We review the detection of the Delta L=2 semileptonic meson decays of the form M(+) -> M'(-) lepton(+) lepton(-) that we studied in a previous work, mediated by a Majorana neutrino with a mass in the range between the masses of the initial and final mesons. For such range of masses, the Majorana neutrino will go on its mass shell and the two charged leptons will appear at displaced vertices or, if the lifetime is long enough, most secondary vertices will fall outside the detector. We study the consequences of this effect on the experimental searches and limits that can be extracted.
We analyze the influence of decaying sterile neutrinos with the masses in the range 1-140 MeV on the primordial Helium-4 abundance, explicitly solving the Boltzmann equations for all particle species, taking into account neutrino flavour oscillations, and paying special attention to systematic uncertainties. We show that the Helium abundance depends only on the sterile neutrino lifetime and not on the way the active-sterile mixing is distributed between flavours, and derive an upper bound on the lifetime. We also demonstrate that the recent results of Izotov & Thuan [arXiv:1001.4440], who find…
Sterile neutrinos can be a possible candidate for dark matter. Sterile neutrinos are radiatively unstable and can inject photon energy into the intergalactic medium (IGM). The injection of photon energy into IGM can modify the temperature and ionization history of IGM gas during cosmic dawn. Theoretical models based on the ΛCDM framework predict an absorption profile in the 21 cm line during the cosmic dawn era. Recently, the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) collaboration confirmed such an adsorption signal. Injection of energy into IGM can modify the abs…
We consider a Mass Varying Neutrinos (MaVaNs) model in supersymmetric theory. The model includes effects of supersymmetry breaking transmitted by the gravitational interaction from the hidden sector, in which supersymmetry was broken, to the dark energy sector. Then evolutions of the neutrino mass and the equation of state parameter of the dark energy are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmological time scale. The finite mixing makes the mass of the…
Constraints on the lifetime of the heavy sterile neutrino, that was proposed as a possible interpretation of the KARMEN anomaly, are derived from primordial nucleosynthesis and SN 1987A. Together with the recent experimental bounds on the nu_s lifetime, SN 1987A completely excludes this interpretation. Nucleosynthesis arguments permit a narrow window for the lifetime in the interval 0.1-0.2 sec. If nu_s possesses an anomalous interaction with nucleons, the SN bounds may not apply, while the nucleosynthesis ones would remain valid.
We consider a simple extension of the Standard Model (SM) by a complex scalar doublet and a singlet along with three sterile neutrinos. The sterile neutrinos mix with the SM neutrinos to produce three light neutrino states consistent with the oscillation data and three heavy sterile states. The lightest sterile neutrino has lifetime longer than the age of the Universe and can provide correct dark matter relic abundance. Utilizing tree-level flavor changing interactions of a light scalar with mass~$\sim\mathcal{O}(100)$~MeV along with sterile neutrinos, we can explain the anomalous magnetic mom…
We derive bounds on the mixing between the left-chiral ("active") and the right-chiral ("sterile") neutrinos, provided from the combination of neutrino oscillation data and direct experimental searches for sterile neutrinos. We demonstrate that the mixing of sterile neutrinos with any flavour can be significantly suppressed, provided that the angle theta_13 is non-zero. This means that the lower bounds on sterile neutrino lifetime, coming from the negative results of direct experimental searches can be relaxed (by as much as the order of magnitude at some masses). We also demonstrate that the …
Model-building issues raised by the prospect of light sterile neutrinos are discussed in a pedagogical way. I first review the na\"ıve proposal that sterile neutrinos be identified with ``right handed neutrinos''. A critical discussion of the simple expedient of adding three gauge singlet fermions to the usual minimal standard model matter content is followed by an examination of right handed neutrinos in extended theories. I introduce the terminology of ``fully sterile'' and ``weakly sterile'' to classify varieties usually conflated under the sterile neutrino banner. After introducing the con…
The phenomenon of neutrino flavor oscillations motivates searches for sterile neutrinos in a broad range of masses and mixing-parameter values. A sterile neutrino $N$ that mixes predominantly with the $τ$ neutrino is particularly challenging experimentally. To address this challenge, we propose a new method to search for a $ν_τ$-mixing with $N$ lighter than the $τ$ lepton. The method uses the large $e^+e^-\toτ^+τ^-$ samples collected at $B$-factory experiments to produce the $N$ in $τ$-lepton decays. We exploit the long lifetime of a sterile neutrino in this mass range to suppress background a…
Considering the gauge model SU(2)_L x U(1) with the extension of the lepton sector by right-handed sterile Majorana neutrinos, we distinguish a "minimal parametric mixing scenario" for a complete matrix of 6 x 6 light (active) and sterile neutrinos, which depends, in addition to experimentally measured physical parameters, only on the masses of sterile neutrinos. For such a scenario, improved cosmological bounds are provided, resulting from the lifetime of sterile neutrinos and the fraction of energy carried by sterile neutrino dark matter.
