Observational Constraints on Secret Neutrino Interactions from Big Bang Nucleosynthesis

We investigate possible interactions between neutrinos and massive scalar bosons via $g^{}_{\phi} \overline{\nu} \nu \phi$ (or massive vector bosons via $g^{}_V \overline{\nu} \gamma^\mu \nu V^{}_\mu$) and explore the allowed parameter space of the coupling constant $g^{}_{\phi}$ (or $g^{}_V$) and the scalar (or vector) boson mass $m^{}_\phi$ (or $m^{}_V$) by requiring that these secret neutrino interactions (SNIs) should not spoil the success of Big Bang nucleosynthesis (BBN). Incorporating the SNIs into the evolution of the early Universe in the BBN era, we numerically solve the Boltzmann equations and compare the predictions for the abundances of light elements with observations. It turns out that the constraint on $g^{}_{\phi}$ and $m^{}_\phi$ in the scalar-boson case is rather weak, due to a small number of degrees of freedom. However, in the vector-boson case, the most stringent bound on the coupling $g^{}_V \lesssim 6\times 10^{-10}$ at $95~\%$ confidence level is obtained for $m^{}_V \simeq 1~{\rm MeV}$, while the bound becomes much weaker $g^{}_V \lesssim 8\times 10^{-6}$ for smaller masses $m^{}_V \lesssim 10^{-4}~{\rm MeV}$. Moreover, we discuss in some detail how the SNIs affect the cosmological evolution and the abundances of the lightest elements.Comment: 18 pages, 5 figure

Discovery potential of the Glashow resonance in an air shower neutrino telescope

The in-ice or in-water Cherenkov neutrino telescope such as IceCube has already proved its power in measuring the Glashow resonance by searching for the bump around $E^{}_{\rm \nu} = 6.3~{\rm PeV}$ arising from the $W$-boson production. In the next few decades, there are many proposals that observe cosmic tau neutrinos with extensive air showers, also known as tau neutrino telescopes. As has been recognized, the air shower telescope is in principle sensitive to the Glashow resonance via the channel $W \to \tau \nu^{}_{\tau}$ followed by the tau decay in the air. However, with a thorough numerical analysis we have identified several limitations for those telescopes on hunting the resonance. If ultrahigh-energy neutrinos are dominantly produced from the meson decay, it will be statistically difficult for a rather advanced proposal, such as TAMBO with a geometric area around $500~{\rm km^2}$, to discriminate the Glashow resonance induced by $\overline{\nu}^{}_{e}$ from the intrinsic $\nu^{}_{\tau}/\overline{\nu}^{}_{\tau}$ background. The discovery significance is only around $1\sigma$ considering the flux parameters measured by IceCube as the input. Nevertheless, the significance will be improved to $90\%$ if PeV neutrinos mainly originate from the neutron decay, which is, however, thought to be only a subdominant neutrino source. The presence of new physics can also increase the significance. Compared to the in-ice or in-water telescope, the challenge for the Glashow resonance search is ascribed to several factors: (i) a suppressed branching ratio of $11\%$ for the decay $W \to \tau \nu^{}_{\tau}$; (ii) the smearing effect and the reduced acceptance because the daughter neutrino takes away $\langle y \rangle \sim 75\%$ of the energy from the $W$ decay; (iii) a large attenuation effect for Earth-skimming neutrinos with the resonance.Comment: 21 pages, 4 figures, and comments are welcom

Neutrinophilic Axion-Like Dark Matter

The axion-like particles (ALPs) are very good candidates of the cosmological dark matter, which can exist in many extensions of the standard model (SM). The mass range of the ALPs as the dark matter can extend from a sub-eV scale to almost $10^{-22}~{\rm eV}$. On the other hand, the neutrinos are found to be massive and the SM must be extended to explain the sub-eV neutrino masses. It becomes very interesting to consider an exclusive coupling between these two low scale frontiers that are both beyond the SM. The propagation of neutrinos inside the Milky Way would undergo the coherent forward scattering effect with the ALP background, and the neutrino oscillation behavior can be modified by the ALP-induced potential. Assuming a derivative coupling between the ALP and the three generations of active neutrinos, possible impacts on the neutrino oscillation experiments have been explored in this paper. In particular, we have numerically studied the sensitivity of the Deep Underground Neutrino Experiment (DUNE). The astrophysical consequences of such coupling have also been investigated systematically.Comment: 12 pages, 3 figure

Tritium beta decay with modified neutrino dispersion relations: KATRIN in the dark sea

We discuss beta decays in a dark background field, which could be formed by dark matter, dark energy or a fifth force potential. In such scenarios, the neutrino's dispersion relation will be modified by its collective interaction with the dark field, which can have observable consequences in experiments using tritium beta decays to determine the absolute neutrino mass. Among the most general interaction forms, the (pseudo)scalar and (axial-)vector ones are found to have interesting effects on the spectrum of beta decays. In particular, the vector and axial-vector potentials can induce distinct signatures by shifting the overall electron energy scale, possibly beyond the usually defined endpoint. The scalar and pseudoscalar potentials are able to mimic a neutrino mass beyond the cosmological bounds. We have placed stringent constraints on the dark potentials based on the available experimental data of KATRIN, and the sensitivity of future KATRIN runs is also discussed.Comment: 15 pages, 4 figure