Aoki, M., Toma, T., & Vicente, A. (2015). Non-thermal production of minimal dark matter via right-handed neutrino decay. J. Cosmol. Astropart. Phys., 09(9), 063–19pp.
Abstract: Minimal Dark Matter (MDM) stands as one of the simplest dark matter scenarios. In MDM models, annihilation and co-annihilation processes among the members of the MDM multiplet are usually very efficient, pushing the dark matter mass above O(10) TeV in order to reproduce the observed dark matter relic density. Motivated by this little drawback, in this paper we consider an extension of the MDM scenario by three right-handed neutrinos. Two specific choices for the MDM multiplet are studied: a fermionic SU(2)(L) quintuplet and a scalar SU(2)(L) septuplet. The lightest right-handed neutrino, with tiny Yukawa couplings, never reaches thermal equilibrium in the early universe and is produced by freeze-in. This creates a link between dark matter and neutrino physics: dark matter can be non-thermally produced by the decay of the lightest right-handed neutrino after freeze-out, allowing to lower significantly the dark matter mass. We discuss the phenomenology of the non-thermally produced MDM and, taking into account significant Sommerfeld corrections, we find that the dark matter mass must have some specific values in order not to be in conflict with the current bounds from gamma-ray observations.
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Archidiacono, M., Gariazzo, S., Giunti, C., Hannestad, S., & Tram, T. (2020). Sterile neutrino self-interactions: H-0 tension and short-baseline anomalies. J. Cosmol. Astropart. Phys., 12(12), 029–20pp.
Abstract: Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples to a new light pseudoscalar degree of freedom. Consistently with previous analyses, we find that the model provides a good fit to all cosmological data and allows the high value of H-0 measured in the local universe to be consistent with measurements of the cosmic microwave background. However, new high l polarisation data constrain the sterile neutrino mass to be less than approximately 1 eV in this scenario. Finally, we combine the cosmological bounds on the pseudoscalar model with a Bayesian inference analysis of SBL data and conclude that only a sterile mass in narrow ranges around 1 eV remains consistent with both cosmology and SBL data.
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LISA Cosmology Working Group(Auclair, P. et al), & Figueroa, D. G. (2023). Cosmology with the Laser Interferometer Space Antenna. Living Rev. Relativ., 26(1), 5–254pp.
Abstract: The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe.
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Barenboim, G., Park, W. I., & Kinney, W. H. (2016). Eternal hilltop inflation. J. Cosmol. Astropart. Phys., 05(5), 030–15pp.
Abstract: We consider eternal inflation in hilltop-type inflation models, favored by current data, in which the scalar field in inflation rolls off of a local maximum of the potential. Unlike chaotic or plateau-type inflation models, in hilltop inflation the region of field space which supports eternal inflation is finite, and the expansion rate H-EI during eternal inflation is almost exactly the same as the expansion rate H-* during slow roll inflation. Therefore, in any given Hubble volume, there is a finite and calculable expectation value for the lifetime of the “eternal” inflation phase, during which quantum flucutations dominate over classical field evolution. We show that despite this, inflation in hilltop models is nonetheless eternal in the sense that the volume of the spacetime at any finite time is exponentially dominated by regions which continue to inflate. This is true regardless of the energy scale of inflation, and eternal inflation is supported for inflation at arbitrarily low energy scale.
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Barenboim, G., & Park, W. I. (2016). New- vs. chaotic- inflations. J. Cosmol. Astropart. Phys., 02(2), 061–20pp.
Abstract: We show that “spiralized” models of new-inflation can be experimentally identified mostly by their positive spectral running in direct contrast with most chaotic-inflation models which have negative runnings typically in the range of O(10(-4)-10(-3)).
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