We generalize gravitational particle production in a radiation-dominated $CPT$-symmetric universe to non-standard, but also $CPT$-symmetric early universe cosmologies. We calculate the mass of a right-handed "sterile" neutrino needed for it to be the cosmological dark matter. Since generically sterile neutrinos mix with the Standard Model active neutrinos, we use state-of-the-art tools to compute the expected spectrum of gamma rays and high-energy active neutrinos from ultra-heavy sterile neutrino dark matter decay. We demonstrate that the sterile neutrinos are never in thermal equilibrium in …
We consider the possibility of the lightest sterile neutrino dark matter which has dipole interaction with heavier sterile neutrinos. The lifetime can be long enough to be a dark matter candidate without violating other constraints and the correct amount of relic abundance can be produced in the early Universe. We find that a sterile neutrino with the mass of around MeV and the dimension-five non-renormalisable dipole interaction suppressed by $Λ_5 \gtrsim 10^{15}$ GeV can be a good candidate of dark matter, while heavier sterile neutrinos with masses of the order of GeV can explain the active…
We examine the possibility that direct dark matter detection experiments find decay products from sterile neutrino dark mater in $U(1)_{B-L}$ and $U(1)_R$ models. This is possible if the sterile neutrino interacts with a light gauge boson and decays into a neutrino and the light gauge boson with a certain lifetime. This decay produces energetic neutrinos scattering off nuclei with a large enough recoil energy in direct dark matter detection experiments. We stress that direct dark matter detection experiments can explore not only WIMP but also sterile neutrino dark matter.
We consider a simple extension of the Standard Model to consistently explain the observation of a peak in the galactic X-ray spectrum at 3.55 keV and the light neutrino masses along with the baryon asymmetry of the universe. The baryon asymmetry is generated through leptogenesis, the lepton asymmetry being generated by the decay of a heavy neutrino with TeV mass scale. The extra singlet fermion introduced in the model can be identified as a dark matter candidate of mass 7.1 keV. It decays with a lifetime much larger than the age of the universe, producing a final state photon. The Yukawa inter…
Three light sterile neutrinos (ν_e^s, ν_μ^s and ν_τ^s) are introduced to accommodate all the available neutrino data: the atmospheric neutrino anomaly is explained by ν_μ-ν_μ^s oscillation with maximal mixing; the solar one is due to ν_e-ν_e^s oscillation of small angle Mikheyev-Smirnov-Wolfenstein type; the Liquid Scintillation Neutrino Detector data is from ν_e -ν_μoscillations, so that the neutrinos can be the hot component of the dark matter. The big bang nucleosynthesis constraint is satisfied by taking the tau neutrino to be 10 MeV heavy. The ν_τdecay is discussed in a model of gauge med…
We explore the implications of the existence of heavy neutral fermions (i.e., sterile neutrinos) for the thermal history of the early universe. In particular, we consider sterile neutrinos with rest masses in the 100 MeV to 500 MeV range, with couplings to ordinary active neutrinos large enough to guarantee thermal and chemical equilibrium at epochs in the early universe with temperatures T > 1 GeV, but in a range to give decay lifetimes from seconds to minutes. Such neutrinos would decouple early, with relic densities comparable to those of photons, but decay out of equilibrium, with conseque…
Seesaw mechanism constrains from below mixing between active and sterile neutrinos for fixed sterile neutrino masses. Signal events associated with sterile neutrino decays inside a detector at fixed target experiment are suppressed by the mixing angle to the power of four. Therefore sensitivity of experiments such as SHiP and DUNE should take into account minimal possible values of the mixing angles. We extend the previous study of this subject arXiv:1312.2887 to a more general case of non-zero CP-violating phases in the neutrino sector. Namely, we provide numerical estimate of minimal value o…
