DOCSLIB.ORG

TASI Lectures on Inflation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
TASI Lectures on Inflation TASI Lectures on Inflation Daniel Baumann Department of Physics, Harvard University, Cambridge, MA 02138, USA School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540, USA Abstract In a series of five lectures I review inflationary cosmology. I begin with a description of the initial conditions problems of the Friedmann-Robertson-Walker (FRW) cosmology and then explain how inflation, an early period of accelerated expansion, solves these problems. Next, I describe how infla- tion transforms microscopic quantum fluctuations into macroscopic seeds for cosmological structure formation. I present in full detail the famous calculation for the primordial spectra of scalar and tensor fluctuations. I then define the inverse problem of extracting information on the inflationary era from observations of cosmic microwave background fluctuations. The current observational ev- idence for inflation and opportunities for future tests of inflation are discussed. Finally, I review the challenge of relating inflation to fundamental physics by giving an account of inflation in string theory. Lecture 1: Classical Dynamics of Inflation The aim of this lecture is a first-principles introduction to the classical dynamics of inflationary cosmology. After a brief review of basic FRW cosmology we show that the conventional Big Bang theory leads to an initial conditions problem: the universe as we know it can only arise for very spe- cial and finely-tuned initial conditions. We then explain how inflation (an early period of accelerated expansion) solves this initial conditions problem and allows our universe to arise from generic initial conditions. We describe the necessary conditions for inflation and explain how inflation modifies the causal structure of spacetime to solve the Big Bang puzzles. Finally, we end this lecture with a discussion of the physical origin of the inflationary expansion. Lecture 2: Quantum Fluctuations during Inflation In this lecture we review the famous calculation of the primordial fluctuation spectra gener- ated by quantum fluctuations during inflation. We present the calculation in full detail and try to avoid `cheating' and approximations. After a brief review of fundamental aspects of cosmological perturbation theory, we first give a qualitative summary of the basic mechanism by which inflation converts microscopic quantum fluctuations into macroscopic seeds for cosmological structure forma- tion. As a pedagogical introduction to quantum field theory in curved spacetime we then review the quantization of the simple harmonic oscillator. We emphasize that a unique vacuum state is chosen by demanding that the vacuum is the minimum energy state. We then proceed by giving the 1 corresponding calculation for inflation. We calculate the power spectra of both scalar and tensor fluctuations. Lecture 3: Contact with Observations In this lecture we describe the inverse problem of extracting information on the inflationary perturbation spectra from observations of the cosmic microwave background and the large-scale structure. We define the precise relations between the gauge-invariant scalar and tensor power spec- tra computed in the previous lecture and the observed CMB anisotropies and galaxy power spectra. We give the transfer functions that relate the primordial fluctuations to the late-time observables. We then use these results to discuss the current observational evidence for inflation. Finally, we indicate opportunities for future tests of inflation. Lecture 4: Primordial Non-Gaussianity In this lecture we summarize key theoretical results in the study of primordial non-Gaussianity. Most results are stated without proof, but their significance for constraining the fundamental phys- ical origin of inflation is explained. After introducing the bispectrum as a basic diagnostic of non- Gaussian statistics, we show that its momentum dependence is a powerful probe of the inflationary action. Large non-Gaussianity can only arise if inflaton interactions are significant during inflation. In single-field slow-roll inflation non-Gaussianity is therefore predicted to be unobservably small, while it can be significant in models with multiple fields, higher-derivative interactions or non- standard initial states. Finally, we end the lecture with a discussion of the observational prospects for detecting or constraining primordial non-Gaussianity. Lecture 5: Inflation in String Theory We end this lecture series with a discussion of a slightly more advanced topic: inflation in string theory. We provide a pedagogical overview of the subject based on a recent review article with Liam McAllister. The central theme of the lecture is the sensitivity of inflation to Planck-scale physics, which we argue provides both the primary motivation and the central theoretical challenge for realizing inflation in string theory. We illustrate these issues through two case studies of inflationary scenarios in string theory: warped D-brane inflation and axion monodromy inflation. Finally, we indicate opportunities for future progress both theoretically and observationally. email: [email protected] November 15, 2019 2 Contents I Introduction9 1 The Microscopic Origin of Structure9 1.1 TASI 2009: The Physics of the Large and the Small ..................9 1.2 Structure and Evolution of the Universe......................... 10 1.3 The First 10−10 Seconds.................................. 12 2 Outline of the Lectures 12 II Lecture 1: Classical Dynamics of Inflation 15 3 Review: The Homogeneous Universe 15 3.1 FRW Spacetime....................................... 