Cosmic Superstrings Revisited in Light of NANOGrav 15-Year Data
- Ellis, John et al
- arXiv:2306.17147KCL-PH-TH/2023-38CERN-TH-2023-126AION-REPORT/2023-07
| \it The curves show the SGWB from cosmic superstrings assuming standard cosmological expansion and the `violins' show the NANOGrav 15-year data. Different curves correspond to choices of $(G\mu, p)$ indicated by points indicated with the same colours in Fig~\ref{fig:SuperCScontours}. |
| \it The blue contours correspond to the 68, 95 and 99\% CL ranges for the superstring fit of the NANOGrav 15-year data assuming standard cosmological expansion. The coloured dots correspond to the curves with specific values of the string tension $G\mu$ and intercommutation probability $p$ shown in Figs.~\ref{fig:fit} and \ref{fig:superstringspectra}. The orange regions show the present and projected LVK sensitivities to the SGWB generated by cosmic superstrings. |
| \it Extrapolations to higher frequencies of the SGWB calculated in the cosmic superstring fits to NANOGrav data assuming standard cosmological expansion (solid lines) and including the longest possible period of early matter domination ending at $T=5$ MeV just before BBN (dashed lines). The sensitivities of present and projected experiments are indicated, including LIGO/Virgo/KAGRA (LVK)~\cite{TheLIGOScientific:2014jea,TheLIGOScientific:2016wyq,LIGOScientific:2019vic}, ET~\cite{Punturo:2010zz,Hild:2010id}, AION~\cite{Badurina:2019hst}, AEDGE~\cite{AEDGE:2019nxb}, LISA~\cite{Bartolo:2016ami,Caprini:2019pxz,LISACosmologyWorkingGroup:2022jok}, the Nancy Roman telescope (ROMAN)~\cite{Wang:2022sxn} and SKA~\cite{Janssen:2014dka}. |
| \it The impacts of a period of inflation on SGWB signals in Fig~\ref{fig:superstringspectra}. Dashed lines show the modification of the spectra by thermal inflation reheating to $T_{\rm reh}=10^3$\,GeV with $N_e$ indicating how long the inflation lasted. The upper panel shows the impact on the strongest signal in Fig~\ref{fig:superstringspectra}, shown there in green. Short periods of inflation up to 20 e-folds have little impact on the fit. However, 21 (22) e-folds are excluded by NANOGrav at the 95\% and 99\% CLs, respectively. The lower panel shows the impact on the weakest signal in Fig~\ref{fig:superstringspectra}, shown there in red. Without any modification, this point was already disfavoured at the 99\% CL. Even the shortest period of inflation, corresponding to 19 e-folds, modifies the SGWB signal at low frequencies, reducing the CL to an unacceptable level. |
| \it The impacts of a period of inflation on SGWB signals in Fig~\ref{fig:superstringspectra}. Dashed lines show the modification of the spectra by thermal inflation reheating to $T_{\rm reh}=10^3$\,GeV with $N_e$ indicating how long the inflation lasted. The upper panel shows the impact on the strongest signal in Fig~\ref{fig:superstringspectra}, shown there in green. Short periods of inflation up to 20 e-folds have little impact on the fit. However, 21 (22) e-folds are excluded by NANOGrav at the 95\% and 99\% CLs, respectively. The lower panel shows the impact on the weakest signal in Fig~\ref{fig:superstringspectra}, shown there in red. Without any modification, this point was already disfavoured at the 99\% CL. Even the shortest period of inflation, corresponding to 19 e-folds, modifies the SGWB signal at low frequencies, reducing the CL to an unacceptable level. |