We study the phenomenology of neutrino decay together with neutrino oscillations in the context of eV-scale sterile neutrinos. We review the formalism of visible neutrino decay in which one of the decay products is a neutrino that potentially can be observed. We apply the formalism developed for decay to the recent sterile neutrino search performed by IceCube with TeV neutrinos. We show that for $ν_4$ lifetime $τ_4/m_4 \lesssim 10^{-16} {\rm eV^{-1}s}$, the interpretation of the high-energy IceCube analysis can be significantly changed.
In the standard model extended with a seesaw mass matrix, we study the production of sterile neutrinos from the decay of vector bosons at $T\simeq M_{W,Z}$. We derive a general quantum kinetic equation for the production of sterile neutrinos and their effective mixing angles valid in a wide range of temperature, to all orders in interactions of the standard model, and to leading order mixing angle $θ\ll 1$. Production rates and effective mixing angles depend sensitively on helicity. Positive helicity states interact more weakly with the medium and their effective mixing angle is not modified s…
Recent experimental data is indicative of the existence of sterile neutrinos. The minimal scheme that can account for the data and is consistent with cosmological observations is the 3+1 picture which consists of three predominantly active and one predominantly sterile neutrino with the fourth neutrino being heavier than the other three. Within this scheme there are two possibilities depending on whether the three light states obey normal or inverted hierarchy. In this paper we consider the two zero textures of the low energy neutrino mass matrix in presence of one additional sterile neutrino.…
It is shown that the non-zero transition magnetic moment ($μ_{tran}$) between the sterile neutrino ($ν_{s}$) and the muon neutrino ($ν_μ$) could be effectively searched for via the Primakoff effect, in the process of $ν_μ Z \to ν_{s}Z$ conversion in the external Coulomb field of a nucleus $Z$, with the subsequent $ν_{s}\to ν_μ + γ$ decay. From the recent results of the NOMAD neutrino detector at CERN a model-independent constraint of $μ_{tran} < (10^{-6} - 10^{-9}) μ_{B}$ is obtained depending on the value of $ν_{s}$ mass. For the $m_{s}\sim O(1) GeV$ region these bounds are comparable with th…
The search for new physics with long-lived particles is an ongoing and thriving effort in the High Energy Physics community which necessitates new search strategies such as novel algorithms, novel detectors, etc...For these reasons, one could perhaps add another frontier, the Lifetime Frontier, to the standard three (Energy, Intensity and Cosmic). In this talk, I will describe a BSM physics model whose characteristic signatures are decays of new (mirror) fermions at displaced vertices, a domain belonging to the Lifetime Frontier. It is a model of {\em non-sterile} right-handed neutrinos whose …
The flavor composition of astrophysical neutrinos observed in neutrino telescopes is a powerful discriminator between different astrophysical neutrino production mechanisms and can also teach us about the particle physics properties of neutrinos. In this paper, we investigate how the possible existence of light sterile neutrinos can affect these flavor ratios. We consider two scenarios: (i) neutrino production in conventional astrophysical sources, followed by partial oscillation into sterile states; (ii) neutrinos from dark matter decay with a primary flavor composition enhanced in tau neutri…
We study the possibility to observe sterile neutrinos with masses in the range between 5 GeV and 20 GeV at the LHC, using the exclusive semileptonic modes involving pions, namely W to lepton + N to n pions + lepton+lepton (n = 1, 2, 3). The two pion and three pion modes require extrapolations of form factors to large time-like $q^2$, which we do using vector dominance models as well as light front holographic QCD, with remarkable agreement. This mass region is difficult to explore with inclusive dilepton+dijet modes or trilepton modes and impossible to explore in rare meson decays. While parti…
