Sterile Neutrinos or Flux Uncertainties? - Status of the Reactor Anti-Neutrino Anomaly

The $\sim 3\sigma$ discrepancy between the predicted and observed reactor anti-neutrino flux, known as the reactor anti-neutrino anomaly, continues to intrigue. The recent discovery of an unexpected bump in the reactor anti-neutrino spectrum, as well as indications that the flux deficit is different for different fission isotopes seems to disfavour the explanation of the anomaly in terms of sterile neutrino oscillations. We critically review this conclusion in view of all available data on electron (anti)neutrino disappearance. We find that the sterile neutrino hypothesis cannot be rejected based on global data and is only mildly disfavored compared to an individual rescaling of neutrino fluxes from different fission isotopes. The main reason for this is the presence of spectral features in recent data from the NEOS and DANSS experiments. If state-of-the-art predictions for reactor fluxes are taken at face value, sterile neutrino oscillations allow a consistent description of global data with a significance close to $3\sigma$ relative to the no-oscillation case. Even if reactor fluxes and spectra are left free in the fit, a $2\sigma$ hint in favour of sterile neutrinos remains, with allowed parameter regions consistent with an explanation of the anomaly in terms of oscillations.Comment: 25 pages, 5 figures. 1 page and table 4 added. Published in JHE

HETDEX Public Source Catalog 1: 220K Sources Including Over 50K Lyman Alpha Emitters from an Untargeted Wide-area Spectroscopic Survey

We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88<z<3.52 by using the spatial distribution of more than a million Ly-alpha-emitting galaxies over a total target area of 540 deg^2. The catalog comes from contiguous fiber spectra coverage of 25 deg^2 of sky from January 2017 through June 2020, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Ly{\alpha}-emitting galaxy (LAE) identifications and 123,891 OII-emitting galaxies at z<0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift (z<0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, OII and Ly-alpha line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within deltaz < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r-band continuum counterpart down to a limiting magnitude of r~26.2 mag (AB) indicating that an LAE search of similar sensitivity with photometric pre-selection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/.Comment: 38 pages, 20 figures. Data access and details about the catalog can be found online at http://hetdex.org/. A copy of the catalogs presented in this work (Version 3.2) is available to download at Zenodo doi:10.5281/zenodo.744850

