Neutrino Dark Matter Research Articles

Reviving keV sterile neutrino dark matter

We propose a new production mechanism for keV sterile neutrino dark matter which relies neither on the oscillations between sterile and active neutrinos nor on the decay of additional heavier particles. The dark matter neutrinos are instead produced by thermal freeze-out, much like a typical WIMP. The challenge consists in balancing a large Yukawa coupling so that the sterile neutrinos thermalize in the early universe on the one hand, and a small enough Yukawa coupling such that they are stable on cosmological scales on the other. We solve this problem by implementing varying Yukawa couplings. We achieve this by using a three-sterile neutrino seesaw extension to the SM and embedding it in a Froggatt-Nielsen model with a single flavon. Because the vev of the flavon changes during the electroweak phase transition, the effective Yukawa couplings of the fermions have different values before and after the phase transition, thus allowing for successful dark matter genesis. Additionally, the hierarchy in the flavour structure is alleviated and the origin of the light neutrino masses is explained by the interplay of the seesaw and Froggatt-Nielsen mechanisms.

Sensitivity of accelerator-based neutrino experiments to neutrino-dark matter interaction: Elko as a viable dark matter candidate

We analyze the potential of accelerator-based neutrino experiments, such as the Deep Underground Neutrino Experiment, to constrain a five-dimensional operator mediating a beyond standard model interaction between a mass-dimension-one fermion field, labeled elko, and neutrino. We identify the parameter space where elko is a viable dark matter candidate.

On Maxwell’s Reversed Laws as Root of Magnetic ‎Monopoles in Dark Matter

We propose the magnetic sterile neutrino as a possible candidate for dark matter. We bring the idea that dark matter would be ‎made up of substances originating from black holes, in particular sterile neutrinos associated with a magnetic charge. These ‎would not be sensitive only to the gravitational force. First, we conjectured that when baryonic matter crosses the black holes ‎event horizon, Maxwell's laws are reversed, the electric charge turns into a magnetic charge. Sterile magnetic neutrinos and ‎antineutrinos would be created and emitted, true magnetic monopoles. Second, we discuss dark matter consisting of sterile ‎magnetic neutrinos, the cosmic microwave background, mini primordial black holes, and the formation of intermediate mass ‎black holes linked to the formation of galaxies. Third, we review different mechanisms of how sterile magnetic neutrino could ‎have escaped from the black hole. Fourth, we investigate the possibility that ordinary neutrinos could be produced by the ‎weak interaction if sterile magnetic dark matter neutrinos interact with active ordinary matter neutrinos. Fifth, after examining ‎equations of possible production of gamma rays from the annihilation of neutrinos-antineutrinos, we propose the “anapole”, ‎which would be weakly sensitive to electromagnetic forces. Before concluding, we underline the relation between the ‎distribution of the magnetic fields coming from baryonic matter and that from dark matter, and we highlight the gamma ray ‎glows in the dark that can be attributed to the annihilation of dark matter with itself.‎

Freeze-In of radiative keV-scale neutrino dark matter from a new U(1)B-L

We extend the Dirac Scotogenic model with the aim of realizing neutrino masses together with the mass of a keV-scale dark matter (DM) candidate via the same one-loop topology. Two of the Standard Model (SM) neutrinos become massive Dirac fermions while the third one remains massless. Our particle content is motivated by an anomaly free U(1)B-L gauge symmetry with exotic irrational charges and we need to enforce an additional mathcal{Z} 5 symmetry. The dark matter candidate does not mix with the active neutrinos and does not have any decay modes to SM particles. DM is produced together with dark radiation in the form of right handed neutrinos via out of equilibrium annihilations of the SM fermions mediated by the heavy B-L gauge boson. In order to avoid DM over-production from Higgs decays and to comply with Lyman-α bounds we work in a low temperature reheating scenario with 4 MeV ≲ TRH ≲ 5 GeV. Our setup predicts a contribution to ∆Neff. that decreases for larger DM masses and is below the sensitivity of upcoming precision measurements such as CMB-S4. A future observation of a signal with ∆Neff. ≳ 0.012 would exclude our scenario. We further sketch how inflation, reheating and Affleck-Dine baryogenesis can also be potentially realized in this unified framework.

