Inflation: a Status Report

1. Inflation: a Status Report Jérôme Martin Institut d’Astrophysique de Paris (IAP) Annecy, LAPTH, February 3, 2011

2. Outline • Introduction: definition of inflation • Perturbations of quantum-mechanical origin: the « cosmological Schwinger effect » • Constraints on slow-roll and k-inflation • An inflationary pipeline: testing inflationary models exactly (numerically) • Conclusions

3. Defining inflation Inflation is a phase of accelerated expansion taking place in the very early Universe. • This assumption allows us to solve • several problems of the standard • hot Big Bang model: • Horizon problem • Flatnessproblem • Monopoles problem … • The energy scale of inflation • is poorly constrained • Accelerated expansion can be produced • if the pressure of the dominating fluid is • negative. A scalar field is a well-motivated • candidate Inflation

4. Inflation: basic mechanism Oscillatory phase p=4 p=2 Slow-roll phase Reheating phase Slow-roll phase

5. End of Inflation • The reheating phase depends on the • coupling of the inflaton with the rest • of the world • Γ is the inflaton decay rate

6. End of Inflation (II) After inflation, the radiation dominated era starts. The first temperature in the Universe is called the reheating temperature Slow-roll phase p=4

7. Implementing Inflation • The common way to realize inflation is to assume that there is a scalar field (or several scalar fields) dominating in the early Universe

8. Implementing Inflation (II) • The common way to realize inflation is to assume that there is a scalar field (or several scalar fields) dominating in the early Universe. • There are plenty of different models • 1- Single field inflation with standard kinetic term Different models are characterized by different potentials

9. Implementing Inflation (III) • The common way to realize inflation is to assume that there is a scalar field (or several scalar fields) dominating in the early Universe. • There are plenty of different models • 1- Single field inflation with standard kinetic term • 2- Single field with non-standard kinetic term (K-inflation) Different models are characterized by different potentials and different kinetic terms

10. Implementing Inflation (IV) • The common way to realize inflation is to assume that there is a scalar field (or several scalar fields) dominating in the early Universe. • There are plenty of different models • 1- Single field inflation with standard kinetic term • 2- Single field with non-standard kinetic term (K-inflation) • 3- Multiple field inflation Different models are characterized by different potentials; the inflationary trajectory can be complicated

11. Conditions for Inflation • During inflation, the Hubble radius is almost a constant Conditions for inflation Conditions for slow-roll inflation Slow-roll regime: Flat potential Lorentz factor: DBI regime: Small sound velocity

12. Primordial fluctuations small fluctuations of the geometry and matter on top of the FLRW Universe • - In order to have a more realistic description of the (early) universe (CMB, structure formation …) one must go beyond the cosmological principle. • In the early universe, the deviations are small since T/T» 10-5. This allows us to use a linear theory • The source of these fluctuations will be the unavoidable quantum fluctuations of the coupled gravitational field and matter. • The main mechanism is a very conservative one: particles creation under the influence of an external classical field. Similar to the Schwinger effect.

13. The Schwinger Effect Production of cosmological perturbations in the Early universe is very similar to pair creation in a static electric field E J. Martin, Lect. Notes Phys. 738: 193-241, 2008, arXiv:0704.3540 One works in the Fourier space The frequency is time-dependent: one has to deal with a parametric oscillator

14. The Schwinger Effect (II) The exact solution of the mode equation can be found but what are the initial conditions? The WKB mode function is given by wkb is valid particle creation The initial conditions are chosen to be the adiabatic vacuum The validity of the WKB approximation is necessary in order to choose well-defined initial conditions

15. The Schwinger Effect (III) With the previous Gaussian wave function, one can compute the number of pair created per spacetime volume. It is given vacuum (WKB) initial state particles creation The “functional” integral can be done because it is still Gaussian Difficult to see in the laboratory:

16. Inflationary fluctuations vs Schwinger effect Inflationary cosmological perturbations Schwinger effect - Scalar field - Perturbed metric - Background gravitational field: scale factor - Classical electric field • Amplitude controlled by the Hubble • parameter H • Amplitude of the effect controlled • by E

17. Inflationary fluctuations • The Fourier amplitude of the fluctuations obey the • equation of a parametric oscillator. • The shape of the effective potential depends on • the shape of the inflaton potential through the sr • Parameters • The initial conditions are natural in inflation • because, initially, the modes are sub-Hubble. The • initial state is chosen to be the Bunch-Davis • vacuum Inflation Radiation These initial conditions are crucial in order to get a scale invariant power spectrum

18. Inflationary predictions: the two-point correlation function • - The amplitude is controlled by H (for the • Schwinger effect, this was E) • For the scalar modes, the amplitude also • depends on 1 The power spectra are scale-invariant plus logarithmic corrections the amplitude of which depend on the sr parameters, ie on the microphysics of inflation The ratio of dp to gw amplitudes is given by The spectral indices are given by Gravitational waves are subdominant The running, i.e. the scale dependence of the spectral indices, of dp and gw are

19. K-inflationary Perturbations At the perturbed level, the Mukhanov-Sasaki variable obeys the following equation of motion The “sound speed” is now time-dependent (DBI) - One needs to define a new hierarchy of slow-roll parameters - The usual calculation of the spectrum in terms of Bessel functions breaks down - One has to worry about the initial conditions with

