In sterile neutrino (3+1) parameterisation, we observe that sterile phases ($δ_{14},δ_{24}$) are always together in oscillation probability, even when the MSW effect is considered. We see that the difference between the sterile phases has a more dominating effect over event rates compared to small variations due to changes in individual values. In this work, we show the value of sterile phase difference ($δ_{14}-δ_{24}$) that least affects the parameter degeneracy resolution of $δ_{13},θ_{23}$ at long-baseline experiments.
Long baseline Experiment (LBL) have promised to be a very powerful experimental set up to study various issues related to Neutrinos. Some ongoing and planned LBL and medium baseline experiments are - T2K, MINOS, NOvA, LBNE, LBNO etc. But the long baseline experiments are crippled due to presence of some parameter degeneracies, like the Octant degeneracy. In this work, we first show the presence of Octant degeneracy in LBL experiments, and then combine it with Daya Bay Reactor experiment, at different values of CP violation phase. We show that the Octant degeneracy in LBNE can be resolved compl…
Several anomalies observed in short-baseline neutrino experiments indicate that the standard 3-flavor framework may be incomplete and point towards the existence of light sterile neutrinos. Here, we present a concise review of the status of the neutrino oscillations within the 3+1 scheme, which is a minimal extension of the standard 3-flavor framework with one sterile neutrino species. We emphasize the potential role of LBL experiments in the searches of CP violation connected to sterile neutrinos and their complementarity with the SBL experiments.
We investigate the implications of a sterile neutrino on the physics potential of the proposed experiment DUNE and future runs of NO$ν$A using latest NO$ν$A results. Using combined analysis of the disappearance and appearance data, NO$ν$A reported preferred solutions at normal hierarchy (NH) with two degenerate best-fit points one in the lower octant (LO) and $δ_{13}$ = 1.48$π$ and other in higher octant (HO) and $δ_{13}$ = 0.74$π$. Another solution of inverted hierarchy (IH) which is 0.46$σ$ away from best fit was also reported. We discuss chances of resolving these degeneracies in the presen…
Present global fits of world neutrino data hint towards non-maximal $θ_{23}$ with two nearly degenerate solutions, one in the lower octant ($θ_{23} <π/4$), and the other in the higher octant ($θ_{23} >π/4$). This octant ambiguity of $θ_{23}$ is one of the fundamental issues in the neutrino sector, and its resolution is a crucial goal of next-generation long-baseline (LBL) experiments. In this letter, we address for the first time, the impact of a light eV-scale sterile neutrino towards such a measurement, taking the Deep Underground Neutrino Experiment (DUNE) as a case study. In the so-called …
Recent studies have evidenced that long-baseline (LBL) experiments are sensitive to the extra CP-phases involved with light sterile neutrinos, whose existence is suggested by several anomalous short-baseline (SBL) results. We show that, within the 3+1 scheme, the combination of the existing SBL data with the LBL results coming from the two currently running experiments NO$ν$A and T2K, enables us to simultaneously constrain two active-sterile mixing angles $θ_{14}$ and $θ_{24}$ and two CP-phases $δ_{13} \equiv δ$ and $δ_{14}$, albeit the information on the second CP-phase is still weak at the m…
The first hint of neutrino mass hierarchy is expected to come from the NO$ν$A experiment in Fermilab as the present best-fit parameter space i.e., normal hierarchy and $δ_{CP}=-90^\circ$ is the favourable parameter space for NO$ν$A where there is no degeneracy. But this situation may change if the standard three flavour framework is not complete and there is existence of new physics. In this work we consider the presence of an extra light sterile neutrino at the eV scale and study the new degeneracies which are absent in the standard three flavour framework. We also study the effect of these n…
The first hint of the neutrino mass hierarchy is believed to come from the long-baseline experiment NO$ν$A. Recent results from the NO$ν$A shows a mild preference towards the CP phase $δ_{13} = -90^\circ$ and normal hierarchy. Fortunately this is the favorable area of the parameter space which does not suffer from the hierarchy-$δ_{13}$ degeneracy and thus NO$ν$A can have good hierarchy sensitivity for this true combination of hierarchy and $δ_{13}$. Apart from the hierarchy-$δ_{13}$ degeneracy there is also the octant-$δ_{13}$ degeneracy. But this does not affect the favorable parameter space…
The renormalization-group equation (RGE) approach to neutrino matter effects is further developed in this work. We derive a complete set of differential equations for effective mixing elements, masses and Jarlskog-like invariants in presence of a light sterile neutrino. The evolutions of mixing elements as well as Jarlskog-like invariants are obtained by numerically solving these differential equations. We calculate terrestrial matter effects in long-baseline (LBL) experiments, taking NOvA, T2K and DUNE as examples. In both three-flavor and four-flavor frameworks, electron-neutrino survival pr…
The quasi-degeneracy of heavier sterile neutrino masses in the Neutrino Minimal Standard Model ($ν$MSM) facilitates the production of lepton asymmetry below the electroweak scale. The first order loop corrections to this mass-difference has been computed in this work along with a numerical estimate of the contribution.