In view of the projected high number of produced $B$ mesons in Belle II experiment ($\sim 10^{10}$ per year), in addition to the presently ongoing LHC-b, we calculate the rate of decay for the rare decays of $B$ mesons via a sterile on-shell neutrino $N$, which subsequently may decay leptonically or semileptonically within the detector: $B \to (D^{(*)}) \ell_1^{\pm} N$, then $N \to \ell_1^{\pm} \ell_2^{\mp} ν$ or $N \to \ell^{\pm} π^\mp$. Here, $\ell_1 \not= \ell_2$ in order to avoid serious QED background. We account for the possible effects of the strong neutrino lifetime on the observabilit…
We propose the radiative decay of sterile neutrinos which fill a fraction of the halo dark matter with a mass of 27.4 eV and lifetime of $\sim 10^{22}$ sec. as a way to explain the observed diffuse ionization in the Milky Way galaxy. Since the sterile neutrino number density in the present universe can be adjusted by arranging its dynamics appropriately, the resulting hot dark matter contribution to $Ω_m$ can be small as required by many scenarios of structure formation. On the other hand a 27.4 eV neutrino could easily be the partial halo dark matter. One realization of this idea could be in …
Sterile neutrinos are SU(2) singlets that mix with active neutrinos via a mass matrix, its diagonalization leads to mass eigenstates that couple via standard model vertices. We study the cosmological production of heavy neutrinos via standard model charged and neutral current vertices under a minimal set of assumptions: i) the mass basis contains a hierarchy of heavy neutrinos, ii) these have very small mixing angles with the active (flavor) neutrinos, iii) standard model particles, including light (active-like) neutrinos are in thermal equilibrium. The same weak interaction processes that pro…
The presence of small neutrino masses and flavour mixings can be accounted for naturally in various models about extensions of the standard model, particularly in the seesaw mechanism models. In this work, we present a minimally extended seesaw framework with two right-handed neutrinos, where the active neutrino masses are derived in the radiative regime. Using the framework it can be shown that within certain mass limits, the light neutrino mass term can approach a form that is similar to its form under the type-I seesaw mechanism. Apart from this, we show that the decay width of right-handed…
Left-Right symmetric theories solve the strong CP problem and explain the small Higgs quartic coupling at high energy scales via the Higgs Parity mechanism, which forces the Higgs quartic coupling to vanish at the Left-Right symmetry breaking scale. They also predict three right-handed neutrinos; one may be stable and provide dark matter, and another may decay and explain the baryon asymmetry of the universe through leptogenesis. For the dark matter abundance to arise from freeze-out, the required range of the Left-Right symmetry breaking scale is $10^{10}$-$10^{13}$ GeV, in remarkable agreeme…
We present a model where sterile neutrinos with rest masses in the range ~ keV to ~ MeV can be the dark matter and be consistent with all laboratory, cosmological, large-scale structure, as well as x-ray constraints. These sterile neutrinos are assumed to freeze out of thermal and chemical equilibrium with matter and radiation in the very early Universe, prior to an epoch of prodigious entropy generation ("dilution") from out-of-equilibrium decay of heavy particles. In this work, we consider heavy, entropy-producing particles in the ~ TeV to ~ EeV rest-mass range, possibly associated with new …
Motivated by the null results of the BSM searches in the post-Higgs era of the LHC, our current approach is to look for new physics shifting from theory driven search strategies to signature driven ones. One possible direction might come from investigating the long-lived particles (LLPs) present in various theoretical scenarios through the newly formed Lifetime frontier. In this talk, I discuss a non-sterile right-handed neutrino model consisting of EW-scale Majorana masses, having signals with large displaced vertices arising in both the fermion and scalar sectors. The characteristic features…