New Physics with Neutrinos

Due to open problems in theory and unresolved anomalies in various oscillation experiments, neutrino physics appears to be an excellent starting point in the quest for physics beyond the Standard Model. The 3+1 framework featuring an additional, sterile neutrino mixing with the known neutrinos, is a minimalist extension of the Standard Model which can account for oscillation phenomenology beyond the standard three flavor paradigm. However, two orthogonal arguments militate against this model. First, the increasing amount of ambiguous experimental results makes a consistent interpretation of the data in the 3+1 framework appear unlikely. In this regard, global fits provide a useful tool to investigate this objection. This thesis reports on the results of an up-to-date global fit to all relevant, available datasets, including the data corresponding to the reactor antineutrino anomaly, the gallium anomaly and the short baseline anomaly. The reactor data as a special case can plausibly be explained by the hypothesis of a misprediction of the reactor antineutrino flux. Therefore, this hypothesis is tested against the 3+1 framework. Both hypotheses are found to be similarly likely, with a slight preference for the 3+1 framework, mainly driven by the data from DANSS and NEOS, which measure antineutrino spectra. However, a combination of both hypotheses fits the data best, with the hypothesis of a mere misprediction of the reactor flux rejected at $2.9 sigma$. Despite mild tensions, adding the remaining datasets in the $parenbar nu_e$ disappearance channel increases the evidence for the 3+1 framework to $3.2 sigma$. This result is independent from any prediction on the reactor flux. Similarly, the data taken in the $parenbar nu_e$ appearance channel favor the 3+1 framework with a significance of up to $6.5 sigma$, depending on the LSND datasets included, although the goodness of fit is poor. These results are in strong contrast to the lack of evidence for the 3+1 framework in the $parenbar nu_mu$ disappearance channel. Especially driven by the new results from IceCube and MINOS, this lack of evidence allows for rigorous constraints on the parameter space in the $parenbar nu_mu$ disappearance channel. The combined fit to the global data proves that the different subsets are incompatible with each other at the $4.7sigma$ level. This tension is in particular driven by LSND and robust with regard to the choice of the fitted dataset and the underlying reactor flux model. The second objection to the 3+1 framework are the strong constraints on the effective number $N_text{eff}$ and the sum of masses $sum m_nu$ of neutrino-like particles implied by different cosmological probes. These constraints are in conflict with the presence of an additional, sterile neutrino species in the early universe. However, if their production was prevented throughout the evolution of the universe, the constraints from cosmology would not apply for sterile neutrinos. The generation of sterile neutrinos can be suppressed by a new type of interaction, termed secret interaction&#039;&#039;. Still, as this thesis confirms, the secret interaction model is disfavored in all of the viable parameter space. Therefore, inverse symmetry breaking, additional sterile neutrinos, additional free-streaming particles or neutrino decay are proposed as potential extensions of the secret interaction model.Aufgrund ungelöster Fragestellungen in der theoretischen Beschreibung und im Raume stehender Anomalien in diversen Oszillationsexperimenten erscheint die Neutrinophysik als exzellenter Ausgangspunkt für die Suche nach Physik jenseits des Standard Modells. Das 3+1 Modell, welches sich durch ein zusätzliches, steriles Neutrino auszeichnet, ist eine minimalistische Erweiterung des Standard Modells, die Oszillationsphänomenologie jenseits des standardmäßigen drei-Flavor Paradigmas Rechnung tragen kann. Gegen dieses Modell sprechen jedoch zwei diametrale Argumente. Erstens lässt die zunehmende Zahl an widersprüchlichen experimentellen Ergebnissen eine konsistente Erklärung der Daten im Rahmen des 3+1 Modells unwahrscheinlich wirken. Um diesen Einwand zu untersuchen erweisen sich in diesem Zusammenhang Globale Fits als ein nützliches Werkzeug. Die vorliegende Arbeit stellt die Ergebnisse eines auf dem neusten Stand befindlichen, globalen Fits an alle relevanten, verfügbaren Datensätze, einschließlich der Reaktor Anomalien, der Gallium Anomalien und der Short-Baseline Anomalien vor. Als Sonderfall können die Reaktor Anomalien auf plausible Weise durch die Hypothese einer falschen Vorhersage des Reaktor Antineutrinoflusses erklärt werden. Daher wird diese Hypothese gegen das 3+1 Modell getestet. Beide Hypothesen stellen sich als ähnlich wahrscheinlich heraus, mit einer leichten Präferenz für das 3+1 Modell, die sich vor allem in den Daten von DANSS und NEOS begründet, welche Antineutrinospektren messen. Am besten entspricht jedoch eine Kombination der beiden Hypothesen den Daten, wobei die Hypothese einer bloßen Falschvorhersage des Reaktorflusses mit $3.2 sigma$ abgelehnt wird. Dieses Ergebnis ist unabhängig von jeder Vorhersage des Reaktorflusses. Auf ähnliche Weise favorisieren die Daten im $parenbar nu_e$ Appearance Channel das 3+1 Modell mit einer Signifikanz von bis zu $6.5 sigma$, abhängig davon, welcher LSND Datensatz berücksichtigt wird, wobei jedoch der Goodness-of-Fit-Wert gering ist. Diese Ergebnisse stehen in starken Gegensatz zu dem Mangel an Anzeichen für das 3+1 Modell im $parenbar nu_mu$ Disappearance Channel. Der gemeinsame Fit an die globalen Daten belegt, dass die unterschiedlichen Teilmengen untereinander auf dem $4.7 sigma$ Niveau unvereinbar sind. Diese Spannung wird insbesondere von LSND hervorgerufen und ist robust bezüglich der Auswahl der gefitteden Datensätze sowie des zugrunde liegende Reaktorflussmodels. Den zweiten Einwand gegen das 3+1 Modell stellen die starken Beschränkungen der effektiven Zahl $N_text{eff}$ sowie der Summe der Massen $sum m_nu$ von neutrinoartigen Teilchen dar, welche von verschieden kosmologischen Messobjekten impliziert werden. Diese Beschränkungen stehen im Konflikt mit dem Vorhandensein einer weiteren, sterilen Neutrinosspezies im frühen Universum. Würde allerdings deren Entstehung während der Entwicklung des Universums verhindert, würden die Beschränkungen aus der Kosmologie für sterile Neutrinos nicht gelten. Die Produktion von sterilen Neutrinos kann durch eine neue Art von Wechselwirkung, welche als Secret Interaction&#039;&#039; bezeichnet wird, unterdrückt werden. Das Secret Interaction Modell ist dennoch, wie die vorliegende Arbeit bestätigt, im gesamten Parameterraum abzulehnen. Aus diesem Grund werden inverse Symmetriebrechung, weitere sterile Neutrinos, zusätzliche, durch free-streaming&#039;&#039; charakterisierte Teilchen oder Neutrinozerfall als mögliche Erweiterungen des Secret Interaction Modells vorgeschlagen

