Time-varying neutrino mass from a supercooled phase transition: current cosmological constraints and impact on the Ωm−σ8 plane

Lorenz, Christiane S., Funcke, Lena, Calabrese, Erminia ORCID: https://orcid.org/0000-0003-0837-0068 and Hannestad, Steen 2019. Time-varying neutrino mass from a supercooled phase transition: current cosmological constraints and impact on the Ωm−σ8 plane. Physical Review D 99 (2) , -. 10.1103/PhysRevD.99.023501

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Abstract

In this paper we investigate a time-varying neutrino mass model, motivated by the mild tension between cosmic microwave background (CMB) measurements of the matter fluctuations and those obtained from low-redshift data. We modify the minimal case of the model proposed by [G. Dvali and L. Funcke, Phys. Rev. D 93, 113002 (2016)] that predicts late neutrino mass generation in a postrecombination cosmic phase transition, by assuming that neutrino asymmetries allow for the presence of relic neutrinos in the late-time Universe. We show that, if the transition is supercooled, current cosmological data (including CMB temperature, polarization and lensing, baryon acoustic oscillations, and type Ia supernovae) prefer the scale factor as of the phase transition to be very large, peaking at as∼1, and therefore supporting a cosmological scenario in which neutrinos are almost massless until very recent times. We find that in this scenario the cosmological bound on the total sum of the neutrino masses today is significantly weakened compared to the standard case of constant-mass neutrinos, with ∑mν<4.8  eV at 95% confidence, and in agreement with the model predictions. The main reason for this weaker bound is a large correlation arising between the dark energy and neutrino components in the presence of false vacuum energy that converts into the nonzero neutrino masses after the transition. This result provides new targets for the coming KATRIN and PTOLEMY experiments. We also show that the time-varying neutrino mass model considered here does not provide a clear explanation of the existing cosmological Ωm−σ8 discrepancies.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Physical Society
ISSN:	2470-0010
Date of First Compliant Deposit:	17 January 2019
Date of Acceptance:	13 December 2018
Last Modified:	05 May 2023 00:01
URI:	https://orca.cardiff.ac.uk/id/eprint/118515

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