Kuo, J. L., Lattanzi, M., Cheung, K., & Valle, J. W. F. (2018). Decaying warm dark matter and structure formation. J. Cosmol. Astropart. Phys., 12(12), 026–24pp.
Abstract: We examine the cosmology of warm dark matter (WDM), both stable and decaying, from the point of view of structure formation. We compare the matter power spectrum associated to WDM masses of 1.5 keV and 0.158 keV, with that expected for the stable cold dark matter ACDM Xi SCDM paradigm, taken as our reference model. We scrutinize the effects associated to the warm nature of dark matter, as well as the fact that it decays. The decaying warm dark matter (DWDM) scenario is well-motivated, emerging in a broad class of particle physics theories where neutrino masses arise from the spontaneous breaking of a continuous global lepton number symmetry. The majoron arises as a Nambu-Goldstone boson, and picks up a mass from gravitational effects, that explicitly violate global symmetries. The majoron necessarily decays to neutrinos, with an amplitude proportional to their tiny mass, which typically gives it cosmologically long lifetimes. Using N-body simulations we show that our DWDM picture leads to a viable alternative to the ACDM scenario, with predictions that can differ substantially on small scales.
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Lattanzi, M., Gerbino, M., Freese, K., Kane, G., & Valle, J. W. F. (2020). Cornering (quasi) degenerate neutrinos with cosmology. J. High Energy Phys., 10(10), 213–24pp.
Abstract: In light of the improved sensitivities of cosmological observations, we examine the status of quasi-degenerate neutrino mass scenarios. Within the simplest extension of the standard cosmological model with massive neutrinos, we find that quasi-degenerate neutrinos are severely constrained by present cosmological data and neutrino oscillation experiments. We find that Planck 2018 observations of cosmic microwave background (CMB) anisotropies disfavour quasi-degenerate neutrino masses at 2.4 Gaussian sigma 's, while adding baryon acoustic oscillations (BAO) data brings the rejection to 5.9 sigma 's. The highest statistical significance with which one would be able to rule out quasi-degeneracy would arise if the sum of neutrino masses is Sigma m(v) = 60 meV (the minimum allowed by neutrino oscillation experiments); indeed a sensitivity of 15 meV, as expected from a combination of future cosmological probes, would further improve the rejection level up to 17 sigma. We discuss the robustness of these projections with respect to assumptions on the underlying cosmological model, and also compare them with bounds from beta decay endpoint and neutrinoless double beta decay studies.
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Lattanzi, M., Riemer-Sorensen, S., Tortola, M., & Valle, J. W. F. (2013). Updated CMB and x- and gamma-ray constraints on Majoron dark matter. Phys. Rev. D, 88(6), 063528–8pp.
Abstract: The Majoron provides an attractive dark matter candidate, directly associated with the mechanism responsible for spontaneous neutrino mass generation within the standard model SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) framework. Here we update the cosmological and astrophysical constraints on Majoron dark matter coming from the cosmic microwave background and a variety of x- and gamma-ray observations.
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Lavoura, L., Morisi, S., & Valle, J. W. F. (2013). Accidental stability of dark matter. J. High Energy Phys., 02(2), 118–17pp.
Abstract: We propose that dark matter is stable as a consequence of an accidental Z(2) that results from a flavour symmetry group which is the double-cover group of the symmetry group of one of the regular geometric solids. Although model-dependent, the phenomenology resembles that of a generic “inert Higgs” dark matter scheme.
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Lazarides, G., Reig, M., Shafi, Q., Srivastava, R., & Valle, J. W. F. (2019). Spontaneous Breaking of Lepton Number and the Cosmological Domain Wall Problem. Phys. Rev. Lett., 122(15), 151301–5pp.
Abstract: We show that if global lepton number symmetry is spontaneously broken in a postinflation epoch, then it can lead to the formation of cosmological domain walls. This happens in the well-known “Majoron paradigm” for neutrino mass generation. We propose some realistic examples that allow spontaneous lepton number breaking to be safe from such domain walls.
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