Decaying Sterile Neutrinos and the Short Baseline Oscillation Anomalies

The MiniBooNE experiment has observed a significant excess of electron neutrinos in a muon neutrino beam, in conflict with standard neutrino oscillations. We discuss the possibility that this excess is explained by a sterile neutrino with a mass ∼1  keV that decays quickly back into active neutrinos plus a new light boson. This scenario satisfies terrestrial and cosmological constraints because it has neutrino self-interactions built-in. Accommodating also the LSND, reactor, and gallium anomalies is possible, but requires an extension of the model to avoid cosmological limits.The MiniBooNE experiment has observed a significant excess of electron neutrinos in a muon neutrino beam at source-detector distances too short to be compatible with standard neutrino oscillations. The most straightforward explanation for this signal in terms of oscillations between Standard Model neutrinos and a new, sterile, neutrino, is disfavored by null results from experiments looking for muon neutrino disappearance. Here, we discuss the possibility that MiniBooNE data are instead explained by a sterile neutrino that decays quickly back into active neutrinos plus a light boson. The flavor composition of the secondary neutrinos is determined by the sterile neutrino mixing angles, and we show that the data is best explained if the sterile neutrino mixes mostly with electron neutrinos. The preferred range for the mass of the sterile neutrino is between 100 eV and 1 keV. We argue that the model can easily satisfy cosmological constraints because it has the "secret interactions" mechanism built-in. Accommodating in addition to the MiniBooNE anomaly also the LSND, reactor, and gallium anomalies is possible, but in this case the model needs to be extended to avoid cosmological limits

Sterile Neutrinos with Secret Interactions -- Cosmological Discord?

Several long-standing anomalies from short-baseline neutrino oscillation experiments—most recently corroborated by new data from MiniBooNE—have led to the hypothesis that extra, "sterile", neutrino species might exist. Models of this type face severe cosmological constraints, and several ideas have been proposed to avoid these constraints. Among the most widely discussed ones are models with so-called "secret interactions" in the neutrino sector. In these models, sterile neutrinos are hypothesized to couple to a new interaction, which dynamically suppresses their production in the early Universe through finite-temperature effects. Recently, it has been argued that the original calculations demonstrating the viability of this scenario need to be refined. Here, we update our earlier results from \arXivid{1310.6337} [JCAP 10 (2015) 011] accordingly. We confirm that much of the previously open parameter space for secret interactions is in fact ruled out by cosmological constraints on the sum of neutrino masses and on free-streaming of active neutrinos. We then discuss possible modifications of the vanilla scenario that would reconcile sterile neutrinos with cosmology.Several long-standing anomalies from short-baseline neutrino oscillation experiments -- most recently corroborated by new data from MiniBooNE -- have led to the hypothesis that extra, 'sterile', neutrino species might exist. Models of this type face severe cosmological constraints, and several ideas have been proposed to avoid these constraints. Among the most widely discussed ones are models with so-called 'secret interactions' in the neutrino sector. In these models, sterile neutrinos are hypothesized to couple to a new interaction, which dynamically suppresses their production in the early Universe through finite-temperature effects. Recently, it has been argued that the original calculations demonstrating the viability of this scenario need to be refined. Here, we update our earlier results from arXiv:1310.6337 [JCAP 1510 (2015) no.10, 011] accordingly. We confirm that much of the previously open parameter space for secret interactions is in fact ruled out by cosmological constraints on the sum of neutrino masses and on free-streaming of active neutrinos. We then discuss possible modifications of the vanilla scenario that would reconcile sterile neutrinos with cosmology