We consider the possibility that sterile neutrinos exist and admit a description as unparticles; we call these {\em unsterile} neutrinos. We then examine the nature of neutrino oscillations in a model where an unsterile can mix with two active flavors with a very simple mass matrix of the see-saw type. Despite these simplifications, we find a number of remarkable features, all of which will occur generically when more realistic cases are considered. These include momentum dependent mixing angles, "invisible" decay widths for the unsterile-like mode, as well as the inheritance of a non-vanishin…
We study the Peccei-Quinn (PQ) symmetry of the sterile right-handed neutrino sector and the gauge symmetries of the Standard Model. Due to four-fermion interactions, spontaneous breaking of these symmetries at the electroweak scale generates top-quark Dirac mass and sterile-neutrino Majorana mass. The top quark channel yields massive Higgs, $W^\pm$ and $Z^0$ bosons. The sterile neutrino channel yields the heaviest sterile neutrino Majorana mass, sterile Nambu-Goldstone axion (or majoron) and massive scalar $χ$boson. Four-fermion operators effectively induce their tiny couplings to SM particles…
We study the zero textures of the Yukawa matrices in the minimal extended type-I seesaw (MES) model which can give rise to $\sim$ eV scale sterile neutrinos. In this model, three right handed neutrinos and one extra singlet $S$ are added to generate a light sterile neutrino. The light neutrino mass matrix for the active neutrinos, $ m_ν$, depends on the Dirac neutrino mass matrix ($ M_{D} $), Majorana neutrino mass matrix ($ M_{R} $) and the mass matrix ($ M_{S} $) coupling the right handed neutrinos and the singlet. The model predicts one of the light neutrino masses to vanish. We systematica…
We investigate for the first time the potential of angular auto- and cross-correlation power spectra in identifying sterile neutrino dark matter in the cosmic X-ray background. We take as reference the performance of the soon-to-be-launched eROSITA satellite. The main astrophysical background sources against sterile neutrino decays are active galactic nuclei, galaxies powered by X-ray binaries, and clusters of galaxies. While sterile neutrino decays are always subdominant in the auto-correlation power spectra, they can be efficiently enhanced when cross-correlating with tracers of the dark mat…
We investigate mixing of neutrinos in the $ν$MSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos. Especially, we study elements of the mixing matrix $Θ_{αI}$ between three left-handed neutrinos $ν_α$ ($α= e,μ,τ$) and two sterile neutrinos $N_I$ ($I=2,3$) which are responsible to the seesaw mechanism generating the suppressed masses of active neutrinos as well as the generation of the baryon asymmetry of the universe (BAU). It is shown that $Θ_{eI}$ can be suppressed by many orders of magnitude compared with $Θ_{μI}$ and $Θ_{τI}$, when the Chooz angl…
We investigate the pair production of right-handed neutrinos from the decay of an additional neutral $Z^{\prime}$ boson in the gauged $B-L$ model. Taking into account current constraints on the $Z^{\prime}$ mass and the associated gauge coupling $g_{1}^{\prime}$, we analyse the sensitivity of proposed experiments at the lifetime frontier, FASER 2, CODEX-b, MATHUSLA as well as a hypothetical version of the MAPP detector to a long lived heavy neutrino $N$ originating in the decays of the $Z^{\prime}$. We further complement this study with determining the reach of LHCb and a CMS-type detector for…
The MiniBooNE and LSND experiments are compatible with each other when two sterile neutrinos are added to the three active ones. In this case there are eight possible mass orderings. In two of them both sterile neutrinos are heavier than the three active ones. In the next two scenarios both sterile neutrinos are lighter than the three active ones. The remaining four scenarios have one sterile neutrino heavier and another lighter than the three active ones. We analyze all scenarios with respect to their predictions for mass-related observables. These are the sum of neutrino masses as constraine…
