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The Impact of a Midband Gravitational Wave Experiment On Detectability of Cosmological Stochastic Gravitational Wave Backgrounds

Barish, Barry C. and Bird, Simeon and Cui, Yanou (2020) The Impact of a Midband Gravitational Wave Experiment On Detectability of Cosmological Stochastic Gravitational Wave Backgrounds. . (Unpublished)

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We make forecasts for the impact a future "midband" space-based gravitational wave experiment, most sensitive to 10⁻²−10 Hz, could have on potential detections of cosmological stochastic gravitational wave backgrounds (SGWBs). Specific proposed midband experiments considered are TianGo, B-DECIGO and AEDGE. We propose a combined power-law integrated sensitivity (CPLS) curve combining GW experiments over different frequency bands, which shows the midband improves sensitivity to SGWBs by up to two orders of magnitude at 10⁻²−10 Hz. We consider GW emission from cosmic strings and phase transitions as benchmark examples of cosmological SGWBs. We explicitly model various astrophysical SGWB sources, most importantly from unresolved black hole mergers. Using Markov Chain Monte Carlo, we demonstrated that midband experiments can, when combined with LIGO A+ and LISA, significantly improve sensitivities to cosmological SGWBs and better separate them from astrophysical SGWBs. In particular, we forecast that a midband experiment improves sensitivity to cosmic string tension Gμ by up to a factor of 10, driven by improved component separation from astrophysical sources. For phase transitions, a midband experiment can detect signals peaking at 0.1−1 Hz, which for our fiducial model corresponds to early Universe temperatures of T∗∼10⁴−10⁶ GeV, generally beyond the reach of LIGO and LISA. The midband closes an energy gap and better captures characteristic spectral shape information. It thus substantially improves measurement of the properties of phase transitions at lower energies of T∗∼O(10³) GeV, potentially relevant to new physics at the electroweak scale, whereas in this energy range LISA alone will detect an excess but not effectively measure the phase transition parameters. Our modelling code and chains are publicly available.

Item Type:Report or Paper (Discussion Paper)
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Additional Information:SB was supported by NSF grant AST-1817256 and would like to thank his wife, Priya Bird. YC is supported in part by the US Department of Energy under award number DE-SC0008541, and thanks the Kavli Institute for Theoretical Physics (supported by the National Science Foundation under Grant No. NSF PHY-1748958) for support and hospitality while the work was being completed. We thank Mark Hindmarsh, Marek Lewicki and David Weir for helpful discussions.
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Department of Energy (DOE)DE-SC0008541
Record Number:CaltechAUTHORS:20210217-153511550
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108099
Deposited By: Tony Diaz
Deposited On:18 Feb 2021 17:19
Last Modified:18 Feb 2021 17:19

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