15 3.2 Kinematics: Conformal Time and Horizons....................... 16 3.3 Dynamics: Einstein Equations............................... 18 3.4 The Concordance Model.................................. 21 4 Big Bang Puzzles 22 4.1 The Cauchy Problem of the Universe........................... 22 4.2 Horizon Problem...................................... 23 4.3 Flatness Problem...................................... 23 4.4 On the Problem of Initial Conditions........................... 24 5 A First Look at Inflation 25 5.1 The Shrinking Hubble Sphere............................... 25 5.1.1 Comoving Horizon during Inflation........................ 25 5.1.2 Flatness Problem Revisited............................ 26 5.1.3 Horizon Problem Revisited............................ 26 5.2 Conditions for Inflation.................................. 26 5.3 Conformal Diagram of Inflation.............................. 27 6 The Physics of Inflation 28 6.1 Scalar Field Dynamics................................... 28 6.2 Slow-Roll Inflation..................................... 29 6.3 Case Study: m2φ2 Inflation................................ 31 6.4 Reheating.......................................... 32 6.5 Models of Inflation..................................... 32 6.5.1 Single-Field Slow-Roll Inflation.......................... 32 6.5.2 Beyond Single-Field Slow-Roll.......................... 34 7 Summary: Lecture 1 36 3 8 Problem Set: Lecture 1 37 III Lecture 2: Quantum Fluctuations during Inflation 39 9 Review: Cosmological Perturbations 39 9.1 Generalities......................................... 40 9.1.1 Linear Perturbations................................ 40 9.1.2 Gauge Choice.................................... 41 9.1.3 Scalars, Vectors and Tensors........................... 41 9.2 The Inhomogeneous Universe............................... 42 9.2.1 Metric Perturbations................................ 42 9.2.2 Matter Perturbations............................... 43 9.2.3 Gauge-Invariant Variables............................. 44 9.2.4 Superhorizon (Non-)Evolution.......................... 45 9.3 Statistics of Cosmological Perturbations......................... 45 10 Preview: The Quantum Origin of Structure 46 10.1 Quantum Zero-Point Fluctuations............................ 47 10.2 Horizon Exit and Re-Entry................................ 47 11 Quantum Mechanics of the Harmonic Oscillator 47 11.1 Action............................................ 48 11.2 Canonical Quantization.................................. 48 11.3 Non-Uniqueness of the Mode Functions......................... 49 11.4 Zero-Point Fluctuations in the Ground State...................... 50 12 Quantum Fluctuations in de Sitter Space 51 12.1 Summary of the Computational Strategy........................ 51 12.2 Scalar Perturbations.................................... 52 12.2.1 Free Field Action.................................. 52 12.2.2 Quantization.................................... 53 12.2.3 Boundary Conditions and Bunch-Davies Vacuum................ 53 12.2.4 Solution in de Sitter Space............................ 54 12.2.5 Power Spectrum in Quasi-de Sitter........................ 54 12.2.6 Spatially-Flat Gauge................................ 55 12.3 Tensor Perturbations.................................... 55 12.3.1 Action........................................ 56 12.3.2 Quantization.................................... 56 12.3.3 Power Spectrum.................................. 57 12.4 The Energy Scale of Inflation............................... 57 12.5 The Lyth Bound...................................... 57 4 13 Primordial Spectra 58 13.1 Scale-Dependence...................................... 58 13.2 Slow-Roll Results...................................... 59 13.3 Case Study: m2φ2 Inflation................................ 59 14 Summary: Lecture 2 60 15 Problem Set: Lecture 2 61 IV Lecture 3: Contact with Observations 63 16 Connecting Observations to the Early Universe 63 17 Review: The Cosmic
Load more

Recommended publications
  • Lecture 8: the Big Bang and Early Universe
    Astr 323: Extragalactic Astronomy and Cosmology Spring Quarter 2014, University of Washington, Zeljkoˇ Ivezi´c Lecture 8: The Big Bang and Early Universe 1 Observational Cosmology Key observations that support the Big Bang Theory • Expansion: the Hubble law • Cosmic Microwave Background • The light element abundance • Recent advances: baryon oscillations, integrated Sachs-Wolfe effect, etc. 2 Expansion of the Universe • Discovered as a linear law (v = HD) by Hubble in 1929. • With distant SNe, today we can measure the deviations from linearity in the Hubble law due to cosmological effects • The curves in the top panel show a closed Universe (Ω = 2) in red, the crit- ical density Universe (Ω = 1) in black, the empty Universe (Ω = 0) in green, the steady state model in blue, and the WMAP based concordance model with Ωm = 0:27 and ΩΛ = 0:73 in purple. • The data imply an accelerating Universe at low to moderate redshifts but a de- celerating Universe at higher redshifts, consistent with a model having both a cosmological constant and a significant amount of dark matter. 3 Cosmic Microwave Background (CMB) • The CMB was discovered by Penzias & Wil- son in 1965 (although there was an older mea- surement of the \sky" temperature by McKel- lar using interstellar molecules in 1940, whose significance was not recognized) • This is the best black-body spectrum ever mea- sured, with T = 2:73 K. It is also remark- ably uniform accross the sky (to one part in ∼ 10−5), after dipole induced by the solar mo- tion is corrected for. • The existance of CMB was predicted by Gamow in 1946.