We investigate whether right-handed neutrinos can play the role of the dark matter of the Universe and be generated by the freeze-out production mechanism. In the standard picture, the requirement of a long lifetime of the right-handed neutrinos implies a small neutrino Yukawa coupling. As a consequence, they never reach thermal equilibrium, thus prohibiting production by freeze-out. We note that this limitation is alleviated if the neutrino Yukawa coupling is large enough in the early Universe to thermalize the sterile neutrinos, and then becomes tiny at a certain moment, which makes them dro…
The production of heavy sterile neutrinos from $π^-,K^-$ decay at rest yields charged leptons with negative helicity (positive for $π^+,K^+$). We obtain the branching ratio for this process and argue that a Stern-Gerlach filter leads to spatially separated domains of both helicity components with abundances determined by the branching ratio. Complemented with a search of monochromatic peaks, this setup can yield both the mass and mixing angles for sterile neutrinos with masses in the range $3 MeV \lesssim m_s \lesssim 414 MeV$ in next generation high intensity experiments. We also study oscill…
In a class of Type-II seesaw dominated $SO(10)$ models proposed recently with heavy neutrinos, extra $Z'$ boson, and resonant leptogenesis, at first we show that the lightest first generation sterile neutrino that mediates dominant contributions to neutrinoless double beta decay also generates the displaced vertex leading to verifiable like-sign di-electron as well as di-muon production events outside the LHC detectors having suppressed standard model back-ground and missing energy. Resonant leptogenesis in this case is implemented by a pair of quasi-degenerate sterile neutrinos of the second …
We discuss the effect of the supersymmetry breaking on the Mass Varying Neutrinos(MaVaNs) scenario. Especially, the effect mediated by the gravitational interaction between the hidden sector and the dark energy sector is studied. A model including a chiral superfield in the dark sector and the right handed neutrino superfield is proposed. Evolutions of the neutrino mass and the equation of state parameter are presented in the model. It is remarked that only the mass of a sterile neutrino is variable in the case of the vanishing mixing between the left-handed and a sterile neutrino on cosmologi…
Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolu tion of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just one single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry b…
Recently the Baksan Experiment on Sterile Transitions (BEST) has presented results confirming the gallium anomaly -- a lack of electron neutrinos $ν_e$ at calibrations of SAGE and GALLEX -- at the statistical significance exceeding 5$\,σ$. This result is consistent with explanation of the gallium anomaly as electron neutrino oscillations into sterile neutrino, $ν_s$. Within this explanation the BEST experiment itself provides the strongest evidence for the sterile neutrino among all the previous anomalous results in the neutrino sector. We combine the results of gallium experiments with search…
The possibility that the so-called "lithium problem", i.e. the disagreement between the theoretical abundance predicted for primordial $^7$Li assuming standard nucleosynthesis and the value inferred from astrophysical measurements, can be solved through a non-thermal BBN mechanism has been investigated by several authors. In particular, it has been shown that the decay of a MeV-mass particle, like, e.g., a sterile neutrino, decaying after BBN not only solves the lithium problem, but also satisfies cosmological and laboratory bounds, making such a scenario worth to be investigated in further de…
Standard model of particle physics fails to explain neutrino oscillations, dark matter and baryon asymmetry of the Universe. All these problems can be solved with three sterile neutrinos added to the model. Quite remarkably, if sterile neutrino masses are well below the electroweak scale, this modification --- Neutrino Minimal Standard Model (nuMSM) --- can be tested experimentally. We discuss a new experiment on search for decays of GeV-scale sterile neutrinos, which in the framework of the nuMSM are responsible for the matter-antimatter asymmetry generation and for the active neutrino masses…
