Cosmological bounds on pseudo Nambu-Goldstone bosons

Abstract

Abstract. We review the cosmological implications of a relic population of pseudo NambuGoldstone bosons (pNGB) with an anomalous coupling to two photons, often called axion-like particles (ALPs). We establish constraints on the pNGB mass and two-photon coupling by considering big bang nucleosynthesis, the physics of the cosmic microwave background, and the diffuse photon background. The bounds from WMAP7 and other large-scale-structure data on the effective number of neutrino species can be stronger than the traditional bounds from the primordial helium abundance. These bounds, together with those from primordial deuterium abundance, constitute the most stringent probes of early decays.

3.55 keV hint for decaying axionlike particle dark matter

“…These parameters are not excluded by any of the existing constraints [10,11]. In fact ALPs with these parameter values can be produced in the early universe via the misalignment mechanism and can be the cold dark matter [10].…”

“…The coupling to two photons provides an ALP production channel by the Primakoff process q þ γ → q þ ϕ where q is any charged particle in the plasma. This generates ALPs at a rate [11,19] …”

“…Therefore, the highest temperatures of the early universe determine whether a full thermal population is established. The contribution of a fully thermalized species to the DM abundance is [11] …”

Gauge theories of partial compositeness: scenarios for Run-II of the LHC

“…This value needs to be raised at least by roughly a factor ≈ 3 in order not to conflict with the bounds on the visible axion, coming from beam dump experiments (discussed in [81]) or K → πa searches [82]. (See also [83] for cosmological bounds for ALPS at much higher scale f .) This however is easily achieved.…”

ALPs at colliders

“…[35][36][37] for excellent reviews). Finally, beam dump experiments are a terrestrial probe with a good sensitivity to ALP-γ couplings.…”