Doctoral Thesis in Theoretical Physics Weigh them all! Cosmological searches for the neutrino mass scale and mass ordering Sunny Vagnozzi arXiv:1907.08010v1 [astro-ph.CO] 18 Jul 2019 Oskar Klein Centre for Cosmoparticle Physics and Cosmology, Particle Astrophysics and Strings Department of Physics Stockholm University SE-106 91 Stockholm Stockholm, Sweden, 2019 Weigh them all! Cosmological searches for the neutrino mass scale and mass ordering Sunny Vagnozzi Academic dissertation for the Degree of Doctor of Philosophy in Theoretical Physics at Stockholm University to be publicly defended on Monday 10 June 2019 at 13.00 in FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21. Abstract The elusive neutrinos are among the most intriguing constituents of the particle zoo. The observation of neutrino flavour oscillations, indicating that neutrinos are massive, provides the only direct evidence for physics beyond the Standard Model. Neutrinos imprint peculiar signatures in the Cosmic Microwave Background (CMB) and in the distribution of Large-Scale Structure (LSS) in the Universe, making cosmology a very promising arena for probing neutrino properties. A detection of neutrino masses is avowedly among the key goals of several upcoming CMB and LSS surveys. For such a promise to be robustly realized, a number of issues need to be addressed, particularly on the LSS side. In this thesis, I describe a number of recent important developments in neutrino cosmology on three fronts. Firstly, focusing on LSS data, I will show that current cosmological probes (and particularly galaxy power spectrum data) contain a wealth of information on the sum of the neutrino masses. I will report on the analysis leading to the currently best upper limit on the sum of the neutrino masses of 0.12 eV. I show how cosmological data exhibits a weak preference for the normal neutrino mass ordering because of parameter space volume effects, and propose a simple method to quantify this preference. Secondly, I will discuss how galaxy bias represents a severe limitation towards fully capitalizing on the neutrino information hidden in LSS data. I propose a method for calibrating the scale-dependent galaxy bias using CMB lensing- galaxy cross-correlations. Another crucial issue in this direction is represented by how the bias is defined in first place. In the presence of massive neutrinos, the usual definition of bias becomes inadequate, as it leads to a scale-dependence on large scales which has never been accounted for. I show that failure to define the bias appropriately will be a problem for future LSS surveys, leading to incorrectly estimated cosmological parameters. In doing so, I propose a simple recipe to account for the effect of massive neutrinos on galaxy bias. Finally, I take on a different angle and discuss implications of correlations between neutrino parameters and other cosmological parameters. I show how, in non-phantom dynamical dark energy models (which include quintessence), the upper limit on the sum of the neutrino masses becomes tighter than the ΛCDM limit. Therefore, such models exhibit an even stronger preference for the normal ordering, and their viability could be jeopardized should near-future laboratory experiments determine that the mass ordering is inverted. I then discuss correlations between neutrino and inflationary parameters. I find that our determination of inflationary parameters is relatively stable against reasonable assumptions about the neutrino sector, and thus that neutrino unknowns do not represent an important nuisance for our understanding of inflation and the initial conditions of the Universe. The findings reported in this thesis answer a number of important open questions whose addressing is necessary to ensure a robust detection of neutrino masses (and possibly of the neutrino mass ordering) from future cosmological data, opening the door towards physics beyond the Standard Model. Keywords: neutrinos, neutrino mass, neutrino mass ordering, cosmology, cosmic microwave background, large-scale structure, galaxy surveys, dark energy, cosmic inflation, data analysis. Stockholm 2019 http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-167815 ISBN 978-91-7797-727-8 ISBN 978-91-7797-729-2 Department of Physics Stockholm University, 106 91 Stockholm Printed: 2019-07-19 pp. i–xli, 1–154, © 2019 by Sunny Vagnozzi Typeset in pdfLATEX Weigh them all! Cosmological searches for the neutrino mass scale and mass ordering Sunny Vagnozzi A Cristina, il mio Universo vii Neutrinos, they are very small They have no charge and have no mass And do not interact at all. The earth is just a silly ball To them, through which they simply pass, Like dustmaids down a drafty hall Or photons through a sheet of glass. They snub the most exquisite gas, Ignore the most substantial wall, Cold-shoulder steel and sounding brass, Insult the stallion in his stall, And, scorning barriers of class, Infiltrate you and me! Like tall And painless guillotines, they fall Down through our heads into the grass. At night, they enter at Nepal And pierce the lover and his lass From