Neutrino Background Research Articles

High-energy Neutrino Production from AGN Disk Transients Impacted by the Circum-disk Medium

Various supernovae, compact object coalescences, and tidal disruption events are widely believed to occur embedded in active galactic nucleus (AGN) accretion disks and generate detectable electromagnetic signals. We collectively refer to them as AGN disk transients. The inelastic hadronuclear (pp) interactions between shock-accelerated cosmic rays and AGN disk materials shortly after the ejecta shock breaks out of the disk can produce high-energy neutrinos. However, the expected efficiency of neutrino production would decay rapidly by adopting a pure Gaussian density atmosphere profile applicable for stable gas-dominated disks. On the other hand, AGN outflows and disk winds are commonly found around AGN accretion disks. In this paper, we show that the circum-disk medium would further consume the shock kinetic energy to more efficiently produce high-energy neutrinos, especially for ∼ TeV−PeV neutrinos that IceCube detects. Thanks to the existence of the circum-disk medium, we find that the neutrino production will be enhanced significantly and make a much higher contribution to the diffuse neutrino background. Optimistically, ∼20% of the diffuse neutrino background can be contributed by AGN disk transients.

Implications on cosmology from Dirac neutrino magnetic moments

The mechanism for generating neutrino masses remains a puzzle in particle physics. If neutrino masses follow from a Dirac mass term, then neutrino states exist with opposite chirality compared to their weakly-interacting counterparts. These inactive states do not interact with their active counterparts at measurable scales in the standard model. However, the existence of these states can have implications for cosmology as they contribute to the radiation energy density at early times, and the matter energy density at late times. How Dirac neutrinos may populate thermal states via an anomalous magnetic moment operator is the focus of this work. A class of models where all neutrinos have a magnetic moment independent of flavor or chirality is considered. Subsequently, the cross sections for neutrinos scattering on background plasma particles are calculated so that the relic inactive neutrino energy is derived as a function of plasma temperature. To do so, one needs cross sections for scattering on all electrically charged standard-model particles. Therefore, the scattering cross section between a neutrino and $W$-boson via the magnetic moment vertex is derived. Current measurements put a constraint on the size of the neutrino magnetic moment from the cosmological parameter $N_{\rm eff}$ and light-element primordial abundances. Finally, how the extra Dirac states contribute to the matter energy density at late times is investigated by examining neutrino free-streaming.

Cross-correlation power spectra and cosmic birefringence of the CMB via photon-neutrino interaction

In the context of the standard model of particles, the weak interaction of cosmic microwave background (CMB) and cosmic neutrino background (CνB), can generate non-vanishing TB and EB power spectra in the order of one loop forward scattering, in the presence of scalar perturbation, which is in contrast with the standard scenario cosmology. Comparing our results with the current experimental data may provide, significant information about the nature of CνB, including CMB-CνB forward scattering for TB, TE, and EB power spectra. To this end, different cases were studied, including Majorana CνB and Dirac CνB. On the other hand, it was shown that the mean opacity due to cosmic neutrino background could behave as an anisotropic birefringent medium and change the linear polarization rotation angle. Considering the contributions from neutrino and anti-neutrino forward scattering with CMB photons (in the case of Dirac neutrino), we introduce relative neutrino and anti-neutrino density asymmetry (δν = Δnν /nν = nν -nν̅ /nν ). Then, using the cosmic birefringence angle reported by the Planck data release β = 0.30° ± 0.11° (68%C.L.), some constraints can be put on δν . Also, the value of cosmic birefringence due to Majorana CνB medium is estimated at about β| ν ≃ 0.2 rad. In this respect, since Majorana neutrino and anti-neutrino are exactly the same, both CB contributions will be added together. However, this value is at least two orders larger than the cosmic birefringence angle reported by the Planck data release, β = 0.30° ± 0.11° (68%C.L.). Finally, we shortly discussed this big inconsistency. It is noteworthy that to calculate the contribution of photon-neutrino forward scattering for cosmic birefringence, we just consider the standard model of particles and the standard scenario of cosmology.

