMB Anisotropies Primaryanisotropies : are produced on the last scatteringsurface Intrinsic fluctuations Doppler Effect Sachs-Wolfe Effect Secondaryanisotropies : are producedwhile the radiationtravelsfrom the last scattering surfacetotoday Fluctuations in the gravitationalpotential: (LSW, Rees-Sciama, Lensing) Scatteringwithelectrons: Reionization, SZ (see e.g.HuW. et al., arXiv:astro-ph/9504057)

  5. WeakGravitationalLensing A gravitational source at comovingdistanceχcreates a deflection: observer Adding up the deflections from all the potential gradients between the observer and the source, we have a total deflection : On defines the lensingpotential : (see e.g. Lewis and ChallinorarXiv:astro-ph/0601594 v4 )

  6. CMB Temperature Lensing Whenthe luminous source is the CMB, the lensing effect is essentially to re-maps the temperature field according to : unlensed lensed (http://www.mpia-hd.mpg.de/ Max PlanckInstituteforAstronomy at Heidelberg)

  7. LensingEffect on Temperature PowerSpectrum Weobtain a convolutionbetween the lensingpotentialpowerspectrumand the unlensedanisotropiespowerspectrum: Where the lensingpotentialpowerspectrumisgivenby : The net resultis a 3% broadeningofthe CMB angularpowerspectrumacusticpeaks

  8. ACBAR Lensing Detection At the beginningof the last year, the ACBAR (Arcminute Cosmology Bolometer Array Receiver) team claimeda detection of a lensingsignal at more thanthree standard deviationsbased ONLY on the broadeningof the acousticpeaks Reichardtet al. , arXiv:0801.1491v2 [astro-ph] 10 Jan 2008 : ABSTRACT In this paper, we present results from the complete set of cosmic microwave background (CMB) radiation temperature anisotropy observations made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150GHz. We include new data from the final 2005 observing season, expanding the number of detector-hours by 210% and the sky coverage by 490% over that used for the previous ACBAR release. As a result, the band-power uncertainties have been reduced by more than a factor of two on angular scales encompassing the third to fifth acoustic peaks as well as the damping tail of the CMB power spectrum. The calibration uncertainty has been reduced from 6% to 2.2% in temperature through a direct comparison of the CMB anisotropy measured by ACBAR with that of the dipole-calibrated WMAP3 experiment. The measured power spectrum is consistent with a spatially flat, CDM cosmological model. We see evidence for weak gravitational lensing of the CMB at > 3σ significance by comparing the likelihood for the best-fit lensed/unlensed models to the ACBAR+WMAP3 data.On fine angular scales, there is weak evidence (1.7σ) for excess power above the level expected from primary anisotropies. The source of this power cannot be constrained by the ACBAR 150GHz observations alone; however, if it is the same signal seen at 30GHz by the CBI and BIMA experiments, then it has a spectrum consistent with the Sunyaev-Zel’dovich effect.

  9. AnalysisMethod The ACBAR team just compared the best fitvaluebetween a modelwithlensing and a modelwithoutlensing, thisis a rowanalysisthatdoesn’t tellus the amountof the measuredsignal. Wedecidedtoperform a more carefulanalysis • Wephenomenologically uncoupled weak lensing from primary anisotropies by introducing a new parameter AL thatscales the lensingpotentialsuchas : • AL=0 correspondsto a theoryignoringlensing • AL=1 correspondsto the standard weaklensing scenario. AL can alsobeseenlike a fudge parameter controlling the amount of smoothing of the peaks. In fact in this figure we can see that the curves with increasingly smoothed peak structures correspond to analysis with increasingly values of AL (0, 1, 3, 6, 9).

  10. ACBAR and Standard ModelConsistenceresults • Wecheckedthat a modelwith AL =1 givescosmologicalparameters in agreement with the ΛCDM standard model • AL fixedto 0 and 1, withdatasets WMAP3 and ACBAR (9.46 accordingto the ACBAR TEAM) • Checkofoutliers in the ACBAR dataset Wecalculated the contributionofevery data pointto the modelaccordingto : (where d denotes the data vector, t denotes the theory vector, and C is the covariance matrix) This table shows that there are no significant outliers in the data, as the overall contribution to the χ2 is evenly distributed across the bins. The signal is coming from a range of scales.

  11. Constraints on LensingParameter Letting AL vary, wedidseveralCosmoMCanalysiswithdifferentdatasets in input (marginalizingoverΩb, Ωc , t, ns, As and qs): The results prefer values of ALwhich are considerably higher than the expected value 1 and they are statistically consistent with unity only at the level of 2 or 3 standard deviations. (see E. Calabrese et al, Phys.Rev.D77:123531,2008)

