Non-Gaussianities from ekpyrotic collapse with multiple fields

被引:83
作者
Koyama, Kazuya [1 ]
Mizuno, Shuntaro [2 ]
Vernizzi, Filippo [3 ]
Wands, David [1 ]
机构
[1] Univ Portsmouth, Inst Cosmol & Gravitat, Portsmouth PO1 2EG, Hants, England
[2] Univ Tokyo, Sch Sci, RESCEU, Bunkyo Ku, Tokyo 1130033, Japan
[3] Abdus Salam Int Ctr Theoret Phys, I-34100 Trieste, Italy
来源
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS | 2007年 / 11期
基金
英国科学技术设施理事会; 英国工程与自然科学研究理事会;
关键词
cosmology with extra dimensions; cosmological perturbation theory; string theory and cosmology;
D O I
10.1088/1475-7516/2007/11/024
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We compute the non-Gaussianity of the curvature perturbation generated by ekpyrotic collapse with multiple fields. The transition from the multi-field scaling solution to a single-field dominated regime converts initial isocurvature field perturbations to an almost scale invariant comoving curvature perturbation. In the specific model of two fields, phi(1) and phi(2), with exponential potentials, -V(i)exp(-c(i)phi(i)), we calculate the bispectrum of the resulting curvature perturbation. We find that the non-Gaussianity is dominated by non-linear evolution on super-Hubble scales and hence is of the local form. The non-linear parameter of the curvature perturbation is given by f(NL) = 5c(j)(2)/12, where c(j) is the exponent of the potential for the field which becomes subdominant at late times. Since c(j)(2) must be large, in order to generate an almost scale invariant spectrum, the non-Gaussianity is inevitably large. Thus, the model is strongly constrained by observational bounds on the spectral index and non-Gaussianity.
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页数:21
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