Cosmic Supernova Neutrino and Gamma-Ray Backgrounds in the MeV Regime

Cosmic multimessenger backgrounds include relic diffuse components created in the early universe and contributions from individual sources. Here, we study both type Ia supernovae (SNe Ia) and core-collapse supernovae (CCSNe) contributions to the diffuse neutrino and gamma-ray backgrounds in the MeV regime referred to as DSNB and DSGB respectively. We show that the diffuse SN Ia background is 106 times lower (for ) than the CCSN background making it negligible. Our predicted DSNB flux at earth in the 19.3–32 MeV regime is 0.36 ν cm−2 s−1. We also find that the DSNB flux in the energy range from 11.3 to 32 MeV varies by +29% with a change in the SFRD model from Madau & Fragos which yielded a minimum predicted flux, to the extragalactic background light reconstruction model (maximum predicted flux). The diffuse SN Ia gamma-ray background and its dependence on the progenitor supernova delay time distribution are also evaluated. Furthermore, we address the origin of the CGB (Cosmic Gamma-ray Background) in the 0.1–7 MeV regime by adding contributions from sources such as SNe Ia, CCSNe, radio-quiet Active Galactic Nuclei, Flat spectrum radio quasars (FSRQs) and Neutron star—neutron star mergers. We find that our modeled background (including uncertainties) matches the observed CGB above 1.0 MeV, but is a factor ≈2 lower than the observed flux in the 0.1–1.0 MeV range, highlighting the need for future MeV missions to establish the CGB spectrum more reliably, and to possibly identify additional sources or even source classes in the underexplored MeV band.

Probing sterile neutrino dark matter in the PTOLEMY-like experiment

We study the prospect to detect the cosmic background of sterile neutrinos in the tritium β-decay, such as the PTOLEMY-like experiments. The sterile neutrino with mass between 1 eV–10 keV may contribute to the local density as warm or cold dark matter component. In this study, we investigate the possibility for searching them in the models with different production in the early Universe, without assuming sterile neutrino as full dark matter component.In these models, especially with low-reheating temperature and late-time phase transition, the capture rate per year can be greatly enhanced to be \U0001d4aa(10) around the mass range 10–100 eV without violating other astrophysical and cosmological observations.

Roles of Fast Neutrino-Flavor Conversion on the Neutrino-Heating Mechanism of Core-Collapse Supernova.

One of the greatest uncertainties in any modeling of the inner engine of core-collapse supernova (CCSN) is neutrino-flavor conversions driven by neutrino self-interactions. We carry out large-scale numerical simulations of a multienergy, multiangle, three-flavor framework and general relativistic quantum kinetic neutrino transport in spherical symmetry with an essential set of neutrino-matter interactions under a realistic fluid profile of CCSN. Our result suggests that the neutrino heating in the gain region is reduced by ∼40% due to fast neutrino-flavor conversion (FFC). We also find that the total luminosity of neutrinos is enhanced by ∼30%, for which the substantial increase of heavy-leptonic neutrinos by FFCs are mainly responsible. This study provides evidence that FFC has a significant impact on the delayed neutrino-heating mechanism.

Light curves of BSM-induced neutrino echoes in the optically thin limit

High-energy neutrinos from astrophysical transients serve as a probe of neutrino physics beyond the Standard Model. In particular, nonstandard interaction of neutrinos with the cosmic neutrino background or dark matter (DM) may have imprints on not only their spectra but also the arrival and time-delay distributions. Assuming that the interaction occurs at most once during the neutrino propagation, we provide general analytic formulas for light curves of the neutrino echoes induced by BSM. The formulas can be used for constraining neutrino-neutrino scattering, neutrino-DM scattering, and other scattering processes experienced by relativistic particles.

Neutrino decoherence from generalised uncertainty

Quantum gravity models predict a minimal measurable length which gives rise to a modification in the uncertainty principle. One of the simplest manifestations of these generalised uncertainty principles is the linear quadratic generalised uncertainty principle which leads to a modified Heisenberg algebra. This can alter the usual von-Neumann evolution of density matrix to a Lindblad-type equation. We show how this can give rise to a decoherence in neutrino propagation in vacuum. The decoherence effects due to the linear quadratic generalised uncertainty principle are extremely minimal and is unlikely to be detectable in the existing or upcoming experimental facilities for any of the natural sources of neutrinos. We also show that, in principle, there can be other variants of generalised uncertainty principle which predicts verifiable decoherence effects for the cosmic neutrino background.

