Non-Gaussianity from Quantum Fluctuations during Inflation

Kin-Wang Ng

Institute of Physics & Institute of Astronomy and Astrophysics

Academia Sinica, Taiwan, ROC

2nd KIAS Workshop on Cosmology and Structure Formation KIAS, Seoul, Korea

Sep 20-21, 2006

CH Wu, KW Ng, WL Lee, DS Lee, YY Charng, astro-ph/0604292

• WMAP 3-year data and other CMB expts Challenges to standard slow-roll inflation?! low CMB quadrupole , running spectral index, nongaussia

nity, south-north asymmetry, axis of evil (in Park’s talk),..

• Inflaton coupled to other quantum fields natural, reheating,..

still single-field inflation (see multi-field inflation in Steward’s talk)

• Quantum environment behaves like colored quantum noise – kicks inflaton (Brownian motion)

• Noise-induced (passive) inflaton fluctuations in addition to active de Sitter quantum fluctuations

Introduction

WMAP3-yearTT,TE,EE, CMB power spectra

low quadrupole

Cosmological Parameters

ns=0.961 @ k=0.05Mpc-1

r : tenor/scalarns :scalar spectral indexdns/dlnk: running index

k=0.002Mpc-1 ns 0.05= 0.961

WMAP3 Data on Running Spectral Idex

|dn/dlnk| << |n-1|

PR(k)= (δρ/ρ)2

WMAP3 and inflation models

These models predict that

Curvature potential

Slow-roll inflation

WMAP3 Data on Non-Gaussianity

▽2Φ=δρ/ρ

Radiation transfer function

A Challenge to Standard Slow-roll inflation!?

Slow-roll kinematics Quantum fluctuations

Slow-roll conditions violated after horizon crossing (Leach et al)General slow-roll condition (Steward) |n-1|~|dn/dlnk|Multi-field (Vernizzi, Tent, Rigopoulos, Yokoyama et al)etc

Chaotic inflation – classical fluctuations driven by a white noise (Starobinsky) or by a colored noise (Liguori,

Matarrese et al.) coming from high-k inflatonDriven by a colored noise from interacting quantum environment (Wu et al)Others

Our Inflaton-Scalar Interacting Model

Single-field inflation 〈 σ 〉 = 0

Dissipation Noise

Trace out sigma field to obtain :

Colored, dependent on history

Start of inflation

Dominant passive fluctuations and low CMB quadrupole

assuming no active de Sitter quantum fluctuations

Low CMB quadrupole and onset of inflation

at large kScale-invariant de Sitter inflaton quantum fluctuations

Conclusions• Hints from WMAP3 data on beyond standard slo

w-roll inflation• We propose a new dynamical source for density

perturbation: Colored Quantum Noise

- give a low CMB quadrupole

- probing the first few efoldings of inflation !?• Working on running spectral index and non-Gau

ssianity, both are natural with colored noise

Relative largethree-point functions

ns

Dissipation?