Detection Of Relic Neutrinos Research Articles

Helicity-changing decays of cosmological relic neutrinos

In this paper, we examine the possibility that massive neutrinos are unstable due to their invisible decays ν i → ν j + ϕ, where ν i and ν j (for i, j = 1, 2, 3) are any two of neutrino mass eigenstates with masses m i > m i and ϕ is a massless Nambu-Goldstone boson, and explore the implications for the detection of cosmological relic neutrinos in the present Universe. First, we carry out a complete calculation of neutrino decay rates in the general case where the individual helicities of parent and daughter neutrinos are specified. Then, the invisible decays of cosmological relic neutrinos are studied and their impact on the capture rates on the beta-decaying nuclei (e.g., ν e + 3H → 3He + e -) is analyzed. The invisible decays of massive neutrinos could substantially change the capture rates in the PTOLEMY-like experiments when compared to the case of stable neutrinos. In particular, we find that the helicity-changing decays of Dirac neutrinos play an important role whereas those of Majorana neutrinos have no practical effects. However, if a substantial fraction of heavier neutrinos decay into the lightest one, the detection of relic neutrinos will require a much higher energy resolution and thus be even more challenging.

Limits on the cosmic neutrino background

We present the first comprehensive discussion of constraints on the cosmic neutrino background (CνB) overdensity, including theoretical, experimental and cosmological limits for a wide range of neutrino masses and temperatures. Additionally, we calculate the sensitivities of future direct and indirect relic neutrino detection experiments and compare the results with the existing constraints, extending several previous analyses by taking into account that the CνB reference frame may not be aligned with that of the Earth. The Pauli exclusion principle strongly disfavours overdensities ην ≫ 1 at small neutrino masses, but allows for overdensities ην ≲ 125 at the KATRIN mass bound mν ≃ 0.8 eV. On the other hand, cosmology strongly favours 0.2 ≲ ην ≲ 3.5 in all scenarios. We find that direct detection proposals are capable of observing the CνB without a significant overdensity for neutrino masses mν ≳ 50 meV, but require an overdensity ην ≳ 3 × 105 outside of this range. We also demonstrate that relic neutrino detection proposals are sensitive to the helicity composition of the CνB, whilst some may be able to distinguish between Dirac and Majorana neutrinos.

Navigating the pitfalls of relic neutrino detection

Beta-spectrum of radioactive atoms was long ago predicted to bear an imprint of the cosmic neutrino background ($\mathrm{C}\ensuremath{\nu}\mathrm{B}$) [S. Weinberg, Phys. Rev. 128, 1457 (1962)]. Over the years, it has been recognized that the best chance of achieving the signal-to-noise ratio required for the observation of this effect lies with solid-state designs [E. Baracchini et al., arXiv:1808.01892.]. Here we bring to the fore a fundamental quantum limitation on the type of beta-decayer that can be used in a such a design. We derive a simple usability criterion and show that $^{3}\mathrm{H}$, which is the most popular choice, fails to meet it. We provide a list of potentially suitable isotopes and discuss why their use in $\mathrm{C}\ensuremath{\nu}\mathrm{B}$ detection requires further research.

Dark radiation from inflationary fluctuations

Light new vector bosons can be produced gravitationally through quantum fluctuations during inflation; if these particles are feebly coupled and cosmologically metastable, they can account for the observed dark matter abundance. However, in minimal anomaly-free $U(1)$ extensions to the Standard Model, these vectors generically decay to neutrinos if at least one neutrino mass eigenstate is sufficiently light. If these decays occur between neutrino decoupling and cosmic microwave background (CMB) freeze-out, the resulting radiation energy density can contribute to $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}$ at levels that can ameliorate the Hubble tension and be discovered with future CMB and relic neutrino detection experiments. Since the additional neutrinos are produced from vector decays after Big Bang Nucleosynthesis (BBN), this scenario predicts $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}>0$ at recombination, but $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}=0$ during BBN. Furthermore, due to a fortuitous cancellation, the contribution to $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}$ is approximately mass independent.

Relic neutrino clustering in the Milky Way

The Standard Cosmological Model predicts the existence of relic neutrinos, which are indirectly probed through the effective number of relativistic species in the early Universe. In addition, from neutrino flavour oscillations we know that at least two of the neutrino mass states have a non-zero mass. Since the expansion of the Universe has diluted the energy of relic neutrinos, those that are massive are also non relativistic today. This means that they can be trapped in strong gravitational potentials, such as the one of the Milky Way. We review the calculation of the local overdensity of relic neutrinos produced from the gravitational attraction of our Galaxy, Andromeda and the Virgo cluster, commenting on the implications for an experiment aiming at relic neutrino detection, such as the PTOLEMY project.