Fuzzy dark matter and the Dark Energy Survey Year 1 data

Gravitational weak lensing by dark matter halos leads to a measurable imprint in the shear correlation function of galaxies. Fuzzy dark matter (FDM), composed of ultralight axion-like particles of mass $m\sim 10^{-22}\text{ eV}$, suppresses the matter power spectrum and shear correlation with respect to standard cold dark matter. We model the effect of FDM on cosmic shear using the optimised halo model \textsc{HMCode}, accounting for additional suppression of the mass function and halo concentration in FDM as observed in $N$-body simulations. We combine Dark Energy Survey year 1 (DES-Y1) data with the \emph{Planck} cosmic microwave background anisotropies to search for shear correlation suppression caused by FDM. We find no evidence of suppression compared to the preferred cold DM model, and thus set a new lower limit to the FDM particle mass. Using a log-flat prior and marginalising over uncertainties related to the non-linear model of FDM, we find a new, independent 95\% C.L. lower limit $\log_{10}m>-23$ combining \emph{Planck} and DES-Y1 shear, an improvement of almost two orders of magnitude on the mass bound relative to CMB-only constraints. Our analysis is largely independent of baryonic modelling, and of previous limits to FDM covering this mass range. Our analysis highlights the most important aspects of the FDM non-linear model for future investigation. The limit to FDM from weak lensing could be improved by up to three orders of magnitude with $\mathcal{O}(0.1)$ arcmin cosmic shear angular resolution, if FDM and baryonic feedback can be simultaneously modelled to high precision in the halo model.Comment: 25 pages,16 figures, updated discussion of redshift evolution, massive neutrinos, version accepted for publication in MNRAS, v3: minor correction

Updated global analysis of neutrino oscillations in the presence of eV-scale sterile neutrinos

We discuss the possibility to explain the anomalies in short-baseline neutrino oscillation experiments in terms of sterile neutrinos. We work in a 3 + 1 framework and pay special attention to recent new data from reactor experiments, IceCube and MINOS+. We find that results from the DANSS and NEOS reactor experiments support the sterile neutrino explanation of the reactor anomaly, based on an analysis that relies solely on the relative comparison of measured reactor spectra. Global data from the ν$_{e}$ disappearance channel favour sterile neutrino oscillations at the 3σ level with Δm$_{41}^{2}$  ≈ 1.3 eV$^{2}$ and |U$_{e4}$| ≈ 0.1, even without any assumptions on predicted reactor fluxes. In contrast, the anomalies in the ν$_{e}$ appearance channel (dominated by LSND) are in strong tension with improved bounds on ν$_{μ}$ disappearance, mostly driven by MINOS+ and IceCube. Under the sterile neutrino oscillation hypothesis, the p-value for those data sets being consistent is less than 2.6 × 10$^{−6}$. Therefore, an explanation of the LSND anomaly in terms of sterile neutrino oscillations in the 3 + 1 scenario is excluded at the 4.7σ level. This result is robust with respect to variations in the analysis and used data, in particular it depends neither on the theoretically predicted reactor neutrino fluxes, nor on constraints from any single experiment. Irrespective of the anomalies, we provide updated constraints on the allowed mixing strengths |U$_{α4}$| (α = e, μ, τ ) of active neutrinos with a fourth neutrino mass state in the eV range.We discuss the possibility to explain the anomalies in short-baseline neutrino oscillation experiments in terms of sterile neutrinos. We work in a 3+1 framework and pay special attention to recent new data from reactor experiments, IceCube and MINOS+. We find that results from the DANSS and NEOS reactor experiments support the sterile neutrino explanation of the reactor anomaly, based on an analysis that relies solely on the relative comparison of measured reactor spectra. Global data from the $\nu_e$ disappearance channel favour sterile neutrino oscillations at the $3\sigma$ level with $\Delta m^2_{41} \approx 1.3$ eV$^2$ and $|U_{e4}| \approx 0.1$, even without any assumptions on predicted reactor fluxes. In contrast, the anomalies in the $\nu_e$ appearance channel (dominated by LSND) are in strong tension with improved bounds on $\nu_\mu$ disappearance, mostly driven by MINOS+ and IceCube. Under the sterile neutrino oscillation hypothesis, the p-value for those data sets being consistent is less than $2.6\times 10^{-6}$. Therefore, an explanation of the LSND anomaly in terms of sterile neutrino oscillations in the 3+1 scenario is excluded at the $4.7\sigma$ level. This result is robust with respect to variations in the analysis and used data, in particular it depends neither on the theoretically predicted reactor neutrino fluxes, nor on constraints from any single experiment. Irrespective of the anomalies, we provide updated constraints on the allowed mixing strengths $|U_{\alpha 4}|$ ($\alpha = e,\mu,\tau$) of active neutrinos with a fourth neutrino mass state in the eV range