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@ARTICLE{Servant:462583,
      author       = {Servant, Geraldine and Simakachorn, Peera and Gouttenoire,
                      Yann},
      title        = {{R}evealing the {P}rimordial {I}rreducible {I}nflationary
                      {G}ravitational-{W}ave {B}ackground with a {S}pinning
                      {P}eccei-{Q}uinn {A}xion},
      reportid     = {PUBDB-2021-03484, DESY-21-126. arXiv:2108.10328},
      year         = {2021},
      note         = {7 pages, 6 figures},
      abstract     = {The primordial irreducible gravitational-wave background
                      due to quantum vacuum tensor fluctuations produced during
                      inflation spans a large range of frequencies with an almost
                      scale-invariant spectrum but is too low to be detected by
                      the next generation of gravitational-wave interferometers.
                      We show how this signal is enhanced by a short temporary
                      kination era in the cosmological history (less than 10
                      e-folds), that can arise at any energy scale between a GeV
                      and the inflationary scale $10^{16}$ GeV.We argue that such
                      kination era is naturally generated by a spinning axion
                      before it gets trapped by its potential.It is usually
                      assumed that the axion starts oscillating around its minimum
                      from its initial frozen position at rest.However, the early
                      dynamics of the Peccei-Quinn field can induce a large
                      kinetic energy in the axion field, triggering a kination
                      era, either before or after the axion acquires its mass,
                      leading to a characteristic peak in the primordial
                      gravitational-wave background. This represents a smoking-gun
                      signature of axion physics as no other scalar field dynamics
                      can trigger such a sequence of equations of state in the
                      early universe.We derive the resulting gravitational-wave
                      spectrum, and present the parameter space that leads to such
                      signal as well as the detectability prospects, in particular
                      at LISA, Einstein Telescope, Cosmic Explorer and Big Bang
                      Observer.We show both model-independent predictions and
                      present as well results for two specific well-motivated UV
                      completions for the QCD axion dark matter where this
                      dynamics is built-in.},
      keywords     = {gravitational radiation: background (INSPIRE) / axion: dark
                      matter (INSPIRE) / fluctuation: tensor (INSPIRE) /
                      gravitational radiation: primordial (INSPIRE) /
                      gravitational radiation: spectrum (INSPIRE) / quantum
                      chromodynamics: axion (INSPIRE) / scale: inflation (INSPIRE)
                      / axion: signature (INSPIRE) / energy: kinetic (INSPIRE) /
                      field theory: scalar (INSPIRE) / Peccei-Quinn (INSPIRE) /
                      oscillation (INSPIRE) / equation of state (INSPIRE) / big
                      bang (INSPIRE) / interferometer (INSPIRE) / trigger
                      (INSPIRE) / Einstein Telescope (INSPIRE) / LISA (INSPIRE) /
                      history (INSPIRE)},
      cin          = {T},
      cid          = {I:(DE-H253)T-20120731},
      pnm          = {611 - Fundamental Particles and Forces (POF4-611)},
      pid          = {G:(DE-HGF)POF4-611},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)25},
      eprint       = {2108.10328},
      howpublished = {arXiv:2108.10328},
      archivePrefix = {arXiv},
      SLACcitation = {$\%\%CITATION$ = $arXiv:2108.10328;\%\%$},
      doi          = {10.3204/PUBDB-2021-03484},
      url          = {https://bib-pubdb1.desy.de/record/462583},
}