Tachyon field inflation in light of BICEP2

Nozari, Kourosh; Rashidi, Narges

doi:10.1103/physrevd.90.043522

Cited by 22 publications

(20 citation statements)

References 18 publications

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“…where the dot denotes the derivative with respect to the cosmic time t. Also H ≡ ȧ/a is the Hubble parameter, where a is the scale factor of the Universe. The energy density and pressure of the tachyon scalar field are given by [49][50][51][52][53][54][55][56][57][58]…”

Section: Tachyon Inflationmentioning

confidence: 99%

Tachyon inflation with steep potentials

2017

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Within the framework of tachyon inflation, we consider different steep potentials and check their viability in light of the Planck 2015 data. We see that in this scenario, the inverse power-law potential $V(\phi)=V_{0}(\phi/\phi_{0})^{-n}$ with $n=2$ leads to the power-law inflation with the scale factor $a(t)\propto t^{q}$ where $q>1$, while with $n<2$, it gives rise to the intermediate inflation with the scale factor $a(t)\propto\exp\left(At^{f}\right)$ where $A>0$ and $02$ can be compatible with the 95\% CL region of Planck 2015 TT, TE, EE+lowP data. We further conclude that the exponential potential $V(\phi)=V_{0}e^{-\phi/\phi_{0}}$, the inverse $\cosh$ potential $V(\phi)=V_{0}/\cosh(\phi/\phi_{0})$, and the mutated exponential potential $V(\phi)=V_{0}\left[1+(n-1)^{-(n-1)}(\phi/\phi_{0})^{n}\right]e^{-\phi/\phi_{0}}$ with $n=4$, can be consistent with the 95\% CL region of Planck 2015 TT, TE, EE+lowP data. Moreover, using the $r-n_s$ constraints on the model parameters, we also estimate the running of the scalar spectral index $dn_{s}/d\ln k$ and the local non-Gaussianity parameter $f_{{\rm NL}}^{{\rm local}}$. We find that the lower and upper bounds evaluated for these observables are compatible with the Planck 2015 results.Comment: 13 pages, 1 figur

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Section: Tachyon Inflationmentioning

confidence: 99%

Tachyon inflation with steep potentials

2017

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“…In some extended models, there is some additional terms in consistency relation. In other words, in those cases, the consistency relation is modified [40,41,81,82,83]. As we said, the constraint on the tensor-to-scalar ratio, from Planck2018 TT, TE, EE+ lowEB + lensing data, is as r < 0.16 [66].…”

Section: Dbi Modelmentioning

confidence: 99%

“…In this paper, instead of including the higher order derivatives of the scalar field, we consider a non-canonical setup of the scalar field's derivatives. DBI [33,34,35,36] and tachyon [37,38,39,40,41,42] fields are examples of the non-canonical scalar fields. We add a DBI like term, f −1 (φ) 1 − fφ 2 , in the action of the simple mimetic model with potential.…”

Section: Introductionmentioning

confidence: 99%

Mimetic DBI Inflation in Confrontation with Planck2018 Data

Nozari

Rashidi

2019

ApJ

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We study mimetic gravity in the presence of a DBI-like term which is a non-canonical setup of the scalar field's derivatives. We consider two general cases with varying and constant sound speeds and construct the potentials for both the DBI and Mimetic DBI models. By considering the power-law scale factor as a = a 0 t n , we seek for the observational viability of these models. We show that, the Mimetic DBI model in some ranges of the parameters space is free of ghost and gradient instabilities. By studying r − n s and α s − n s behavior in confrontation with Planck2018 data, we find some constraints on the model's parameters. We show that for the case with varying sound speed, although power-law DBI inflation is not consistent with Planck2018 TT, TE, EE+low E+lensing data, but the Mimetic DBI inflation is consistent with Planck2018 TT, TE, EE+low E+lensing data at 95% CL, in some ranges of the model's parameters space as 40 ≤ n ≤ 55 where the model is instabilities-free in these ranges of parameters too. For the constant sound speed, by adopting some sample values of c s , we study both DBI and Mimetic DBI model numerically and find n ∼ 10 2 for DBI model and n ∼ 10 for Mimetic DBI model. We also compare the results with Planck2018 TT, TE, EE+low E+lensing+BK14+BAO data and see that the DBI and Mimetic DBI model with varying sound speed are ruled out with these joint data. However, these models with constant sound speed are consistent with Planck2018 TT, TE, EE+low E+lensing+BK14+BAO data with n ∼ 10 2 for DBI model and n ∼ 10 for Mimetic DBI model. In this case, we find some tighter constraints on the corresponding sound speed. PACS: 98.80. Bp, 98.80.Cq, 98.80.Es

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“…Further we derive the equation of motion of the scalar fluctuation by extremizing the tachyonic model action as 89) and the factor a H can be expressed in terms of the conformal time η as …”

Section: Computation Of Scalar Power Spectrummentioning

confidence: 99%

“…For more details see also Refs. [87][88][89][90][91][92][93][94][95]. In the context of cosmology, the detailed conse- 1 The other possibilities are: non-minimal interactions between the matter and gravity sector [(example: SM Higgs with Einstein gravity [24,25]], addition of higher derivative terms in the gravity sector (example: Starobinsky model [26]), modification of the gravity sector through extra dimensions (example: 5D membrane models ).…”

Section: Introductionmentioning

confidence: 99%

COSMOS-e’-GTachyon from string theory

Choudhury

Panda

2016

Eur. Phys. J. C

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In this article, our prime objective is to study the inflationary paradigm in the context of the generalized tachyon (GTachyon) living on the world volume of a non-BPS string theory. The tachyon action is considered here is modified compared to the original action. One can quantify the amount of the modification via a power q instead of 1/2 in the effective action. Using this set-up we study inflation by various types of tachyonic potentials, using which we constrain the index q within, 1/2 < q < 2, and a specific combination (∝ α M 4 s /g s ) of the Regge slope α , the string coupling constant g s and the mass scale of tachyon M s , from the recent Planck 2015 and Planck+BICEP2/Keck Array joint data. We explicitly study the inflationary consequences from single field, assisted field and multi-field tachyon set-ups. Specifically for the single field and assisted field cases we derive the results in the quasi-de Sitter background in which we will utilize the details of cosmological perturbations and quantum fluctuations. Also we derive the expressions for all inflationary observables using any arbitrary vacuum and the Bunch-Davies vacuum. For the single field and the assisted field cases we derive the inflationary flow equations, new sets of consistency relations. Also we derive the field excursion formula for the tachyon, which shows that assisted inflation is on the safe side compared to the single field case to validate the effective field theory framework. Further we study the features of the CMB angular power spectrum from TT, TE and EE correlations from scalar fluctuations within the allowed range of q for each of the potentials from the single field set-up. We also put constraints from the temperature anisotropy and polarization spectra, which shows that our analysis is consistent with the Planck 2015 data. Finally, using the δ N formalism we derive Sayantan Choudhury: Presently working as a Visiting (Post-Doctoral) fellow at DTP, TIFR, Mumbai On lien from Harish

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Tachyon field inflation in light of BICEP2

Cited by 22 publications

References 18 publications

Tachyon inflation with steep potentials

Tachyon inflation with steep potentials

Mimetic DBI Inflation in Confrontation with Planck2018 Data

COSMOS-e’-GTachyon from string theory

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