20. K-inflationary predictions The amplitude and the spectral indices are modified by the « sonic flow » parameters The ratio of dp to gw amplitudes is given by The spectral indices are given by The « crossing point » is not the same for tensors and scalars The spectral indices, runnings etc … can be determined at second order e.g. (agree with Kinney arXiv:0712.2043, disagree with Peiris, Baumann, Friedman & Cooray, arXiv:0706.1240, Chen, hep-th/0408084, Bean, Dunkley & Pierpaoli , astro-ph/0606685)

21. Two strategies to constrain inflation How can we test inflation? 1- Using the slow-roll approximation for the power spectrum Cons Pros • Simple and model independent • Usually quite accurate • Important to understand the • model • Not exact • Prior choices not very appropriate • Not well-suited for reheating • breaks down if we go beyond • slow-roll 2- Model by model exactly (ie numerically) Pros Cons • Obviously, it requires to specify • models so maybe it is not generic • enough? • All the sr Cons! • Perfect to compute the • Bayesian evidence We should do both (important: there is also the reconstruction program!). The two approaches are complementary!

22. The slow-roll pipeline Slow-roll power spectrum J. Martin & C. Ringeval, JCAP 0608, 009 (2006), astro-ph/0605367 Hot Big Bang: Data • Slow-roll parameters: • Energy scale: • Gravity waves

23. WMAP5 and K-inflation Mean likelihood Marginalised posterior probability distribution 2D Marginalised posterior probability distribution Uniform prior in [-0.3,0.3] Uniform prior in [-0.3,0.3] - Four parameters instead of two Jeffrey’s prior Jeffrey’s prior • The relevant parameters are • because - The main constraints are L. Lorenz, J. Martin & C. Ringeval, Phys. Rev D78, 083543 (2008), arXiv:0807.2414

24. Including non-Gaussianity: DBI 2D Mean likelihood Mean likelihood Marginalised posterior probability distribution 2D Marginalised posterior probability distribution Uniform prior in [-0.3,0.3] Uniform prior in [-0.3,0.3] • Including non-Gaussianity means a prior on 2 -This breaks the degeneracies between 1 and  Jeffrey’s prior Uniform prior: 22 [1,467] L. Lorenz, J. Martin & C. Ringeval, Phys. Rev D78, 083543 (2008), arXiv:0807.2414

25. Towards an inflationary pipeline Model of inflation (or of the early Universe) Hot Big Bang: NG on the celestial sphere Data: What is the best model of Inflation? Posterior distributions

26. WMAP7 and large field models Mean likelihood Marginalized posteriors (p2 [0.2,5]) J. Martin & C. Ringeval, JCAP 08, 009 (2006) astro-ph/0605367 • This approach allows us to constrain directly the parameters of the • inflaton potential • Large field models are now under pressure:

27. The first calculation of the inflationary evidence J. Martin, C. Ringeval & R. Trotta, arXiv:1009.4157

28. The observational situation: recap • Slow-roll parameters: • Energy scale: • Gravity waves • Tendency for red tilt (3 sigmas) • No prior independent evidence for a running • No entropy mode • No cosmic string • No non-Gaussianities • m^2 2 under pressure, 4 ruled out, small field doing pretty well

29. Conclusions • Inflation is a very consistent paradigm, based on conservative physics • and compatible with all known astrophysical observations. • The continuous flow of high accuracy cosmological data allows us to probe the details of inflation ie to learn about the microphysics of inflation. I have presented the first calculation of the evidence for some inflationary models= first steps towards a complete inflationary pipeline. • For a given model, one can also put constraints on the reheating temperature. First constraints in the case of large and small field models are available. • On the theoretical side, the case of multiple fields inflation is very important. • It must be included in the inflationary pipeline … more complicated. • On the observational side, polarization, Non-Gaussianities, entropy modes and • direct detection of gravity waves have an important role to play.

30. Waiting for Planck! Thankyou! Galaxy foreground The CMB is just behind! First Planck data

31. The CMB can (also) constrain the reheating temperature! Matter–dominated era Radiation-dominated era

32. Constraining the reheating Large field inflation

33. The first CMB constraints on reheating! Mean likelihood Marginalized posterior pdf wreh=-0.2 _ _ _ wreh=0 wreh=-0.3 wreh=-0.1 • Rescaled reheating parameter constrained • Reheating temperature (but with extra assumptions) - LF: - SF: J. Martin & C. Ringeval, Phys. Rev. D82: 023511 (2010), arXiv:1004.5525

34. Testing the initial conditions? Is the Bunch-Davies state justified? • Below the Planck length, we expect corrections • from string theory • Inflation has maybe the potential to keep an • inprint from this regime: window of opportunity. • If physics in non-adiabatic beyond the Planck, • then one expects corrections. • Any new physics will generate the other WKB • branch and, therefore superimposed oscillations • the shape of which will be model dependent. In • the minimal approach the amplitude is • proportional to J. Martin & R. H. Brandenberger, PRD 68 063513 (2003), hep-th/0305161

35. WMAP and super-imposed oscillations Superimposed oscillations J. Martin & C. Ringeval, PRD 69 083515 (2004), astro-ph/0310382

36. WMAP and super-imposed oscillations Marginalized probalities Mean likelihood Power-spectrum of super-imposed oscillations flat 1 2 |x | Log(1/ )2 [1,2.6] [0,0.45] Usual SR power spectrum Logarithmic oscillations Results From the Baeysian point of view (ie taking into account volume effects in the parameter space), the no-oscillation solution remains favored 2  [0,2] J. Martin & C. Ringeval, JCAP 08, 009 (2006) astro-ph/0605367