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SUMMARY:Multi-Band Constraints on Cosmic Strings: Unifying Harmonic and Bu
 rst Spectra
DTSTART;VALUE=DATE-TIME:20261025T062000Z
DTEND;VALUE=DATE-TIME:20261025T064000Z
DTSTAMP;VALUE=DATE-TIME:20261025T062658Z
UID:indico-contribution-3017@indico.itp.ac.cn
DESCRIPTION:Speakers: Hansong Zhang (ICTP-AP)\nCosmic-string loops generat
 e a broadband gravitational-wave background (GWB) that is typically modele
 d via two distinct formalisms: a discrete harmonic expansion\, commonly us
 ed in pulsar-timing-array (PTA) studies\, and a continuous burst superposi
 tion\, employed in ground-based GWB searches. In this work\, we formally u
 nify the two formalisms\, showing that they provide discrete and continuou
 s representations of the same underlying radiation process and converge on
  the scale-invariant spectrum plateau. On the rising low-frequency branch\
 , where the first few harmonics dominate\, the discrete nature becomes imp
 ortant\, causing the two formalisms to diverge. Within this unified framew
 ork\, the spectral calculation is more consistent across frequency bands\,
  enabling multi-band inference. Leveraging this physical insight\, we perf
 orm joint Bayesian inference across four representative loop-distribution 
 models using the NANOGrav\, EPTA\, and LIGO--Virgo--KAGRA (LVK) datasets. 
 By jointly sampling the string tension $G\\mu$ alongside the average cusp 
 and kink numbers $\\{N_c\, N_k\\}$\, the loop-radiation uncertainties are 
 accounted for. We find that employing the harmonic expansion strengthens t
 he LVK bounds by $21\\%-31\\%$ for three of these models. Additionally\, t
 he stringent LVK bounds preclude three of these models from explaining the
  observed PTA common signal. For the sole surviving model\, our multi-band
  analysis improves the inferred limit on $G\\mu$.\n\nhttps://indico.itp.ac
 .cn/event/427/contributions/3017/
LOCATION:
URL:https://indico.itp.ac.cn/event/427/contributions/3017/
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