Fuzzy Dark Matter from Clockwork Axion Model
- PDF / 153,507 Bytes
- 6 Pages / 595.22 x 842 pts (A4) Page_size
- 6 Downloads / 207 Views
Fuzzy Dark Matter from Clockwork Axion Model Kyu Jung Bae∗ Department of Physics, Kyungpook National University, Daegu 41566, Korea
Jinn-Ouk Gong† Department of Science Education, Ewha Womans University, Seoul 03760, Korea (Received 28 September 2020; revised 22 October 2020; accepted 26 October 2020) We consider in the clockwork axion model the realization of an ultralight axion which can serve as a fuzzy dark matter candidate. With the mixing terms between adjacent axions, the shift symmetries are broken except for one, which is responsible for the ultralight axion and its mass can be as light as 10−21 eV. This ultralight axion can satisfy easily the observed dark matter abundance and the isocurvature bound. The heavier axions resulting from the clockwork gears quickly decay before the big bang nucleosynthesis. Keywords: Axion, Dark matter, Clockwork, Fuzzy dark matter DOI: 10.3938/jkps.77.1107
I. INTRODUCTION ma ∼ Recent developments in cosmology and astrophysics have seen growing evidences that most of matter in the Universe is invisible, which leaves its impacts via gravitational interaction. Such invisible matter component is called dark matter (DM). From the observations on the power spectrum of the cosmic microwave background (CMB) and the large-scale distribution of galaxies, we have learned that DM accounts for 27% of the total energy of the Universe [1]. While these observations support cold dark matter (CDM) on scales in the range Mpc − Gpc, there are still debates for possible non-cold DM signatures on scales smaller than Mpc [2]. Axion is an attractive CDM candidate. If it couples to the QCD gauge bosons, the axion dynamically relaxes the QCD vacuum to the CP-conserving one [3–9]. In the early Universe, its initial displacement drives a bosonic coherent motion which can play the role of CDM with the correct abundance [10–16]. Such an axion appears as a pseudo-Nambu-Goldsone boson (pNGB) when U (1) Peccei-Quinn (PQ) symmetry is spontaneously broken. In string theory, furthermore, axions can arise from various origins with vast range of masses and couplings [17]. Because of the shift symmetry inherited from the ultraviolet theory, axions are massless. However, the shift symmetry is softly broken due to the strong dynamics or some non-perturbative effects [18–22], so the corresponding axion acquires a mass ∗ E-mail: † E-mail:
[email protected] [email protected]
pISSN:0374-4884/eISSN:1976-8524
Λ2 , f
(1)
where Λ is the scale determined by the strong dynamics or non-perturbative effects, and f is the axion decay constant. In the case of QCD axion, Λ reflects the QCD confinement so that Λ ∼ 100 MeV, and f is determined by the PQ symmetry breaking. In the QCD axion window 109 GeV< f < 1012 GeV, the axion mass is of order μeV–meV. If the axion acquires its mass from another QCD-like sector or non-perturbative effects, Λ can be different from GeV scale. For non-QCD axions, f in a different scale may be also viable depending on the axion couplings and cosmological scenarios. Meanwhile, if an axion mass is arou
Data Loading...