Astroparticle Constraints from Cosmic Reionization and Primordial Galaxy Formation

We derived astroparticle constraints in different dark matter scenarios that are alternatives to cold dark matter (CDM): thermal relic warm dark matter, WDM; fuzzy dark matter, ψDM; self-interacting dark matter, SIDM; sterile neutrino dark matter, νDM. Our framework is based on updated determinations of the high-redshift UV luminosity functions for primordial galaxies to redshift z∼10, on redshift-dependent halo mass functions in the above DM scenarios from numerical simulations, and on robust constraints on the reionization history of the Universe from recent astrophysical and cosmological datasets. First, we built an empirical model of cosmic reionization characterized by two parameters, namely the escape fraction fesc of ionizing photons from primordial galaxies, and the limiting UV magnitude MUVlim down to which the extrapolated UV luminosity functions steeply increased. Second, we performed standard abundance matching of the UV luminosity function and the halo mass function, obtaining a relationship between UV luminosity and the halo mass, whose shape depends on an astroparticle quantity X specific to each DM scenario (e.g., WDM particle mass); we exploited such a relationship to introduce (in the analysis) a constraint from primordial galaxy formation, in terms of the threshold halo mass above which primordial galaxies can efficiently form stars. Third, we performed Bayesian inference on the three parameters fesc, MUVlim, and X via a standard MCMC technique, and compared the outcomes of different DM scenarios on the reionization history. We also investigated the robustness of our findings against educated variations of still uncertain astrophysical quantities. Finally, we highlight the relevance of our astroparticle estimates in predicting the behavior of the high-redshift UV luminosity function at faint, yet unexplored magnitudes, which may be tested with the advent of the James Webb Space Telescope.

Cosmological dependence of sterile neutrino dark matter with self-interacting neutrinos

Unexplored interactions of neutrinos could be the key to understanding the nature of the dark matter (DM). In particular, active neutrinos with new self-interactions can produce keV-mass sterile neutrinos that account for the whole of the DM through the Dodelson-Widrow mechanism for a large range of active-sterile mixing values. This production typically occurs before Big-Bang Nucleosynthesis (BBN) in a yet uncharted era of the Universe. We assess how the mixing range for keV-mass sterile neutrino DM is affected by the uncertainty in the early Universe pre-BBN cosmology.This is particularly relevant for identifying the viable parameter space of sterile neutrino searches allowed by all astrophysical limits, as well as for cosmology, since the detection of a sterile neutrino could constitute the first observation of a particle providing information about the pre-BBN epoch. We find that the combined uncertainties in the early Universe cosmology and neutrino interactions significantly expand the allowed parameter space for sterile neutrinos that can constitute the whole of the DM.

Flavour and dark matter in a scoto/type-II seesaw model

The neutrino mass and dark matter (DM) problems are addressed in a Standard Model extension where the type-II seesaw and scotogenic mechanisms coexist. The model features a flavour \U0001d4b58 discrete symmetry which is broken down to a \U0001d4b52, stabilising the (scalar or fermion) DM particle. Spontaneous CP violation is implemented through the complex vacuum expectation value of a singlet scalar field, inducing observable CP-violating effects in the lepton sector. The structure of the effective neutrino mass matrix leads to constraints on the low-energy neutrino observables, namely the atmospheric neutrino mixing angle θ23, the Dirac CP-violating phase δ and the absolute neutrino mass scale mlightest. In particular, in most cases, the model selects one θ23 octant with δ ≃ 3π/2. Moreover, the obtained lower bounds on mlightest are typically in the range probed by cosmology. We also analyse the constraints imposed on the model by current experimental limits on charged lepton flavour violating (cLFV) processes, as well as future projected sensitivities. It is shown that the Higgs triplet and scotogenic contributions to cLFV never overlap and that the interplay among Yukawa couplings, dark charged scalar masses and mixing leads to a wide parameter-space region compatible with current experimental bounds. We investigate the scalar and fermion DM parameter space of our model by considering relic density, direct-detection (DD) and collider constraints. For scalar DM the mass interval 68 GeV ≲ mDM ≲ 90 GeV is viable and will be probed by future DD searches. In the fermion DM case, correct relic density is always obtained for mDM ≳ 45 GeV thanks to dark fermion-scalar coannihilation channels.

Freeze-in and freeze-out of sterile neutrino dark matter

A sterile neutrino with a keV-scale mass is a compelling dark matter candidate. We propose a new production mechanism involving the decay and annihilation of a complex scalar singlet with a Higgs portal coupling which develops a vacuum expectation value. The interactions of the resulting pseudo Nambu-Goldstone boson may thermalise the dark sector.We determine the region of parameter space where dark sector thermalisation is reached and discuss the most relevant cosmological observables.The scenario can be considered as the combination of a freeze-in of the dark sector followed by relativistic freeze-out.

