Cosmology of an Axion-Like Majoron Cuesta, A. J. Illana Calero, José Ignacio Masip Mellado, Manuel We would like to thank Mar Bastero, Adrian Carmona, Mikael R. Chala, Miguel Escud-ero, Javier Olmedo, Jose Santiago and Samuel Witte for discussions. This work was par-tially supported by the Spanish Ministry of Science, Innovation and Universities (PID2019-107844GB-C21/AEI/10.13039/501100011033) and by the Junta de Andalucia (FQM 101, SOMM17/6104/UGR, P18-FR-1962, P18-FR-5057) . We propose a singlet majoron model that defines an inverse seesaw mechanism in the v sector. The majoron phi has a mass m(phi) approximate to 0.5 eV and a coupling to the tau lepton similar to the one to neutrinos. In the early universe it is initially in thermal equilibrium, then it decouples at T approximate to 500 GeV and contributes with just Delta N-eff = 0.026 during BBN. At T = 26 keV (final stages of BBN) a primordial magnetic field induces resonant gamma <-> phi oscillations that transfer 6% of the photon energy into majorons, implying Delta N-eff = 0.55 and a 4.7% increase in the baryon to photon ratio. At T approximate to m(phi) the majoron enters in thermal contact with the heaviest neutrino and it finally decays into v (v) over bar pairs near recombination, setting Delta N-eff = 0.85. The boost in the expansion rate at later times may relax the Hubble tension (we obtain H-0 = (71.4 +/- 0.5) km/s/Mpc), while the processes v (v) over bar <-> phi suppress the free streaming of these particles and make the model consistent with large scale structure observations. Its lifetime and the fact that it decays into neutrinos instead of photons lets this axion-like majoron avoid the strong bounds that affect other axion-like particles of similar mass and coupling to photons. 2022-05-11T10:47:04Z 2022-05-11T10:47:04Z 2022-04-05 info:eu-repo/semantics/article Published version: A.J. Cuesta... [et al.]. JCAP04(2022)009. DOI: [10.1088/1475-7516/2022/04/009] http://hdl.handle.net/10481/74798 eng http://creativecommons.org/licenses/by-nc-nd/3.0/es/ info:eu-repo/semantics/openAccess Atribución-NoComercial-SinDerivadas 3.0 España Institute of Physics