We discuss a comprehensive way to study the parameter degeneracies in the form of a generalized degeneracy in the neutrino oscillation experiments. First we describe the various degeneracies by considering only neutrino run of the long baseline experiment (LBL), NO$ ν$A. Then we discuss the role of antineutrinos. Later, we present the combined role of T2K (LBL experiment) and ICAL@INO (atmospheric experiment) to resolve these degeneracies. We also discuss the affect of new physics like non-standards interactions (NSI) on the determination of neutrino mass hierarchy in DUNE.
The generation of lepton asymmetry below the electroweak scale has a considerable impact on production of dark matter sterile neutrinos. Oscillations or decays of the heavier sterile neutrinos in the neutrino minimal standard model can give rise to the requisite lepton asymmetry, provided the masses of the heavier neutrinos are sufficiently degenerate. We study the renormalization group evolution of the mass difference of these singlet fermions to understand the degree of necessary fine-tuning. We construct an example of the model that can lead to a technically natural realization of this low-…
For Leptogenesis based on the type-I seesaw mechanism, we present a systematic calculation of lepton-number violating and purely flavoured asymmetries within nonequilibrium Quantum Field Theory. We show that sterile neutrinos with non-degenerate masses in the GeV range can explain the baryon asymmetry of the Universe via flavoured Leptogenesis. This is possible due to the interplay of thermal and flavour effects. Our approach clarifies the relation between Leptogenesis from the oscillations of sterile neutrinos and the more commonly studied scenarios from decays and inverse decays. We explain …
In this paper we examine the sensitivity of the Long Baseline Neutrino Oscillation Experiment to the inclusion of two new sterile neutrino flavors with masses in the eV range. We implement a model with a modified Casas-Ibarra parametrization which can accommodate medium scale mass eigenstates and introduces a new complex mixing angle. We explore the new mixing angle parameter space and demonstrate how LBNE can be used to either provide evidence for or rule out a particular model of sterile neutrinos. Certain three-flavor CP-violation scenarios cannot be distinguished from the sterile neutrinos…
The various global analyses of available neutrino oscillation data indicate the presence of the standard $3+0$ neutrino oscillation picture. However, there are a few short baseline anomalies that point to the possible existence of a fourth neutrino (with mass in the eV-scale), essentially sterile in nature. Should sterile neutrino exist in nature and its presence is not taken into consideration properly in the analyses of neutrino data, the interference terms arising due to the additional CP phases in presence of a sterile neutrino can severely impact the physics searches in long baseline (LBL…
Future neutrino detectors will obtain high-statistics data from a nearby core-collapse supernova. We study the mixing with eV-mass sterile neutrinos in a supernova environment and its effects on the active neutrino fluxes as detected by Hyper-Kamiokande and IceCube. Using a Markov Chain Monte Carlo analysis, we make projections for how accurately these experiments will measure the active-sterile mixing angle $θ_s$ given that there are substantial uncertainties on the expected luminosity and spectrum of active neutrinos from a galactic supernova burst. We find that Hyper-Kamiokande can reconstr…
Now that the NOvA experiment is approaching two years run time and has released some preliminary data, some constraints for the oscillation parameters can be inferred. Currently the best fits for NOvA are three separate results, the reason they are indistinct is that they produce almost degenerate probability curves. It has been postulated that these degeneracies can be resolved by running antineutrinos at NOvA and/or combining its data with T2K. However, this degeneracy resolution power can be compromised if sterile neutrinos are present due to additional degrees of freedom that can significa…
We extend a simple and compact method for calculating the three flavor neutrino oscillation probabilities in uniform matter density to schemes with sterile neutrinos, with favorable features inherited. The only constraint of the extended method is that the scale of the matter potential is not significantly larger than the atmospheric $Δm^2$, which is satisfied by all the running and proposed accelerator oscillation experiments. Degeneracy of the zeroth order eigensystem around solar and atmospheric resonances are resolved. Corrections to the zeroth order results are restricted to no larger tha…
