Motivation ArXiv:1909.04044, Miguel Escudero[a] and Sam Witte[b] [a] King's College London, [b] Instituto de Física Corpuscular Conclusions and Outlook References [1] Riess et. al. 1903.07603. Astrophys. J. 876 (2019) 85. [2] Planck Collaboration, 2018 Cosmological Parameters, 1807.06209. [3] The Hubble Hunter's Guide, L. Knox and M. Millea, 1908.03663. [4] Y. Chikashige, R. N. Mohapatra & R. D. Peccei, Phys. Lett B98 (1981) 265-268. [5] Z. Chacko, L. J. Hall, T. Okui & S.J. Oliver, PRD 70 (2004) 085008, hep-ph/0312267. [6] M. Escudero, JCAP 1902 (2019) 007, 1812.05605, 2001.04466. [7] M. Escudero & S. J. Witte 1909.04044. Corresponding Author: miguel.escudero@kcl.ac.uk NuPhys2019: Prospects in Neutrino Physics (London) Could the Hubble Tension be Pointing Towards the Neutrino Mass Mechanism? m⌫6= 0 ⌫e ! ⌫µ ¯⌫ ⌫ φ H0 The Hubble Tension Neutrino Masses The Scenario Physics beyond ΛCDM? Physics beyond the SM 4.4σ discrepancy between the local determination of the Hubble constant [1] as measured using Cepheids and type-Ia SN to the value inferred from Planck CMB observations within ΛCDM [2]. Planck data has been exhaustively checked against systematics and CMB systematics cannot be responsible for the tension. Several groups have reanalysed the local measurements and so far there is no known systematic capable of substantially ameliorating the tension. Strong lensing measurements of H0 are in agreement with local determinations while Baryon Acoustic Oscillations agree with the CMB. Neutrinos oscillate and at least two of them have a mass. Neutrino masses are the only laboratory evidence of physics beyond the Standard Model, since mνSM = 0. Viable solutions to the tension require an enhanced expansion history close and prior to recombination. However, simply enhancing Neff does not work [2,3]. Furthermore, BBN constraints typically apply. The Majoron: a Neutrinophilic pseudo-Goldstone boson from the seesaw mechanism with Global Lepton number Neutrino masses via the type-I seesaw mechanism But heavy neutrino Majorana masses should come from somewhere. Here, via the spontaneous symmetry breaking of U(1)L. Majoron Properties Cosmological Implications Main Results If Lepton number is a global symmetry (as in the SM) then a physical pseudo-Goldstone boson appears in the spectrum: the Majoron [4]. Very feeble interactions with neutrinos λ ' 10−13 m⌫ 0.05 eV 1 TeV vL Extremely weak interactions with matter λφee ' 10−20 Gravity breaks all global symmetries. Dim-5 Planck suppressed operators: Lint = iλ φ ¯⌫γ5 ⌫ ¯⌫ ⌫ φ Performed a full MCMC ﬁt to Planck2018 data and found very strong constraints ⚑. Ruling out masses compatible with dim-5 Planck suppressed operators ⚑ and testing couplings as small as λ ~ 10-13 and scales of lepton number breaking up to 1 TeV. Γφ ≥H(T⌫= mφ/3) Neutrino-Majoron interactions lead to [5]: Non-standard expansion history between BBN and recombination. Erase of the Neutrino anisotropic stress. provided We account [7] for these effects by solving the background evolution using [6] and by implementing in the Boltzmann code CLASS the non- standard expansion history and the impact on the neutrino perturbations. λ ⌧1 equivalently λ > 4 ⇥10−12 r mφ 1 keV Impact on the CMB Γe↵= ✓ λ 4 ⇥10−12 ◆2 ✓1 keV mφ ◆ Non-standard expansion history Leads to a contribution of across wide regions of parameter space. ∆Ne↵' 0.11 Modiﬁcation to the neutrino perturbations Leads to a suppression of the neutrino anisotropic stress that has very important implications for the CMB spectra. ˙δ⌫φ = −4 3✓⌫φ −2 3 ˙h , ˙✓⌫φ = k2 ✓1 4δ⌫φ −σ⌫φ ◆ , ˙F⌫φ2 = 2 ˙σ⌫φ = 8 15✓⌫φ −3 5kF⌫φ 3 + 4 15 ˙h + 8 5 ˙⌘−2aΓσ⌫φ , ˙F⌫φ ` = k 2` + 1 ⇥ ` F⌫φ (`−1) −(` + 1)F⌫φ (`+1) ⇤ −aΓF⌫φ ` , ` ≥3 . Γ = Γφ 2 m2 φ T 2⌫ e µ⌫ T⌫K1 ✓mφ T⌫ ◆ Γφ ' λ2 16⇡mφ Since , the only relevant processes are Majoron decays and inverse neutrino decays: The Majoron leads to across wide regions of parameter space ⚑ and hence ameliorates the Hubble tension without suffering from BBN constraints