Morphology of Inflationary Gravitational Wave Spectra imprinted by a Sequence of Post-Inflationary Epochs $via$ ${\rm GWInSpect}$
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| Format: | Preprint |
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2025
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| _version_ | 1866914165257404416 |
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| author | Mishra, Swagat S. Soman, Athul K. |
| author_facet | Mishra, Swagat S. Soman, Athul K. |
| contents | The expansion history of the Universe prior to Big Bang Nucleosynthesis (BBN) remains largely unconstrained. The high-energy post-inflationary era may involve multiple distinct epochs, each characterized by a different equation of state (EoS). A key prediction of inflation is the generation of tensor perturbations that later manifest as a stochastic background of primordial gravitational waves (GWs). The large-scale amplitude and small-scale spectral tilt ($n_{\rm GW}$) of these GWs encode the inflationary energy scale and the subsequent expansion history, respectively. A soft post-inflationary EoS ($w<1/3$) yields red-tilted GW spectra ($n_{\rm GW}<0$), while a stiff EoS ($w>1/3$) results in a blue-tilt ($n_{\rm GW}>0$). In our previous work [arXiv:2407.07956], we developed an analytical framework for computing the GW spectral energy density, $Ω_{\rm GW}(f)$, for multiple post-inflationary transitions ($w_1 \to w_2 \to \cdots \to w_n \to 1/3$), focusing on the parameter space relevant for future GW observations. In this paper, we extend that framework to systematically investigate the $morphological~diversity$ of inflationary GW spectra generated by multi-epoch post-inflationary histories. Remaining model agnostic, we demonstrate that a wide variety of spectral shapes, ranging from convex and concave monotonic profiles to multi-peaked non-monotonic spectra, can naturally emerge depending on the sequence and duration of these epochs. We also introduce GWInSpect, a publicly available Python package that computes $Ω_{\rm GW}(f)$ for arbitrary sequences of EoS transitions, providing a practical tool to study the pre-BBN expansion history of the Universe. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_25672 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Morphology of Inflationary Gravitational Wave Spectra imprinted by a Sequence of Post-Inflationary Epochs $via$ ${\rm GWInSpect}$ Mishra, Swagat S. Soman, Athul K. Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory The expansion history of the Universe prior to Big Bang Nucleosynthesis (BBN) remains largely unconstrained. The high-energy post-inflationary era may involve multiple distinct epochs, each characterized by a different equation of state (EoS). A key prediction of inflation is the generation of tensor perturbations that later manifest as a stochastic background of primordial gravitational waves (GWs). The large-scale amplitude and small-scale spectral tilt ($n_{\rm GW}$) of these GWs encode the inflationary energy scale and the subsequent expansion history, respectively. A soft post-inflationary EoS ($w<1/3$) yields red-tilted GW spectra ($n_{\rm GW}<0$), while a stiff EoS ($w>1/3$) results in a blue-tilt ($n_{\rm GW}>0$). In our previous work [arXiv:2407.07956], we developed an analytical framework for computing the GW spectral energy density, $Ω_{\rm GW}(f)$, for multiple post-inflationary transitions ($w_1 \to w_2 \to \cdots \to w_n \to 1/3$), focusing on the parameter space relevant for future GW observations. In this paper, we extend that framework to systematically investigate the $morphological~diversity$ of inflationary GW spectra generated by multi-epoch post-inflationary histories. Remaining model agnostic, we demonstrate that a wide variety of spectral shapes, ranging from convex and concave monotonic profiles to multi-peaked non-monotonic spectra, can naturally emerge depending on the sequence and duration of these epochs. We also introduce GWInSpect, a publicly available Python package that computes $Ω_{\rm GW}(f)$ for arbitrary sequences of EoS transitions, providing a practical tool to study the pre-BBN expansion history of the Universe. |
| title | Morphology of Inflationary Gravitational Wave Spectra imprinted by a Sequence of Post-Inflationary Epochs $via$ ${\rm GWInSpect}$ |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2510.25672 |