Inflation in Realistic D-Brane Models

Abstract

We find successful models of D-brane/anti-brane inflation within a string context. We work within the GKP-IKLT class of type IIB string vacua for which many moduli are stabilized through fluxes, as recently modified to include 'realistic' orbifold sectors containing standard-model type particles. We allow all moduli to roll when searching for inflationary solutions and find that inflation is not generic inasmuch as special choices must be made for the parameters describing the vacuum.But given these choices inflation can occur for a reasonably wide range of initial conditions for the brane and antibrane. We find that D-terms associated with the orbifold blowing-up modes play an important role in the inflationary dynamics. Since the models contain a standard-model-like sector after inflation, they open up the possibility of addressing reheating issues. We calculate predictions for the CMB temperature fluctuations and find that these can be consistent with observations, but are generically not deep within the scale-invariant regime and so can allow appreciable values for dn s /d ln k as well as predicting a potentially observable gravity-wave signal.It is also possible to generate some admixture of isocurvature fluctuations.

Stringy effects during inflation and reheating

“…Actually, this tunneling rate has been considered earlier in [128,129], which discuss the tunneling of localized 13 See also the recent discussion in [57,58]. 14 We discuss possible generalizations of this mechanism and reheating in other string embeddings of inflation in Appendix C. 15 See also [134] for a review and further references.…”

“…One difficulty of brane inflation scenarios as described by [11] is a supergravity problem; in the most basic setting for brane inflation, it seems that some fine-tuning is necessary to get a small enough slow-roll parameter . This problem has been the focus of much recent work (see, for example, [12,13,[92][93][94]). 7 We will, however, simply assume that 1 without worrying about whether that assumption requires fine-tuning or not.…”

“…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.…”

Inflation and String Theory

“…This is an exponentially slow process, as the potential due to the warp factor confines the strings to the bottom of their respective throats, and for practical purposes breakage via the orientifold image can be ignored [601]. A more significant risk comes from D3-branes or anti-D3-branes in the inflationary throat, which could serve as the substrate for the Standard Model [685] or as a source of supersymmetry-breaking energy [425]. If any D3-branes or anti-D3-branes are present, cosmic strings fragment immediately and are cosmologically irrelevant.…”

Kähler moduli inflation

“…There has been much recent effort devoted to inflationary model building, particularly since the appearance of the KKLT scenario of moduli stabilisation [2]. For recent discussions, [9,10,11,12] may be consulted.…”