Dark energy, D-branes, and Pulsar Timing Arrays

Debika Chowdhury; Gianmassimo Tasinato; Ivonne Zavala

Dark energy, D-branes, and Pulsar Timing Arrays

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arxiv 2307.01188 v3 pith:55HR55MC submitted 2023-07-03 hep-th astro-ph.CO

Debika Chowdhury , Gianmassimo Tasinato , Ivonne Zavala This is my paper

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keywords darkenergycosmologicalamplitudebackgrounddetectiondynamicsearly

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abstract

Several pulsar timing array (PTA) collaborations recently announced the first detection of a stochastic gravitational wave (GW) background, leaving open the question of its source. We explore the possibility that it originates from cosmic inflation, a guaranteed source of primordial GW. The inflationary GW background amplitude is enhanced at PTA scales by a non-standard early cosmological evolution, driven by Dirac-Born-Infeld (DBI) scalar dynamics motivated by string theory. The resulting GW energy density has a broken power-law frequency profile, entering the PTA band with a peak amplitude consistent with the recent GW detection. After this initial DBI kination epoch, the dynamics starts a new phase mainly controlled by the scalar potential. It provides a realization of an early dark energy scenario aimed at relaxing the $H_0$ tension, and a late dark energy model which explains the current cosmological acceleration with no need of a cosmological constant. Hence our mechanism - besides providing a possible explanation for the recent PTA results - connects them with testable properties of the physics of the dark universe.

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