Universality in D-brane inflation

Abstract

We study the six-field dynamics of D3-brane inflation for a general scalar potential on the conifold, finding simple, universal behavior. We numerically evolve the equations of motion for an ensemble of more than 7 · 10 7 realizations, drawing the coefficients in the scalar potential from statistical distributions whose detailed properties have demonstrably small effects on our results. When prolonged inflation occurs, it has a characteristic form: the D3-brane initially moves rapidly in the angular directions, spirals down to an inflection point in the potential, and settles into single-field inflation. The probability of N e e-folds of inflation is a power law, P (N e ) ∝ N −3 e , and we derive the same exponent from a simple analytical model. The success of inflation is relatively insensitive to the initial conditions: we find attractor behavior in the angular directions, and the D3-brane can begin far above the inflection point without overshooting. In favorable regions of the parameter space, models yielding 60 e-folds of expansion arise approximately once in 10 3 trials. Realizations that are effectively single-field and give rise to a primordial spectrum of fluctuations consistent with WMAP, for which at least 120 e-folds are required, arise approximately once in 10 5 trials. The emergence of robust predictions from a six-field potential with hundreds of terms invites an analytic approach to multifield inflation.

Inflation and String Theory

“…This suggests that the basic phenomenology is again that of inflection point inflation, and a number of numerical investigations [240,255,535,642,643] have confirmed this expectation.…”

“…Hence, although SUSY ameliorates the eta problem, it does not solve it: successful inflation still requires fine-tuning of the mass term [239,240], although much less than in an EFT without SUSY. The degree of fine-tuning implied by (2.94) depends to some extent on the underlying model.…”

“…e.g. [42,240,534]. 19 See §2.3.2 for an explanation of the cutoff value δ ∼ 6 in small-field inflation.…”

“…Although numerical experiments in the particular example of warped Dbrane inflation (see §5.1) give strong evidence that six fields can be large enough for universality to take hold [240,535], much remains to be learned about the statistics of general multi-field models -see [255,488,[536][537][538][539][540][541][542] for related work.…”

“…The exact power spectra for more than 10 4 realizations from the ensemble of [240] were obtained in [255], with key results summarized in §5.1.6.…”