Braneworld cosmological effect on freeze-in dark matter density and lifetime frontier

In the 5-dimensional braneworld cosmology, the Friedmann equation of our 4-dimensional universe on a brane is modified at high temperatures while the standard Big Bang cosmology is reproduced at low temperatures. Based on two well-known scenarios, the Randall–Sundrum and Gauss–Bonnet braneworld cosmologies, we investigate the braneworld cosmological effect on the relic density of a non-thermal dark matter particle whose interactions with the Standard Model particles are so weak that its relic density is determined by the freeze-in mechanism. For dark matter production processes in the early universe, we assume a simple scenario with a light vector-boson mediator for the dark matter particle to communicate with the Standard Model particles. We find that the braneworld cosmological effect can dramatically alters the resultant dark matter relic density from the one in the standard Big Bang cosmology. As an application, we consider a right-handed neutrino dark matter in the minimal B-L extended Standard Model with a light B-L gauge boson (Z^prime ) as a mediator. We find an impact of the braneworld cosmological effect on the search for the long-lived Z^prime boson at the planned/proposed Lifetime Frontier experiments.

TeV scale modified type-II seesaw mechanism and dark matter in a gauged U(1)B−L symmetric model

In an endeavor to explain the light neutrino masses and dark matter (DM) simultaneously, we study a gauged $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ extension of the standard model (SM). The neutrino masses are generated through a variant of type-II seesaw mechanism in which one of the scalar triplets has a mass in a scale that is accessible at the present generation colliders. Three SM singlet right chiral fermions ${\ensuremath{\chi}}_{iR}$ ($i=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$) with $\mathrm{B}\ensuremath{-}\mathrm{L}$ charges $\ensuremath{-}4$, $\ensuremath{-}4$, $+5$ are invoked to cancel the $\mathrm{B}\ensuremath{-}\mathrm{L}$ gauge anomalies and the lightest one among these three fermions becomes a viable DM candidate as their stability is guaranteed by a remnant ${\mathcal{Z}}_{2}$ symmetry to which $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ gauge symmetry gets spontaneously broken. Interestingly in this scenario, the neutrino mass and the coannihilation of DM are interlinked through the breaking of $U(1{)}_{\mathrm{B}\ensuremath{-}\mathrm{L}}$ symmetry. Apart from giving rise to the observed neutrino mass and dark matter abundance, the model also predicts exciting signals at the colliders. Especially we see a significant enhancement in the production cross section of the TeV scale doubly charged scalar in presence of the ${Z}_{\mathrm{BL}}$ gauge boson. We discuss all the relevant constraints on model parameters from observed DM abundance and null detection of DM at direct and indirect search experiments as well as the constraints on the $\mathrm{B}\ensuremath{-}\mathrm{L}$ gauge boson from recent colliders.

Momentum distributions of cosmic relics: Improved analysis

We solve coupled momentum-dependent Boltzmann equations for the phase space distribution of cosmic relic particles, without resorting to approximations of assuming kinetic equilibrium or neglecting backscattering or elastic interactions. Our method is amendable to precision numerical computations. To test it, we consider two benchmark models where the momentum dependence of dark matter distribution function is potentially important: a real singlet scalar extension near the Higgs resonance and a sterile neutrino dark matter model with a singlet scalar mediator. The singlet scalar example shows that the kinetic equilibrium may hold surprisingly well even near sharp resonances. However, the integrated method may underestimate the relic density by up to 40% in extreme cases. In the sterile neutrino dark matter model, we studied how the inclusion of previously ignored elastic interactions and processes with initial state sterile neutrinos could affect the nonthermal nature of their resulting distributions. Here the effects turned out to be negligible, proving the robustness of the earlier predictions.

Exclusion limits on dark matter-neutrino scattering cross section

We derive new constraints on combination of dark matter-electron cross section (${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$) and dark matter-neutrino cross section (${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$) utilizing the gain in kinetic energy of the dark matter (DM) particles due to scattering with the cosmic ray electrons and the diffuse supernova neutrino background (DSNB). Since the flux of the DSNB neutrinos is comparable to the cosmic ray (CR) electron flux in the energy range $\ensuremath{\sim}1\text{ }\text{ }\mathrm{MeV}--50\text{ }\text{ }\mathrm{MeV}$, scattering with the DSNB neutrinos can also boost low-mass DM significantly in addition to the boost due to interaction with the CR electrons. We use the XENON1T as well as the Super-Kamiokande data to derive bounds on ${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$ and ${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$. While our bounds for ${\ensuremath{\sigma}}_{\ensuremath{\chi}e}$ are comparable with those in the literature, we show that the Super-Kamiokande experiment provides the strongest constraint on ${\ensuremath{\sigma}}_{\ensuremath{\chi}\ensuremath{\nu}}$ for DM masses below a few MeV.