Relic neutrino detection through angular correlations in inverse β-decay

Neutrino capture on beta-decaying nuclei is currently the only known potentially viable method of detection of cosmic background neutrinos. It is based on the idea of separation of the spectra of electrons or positrons produced in captures of relic neutrinos on unstable nuclei from those from the usual β-decay and requires very high energy resolution of the detector, comparable to the neutrino mass. In this paper we suggest an alternative method of discrimination between neutrino capture and β-decay, based on periodic variations of angular correlations in inverse beta decay transitions induced by relic neutrino capture. The time variations are expected to arise due to the peculiar motion of the Sun with respect to the CνB rest frame and the rotation of the Earth about its axis and can be observed in experiments with both polarized and unpolarized nuclear targets. The main advantage of the suggested method is that it does not depend crucially on the energy resolution of detection of the produced β-particles and can be operative even if this resolution exceeds the largest neutrino mass.

Neutrino Mass Ordering from Oscillations and Beyond: 2018 Status and Future Prospects

The ordering of the neutrino masses is a crucial input for a deep understanding of flavor physics, and its determination may provide the key to establish the relationship among the lepton masses and mixings and their analogous properties in the quark sector. The extraction of the neutrino mass ordering is a data-driven field expected to evolve very rapidly in the next decade. In this review, we both analyze the present status and describe the physics of subsequent prospects. Firstly, the different current available tools to measure the neutrino mass ordering are described. Namely, reactor, long-baseline (accelerator and atmospheric) neutrino beams, laboratory searches for beta and neutrinoless double beta decays and observations of the cosmic background radiation and the large scale structure of the universe are carefully reviewed. Secondly, the results from an up-to-date comprehensive global fit are reported: the Bayesian analysis to the 2018 publicly available oscillation and cosmological data sets provides \emph{strong} evidence for the normal neutrino mass ordering versus the inverted scenario, with a significance of 3.5 standard deviations. This preference for the normal neutrino mass ordering is mostly due to neutrino oscillation measurements. Finally, we shall also emphasize the future perspectives for unveiling the neutrino mass ordering. In this regard, apart from describing the expectations from the aforementioned probes, we also focus on those arising from alternative and novel methods, as 21~cm cosmology, core-collapse supernova neutrinos and the direct detection of relic neutrinos.

Galactic abundances as a relic neutrino detection scheme

We propose to use the threshold-free process of neutrino capture on β-decaying nuclei (NCB) with all available candidate nuclei in the Milky Way as target material in order to detect the presence of the Cosmic Neutrino Background (CνB). By integrating over the lifetime of the galaxy one might be able to see the effect of NCB processes as a slightly eschewed abundance ratio of selected β-decaying nuclei. First, the candidates must be chosen so that both the mother and daughter nuclei have a lifetime comparable to that of the Milky Way or the signal could be easily washed out by additional decays. Secondly, relic neutrinos have so low energy that their de Broglie wavelengths are macroscopic and they may therefore scatter coherently on the electronic cloud of the candidate atoms. One must therefore compare the cross sections for the two processes (induced β-decay by neutrino capture, and coherent scattering of the neutrinos on atomic nuclei) before drawing any conclusions. Finally, the density of target nuclei in the galaxy must be calculated. We assume supernovae as the only production source and approximate the neutrino density as a homogenous background. Here we perform the full calculation for 187Re and 138La and find that one needs abundance measurements with 24 digit precision in order to detect the effect of relic neutrinos. Or alternatively an enhancement of ρν by a factor of ∼ 1015 to produce an effect within the current abundance measurement precision.

Towards the detection of light and heavy relic neutrinos

The standard Big Bang cosmology predicts that the universe is abundantly populated with neutrinos. As expected there are at least 114 neutrinos per cubic centimeter averaged over the whole space. Like the cosmic background radiation the cosmic neutrinos at present posses a very small kinetic energy due to expansion of the universe. This prediction is one of the cornerstones of modern cosmology. On the other hand the existence of cosmic neutrinos has not yet been confirmed by direct detection experiments. For now we only have a lower limit on the total mass of this free floating ghostly gas of neutrinos, but even so it is roughly equivalent to the total mass of all the visible stars in universe. There could be many more neutrinos at Earth because of condensation of neutrinos, now moving slowly under the gravitational pull of our galaxy. Here we discuss the possibility of detection of relic neutrinos in KATRIN and MARE experiments via neutrino capture on tritium and rhenium, respectively. We also examine single and double relic neutrino capture on double β -decaying nuclei which might be relevant in the context of the new generation double beta decay experiments. Further we explore feasibility of experiments for detection of heavy sterile neutrinos with masses in MeV region, which may have important astrophysical and cosmological implications.