    [Show full text]
  • Arxiv:Hep-Ph/9912247V1 6 Dec 1999 MGNTV COSMOLOGY IMAGINATIVE Abstract
    IMAGINATIVE COSMOLOGY ROBERT H. BRANDENBERGER Physics Department, Brown University Providence, RI, 02912, USA AND JOAO˜ MAGUEIJO Theoretical Physics, The Blackett Laboratory, Imperial College Prince Consort Road, London SW7 2BZ, UK Abstract. We review1 a few off-the-beaten-track ideas in cosmology. They solve a variety of fundamental problems; also they are fun. We start with a description of non-singular dilaton cosmology. In these scenarios gravity is modified so that the Universe does not have a singular birth. We then present a variety of ideas mixing string theory and cosmology. These solve the cosmological problems usually solved by inflation, and furthermore shed light upon the issue of the number of dimensions of our Universe. We finally review several aspects of the varying speed of light theory. We show how the horizon, flatness, and cosmological constant problems may be solved in this scenario. We finally present a possible experimental test for a realization of this theory: a test in which the Supernovae results are to be combined with recent evidence for redshift dependence in the fine structure constant. arXiv:hep-ph/9912247v1 6 Dec 1999 1. Introduction In spite of their unprecedented success at providing causal theories for the origin of structure, our current models of the very early Universe, in partic- ular models of inflation and cosmic defect theories, leave several important issues unresolved and face crucial problems (see [1] for a more detailed dis- cussion). The purpose of this chapter is to present some imaginative and 1Brown preprint BROWN-HET-1198, invited lectures at the International School on Cosmology, Kish Island, Iran, Jan.
    [Show full text]
  • Inflation Without Quantum Gravity
    Inflation without quantum gravity Tommi Markkanen, Syksy R¨as¨anen and Pyry Wahlman University of Helsinki, Department of Physics and Helsinki Institute of Physics P.O. Box 64, FIN-00014 University of Helsinki, Finland E-mail: tommi dot markkanen at helsinki dot fi, syksy dot rasanen at iki dot fi, pyry dot wahlman at helsinki dot fi Abstract. It is sometimes argued that observation of tensor modes from inflation would provide the first evidence for quantum gravity. However, in the usual inflationary formalism, also the scalar modes involve quantised metric perturbations. We consider the issue in a semiclassical setup in which only matter is quantised, and spacetime is classical. We assume that the state collapses on a spacelike hypersurface, and find that the spectrum of scalar perturbations depends on the hypersurface. For reasonable choices, we can recover the usual inflationary predictions for scalar perturbations in minimally coupled single-field models. In models where non-minimal coupling to gravity is important and the field value is sub-Planckian, we do not get a nearly scale-invariant spectrum of scalar perturbations. As gravitational waves are only produced at second order, the tensor-to-scalar ratio is negligible. We conclude that detection of inflationary gravitational waves would indeed be needed to have observational evidence of quantisation of gravity. arXiv:1407.4691v2 [astro-ph.CO] 4 May 2015 Contents 1 Introduction 1 2 Semiclassical inflation 3 2.1 Action and equations of motion 3 2.2 From homogeneity and isotropy to perturbations 6 3 Matching across the collapse 7 3.1 Hypersurface of collapse 7 3.2 Inflation models 10 4 Conclusions 13 1 Introduction Inflation and the quantisation of gravity.
