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Differentiating G-inflation from string gas cosmology using the effective field theory approach

He, Minxi and Liu, Junyu and Lu, Shiyun and Zhou, Siyi and Cai, Yi-Fu and Wang, Yi and Brandenberger, Robert (2016) Differentiating G-inflation from string gas cosmology using the effective field theory approach. Journal of Cosmology and Astroparticle Physics, 2016 (12). Art. No. 040. ISSN 1475-7516. https://resolver.caltech.edu/CaltechAUTHORS:20170103-130922655

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Abstract

A characteristic signature of String Gas Cosmology is primordial power spectra for scalar and tensor modes which are almost scale-invariant but with a red tilt for scalar modes but a blue tilt for tensor modes. This feature, however, can also be realized in the so-called G-inflation model, in which Horndeski operators are introduced which leads to a blue tensor tilt by softly breaking the Null Energy Condition. In this article we search for potential observational differences between these two cosmologies by performing detailed perturbation analyses based on the Effective Field Theory approach. Our results show that, although both two models produce blue tilted tensor perturbations, they behave differently in three aspects. Firstly, String Gas Cosmology predicts a specific consistency relation between the index of the scalar modes n_s and that of tensor ones n_t, which is hard to be reproduced by G-inflation. Secondly, String Gas Cosmology typically predicts non-Gaussianities which are highly suppressed on observable scales, while G-inflation gives rise to observationally large non-Gaussianities because the kinetic terms in the action become important during inflation. However, after finely tuning the model parameters of G-inflation it is possible to obtain a blue tensor spectrum and negligible non-Gaussianities with a degeneracy between the two models. This degeneracy can be broken by a third observable, namely the scale dependence of the nonlinearity parameter, which vanishes for G-inflation but has a blue tilt in the case of String Gas Cosmology. Therefore, we conclude that String Gas Cosmology is in principle observationally distinguishable from the single field inflationary cosmology, even allowing for modifications such as G-inflation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/1475-7516/2016/12/040DOIArticle
http://iopscience.iop.org/article/10.1088/1475-7516/2016/12/040/metaPublisherArticle
https://arxiv.org/abs/1608.05079arXivDiscussion Paper
ORCID:
AuthorORCID
Liu, Junyu0000-0003-1669-8039
Wang, Yi0000-0002-4174-8790
Additional Information:© 2017 IOP Publishing. Received 30 August 2016; Accepted 13 December 2016; Published 23 December 2016. We thank E. Ferreira, D. G. Wang and Z. Wang for useful discussions. We also thank Y. Chen and T. Wrase for helpful discussions about string phenomenology at the SPSC2016 conference. The research of RB is supported in part by funds from NSERC and the Canada Research Chair program. YFC and MH are supported in part by the Chinese National Youth Thousand Talents Program (Grant No. KJ2030220006), by the USTC start-up funding (Grant No. KY2030000049) and by the National Natural Science Foundation of China (Grant No. 11421303). The works of JL and SL are supported in part by the Fund for Fostering Talents in Basic Science of the National Natural Science Foundation of China (Grant No. J1310021), the Outstanding Student International Exchange Funding Scheme and the Yan Ji-Ci Class in the University of Science and Technology of China. MH, JL are also grateful for PhD assistantships from the departments of physics of Tokyo University and Caltech respectively. YW is supported by Grant HKUST4/CRF/13G issued by the Research Grants Council (RGC) of Hong Kong. SZ is supported by the the Hong Kong PhD Fellowship Scheme (HKPFS) issued by the Research Grants Council (RGC) of Hong Kong. Part of numerical computations are operated on the computer cluster LINDA in the particle cosmology group at USTC.
Funders:
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Research Chairs ProgramUNSPECIFIED
Chinese National Youth Thousand Talents ProgramKJ2030220006
University of Science and Technology of ChinaKY2030000049
National Natural Science Foundation of China11421303
National Natural Science Foundation of ChinaJ1310021
Tokyo UniversityUNSPECIFIED
CaltechUNSPECIFIED
Research Grants Council of Hong KongHKUST4/CRF/13G
Issue or Number:12
Record Number:CaltechAUTHORS:20170103-130922655
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170103-130922655
Official Citation:Minxi He et al JCAP12(2016)040
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73178
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Jan 2017 21:31
Last Modified:09 Mar 2020 13:19

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