Multibrane inflation and dynamical flattening of the inflaton potential

Abstract

We investigate the problem of fine tuning of the potential in the IKLIMT warped flux compactification scenario for brane-antibrane inflation in Type IIB string theory. We argue for the importance of an additional parameter ψ0 (approximated as zero by IKLIMT), namely the position of the antibrane, relative to the equilibrium position of the brane in the absence of the antibrane. We show that for a range of values of a particular combination of the Kähler modulus, warp factor, and ψ0, the inflaton potential can be sufficiently flat. We point out a novel mechanism for dynamically achieving flatness within this part of parameter space: the presence of multiple mobile branes can lead to a potential which initially has a metastable local minimum, but gradually becomes flat as some of the branes tunnel out. Eventually the local minimum disappears and the remaining branes slowly roll together, with assisted inflation further enhancing the effective flatness of the potential. With the addition of Kähler and superpotential corrections, this mechanism can completely remove the fine tuning problem of brane inflation, within large regions of parameter space. The model can be falsified if future cosmic microwave background observations confirm the hint of a large running spectral index.

Inflation and String Theory

“…Discrete symmetries can be used to forbid problematic mass terms [652], and in some cases have been shown to be compatible with moduli stabilization [657]. Dynamical mechanisms have also been found: it was shown in [653,655] that if N D3-branes become trapped in a metastable 13 The restriction to irrelevant perturbations in [553] rests on the requirement that the background throat solution is a good approximation in the infrared. However, [42,534] showed that certain relevant perturbations are necessarily present in Klebanov-Strassler regions of KKLT compactifications.…”

“…Considerable effort has been directed at finding mechanisms that can alleviate the fine-tuning of the potential in warped D-brane inflation -see [38,[651][652][653][654][655][656]. Here, we will outline a few of the leading approaches.…”

Large nonlocal non-Gaussianity from a curvaton brane

“…This idea was later extended into the scenario of multiple brane inflation and appeared in Refs. [12,13] (see [14,15] for earlier studies under slow-roll approximation). A distinguishing feature of the model in this type is that a large positive nonlocal non-Gaussianity can be obtained due to an enhancement of a small sound speed for the perturbation [16,17], which is in contrast to the prediction of a canonical single-field inflation model [18].…”

Stringy effects during inflation and reheating

“…With the great success of inflationary cosmology in explaining the spectrum of cosmic microwave background (CMB) fluctuations [1][2][3][4], as well as recent progress in understanding inflation in string theory -see, for example, [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]-the time is ripe to ask what signals string theory might have in cosmology. Historically speaking, there has not been much cause for optimism.…”