    [Show full text]
  • Homework 2: Classical Cosmology
    Homework 2: Classical Cosmology Due Mon Jan 21 2013 You may find Hogg astro-ph/9905116 a useful reference for what follows. Ignore radiation energy density in all problems. Problem 1. Distances. a) Compute and plot for at least three sets of cosmological parameters of your choice the fol- lowing quantities as a function of redshift (up to z=10): age of the universe in Gyrs; angular size distance in Gpc; luminosity distance in Gpc; angular size in arcseconds of a galaxy of 5kpc in intrin- sic size. Choose one of them to be the so-called concordance cosmology (Ωm, ΩΛ, h) = (0.3, 0.7, 0.7), one of them to have non-zero curvature and one of them such that the angular diameter distance becomes negative. What does it mean to have negative angular diameter distance? [10 pts] b) Consider a set of flat cosmologies and find the redshift at which the apparent size of an object of given intrinsic size is minimum as a function of ΩΛ. [10 pts] 2. The horizon and flatness problems 1) Compute the age of the universe tCMB at the time of the last scattering surface of the cosmic microwave background (approximately z = 1000), in concordance cosmology. Approximate the horizon size as ctCMB and get an estimate of the angular size of the horizon on the sky. Patches of the CMB larger than this angular scale should not have been in causal contact, but nonetheless the CMB is observed to be smooth across the entire sky. This is the famous ”horizon problem”.
    [Show full text]
  • Effects of Primordial Chemistry on the Cosmic Microwave Background
    A&A 490, 521–535 (2008) Astronomy DOI: 10.1051/0004-6361:200809861 & c ESO 2008 Astrophysics Effects of primordial chemistry on the cosmic microwave background D. R. G. Schleicher1, D. Galli2,F.Palla2, M. Camenzind3, R. S. Klessen1, M. Bartelmann1, and S. C. O. Glover4 1 Institute of Theoretical Astrophysics / ZAH, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany e-mail: [dschleic;rklessen;mbartelmann]@ita.uni-heidelberg.de 2 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy e-mail: [galli;palla]@arcetri.astro.it 3 Landessternwarte Heidelberg / ZAH, Koenigstuhl 12, 69117 Heidelberg, Germany e-mail: [email protected] 4 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: [email protected] Received 27 March 2008 / Accepted 3 July 2008 ABSTRACT Context. Previous works have demonstrated that the generation of secondary CMB anisotropies due to the molecular optical depth is likely too small to be observed. In this paper, we examine additional ways in which primordial chemistry and the dark ages might influence the CMB. Aims. We seek a detailed understanding of the formation of molecules in the postrecombination universe and their interactions with the CMB. We present a detailed and updated chemical network and an overview of the interactions of molecules with the CMB. Methods. We calculate the evolution of primordial chemistry in a homogeneous universe and determine the optical depth due to line absorption, photoionization and photodissociation, and estimate the resulting changes in the CMB temperature and its power spectrum. Corrections for stimulated and spontaneous emission are taken into account.
    [Show full text]
  • Chapter 4: Linear Perturbation Theory
    Chapter 4: Linear Perturbation Theory May 4, 2009 1. Gravitational Instability The generally accepted theoretical framework for the formation of structure is that of gravitational instability. The gravitational instability scenario assumes the early universe to have been almost perfectly smooth, with the exception of tiny density deviations with respect to the global cosmic background density and the accompanying tiny velocity perturbations from the general Hubble expansion. The minor density deviations vary from location to location. At one place the density will be slightly higher than the average global density, while a few Megaparsecs further the density may have a slightly smaller value than on average. The observed fluctuations in the temperature of the cosmic microwave background radiation are a reflection of these density perturbations, so that we know that the primordial density perturbations have been in the order of 10−5. The origin of this density perturbation field has as yet not been fully understood. The most plausible theory is that the density perturbations are the product of processes in the very early Universe and correspond to quantum fluctuations which during the inflationary phase expanded to macroscopic proportions1 Originally minute local deviations from the average density of the Universe (see fig. 1), and the corresponding deviations from the global cosmic expansion velocity (the Hubble expansion), will start to grow under the influence of the involved gravity perturbations. The gravitational force acting on each patch of matter in the universe is the total sum of the gravitational attraction by all matter throughout the universe. Evidently, in a homogeneous Universe the gravitational force is the same everywhere.