Directional neutrino searches for Galactic Center dark matter at large underground LArTPCs

We investigate the sensitivity of a large, underground LArTPC-based neutrino detector to dark matter in the Galactic Center annihilating into neutrinos. Such a detector could have the ability to resolve the direction of the electron in a neutrino scattering event, and thus to infer information about the source direction for individual neutrino events. We consider the improvements on the expected experimental sensitivity that this directional information would provide. Even without directional information, we find a DUNE-like LArTPC detector is capable of setting limits on dark matter annihilation to neutrinos for dark matter masses above 30 MeV that are competitive with or exceed current experimental reach. While currently-demonstrated angular resolution for low-energy electrons is insufficient to allow any significant increase in sensitivity, these techniques could benefit from improvements to algorithms and the additional spatial information provided by novel 3D charge imaging approaches. We consider the impact of such enhancements to the resolution for electron directionality, and find that where electron-scattering events can be distinguished from charged-current neutrino interactions, limits on dark matter annihilation in the mass range where solar neutrino backgrounds dominate ($\lesssim 15$ MeV) can be significantly improved using directional information, and would be competitive with existing limits using $40$ kton$\times$year of exposure.

The neutrino floor: a data-driven analysis

We reconsider the discovery limit of multi-ton direct detection dark matter experiments in the light of recent measurements of the coherent elastic neutrino-nucleus scattering process. Assuming the cross section to be a parameter entirely determined by data, rather than using its Standard Model prediction, we use the COHERENT CsI and LAr data sets to determine WIMP discovery limits. Being based on a data-driven approach, the results are thus free from theoretical assumptions and fall within the WIMP mass regions where XENONnT and DARWIN have best expected sensitivities. We further determine the impact of subleading nuclear form factor and weak mixing angle uncertainties effects on WIMP discovery limits. We point out that these effects, albeit small, should be taken into account. Moreover, to quantify the impact of new physics effects in the neutrino background, we revisit WIMP discovery limits assuming light vector and scalar mediators as well as neutrino magnetic moments/transitions. We stress that the presence of new interactions in the neutrino sector, in general, tend to worsen the WIMP discovery limit.

Core-collapse supernovae and neutrino properties

We highlight developments in the domain of supernova neutrinos. We discuss the importance of the future observation, by running and upcoming experiments, of the neutrino signals from the next supernova as well as of the diffuse supernova neutrino background.

The Catalytic Role of Electrons and Positrons in the Synthesis of Chemicals and of Hadrons

We discuss the similarities and differences between catalysis/electrocatalysis of chemical processes, such as ammonia synthesis or H2O electrolysis on one hand, and of nuclear catalytic processes, commonly called baryosynthesis, such as the synthesis of neutrons and protons from quarks, on the other. In chemical synthesis the underlying forces are well known to be electrostatic in nature while in the synthesis of hadrons or nuclei from quarks (known as hadronization or nucleosynthesis) the underlying forces are known as the Strong nuclear forces, whereas if electrons are also involved, as Weak nuclear forces. Here we discuss for the first time from a catalytic viewpoint the importance of some recent developments in our understanding of the structure and synthesis of hadrons via a model entitled Rotating Lepton Model (RLM), which is quite similar to the Bohr model of the H atom used in Chemistry but which has shown that the Strong Force is a gravitational force between three very fast (relativistic) neutrinos, rotating symmetrically on a circular orbit, whose gravitational masses and gravitational attraction increases dramatically with increasing rotational speed, according to the theory of Special Relativity (SR), thus reaching the masses of quarks and the value of the Strong Force respectively. We show that, interestingly, positrons and electrons, which quite often play a very important and well established catalytic role in chemical synthesis due to their electrical charge, also play an equally important and central catalytic role in nuclear synthesis due to their enormous mass, relative to the mass of the neutrinos, and the concomitant dramatic acceleration of neutrinos to ultrarelativistic speeds and huge mass increase, resulting to enhanced very strong gravitational binding between them which reaches the value of the Strong Force. Consequently, electrons and positrons are the dual, electrostatic and gravitational, catalysts of our Universe for the production of chemicals and baryons.

