The inflationary brane-antibrane universe

Abstract

We show how the motion through the extra dimensions of a gas of branes and antibranes can, under certain circumstances, produce an era of inflation as seen by observers trapped on a 3-brane, with the inflaton being the inter-brane separation. Although most of our discussion refers to arbitrary p-branes, when we need to be specific we assume that they are D-branes of Type II or Type I string theory. For realistic brane couplings, such as those arising in string theory, the inter-brane potentials are too steep to inflate the universe for acceptably long times. However, for special regions of the parameter space of brane-antibrane positions the brane motion is slow enough for there to be sufficient inflation. Inflation would be more generic in models where the inter-brane interactions are much weaker. The spectrum of primordial density fluctuations predicted has index n slightly less than 1, and an acceptable amplitude, provided that the extra dimensions have linear size 1/r ∼ 10 12 GeV. Reheating occurs as in hybrid inflation, with the tachyonic instability of the brane-antibrane system taking over for small separations. The tachyon field can induce a cascade mechanism within which higher-dimension branes annihilate into lower-dimension ones. We argue that such a cascade naturally stops with the production of 3-branes in 10-dimensional string theory.

Kähler moduli inflation

“…6 This can be quantified in explicit models. For large volumes the condition on the ratio ρ is that 9.5(ln V)ρ < 1.…”

“…The most common open string inflaton is a brane/antibrane separation [6,7,8], whereas closed string inflatons typically correspond to geometric moduli [9]. There has been much recent effort devoted to inflationary model building, particularly since the appearance of the KKLT scenario of moduli stabilisation [2].…”

Lumps in the throat

“…As will be clear soon, our background is a close approximation to both these models, but differs from them because of the presence of extra fluxes and branes. We will also consider the backreactions on the 5 This also means that a sudden emergence of global symmetries may render an unstable defect stable for some time. For details on this see [42].…”

Poly-instanton inflation

“…The progress in moduli stabilisation also opened up the possibility of realising inflation in the moduli sector. String inflationary models based on single-field slow-roll can be broadly classified, based on the origin of the inflaton field [9], into open string models [10][11][12] and closed string models [13][14][15][16][17][18][19][20].…”