    [Show full text]
  • New Varying Speed of Light Theories
    New varying speed of light theories Jo˜ao Magueijo The Blackett Laboratory,Imperial College of Science, Technology and Medicine South Kensington, London SW7 2BZ, UK ABSTRACT We review recent work on the possibility of a varying speed of light (VSL). We start by discussing the physical meaning of a varying c, dispelling the myth that the constancy of c is a matter of logical consistency. We then summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz invariance; bimetric theories (where the speeds of gravity and light are not the same); locally Lorentz invariant VSL theories; theories exhibiting a color dependent speed of light; varying c induced by extra dimensions (e.g. in the brane-world scenario); and field theories where VSL results from vacuum polarization or CPT violation. We show how VSL scenarios may solve the cosmological problems usually tackled by inflation, and also how they may produce a scale-invariant spectrum of Gaussian fluctuations, capable of explaining the WMAP data. We then review the connection between VSL and theories of quantum gravity, showing how “doubly special” relativity has emerged as a VSL effective model of quantum space-time, with observational implications for ultra high energy cosmic rays and gamma ray bursts. Some recent work on the physics of “black” holes and other compact objects in VSL theories is also described, highlighting phenomena associated with spatial (as opposed to temporal) variations in c. Finally we describe the observational status of the theory. The evidence is slim – redshift dependence in alpha, ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data.
    [Show full text]
  • “The Constancy, Or Otherwise, of the Speed of Light”
    “Theconstancy,orotherwise,ofthespeedoflight” DanielJ.Farrell&J.Dunning-Davies, DepartmentofPhysics, UniversityofHull, HullHU67RX, England. [email protected] Abstract. Newvaryingspeedoflight(VSL)theoriesasalternativestotheinflationary model of the universe are discussed and evidence for a varying speed of light reviewed.WorklinkedwithVSLbutprimarilyconcernedwithderivingPlanck’s black body energy distribution for a gas-like aether using Maxwell statistics is consideredalso.DoublySpecialRelativity,amodificationofspecialrelativityto accountforobserverdependentquantumeffectsatthePlanckscale,isintroduced and it is found that a varying speed of light above a threshold frequency is a necessityforthistheory. 1 1. Introduction. SincetheSpecialTheoryofRelativitywasexpoundedandaccepted,ithasseemedalmost tantamount to sacrilege to even suggest that the speed of light be anything other than a constant.ThisissomewhatsurprisingsinceevenEinsteinhimselfsuggestedinapaperof1911 [1] that the speed of light might vary with the gravitational potential. Interestingly, this suggestion that gravity might affect the motion of light also surfaced in Michell’s paper of 1784[2],wherehefirstderivedtheexpressionfortheratioofthemasstotheradiusofastar whose escape speed equalled the speed of light. However, in the face of sometimes fierce opposition, the suggestion has been made and, in recent years, appears to have become an accepted topic for discussion and research. Much of this stems from problems faced by the ‘standardbigbang’modelforthebeginningoftheuniverse.Problemswiththismodelhave
    [Show full text]
  • Planck 'Toolkit' Introduction
    Planck ‘toolkit’ introduction Welcome to the Planck ‘toolkit’ – a series of short questions and answers designed to equip you with background information on key cosmological topics addressed by the Planck science releases. The questions are arranged in thematic blocks; click the header to visit that section. Planck and the Cosmic Microwave Background (CMB) What is Planck and what is it studying? What is the Cosmic Microwave Background? Why is it so important to study the CMB? When was the CMB first detected? How many space missions have studied the CMB? What does the CMB look like? What is ‘the standard model of cosmology’ and how does it relate to the CMB? Behind the CMB: inflation and the meaning of temperature fluctuations How did the temperature fluctuations get there? How exactly do the temperature fluctuations relate to density fluctuations? The CMB and the distribution of matter in the Universe How is matter distributed in the Universe? Has the Universe always had such a rich variety of structure? How did the Universe evolve from very smooth to highly structured? How can we study the evolution of cosmic structure? Tools to study the distribution of matter in the Universe How is the distribution of matter in the Universe described mathematically? What is the power spectrum? What is the power spectrum of the distribution of matter in the Universe? Why are cosmologists interested in the power spectrum of cosmic structure? What was the distribution of the primordial fluctuations? How does this relate to the fluctuations in the CMB?