Status of Experiments for Direct Detection of Galactic Dark Matter Particles

There is increasing evidence that the majority of dark matter is non-baryonic. Principal candidates are weakly interacting massive particles (WIMPS), axions, and neutrinos. There has been increasing effort on sensitive WIMP searches, motivated in particular by supersymmetry theory, which predicts a stable neutral particle in the mass range 10-1000 GeV. Interactions of these with normal matter would produce low energy nuclear recoils which could be observed by underground detectors capable of discriminating these from background. Current experimental progress is summarised, together with plans for more sensitive experiments. These include gaseous detectors with directional sensitivity, offering the prospect of a ‘dark matter telescope’ which would provide information on the dark matter velocity distribution. Axions could be detected by conversion to microwave photons, and experimental sensitivity is approaching the theoretically-required levels. Relic neutrinos could also form a component of the dark matter if any has a cosmologically significant mass, and the latter could be checked with a new detector able to detect the higher neutrino flavours from a Galactic supernova burst. More distant future possibilities are outlined for direct detection of relic neutrinos by coherent scattering.

New possible detection schemes for relic Galactic neutrinos

We discuss the feasibility of the detection of relic neutrinos that may be present in the Galactic halo. We analyse their effect on macroscopic targets, comparing the detection proposals made so far and presenting new experimental schemes. In all cases the acceleration of the test masses is bounded by the value of the refractive index of neutrinos N as follows: , where for all materials and x = 0.5 in the best case. 1315, 9880, 0480

Dark matter detectors

A fundamental question of astrophysics and cosmology is the nature of dark matter. Astrophysical observations show clearly the existence of some kind of dark matter, though they cannot yet reveal its nature. Dark matter can consist of baryonic particles, or of other (known or unknown) elementary particles. Baryonic dark matter probably exists in the form of dust, gas, or small stars. Other elementary particles constituting the dark matter can possibly be measured in terrestrial experiments. Possibilities for dark matter particles are neutrinos, axions, and weakly interacting massive particles (WIMPs). While a direct detection of relic neutrinos seems at the moment impossible, there are experiments looking for baryonic dark matter in the form of Massive Compact Halo Objects, and for particle dark matter in the form of axions and WIMPS.

Dark Matter Detectors

A fundamental question of astrophysics and cosmology is the nature of dark matter. Astrophysical observations show clearly the existence of some kind of dark matter, though they cannot yet reveal its nature. Dark matter can consist of baryonic particles, or of other (known or unknown) elementary particles. Baryonic dark matter probably exists in the form of dust, gas, or small stars. Other elementary particles constituting the dark matter can possibly be measured in terrestrial experiments. Possibilities for dark matter particles are neutrinos, axions, and weakly interacting massive particles (WIMPs). While a direct detection of relic neutrinos seems at the moment impossible, there are experiments looking for baryonic dark matter in the form of Massive Compact Halo Objects, and for particle dark matter in the form of axions and WIMPS.

Big bang cosmology, relic neutrinos, and absorption of neutrino cosmic rays

view Abstract Citations (87) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Big bang cosmology, relic neutrinos, and absorption of neutrino cosmic rays Weiler, T. Abstract The proposal to search for relic neutrinos through their absorption effect on the neutrino cosmic-ray flux is carefully examined. Resonant absorption at E(v) of about 10 to the 21st eV-squared/m(1+z), where m is the neutrino mass and z is the cosmological redshift of the neutrino source, has been previously predicted. However, it is shown that detection of the neutrino flux in the absorption region requires an improbable power output for a single source. A summation over a distribution of sources is then performed, using the quasar distribution as a model. This summation increases the neutrino flux but spreads the absorption dip. It is concluded that within the context of big bang cosmology, detection of relic neutrinos through their absorption effects depends crucially on whether or not there exist sources at large z, emitting a sufficient flux of ultraenergy neutrinos. The astrophysical conditions which allow detection appear very unlikely but not impossible. Publication: The Astrophysical Journal Pub Date: October 1984 DOI: 10.1086/162524 Bibcode: 1984ApJ...285..495W Keywords: Big Bang Cosmology; Cosmic Rays; Elementary Particle Interactions; Neutrinos; Radiation Absorption; Relic Radiation; Energy Spectra; Particle Flux Density; Quasars; Astrophysics full text sources ADS |