underneath the bed—you call It wonderful; I call it crass. –Cosmic Gall, John Updike (1960) Neutrinos...win the minimalist contest: zero charge, zero radius, and very possibly zero mass –In The God Particle: If the Universe is the Answer, What is the Question?, Leon M. Lederman and Dick Teresi (1993), p. xiii Neutrinos have mass? I didn’t even know they were Catholic! –Robert Langdon to Vittoria Vetra in Angels and Demons, Dan Brown (2000), p. 476 ix Abstract The elusive neutrinos are among the most intriguing constituents of the particle zoo. The observation of neutrino flavour oscillations, indicating that neutrinos are massive, provides the only direct evidence for physics beyond the Standard Model. Neutrinos imprint pe- culiar signatures in the Cosmic Microwave Background (CMB) and in the distribution of Large-Scale Structure (LSS) in the Universe, making cosmology a very promising arena for probing neutrino properties. A detection of neutrino masses is avowedly among the key goals of several upcoming CMB and LSS surveys. For such a promise to be robustly realized, a number of issues need to be addressed, particularly on the LSS side. In this thesis, I describe a number of recent important developments in neutrino cosmology on three fronts. Firstly, focusing on LSS data, I will show that current cosmological probes (and particularly galaxy power spectrum data) contain a wealth of information on the sum of the neutrino masses. I will report on the analysis leading to the currently best upper limit on the sum of the neutrino masses of 0.12 eV. I show how cosmological data exhibits a weak preference for the normal neutrino mass ordering because of parameter space volume effects, and propose a simple method to quantify this preference. Secondly, I will discuss how galaxy bias represents a severe limitation towards fully capitaliz- ing on the neutrino information hidden in LSS data. I propose a method for calibrating the scale-dependent galaxy bias using CMB lensing-galaxy cross-correlations. Another crucial issue in this direction is represented by how the bias is defined in first place. In the pres- ence of massive neutrinos, the usual definition of bias becomes inadequate, as it leads to a scale-dependence on large scales which has never been accounted for. I show that failure to define the bias appropriately will be a problem for future LSS surveys, leading to incorrectly estimated cosmological parameters. In doing so, I propose a simple recipe to account for the effect of massive neutrinos on galaxy bias. Finally, I take on a different angle and discuss implications of correlations between neutrino parameters and other cosmological parameters. I show how, in non-phantom dynamical dark energy models (which include quintessence), the upper limit on the sum of the neu- trino masses becomes tighter than the ΛCDM limit. Therefore, such models exhibit an even stronger preference for the normal ordering, and their viability could be jeopardized should near-future laboratory experiments determine that the mass ordering is inverted. I then discuss correlations between neutrino and inflationary parameters. I find that our determination of inflationary parameters is relatively stable against reasonable assumptions about the neutrino sector, and thus that neutrino unknowns do not represent an important nuisance for our understanding of inflation and the initial conditions of the Universe. The findings reported in this thesis answer a number of important open questions whose addressing is necessary to ensure a robust detection of neutrino masses (and possibly of the neutrino mass ordering) from future cosmological data, opening the door towards physics beyond the Standard Model. xi Svensk sammanfattning De svårfångade neutrinerna är bland de mest fängslande beståndsdelarna i partiklarnas zoo. Observationen av neutrinooscillationer, som tyder på att neutriner har massa, utgör det enda direkta beviset för fysik utöver Standardmodellen. Neutriner lämnar annorlunda signaturer i den kosmiska bakgrundsstrålningen (CMB) och i fördelningen av Universums storskaliga struktur (LSS), vilka gör kosmologi till en mycket lovande arena för att undersöka neutrinernas egenskaper. Att upptäcka neutrinomassorna är också bland de viktigaste målen för flera kommande CMB- och LSS-experiment. För att det här löftet ska realiseras måste ett antal frågor behandlas, särskilt på LSS-sidan. I denna avhandling beskriver jag ett antal nya viktiga utvecklingar i neutrinokosmologi på tre fronter. För det första, med fokus på LSS-data, kommer jag att visa att nuvarande kosmologiska undersökningar innehåller en stor mängd information om summan av neutrinomassorna. Jag kommer att beskriva analysen som leder till den för närvarande bästa övre gränsen för summan av neutrinomassorna av 0.12 eV. Jag visar hur kosmologiska data indikerar en svag preferens för den normala neutrino massordningen (där man har två lätta neutriner och en tyngre neutrino, i motsats till den omvända massordningen med en lätt neutrino och två tunga neutriner) och lägger fram en enkel metod för att kvantifiera denna preferens.