    [Show full text]
  • A873: Cosmology Course Notes VIII. Linear Fluctuations Linear
    A873: Cosmology Course Notes VIII. Linear Fluctuations Linear perturbation theory in general Start with an \unperturbed" solution for quantities xi, i = 1; 2; ::: Write equations for x~i = xi + δxi: Expand, keeping terms linear in δxi, and subtracting off unperturbed solution to get equations for δxi. Hope you can solve them. In GR, the quantities xi might be metric coefficients, densities, velocities, etc. GR pertur- bation theory can be tricky for two reasons. (1) The equations are very complicated. This is a problem of practice, not of principle. (2) In a perturbed universe, the \natural" coordinate choice is no longer obvious. Different coordinate choices have different equations. Results for physically measurable quantities should be the same, but the descriptions can look quite different. For scales l cH−1 and velocities v c, one can usually get by with Newtonian linear perturbationtheory. Newtonian perturbation theory in an expanding universe (This discussion follows Peebles, pp. 111-119.) Basic unperturbed equations In an inertial frame, the equations governing the density ρ(r; t) and velocity u(r; t) of an ideal fluid are: @ρ Continuity equation : + ~ r (ρu) = 0 (mass conservation) @t r r · @u Euler equation : + (u ~ r)u = ~ rΦ (momentum conservation) @t r · r −r 2 Poisson equation : rΦ = 4πGρ. r We have ignored pressure gradients in the Euler equation. Transformation of variables We would like to have these equations in comoving coordinates x = r=a(t) with \peculiar" velocity v = u (a=a_ )r = (a_x) a_x = ax_ : − − We want to use a quantity that will be small when perturbations are small, so define the dimensionless density contrast δ(x; t) by ρ = ρb(t) [1 + δ(x; t)], ρb = background density 1=a3.
    [Show full text]
  • The Primordial Fireball Transcript
    The Primordial Fireball Transcript Date: Wednesday, 23 September 2015 - 1:00PM Location: Museum of London 23 September 2015 The Primordial Fireball Professor Joseph Silk The universe underwent an inflationary period of expansion. From an extremely hot beginning, it cooled down, and then reheated to form the expanding universe that we observe today. The relic radiation generated the fossil glow of the cosmic microwave background radiation, a testament to its fiery origin. Infinitesimal fluctuations in temperature were laid down very soon after the beginning. Gravity triumphed in slightly over-dense regions where galaxies eventually formed. Microwave telescopes map out the structure of the universe long before the galaxies were present. I will describe the current challenges in cosmic microwave background astronomy. The universe began in a state of extreme density and temperature, some 14 billion years ago. Our best estimate is that its density was once higher than its present value by 120 powers of 10. This is at the limit of extrapolation of our current theories of gravity and quantum physics. And it was very hot, hotter than the radiation that presently fills the universe by some 28 powers of 10 in temperature. How do we arrive at such incredible extrapolations from the present? The Expansion of the Universe The story begins with the discovery of the expansion of the universe in 1929 by American astronomer Edwin Hubble. Now confirmed at immense distances from us, over many billions of light years, the extrapolation to an ultra-dense beginning is essentially inevitable. Of course, most of this extrapolation is based on theory.
    [Show full text]
  • Structures in the Early Universe
    Structures in the early Universe Particle Astrophysics chapter 8 Lecture 4 overview • problems in Standard Model of Cosmology: horizon and flatness problems – presence of structures • Need for an exponential expansion in the early universe • Inflation scenarios – scalar inflaton field • Primordial fluctuations in inflaton field • Growth of density fluctuations during radiation and matter dominated eras • Observations related to primordial fluctuations: CMB and LSS 2011-12 Structures in early Universe 2 •Galactic and intergalactic magnetic fields as source of structures? •problems in Standard Model of Cosmology related to initial conditions required: horizon and flatness problems PART 1: PROBLEMS IN STANDARD COSMOLOGICAL MODEL 2011-12 Structures in early Universe 3 Galactic and intergalactic B fields cosmology model assumes Non-uniformity observed uniform & homogeous in CMB and galaxy medium distribution, • Is cltilustering of matter ithin the universe dtdue to galtilactic and intergalactic magnetic fields? • At small = stellar scales : intense magnetic fldfieldsare onlyimportant in later stages of star evolution • At galtilacticscale: magnetic fie ld in Milky Way ≈ 3G3µG • At intergalactic scale : average fields of 10-7 –10-11 G • → itinterga lac ticmagnetic fie ldsprobblbably have very small role in development of large scale structures • DDlevelopmen toflf large scallleesstttructures mailinly dtdue to gravity 2011-12 Structures in early Universe 4 Horizon in static universe • Particle horizon = distance over which one can observe a particle
    [Show full text]