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## Tarun Souradeep

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**Cosmology: towards ‘observing’the early universe**1st Asian Winter School Pheonix Park, Korea (Jan 17, 2007) Tarun Souradeep I.U.C.A.A, Pune, India**Good old Cosmology, … New trend !**Total energy density Dark energy density Baryonic matter density Dawn of Precision cosmology !! NASA/WMAP science team**Planck Surveyor Satellite**European Space Agency: Launch 2008**Near future : High resolution Cl(SPT)**CMB Task force report 2005**Who ordered Dark Energy?**Is it the Cosmological constant? Interestingly enough, current cosmological observations are consistent with it being the L term ‘blunder’ in GR!!!**Near future : SZ Cluster surveys (SPT,ACT)**CMB Task force report 2005 Number count of clusters vs. redshift (dN/dz)**Gravitational Instability**Mildly Perturbed universe at z=1100 Present universe at z=0 Cosmic matter content**Present distribution of matter**Few Gpc. SLOAN DIGITAL SKY SURVEY (SDSS)**150 Mpc.**One little telltale bump !! A small excess in correlation at 150 Mpc.! SDSS survey (astro-ph/0501171) (Einsentein et al. 2005)**Acoustic Baryon oscillations in the matter correlation**function !! 150 Mpc. 105 h-1¼ 150 2-point correlation of density contrast The same CMB oscillations at low redshifts !!! SDSS survey (astro-ph/0501171) Undeniable proof of Gravitational instability mechanism for structure formation (from adiabatic initial perturbations) !!! (Einsentein et al. 2005)**CMB Polarization**Thompson scattering at redshift z=1100 (surface of last scattering) generates a linear polarization pattern in the CMB sky. • Two polarization modesE&B • Four CMB spectra : ClTT, ClEE,ClBB,ClTE • Density (scalar) perturbations generate only E mode polarization. • E-mode ¼ 5 --10 K • Gravitational waves generate both the modes in comparable amounts . B-mode ¼ 0.05 – 0.1 K • B-mode measures cosmic gravity wave background.**CMB Polarization**Thompson scattering of the CMB anisotropy quadrupole at the surface of last scattering generates a linear polarization pattern in the CMB. (Fig:Hu & White , 97)**E modes**(Gradient) B modes (Curl)**Polarization: E modes and B modes**E Modes: • Gradient of the polarization • Produced by both scalar and tensor modes • Have been detected B Modes: • Curl of the polarization • Produced only by tensor modes...or gravitational lensing ...or foregrounds ...or systematics • Expected from inflation • Have not been detected A detection of primordial sourced B modes would provide important evidence for, and determine the energy scale of Inflation E B**WMAP map of CMB Polarization**NASA/WMAP science team 2006**Current status of CMB Spectra**Null BB: Awaiting direct signature of tensor perturbations, a.k.a. cosmic gravity waves !!! Out of phase location of peaks in EE, TE relative to TT implies adiabatic initial perturbations !!! Proof of inflation ! (Boomerang 2003, WMAP-3)**Timeline of CMB experiments**now Next Gen. space CMBPOL WMAP-8yr Planck (ESA) WMAP-1yr WMAP-3yr CMB Task force report 2005**Who pinged the Cosmic drum ?**Quantum fluctuations super adiabatic amplified by inflation (rapid expansion) Galaxy & Large scale Structure formation Via gravitational instability Early Universe The Cosmic screen Present Universe**String theory Landscape:**Non trivial skiing slopes**Generic inflation model**A scalar field displaced from the minima of its potential Linde’s chaotic inflation**Generic inflation model**A scalar field displaced from the minima of its potential**Generic inflation model**A phase of rapid expansion in the scale factor of the universe Hubble Radius time**Adiabatic scalar perturbations**• The inhomogeneous scale factor on which the space creation rate is