Natural Inflation: The Status after WMAP 3-year data

The model of Natural Inflation is examined in light of recent 3-year data from the Wilkinson Microwave Anisotropy Probe and shown to provide a good fit. The inflaton potential is naturally flat due to shift symmetries, and in the simplest version takes the form

V(\phi) = \Lambda^4 [1 \pm \cos(N\phi/f)]

. The model agrees with WMAP3 measurements as long as

f > 0.7 m_{Pl}

(where

m_{Pl} = 1.22 \times 10^{19}

GeV) and

\Lambda \sim m_{GUT}

. The running of the scalar spectral index is shown to be small -- an order of magnitude below the sensitivity of WMAP3. The location of the field in the potential when perturbations on observable scales are produced is examined/ for

f > 5 m_{Pl}

, the relevant part of the potential is indistinguishable from a quadratic, yet has the advantage that the required flatness is well-motivated. Depending on the value of

f

, the model falls into the large field (

f \ge 1.5 m_{Pl}

) or small field (

f < 1.5 m_{Pl}

) classification scheme that has been applied to inflation models. Natural inflation provides a good fit to WMAP3 data.

98.80.Cq
98.80.Bp
Inflation
cosmic microwave background
WMAP

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