Plutonium-241 as a possible isotope for neutrino mass measurement and capture

Tritium has been the isotope of choice for measurements of the absolute neutrino mass and planned detection of the relic neutrino background. The low mass of 3H leads to large recoil energy of the nucleus. This has emerged as a limiting factor in both measurements. We investigate 241Pu as an alternative. The recoil is 80 times smaller and it has similar decay energy and a lifetime to 3H. We evaluate for the first time its soft-neutrino capture cross-section and find (σ v) ν = 1.52 × 10−45 cm2. This is 40% of the capture cross-section for tritium, making 241Pu an interesting alternative for 3H.

On neutrino-mediated potentials in a neutrino background

The exchange of a pair of neutrinos with Standard Model weak interactions generates a long-range force between fermions. The associated potential is extremely feeble, ∝ {G}_F^2/{r}^5 for massless neutrinos, which renders it far from observable even in the most sensitive experiments testing fifth forces. The presence of a neutrino background has been argued to induce a correction to the neutrino propagator that enhances the potential by orders of magnitude. In this brief note, we point out that such modified propagators are invalid if the background neutrino wavepackets have a finite width. By reevaluating the 2-ν exchange potential in the presence of a neutrino background including finite width effects, we find that the background-induced enhancement is reduced by several orders of magnitude. Unfortunately, this pushes the resulting 2-ν exchange potential away from present and near-future sensitivity of tests of new long-range forces.

Microscopic calculation of the β− decays of 151Sm, 171Tm, and 210Pb with implications to detection of the cosmic neutrino background

The electron spectral shapes corresponding to the low-Qβ−-decay transitions Sm151(5/2g.s.−)→Eu151(5/2g.s.+), Sm151(5/2g.s.−)→Eu151(7/21+), Tm171(1/2g.s.+)→Yb171(1/2g.s.−), Tm171(1/2g.s.+)→Yb171(3/21−), Pb210(0g.s.+)→Bi210(1g.s.−), and Pb210(0g.s.+)→Bi210(01−) have been computed using beta-decay theory with several refinements for these first-forbidden nonunique (ff-nu) β− transitions. These ff-nu β− transitions have non-trivial electron spectral shapes with transition nuclear matrix elements (NMEs) computed by using the microscopic Interacting Boson-Fermion Model (IBFM-2) for the decays of 151Sm and 171Tm, and the nuclear shell model (NSM) for the decay of 210Pb. Within the respective Q windows, the computed ff-nu electron spectral shapes deviate maximally at sub-percent level from the universal allowed shape, except for the transition Pb210(0g.s.+)→Bi210(1g.s.−), where the maximal deviation is some 2.7%. This confirms that the so-called ξ approximation is fairly good for most of these low-Qβ− transitions and thus the allowed shape is a rather good first approximation. Our computed spectral shapes could be of interest for experiments aiming to measure the cosmic neutrino background (CνB), like the PTOLEMY experiment. We have also derived CνB cross sections for the ground-state transitions of the considered nuclei at the β endpoint. Our findings indicate that more work on the atomic mismatch correction is needed in the future in order to extract reliable and precise CνB cross sections for any nuclear target.

Stellar Initial Mass Function (IMF) Probed with Supernova Rates and Neutrino Background: Cosmic-average IMF Slope Is ≃2–3 Similar to the Salpeter IMF

The stellar initial mass function (IMF) is expressed by ϕ(m) ∝ m − α with the slope α, and known as a poorly constrained but very important function in studies of star and galaxy formation. There are no sensible observational constraints on the IMF slopes beyond the Milky Way and nearby galaxies. Here we combine two sets of observational results, (1) cosmic densities of core-collapse supernova (CCSN) explosion rates and (2) cosmic far-UV radiation (and infrared reradiation) densities, which are sensitive to massive (≃8–50 M ⊙) and moderately massive (≃2.5–7 M ⊙) stars, respectively, and constrain the IMF slope at m > 1 M ⊙ with a freedom of redshift evolution. Although no redshift evolution is identified beyond the uncertainties, we find that the cosmic-average IMF slope at z = 0 is α = 1.8–3.2 at the 95% confidence level that is comparable with the Salpeter IMF, α = 2.35, which marks the first constraint on the cosmic-average IMF. We show a forecast for the Nancy Grace Roman Space Telescope supernova survey that will provide significantly strong constraints on the IMF slope with δ α ≃ 0.5 over z = 0–2. Moreover, as for an independent IMF probe instead of (1), we suggest to use diffuse supernovae neutrino background (DSNB), relic neutrinos from CCSNe. We expect that the Hyper-Kamiokande neutrino observations over 20 yr will improve the constraints on the IMF slope and the redshift evolution significantly better than those obtained today, if the systematic uncertainties of DSNB production physics are reduced in the future numerical simulations.