  12. ACBAR Claimof a 3 Sigma Lensing Detection IsGone.. Reichardtet al. , arXiv:0801.1491v3 [astro-ph] (latestrevisedversion): ABSTRACT In thispaper, wepresentresultsfrom the complete set ofcosmicmicrowave background (CMB) radiation temperature anisotropyobservationsmadewith the ArcminuteCosmologyBolometerArrayReceiver (ACBAR) operating at 150 GHz. We include new data from the final 2005 observingseason, expanding the numberofdetector-hoursby 210% and the skycoverageby 490% overthatusedfor the previous ACBAR release. As a result, the band-poweruncertaintieshavebeenreducedby more than a factoroftwo on angularscalesencompassing the thirdtofifthacousticpeaksaswellas the dampingtailof the CMB powerspectrum. The calibrationuncertaintyhasbeenreducedfrom 6% to 2.1% in temperature through a directcomparisonof the CMB anisotropymeasuredby ACBAR withthatof the dipole-calibrated WMAP5 experiment. The measuredpowerspectrumisconsistentwith a spatiallyflat, LambdaCDMcosmologicalmodel.We include the effectsofweaklensing in the powerspectrummodelcomputations and findthatthissignificantlyimproves the fitsof the modelsto the combined ACBAR+WMAP5 powerspectrum. The preferredstrengthof the lensingisconsistentwiththeoreticalexpectations. On fine angularscales, thereisweakevidence (1.1 sigma) forexcesspowerabove the levelexpectedfromprimaryanisotropies. Weexpectanyexcesspowertobedominatedby the combinationofemissionfromdustyprotogalaxies and the Sunyaev-Zel'dovicheffect (SZE). However, the excessobservedby ACBAR issignificantlysmallerthan the excesspower at ell > 2000 reportedby the CBI experimentoperating at 30 GHz. Therefore, whileitisunlikelythat the CBI excesshas a primordialorigin; the combined ACBAR and CBI results are consistentwith the source of the CBI excessbeingeither the SZE or radio source contamination. Theclaimof 3 sigma lensing detection isgone... buttoomuchlensingstillthere !

  13. ResultsInterpretation Why data suggest a lensing signal three times larger than the expected value? Statisticalfluctuation (only 2 sigma evidence), data essentially in agreement with the standard scenario ofweaklensing, “LuckyAcbar” ‘newphysics’ Primordial isocurvature barionicmodes Additionalcomponents Unknownsystematics inthe ACBAR dataset

  14. Gravitational Slip Considering a modifiedgravitytheory in which : (Daniel et al., arXiv:0802.1068) Weobtain a relation with the lensingparameter: Butifwewant AL ≈3 weneedvaluesof toolarge ( Daniel et al. , arXiv:0901.091)

  15. Results Interpretation Why data suggest a lensingsignalthreetimeslarger than the expectedvalue? Statisticalfluctuation (only 2 sigma evidence), data essentially in agreement with the standard scenario ofweaklensing, “LuckyAcbar” ‘newphysics’ Primordial isocurvature barionicmodes Additionalcomponents Unknownsystematics inthe ACBAR dataset

  16. Isocurvature Perturbations Isocurvature modesusually produce acousticoscillationsopposite in phasewith the standard adiabaticfluctuations • The sum of the twocontributionscouldsmooth • the angularpowerspectrum An analysiswithanadditionalcomponentof isocurvature barionicperturbationsgives :

  17. Results Interpretation Why data suggest a lensing signal three times larger than the expected value? Statisticalfluctuation (only 2 sigma evidence), data essentially in agreement with the standard scenario ofweaklensing, “LuckyAcbar” ‘newphysics’ Primordial isocurvature barionicmodes Additionalcomponents Unknownsystematics inthe ACBAR dataset

  18. AdditionalComponents The possiblepresenceofstring or SunyaevZel’dovichcontributionshasbeenconsidered: SZ1 is a template expected from the Sunyaev-Zel’dovich effect as given by the analytic model of Komatsu and Seljak(Mon. Not. R. Astron. Soc. 336,1256,2002) SZ2 is a similar template based on smoothed particle hydrodynamics simulations (O. Zahn et al., unpublished) strings template corresponding to the Pogosian and Vachaspati model (Phys. Rev. D 60, 083504,1999) • The effect of these templates on the value of AL is very small. • We conclude that while the data allow for some amount of extra smooth components, it by no means changes the ‘‘detection’’ of lensing.

  19. Results Interpretation Why data suggest a lensing signal three times larger than the expected value? Statisticalfluctuation (only 2 sigma evidence), data essentially in agreement with the standard scenario ofweaklensing, “LuckyAcbar” ‘newphysics’ Primordial isocurvature barionicmodes Additionalcomponents Unknownsystematics inthe ACBAR dataset

  20. Future constraints Planck • HFI 143 GHzChannel: • fsky=1 • θ=7’ • NoiseVar=3,4·10-4 μK2 • fiducialmodelwith ACBAR+WMAP3 best fitparameters Letting the lensingparametervary, the obtainedconstraints are:

  21. Conclusions • Weintroduced a newparameterthatuncouples the gravitationallensingfromprimary CMB anisotropies and thatcontrols the broadeningof the angularpowerspectrumacousticpeaks • Weconfirmed the claimfrom the ACBAR team byperformingtwoanalysiswith AL =0 and AL = 1 • LettingAL vary, withdifferentdatasets in input, weobtainedconstraints on it and the resultsprefer AL ~3 with AL=1 ruled out at 2 sigma level • Wesearchedfor some explanationsofthisinconsistencybetween the results and the expectedvalues (statisticalfluctuations, newphysics or wrong ACBAR datasetestimations). • Wedid a similaranalysissimulating a datasetfor the Planck HFI 143 GHzchannel and wefoundthatwithPlanckwecouldconstraint AL at a levelof 10% . Planckwill solve the question (maybe).

  22. New physics As I showedbeforelargeris the potential and largeris the broadeningof the acousticpeaks, so weneedtoincrease : And so in the standard scenario weneedtomodifythis relation :

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