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This study examines an anisotropic Dirac-Born-Infeld inflationary model of the early universe that incorporates non-vacuum initial states, calculating how primordial perturbations would have evolved and comparing predictions against observational data. Using mathematical expansions up to third order and analyzing parameters like the scalar spectral index and tensor-to-scalar ratio, the researchers find that their model remains consistent with recent cosmological observations from Planck2018, DESI, and other surveys when anisotropy and initial-state parameters fall within specific ranges. The work demonstrates that departures from standard isotropic inflation with vacuum initial conditions can still accommodate current observational constraints.
Why it matters
This research helps refine our understanding of the universe's earliest moments by testing whether more complex inflationary scenarios beyond the standard model remain viable, which could eventually distinguish between competing theories of cosmic origins and inform our understanding of fundamental physics at extremely high energies.
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arXiv:2607.11842v1 Announce Type: new
Abstract: We investigate linear and nonlinear primordial perturbations in an anisotropic Dirac-Born-Infeld (DBI) inflationary model with a non-vacuum initial state. Using the Arnowitt-Deser- Misner (ADM) formalism, we expand the action up to second and third order in the curvature perturbation and derive the corresponding scalar and tensor power spectra, as well as the bispectrum and the equilateral non-linearity parameter (f_{NL}^{mathrm{equil}}). The effects of anisotropic corrections and non-Bunch-Davies (non-BD) initial conditions are incorporated through the slow-roll sector and Bogoliubov coefficients. For the numerical analysis, we consider an intermediate expansion scenario together with a phenomenological ansatz for the excited-state occupation number (N_k). By comparing the model predictions with recent observational datasets, including Planck2018 TT, TE, EE + lowE + lensing + BK18 + BAO and DESI+CMB+DESY5 data, we identify observationally viable regions in the parameter space of the model. Our analysis indicates that the anisotropic DBI scenario with non-vacuum initial conditions can remain compatible with current constraints on the scalar spectral index, tensor-to-scalar ratio, and equilateral non-Gaussianity for suitable ranges of the anisotropy parameter (c) and the initial-state parameter (N_{k,0}).