Improved cosmological constraints on the neutrino mass and lifetime

Abellán, Guillermo F.; Chacko, Zackaria; Dev, Abhish; Du, Peizhi; Poulin, Vivian; Tsai, Yuhsin

doi:10.48550/arxiv.2112.13862

“…In this work, the recently derived and fully general decaying neutrino Boltzmann hierarchy of reference [36] will be the starting point of our analysis. In particular, we will show that in the case of massless decay products and when disregarding inverse decay processes, the decaying neutrino equations of [36] reduce exactly to the decaying warm dark matter equations used in [38], and, by extension, to those used in the recent work [34]. In addition, we provide an approximate analytical expression for the solution to the background equations of motion for both the decaying particle and the decay products.…”

Section: Introductionmentioning

confidence: 76%

“…Studies of decaying massive neutrinos emerged several decades ago (e.g. [32,33] and references therein) when it was realized that finite neutrino lifetimes may significantly relax the bounds on the neutrino mass sum (for the most recent constraints, see [34][35][36][37]). It is only recently, with the work of reference [38], that decaying warm dark matter (DWDM) has been investigated explicitly.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, we provide an approximate analytical expression for the solution to the background equations of motion for both the decaying particle and the decay products. A main contribution is a new method of computing the integrals appearing in the decay product perturbations, which is a bottleneck in the calculations [34,38], removing the need to truncate the collision terms at a low multipole. Furthermore, we conduct Markov chain Monte Carlo (MCMC) analyses with both the initial density, lifetime and for the first time the DWDM mass in order to determine the regions of parameter space preferred by data.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Decaying warm dark matter revisited

Holm¹,

Tram²,

Hannestad³

2022

Preprint

1

0

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Decaying dark matter models provide a physically motivated way of channeling energy between the matter and radiation sectors. In principle, this could affect the predicted value of the Hubble constant in such a way as to accommodate the discrepancies between CMB inferences and local measurements of the same. Here, we revisit the model of warm dark matter decaying non-relativistically to invisible radiation. In particular, we rederive the background and perturbation equations starting from a decaying neutrino model and describe a new, computationally efficient method of computing the decay product perturbations up to large multipoles. We conduct MCMC analyses to constrain all three model parameters, for the first time including the mass of the decaying species, and assess the ability of the model to alleviate the Hubble and σ 8 tensions, the latter being the discrepancy between the CMB and weak gravitational lensing constraints on the amplitude of matter fluctuations on an 8h −1 Mpc −1 scale. We find that the model reduces the H 0 tension from ∼ 4σ to ∼ 3σ and neither alleviates nor worsens the S 8 ≡ σ 8 (Ω m /0.3) 0.5 tension, ultimately showing only mild improvements with respect to ΛCDM. However, the values of the model-specific parameters favoured by data is found to be well within the regime of relativistic decays where inverse processes are important, rendering a conclusive evaluation of the decaying warm dark matter model open to future work.

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“…Observe that the -dependence of the double integral is contained entirely in (i) the term |q ), this dependence simplifies to a quartic polynomial in with -independent coefficients. We shall not write out the polynomial here, but suffice it to say that this is the origin of quartic -dependence of the α coefficients (18).…”

Section: Appendix A: Collision Integralsmentioning

confidence: 99%

“…It is also possible to invoke invisible neutrino decay in the non-relativistic limit as a means to relax cosmological neutrino mass bounds. See, e.g., Refs [17,18]. for recent studies.…”

mentioning

confidence: 99%

Weaker yet again: mass spectrum-consistent cosmological constraints on the neutrino lifetime