Effect of minimal length uncertainty on neutrino oscillation

Abstract In this paper, we study the effect of the minimal length on neutrino oscillation in a static magnetic field. In the framework of the generalized uncertainty principle, we reformulate the Hamiltonian for a relativistic neutrino moving in a magnetic field oriented along the z-direction of Cartesian coordinates. Using the modified energy spectrum, we obtain the oscillation probability for different neutrino flavors. In addition, we obtain the energy differences for the neutrino-mass eigenstates. We find that the energy and energy difference depend on the minimal length parameter α, and the energy difference becomes independent of α when the magnetic field is not present. In addition, we find that the modified probability of oscillation differs from the usual probability of oscillation if a magnetic field is present. Using the current experimental result, we estimate the upper bound on the deformation parameter and the minimal length, and find that the upper bound on the minimal length scale is less than the electroweak scale. If the minimal length is at Planck scale, the minimal length formalism leads to the same result as a quantum theory of gravity with an S U 2 L ⊗ U 1 $SU{\left(2\right)}_{L}\otimes U\left(1\right)$ effective invariant dimension-5 Lagrangian including neutrino and Higgs fields.

Field Mixing in Curved Spacetime and Dark Matter

An extensive review of recent results concerning the quantum field theory of particle mixing in curved spacetime is presented. The rich mathematical structure of the theory for both fermions and bosons, stemming from the interplay of curved space quantization and field mixing, is discussed, and its phenomenological implications are shown. Fermionic and bosonic oscillation formulae for arbitrary globally hyperbolic spacetimes are derived and the transition probabilities are explicitly computed on some metrics of cosmological and astrophysical interest. The formulae thus obtained are characterized by a pure QFT correction to the amplitudes, which is absent in quantum mechanics, where only the phase of the oscillations is affected by the gravitational background. Their deviation from the flat space probabilities is demonstrated, with the aid of numerical analyses. The condensate structure of the flavor vacuum of mixed fermions is studied, assessing its role as a possible dark matter component in a cosmological context. It is shown that the flavor vacuum behaves as a barotropic fluid, satisfying the equation of the state of cold dark matter. New experiments on the cosmic neutrino background, as PTOLEMY, may validate these theoretical results.

Neutrino capture on tritium as a probe of flavor vacuum condensate and dark matter

We show that the study of neutrino capture on tritium, for non-relativistic neutrinos, can allow to distinguish among the various neutrino models, eventually prove the quantum field theory condensation effects and permit to test the hypothesis according to which the flavor vacuum energy gives a contribution to the dark matter of the universe. Indeed, we show that the capture rate depends on the neutrino model considered, and that it brings an imprint of the flavor vacuum condensate. Experiments like PTOLEMY, designed to reveal the cosmic neutrino background, then can give an indication of the existence of the dark matter component induced by neutrino mixing.

Neutrino forces in neutrino backgrounds

The Standard Model predicts a long-range force, proportional to {G}_F^2/{r}^5 , between fermions due to the exchange of a pair of neutrinos. This quantum force is feeble and has not been observed yet. In this paper, we compute this force in the presence of neutrino backgrounds, both for isotropic and directional background neutrinos. We find that for the case of directional background the force can have a 1/r dependence and it can be significantly enhanced compared to the vacuum case. In particular, background effects caused by reactor, solar, and supernova neutrinos enhance the force by many orders of magnitude. The enhancement, however, occurs only in the direction parallel to the direction of the background neutrinos. We discuss the experimental prospects of detecting the neutrino force in neutrino backgrounds and find that the effect is close to the available sensitivity of the current fifth force experiments. Yet, the angular spread of the neutrino flux and that of the test masses reduce the strength of this force. The results are encouraging and a detailed experimental study is called for to check if the effect can be probed.