Phenomenology of one zero texture Yukawa matrix in a flavor symmetric scotogenic model

The scotogenic model is well known for accommodating small neutrino mass and dark matter. Here, we have realized the scotogenic model with the help of discrete flavor symmetry [Formula: see text]. We have obtained three one zero textures of Yukawa coupling matrices from the model and have studied its impact on neutrino phenomenology and related aspects of cosmology. On the basis of [Formula: see text] symmetry, we have further discarded two structures of one zero texture Yukawa coupling matrix. We further analyze if the effective mass of active neutrinos obtained by the virtue of the Yukawa coupling matrix is consistent with the KamLAND-Zen limit for [Formula: see text]. Also different lepton flavor violating (LFV) processes such as [Formula: see text] and [Formula: see text] are implemented and their influence on neutrino phenomenology is studied corresponding to the Yukawa coupling matrix. The entire work is carried out considering the dark matter mass [Formula: see text] in the region 450–750 GeV. We have also obtained some significant results for baryon asymmetry of the Universe in agreement with the one zero texture of the coupling matrices. Furthermore, interesting results for relic abundance on the basis of distinct mass splittings are between the inert scalars.

Five-zero texture in neutrino-dark matter model within the framework of minimal extended seesaw

We study a model of neutrino and dark matter within the framework of a minimal extended seesaw (MES). This model is based on A4 flavour symmetry along with the discrete Z3×Z4 symmetry to stabilize the dark matter and construct desired mass matrices for neutrino mass. Five-zero textures are imposed in the final 4×4 active-sterile mass matrix, which significantly reduces the free parameter in the model. Three right-handed neutrinos were considered, two of them have degenerate masses which help us to achieve baryogenesis via resonant leptogenesis. A singlet fermion (sterile neutrino) with mass ∼O(eV) is also considered, and we are able to put bounds on active-sterile mixing parameters via neutrino oscillation data. Resonant enhancement of lepton asymmetry is studied at the TeV scale, where we discuss a few aspects of baryogenesis considering the flavour effects. The possibility of improvement in effective mass from 0νββ in the presence of a single generation of sterile neutrino flavour is also studied within the fermion sector. In the scalar sector, the imaginary component of the complex singlet scalar (χ) is behaving as a potential dark matter candidate and simultaneously the real part of the complex scalar is associated with the fermion sector for sterile mass generation.

Dark charge versus electric charge

We revisit a theory that proposes a dark charge, $D$, as a dequantization of the electric charge, $Q$. We find that the general arguments of anomaly cancelation and fermion mass generation yield both $D$ and $Q$, nontrivially unified with the weak isospin $T_i$ $(i={1,2,3})$ in a novel gauge symmetry, $SU(3)_C\otimes SU(2)_L\otimes U(1)_Y\otimes U(1)_N$, where $Y$ and $N$ determine $Q$ and $D$ through the $T_3$ operator, i.e. $Q=T_3+Y$ and $D=T_3+N$, respectively. A new observation is that fundamental particles possess a dynamical dark charge which governs both neutrino mass and dark matter, where the neutrino mass is determined via a canonical seesaw, while the dark matter stability is ensured by electric and color charge conservations. We examine the mass spectra of fermions, scalars, and gauge bosons, as well as their interactions, taking into account the kinetic mixing effect of $U(1)_{Y,N}$ gauge fields. The new physics phenomena at colliders are examined. The dark matter relic density and detection are discussed.

First operation of undoped CsI directly coupled with SiPMs at 77 K

The light yield of a small undoped cesium iodide (CsI) crystal directly coupled with two silicon photomultipliers (SiPMs) at about 77 Kelvin was measured to be 43.0 pm 1.1 photoelectrons (PE) per keV electron-equivalent (keV_text {ee}) using X and gamma -ray peaks from an ^{241}Am radioactive source from 18 to 60 keV. The high light yield together with some other technical advantages illustrate the great potential of this novel combination for neutrino and low-mass dark matter detection, particularly at accelerator-based neutrino sources, where random background can be highly suppressed by requiring coincident triggers between SiPMs and beam pulse timing signals. Some potential drawbacks of using cryogenic SiPMs instead of photomultiplier tubes (PMTs) were identified, such as worse energy resolution and optical cross-talks between SiPMs. Their influence to rare-event detection was discussed and possible solutions were provided.