The primordial lithium abundance inferred from observations of metal-poor stars is ~3 times smaller than the theoretical value in standard big bang nucleosynthesis (BBN) model. We assume a simple model including a sterile neutrino nu_H with mass of O(10) MeV which decays long after BBN. We then investigate cosmological effects of a sterile neutrino decay. We formulate the injection spectrum of nonthermal photons induced by electrons and positrons generated at the nu_H decay, as a function of the nu_H mass and the photon temperature. We then consistently solve (1) the cosmic thermal history, (2…
We discuss Big Bang Nucleosynthesis constraints on maximal $ν_μ\leftrightarrowν_s$ mixing. Vacuum $ν_μ\leftrightarrowν_s$ oscillation has been proposed as one possible explanation of the Super Kamiokande atmospheric neutrino data. Based on the most recent primordial abundance measurements, we find that the effective number of neutrino species for Big Bang Nucleosynthesis (BBN) is $N_ν\la 3.3$. Assuming that all three active neutrinos are light (with masses $\ll 1$ MeV), we examine BBN constraints on $ν_μ\leftrightarrowν_s$ mixing in two scenarios: (1) a negligible lepton asymmetry (the standar…
Searching for dark matter X-ray lines from the Large Magellanic Cloud with eROSITA
Istituto Nazionale di Fisica Nucleare, Sezione di Torino（意大利国家核物理研究所都灵分部）；CERN（欧洲核子研究组织）；Dipartimento di Fisica, “Sapienza” Università di Roma & Sezione INFN Roma1（罗马大学物理系及INFN罗马一分部）；Weizmann Institute of Science（魏茨曼科学研究所）；Louisiana State University（路易斯安那州立大学）；Dipartimento di Fisica, Università di Torino（都灵大学物理系）
We present a novel framework within the conformal inverse seesaw scheme allowing large lepton number violation while the neutrino mass formula is still governed by the low-scale inverse seesaw mechanism. This model includes new contributions to rare low-energy lepton number violating processes like neutrinoless double beta decay. We find that the lifetime for this rare process due to heavy sterile neutrinos can saturate current experimental limits. The characteristic collider signature of the present conformal inverse seesaw scheme includes, same-sign dilepton plus two jets and same-sign dilep…
We study the mechanism of generation of 7 keV sterile neutrino Dark Matter (DM) in the model with light inflaton $χ$, which serves as a messenger of scale invariance breaking. In this model the inflaton, in addition to providing reheating to the Standard Model (SM) particles, decays directly into sterile neutrinos. The latter are responsible for the active neutrino oscillations via seesaw type I like formula. While the two sterile neutrinos may also produce the lepton asymmetry in the primordial plasma and hence explain the baryon asymmetry of the Universe, the third one being the lightest may…
We study the impact of the existence of an eV-mass scale sterile neutrino---with parameters in the ballpark of what is required to fit the laboratory anomalies---on the early time profile of the electron neutrino and antineutrino fluxes associated to a core-collapse supernova (SN). In particular, we focus on the universal feature of neutronization burst expected in the first tens of ms of the signal: provided that a detector with sufficient sensitivity is available, it is well-known that in the 3 neutrino framework the detection of the neutronization burst in neutrino channel would signal inve…
Warm dark matter (WDM) means DM particles with mass m in the keV scale. For large scales, (structures beyond ~ 100 kpc) WDM and CDM yield identical results which agree with observations. For intermediate scales, WDM gives the correct abundance of substructures. Inside galaxy cores, below ~ 100 pc, N-body WDM classical physics simulations are incorrect because at such scales quantum WDM effects are important. WDM quantum calculations (Thomas-Fermi approach) provide galaxy cores, galaxy masses, velocity dispersions and density profiles in agreement with the observations. For a dark matter partic…