Chen¹,

Oldengott²,

Pierobon³

et al. 2022

Preprint

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We consider invisible neutrino decay ν H → ν l + φ in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant for the cosmic microwave background (CMB) anisotropies. Improving on our previous work which assumed massless ν l and φ, we reinstate in this work the daughter neutrino mass m νl in a manner consistent with the experimentally determined neutrino mass splittings. We find that a nonzero m νl introduces a new phase space factor in the loss rate Γ T proportional to (∆m 2 ν /m 2 ν H ) 2 in the limit of a small squared mass gap between the parent and daughter neutrinos, i.e., Γ T ∼ (∆m 2 ν /m 2 νH ) 2 (m νH /E ν ) 5 (1/τ 0 ), where τ 0 is the ν H rest-frame lifetime. Using a general form of this result, we update the limit on τ 0 using the Planck 2018 CMB data. We find that for a parent neutrino of mass m νH 0.1 eV, the new phase space factor weakens the constraint on its lifetime by up to a factor of 50 if ∆m 2 ν corresponds to the atmospheric mass gap and up to 10 5 if the solar mass gap, in comparison with naïve estimates that assume m νl = 0. The revised constraints are (i) τ 0 (6 → 10) × 10 5 s and τ 0 (400 → 500) s if only one neutrino decays to a daughter neutrino separated by, respectively, the atmospheric and the solar mass gap, and (ii) τ 0 (1 → 3) × 10 7 s in the case of two decay channels with one near-common atmospheric mass gap. In contrast to previous, naïve limits which scale as m 5 νH , these mass spectrum-consistent τ 0 constraints are remarkably independent of the parent mass and open up a swath of parameter space within the projected reach of IceCube and other neutrino telescopes in the next two decades.

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Weaker yet again: mass spectrum-consistent cosmological constraints on the neutrino lifetime

Chen

¹

,

Oldengott

²

,

Pierobon

³

et al. 2022

View full text Add to dashboard Cite

We consider invisible neutrino decay $$\nu _H \rightarrow \nu _l + \phi $$ ν H → ν l + ϕ in the ultra-relativistic limit and compute the neutrino anisotropy loss rate relevant for the cosmic microwave background (CMB) anisotropies. Improving on our previous work which assumed massless$$\nu _l$$ ν l and $$\phi $$ ϕ , we reinstate in this work the daughter neutrino mass $$m_{\nu l}$$ m ν l in a manner consistent with the experimentally determined neutrino mass splittings. We find that a nonzero $$m_{\nu l}$$ m ν l introduces a new phase space factor in the loss rate $$\varGamma _\mathrm{T}$$ Γ T proportional to $$(\varDelta m_\nu ^2/m_{\nu _H}^2)^2$$ ( Δ m ν 2 / m ν H 2 ) 2 in the limit of a small squared mass gap between the parent and daughter neutrinos, i.e., $$\varGamma _\mathrm{T} \sim (\varDelta m_\nu ^2/m_{\nu H}^2)^2 (m_{\nu H}/E_\nu )^5 (1/\tau _0)$$ Γ T ∼ ( Δ m ν 2 / m ν H 2 ) 2 ( m ν H / E ν ) 5 ( 1 / τ 0 ) , where $$\tau _0$$ τ 0 is the $$\nu _H$$ ν H rest-frame lifetime. Using a general form of this result, we update the limit on $$\tau _0$$ τ 0 using the Planck 2018 CMB data. We find that for a parent neutrino of mass $$m_{\nu H} \lesssim 0.1$$ m ν H ≲ 0.1 eV, the new phase space factor weakens the constraint on its lifetime by up to a factor of 50 if $$\varDelta m_\nu ^2$$ Δ m ν 2 corresponds to the atmospheric mass gap and up to $$10^{5}$$ 10 5 if the solar mass gap, in comparison with naïve estimates that assume $$m_{\nu l}=0$$ m ν l = 0 . The revised constraints are (i) $$\tau ^0 > rsim (6 \rightarrow 10) \times 10^5$$ τ 0 ≳ ( 6 → 10 ) × 10 5 s and $$\tau ^0 > rsim (400 \rightarrow 500)$$ τ 0 ≳ ( 400 → 500 ) s if only one neutrino decays to a daughter neutrino separated by, respectively, the atmospheric and the solar mass gap, and (ii) $$\tau ^0 > rsim (2 \rightarrow 6) \times 10^7$$ τ 0 ≳ ( 2 → 6 ) × 10 7 s in the case of two decay channels with one near-common atmospheric mass gap. In contrast to previous, naïve limits which scale as $$m_{\nu H}^5$$ m ν H 5 , these mass spectrum-consistent $$\tau _0$$ τ 0 constraints are remarkably independent of the parent mass and open up a swath of parameter space within the projected reach of IceCube and other neutrino telescopes in the next two decades.

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Improved cosmological constraints on the neutrino mass and lifetime

Cited by 4 publications

References 51 publications

Decaying warm dark matter revisited

Decaying warm dark matter revisited

Weaker yet again: mass spectrum-consistent cosmological constraints on the neutrino lifetime

Weaker yet again: mass spectrum-consistent cosmological constraints on the neutrino lifetime

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