Freeze-in and freeze-out generation of lepton asymmetries after baryogenesis in the νMSM

The νMSM — an extension of the Standard Model by three relatively light singlet Majorana fermions N 1,2,3 — allows for the generation of lepton asymmetry which is several orders of magnitude larger than the observed baryon asymmetry of the Universe. The lepton asymmetry is produced in interactions of N 2,3 (with masses in the GeV region) at temperatures below the sphaleron freeze out T ≲ 130 GeV and can enhance the cosmological production of dark matter (DM) sterile neutrinos N 1 (with the mass of the keV scale) happening at T ∼ 200 MeV due to active-sterile neutrino mixing.This asymmetry can be generated in freeze-in, freeze-out, or later in decays of heavy neutral leptons.In this work, we address the question of the magnitude of the late-time asymmetry (LTA) generated by the heavy neutral leptons N 2,3 during their freeze-in and freeze-out, leaving the decays for later work. We study how much of this asymmetry can survive down to the lower temperatures relevant for the sterile neutrino DM creation. We find that this LTA could result in the production of a sizeable fraction of dark matter. We also examine a role played by magnetic fields and the Abelian chiral anomaly in the generation of LTA, not accounted for in the previous studies. We argue that the production of LTA can be increased significantly and make an estimate of the influence of this effect.

Scale invariant scotogenic model: Dark matter and the scalar sector

In this paper, we investigate the mutual impact between the dark matter (DM) requirements and the scalar sector in the scale invariant (SI) scotogenic model. The model is motivated by the neutrino mass and DM within a classically SI framework. It is a SI generalization of the scotogenic model, where the standard model (SM) is extended by a real singlet, an inert scalar doublet and three Majorana singlet fermions, where the lightest one ($N_{1}$) could play the DM candidate role. In addition to the annihilation channels $N_{1}N_{1}\rightarrow\ell_{\alpha}\ell_{\beta},\nu_{\alpha}\bar{\nu}_{\beta}$, the DM can be annihilated via few s-channel processes into SM particles, that are mediated by the Higgs/dilaton. This allows the new Yukawa interactions, that are responsible for neutrino mass generation, to take small values and therefore avoid the mass degeneracy between the CP-even and CP-odd inert scalars unlike the case of the minimal scotogenic model. In contrast to many Majorana DM models, the DM in the SI-scotogenic model couples to the quarks at tree-level, and hence the constraint from the direct detection experiments is very important on the space parameter. The aim of this work is to investigate the correlation between the DM requirements and the scalar sector in this model.

Sterile neutrino dark matter production in presence of nonstandard neutrino self-interactions: An EFT approach

Sterile neutrinos with keV-scale masses are popular candidates for warm dark matter. In the most straightforward case they are produced via oscillations with active neutrinos. We introduce effective self-interactions of active neutrinos and investigate the effect on the parameter space of sterile neutrino mass and mixing. Our focus is on mixing with electron neutrinos, which is subject to constraints from several upcoming or running experiments like TRISTAN, ECHo, BeEST and HUNTER. Depending on the size of the self-interaction, the parameter space moves closer to, or further away from, the one testable by those future experiments. In particular, we show that phase 3 of the HUNTER experiment would test a larger amount of parameter space in the presence of self-interactions than without them. We also investigate the effect of the self-interactions on the free-streaming length of the sterile neutrino dark matter, which is important for structure formation observables.

Implications of the S8 tension for decaying dark matter with warm decay products

Recent weak lensing surveys have revealed that the direct measurement of the parameter combination $S_8\equiv\sigma_8(\Omega_m/0.3)^{0.5}$ -- where $\sigma_8$ is a measure of the amplitude of matter fluctuations on 8 $h^{-1}$Mpc scales -- is $\sim3\sigma$ discrepant with the value reconstructed from cosmic microwave background (CMB) data assuming the $\Lambda$CDM model. In this article, we show that it is possible to resolve the tension if dark matter (DM) decays with a lifetime of $\Gamma^{-1} \simeq 55 \ \text{Gyrs}$ into one massless and one massive product, and transfers a fraction $\varepsilon\simeq 0.7 \ \%$ of its rest mass energy to the massless component. The velocity-kick received by the massive daughter leads to a suppression of gravitational clustering below its free-streaming length, thereby reducing the $\sigma_8$ value as compared to that inferred from the standard $\Lambda$CDM model, in a similar fashion to massive neutrino and standard warm DM. Contrarily to the latter scenarios, the time-dependence of the power suppression and the free-streaming scale allows the 2-body decaying DM scenario to accommodate CMB, baryon acoustic oscillation, growth factor and un-calibrated supernova Ia data. We briefly discuss implications for DM model building, galactic small-scale structure problems and the recent Xenon-1T excess. Future experiments measuring the growth factor to high accuracy at $0\lesssim z\lesssim1$ can further test this scenario.