constant is a measure of adiabatic scalar perturbations • It is equivalent to the Gauge invariant Bardeen potential • on super-Hubble radius scales**Early universe from CMB Anisotropy**• Reconstructing the inflaton potential from the primordial power spectrum**Early universe from CMB Anisotropy**• Energy scale and Model of inflation COBE-DMR normalized Hubble parameter during inflation (Souradeep & Sahni, 1992, Souradeep, Ph.D.thesis, 1995)**Scalar & Tensor perturbations**(Fig:Souradeep, Thesis 1995)**Power spectra of perturbations**• Evaluate the mode functions at freeze out values on super-Hubble-radius scales.**Scale Invariant perturbation spectra**Ideal case: Never exactly possible for inflation!! Requires No end to dS phase Scale free perturbation spectra Very specific model : Power law inflation Scalar & tensor spectra have the same shape Relative amplitude and spectral index determined by**Early universe in CMB Anisotropy**The Background universe • Homogeneous & isotropic: Cosmological principle • Flat (Euclidean) Geometry ( but topology ? ) The nature of initial/primordial perturbations ‘Nearly’ Scale invariant /scale free form ( … but are there features ?) • Power spectrum Scalar --- Density perturbations Tensor --- Gravity waves • Spin characteristics Adiabatic --- no entropy fluctuations Isocurvature -- no curvature fluctuations • Type of scalar perturbations Gaussian Non-Gaussian • Underlying statistics**Detecting the relic**GW background : Energy scale of inflation**Early universe in CMB Anisotropy**• Tensor to scalar ratio is crucial discriminant of EU scenarios Scalar --- Density perturbations Large scale structure in galaxy clustering Tensor --- Gravitational waves Relic stochastic GW background Vector --- rotational modes Perhaps unimportant, but primordial magnetic field Tensor to scalar ratio in the CMB COBE WMAP WMAP+SDSS (Souradeep & Sahni, 1992, Souradeep, Ph.D.thesis, 1995)**10-3 : reasonable low end of inflationary possibilities**Courtesy: A. Coorey (EPIC)**Cosmic Gravity wave background from inflation**First COBE-DMR normalized prediction of inflationary GW background spectrum (GW energy density per log interval in wavenumber) (Souradeep & Sahni, 1992, Souradeep, Ph.D.thesis, 1995)**Cosmic Gravity wave background from inflation**Coveted Goal CMB Task force report 2005**Measuring the primordial power spectrum:**Features as signatures of new physics**Dynamics of slow roll parameters**(Souradeep, Thesis 1995)**Breaking Scale Invariance of spectra**(Zelnikov & Mukhanov) Two distinct approaches: 1. Vary H during inflation Changes both scalar & tensor spectra 2. Vary effective mass Changes only scalar spectra**Breaking Scale Invariance of spectra**Response to `delta function’ effective mass : (Starobinsky 1992) Transfer function on the scalar spectra (Memari, TS 2003)**Breaking Scale Invariance of spectra**Response to `delta function’ effective mass : (Starobinsky 1992) Transfer function on the scalar spectra (Memari, TS 2003)**Primordial power spectrum ?**CMB anisotropy has two independent aspects: Post recombination Radiation transport in a given cosmology Primordial power spectrum from Early universe**Determining P(k)**Forward (model comparsion): *Assume model initial power spectrum + * CMB anisotropy data Cosmological parameters + Power spectrum * CMB anisotropy data + * Cosmological parameters. Reverse (direct deconvolution): Initial power spectrum (Kogo et al. ‘03, ’04, Matsumiya et al. ’02, Tegmark & Zaldariagga 97, ..)**Primordial power spectrum from WMAP**(Shafieloo & Souradeep, 2004 PRD ) Cited in WMAP-3 paper Horizon scale Recovered spectrum shows an infra-red cut-off on Horizon scale !!! Is it QG physics ? cosmic topology ? Signature of pre-inflationary phase ? String cosmology ? ….