1. Testing the slow roll inflation paradigm with the Big Bang Observer
Carlo Ungarelli
School of Physics and Astronomy
Astrophysics and Space Research Group
In collaboration with A.Vecchio, P. Corasaniti (Columbia, NY), R. A. Mercer

2. The paradigm of (slow-roll) inflation
Solves the shortcomings of the standard cosmological model (flatness and horizon problem) by postulating the existence of an early phase of accelerated expansion driven by the energy density of a scalar field slowly rolling towards its minimum
Predictions: 1)The Universe is spatially flat 2)Quantum zero-point fluctuations of space-time metric are stretched over astrophysical scales producing a nearly scale invariant spectrum of density perturbations and a spectrum of gravitational waves as a cosmic gravitational wave stochastic background (CGWB)
The first prediction and part of the second have been confirmed by the measurement of the Cosmic Microwave Background (CMB). The existence of CGWB is yet untested

3. CGWB produced during slow-roll inflation
COBE bound
(Koranda, Turner 94)
Almost flat spectrum
(see e.g. Turner ’97)

4. Detection of stochastic backgrounds
Earth-based interferometers
Design sensitivity of current Interferometers
Second generation detectors [Advanced LIGO]
3rd generation European Gravitational Observatory
String-inspired inflationary models
(e.g. pre-big-bang) could be tested by second generation detectors
(Allen, Brustein 97; U, Vecchio 99)
Warnings: the models do not provide
reliable description of transition to
Post-big-bang era; the observability of GW spectrum depends on the detail of the transition
~f 3

5. Detection of stochastic background: LISA
Astrophysical backgrounds
Incoherent superposition
of GW emitted by short-period, solar
mass binary systems (WD,NS..)
Galactic and extra-galactic contribution
(Bender et al, 90,97; Postnov et al, Schneider et al 00)

6. Towards testing slow-roll inflation: BBO
To avoid the astrophysical background the frequency band
should be around 0.1 Hz
(U and Vecchio 01, Bender and Hogan 01, Seto et al 01)
name
Laser
Power
(W)
Wav.
(mm)
Opt.
Eff.
Arm
Length
(km)
Mirror
Diameter
(m)
Acc noise vs
LISA
BBO
lite
100
1.06
0.3
20000 3
0.1
300
0.5
50000
3.5
0.01
grand
500
4.0
0.001

7. GWs in single field slow-roll inflation
Curvature (R) and Tensor (T)
perturbations spectra
(See Turner ’97)
The GW spectrum depends on two primordial parameters (r,nS) and
one cosmological parameter A (~0.7 see e.g. Spergel et al ’03)

8. BBO-lite BBO BBO-grand WMAP 1,2,3-s confidence levels
(U, Vecchio,Corasaniti, Mercer
Astro-ph/…to appear)
BBO-grand
WMAP 1,2,3-s
confidence levels
(Kinney et al 04)

9. BBO vs future CMB experiments (I)
BBO vs PLANCK
BBO-GRAND vs CMBPol

10. BBO vs future CMB experiments (II)
Residual foregrounds
from NS-radio pulsars
CMB B-mode
Foregrounds from
gravitational lensing
impose a lower limit
(Knox and Song ’02)
BBO design sensitivity depends strongly on the antenna
diameter and laser wavelength

11. Some Remarks
Advanced earth-based GW detectors cannot test the standard slow-roll inflation paradigm. They could detect signal from inflation if Universe underwent a ``pre-big-bang phase’’ (or accelerated contraction). More robust predictions are needed.
A dedicated post-LISA mission can detect a stochastic background of GW produced during an epoch of slow-roll inflation with a design sensitivity beyond the sensitivity of PLANCK surveyor one. The sensitivity of post-PLANCK missions to stochastic backgrounds of GW strongly depends on the ability of removing the foregrounds due to lensing