The extension of the minimal standard model by three right-handed sterile neutrinos with masses smaller than the electroweak scale (nuMSM) is discussed in a Q_6 flavor symmetry framework. The lightness of the keV sterile neutrino and the near mass degeneracy of two heavier sterile neutrinos are naturally explained by exploiting group properties of Q_6. A normal hierarchical mass spectrum and an approximately mu-tau symmetric mass matrix are predicted for three active neutrinos. Nonzero theta_{13} can be obtained together with a deviation of theta_{23} from the maximality, where both mixing ang…
We study cosmological models that contain sterile neutrinos with eV-range masses as suggested by reactor and short-baseline oscillation data. We confront these models with both precision cosmological data (probing the CMB decoupling epoch) and light-element abundances (probing the BBN epoch). In the minimal LambdaCDM model, such sterile neutrinos are strongly disfavoured by current data because they contribute too much hot dark matter. However, if the cosmological framework is extended to include also additional relativistic degrees of freedom -- beyond the three standard neutrinos and the put…
We show that existing laboratory experiments have the potential to unveil the origin of matter by probing leptogenesis in the type-I seesaw model with three right-handed neutrinos and Majorana masses in the GeV range. The baryon asymmetry is generated by CP-violating flavour oscillations during the production of the right-handed neutrinos. In contrast to the case with only two right-handed neutrinos, no degeneracy in the Majorana masses is required. The right-handed neutrinos can be found in meson decays at BELLE II and LHCb.
We study in detail the impact of a light sterile neutrino in the interpretation of the latest data of the long baseline experiments NO$ν$A and T2K, assessing the robustness/fragility of the estimates of the standard 3-flavor parameters with respect to the perturbations induced in the 3+1 scheme. We find that all the basic features of the 3-flavor analysis, including the weak indication ($\sim$1.4$σ$) in favor of the inverted neutrino mass ordering, the preference for values of the CP-phase $δ_{13} \sim 1.2π$, and the substantial degeneracy of the two octants of $θ_{23}$, all remain basically u…
We study the production of sterile neutrinos in the region $T\sim M_W$ in an extension beyond the standard model with the see-saw mass matrix originating in Yukawa couplings to Higgs-like scalars with masses and vev's of the order of the electroweak scale. Sterile neutrinos are produced by the decay of scalars and standard model vector bosons. We obtain the index of refraction, dispersion relations, mixing angles in the medium and production rates including those for right-handed sterile neutrinos, from the standard model and beyond the standard model self-energies. For $1 \lesssim M_W/T \less…
In this paper, we constrain the dimensionless Compton wavelength parameter $B_0$ of $f(R)$ gravity as well as the mass of sterile neutrino by using the cosmic microwave background observations, the baryon acoustic oscillation surveys, and the linear growth rate measurements. Since both the $f(R)$ model and the sterile neutrino generally predict scale-dependent growth rates, we utilize the growth rate data measured in different wavenumber bins with the theoretical growth rate approximatively scale-independent in each bin. The employed growth rate data come from the peculiar velocity measurement…
It has been pointed out that the mixing of an eV-scale sterile neutrino with active flavors can lead to loss of sensitivity to the $θ_{23}$ octant (sign of $\sin^2θ_{23}-1/2$) in long baseline experiments, because the main oscillation probability $P_0=4\sin^2θ_{23}\sin^2θ_{13}\sin^2Δ_{31}$ can be degenerate with the sum of the interferences with the solar oscillation amplitude and an active-sterile oscillation amplitude in both neutrino and antineutrino oscillations, depending on CP phases. In this paper, we show that the above degeneracy is resolved by measuring the same beam at different bas…
We consider the possibility of simultaneously addressing the baryon asymmetry of the Universe, the dark matter problem and the neutrino mass generation in minimal extensions of the Standard Model via sterile fermions with (small) total lepton number violation. Within the framework of Inverse and Linear Seesaw models, the small lepton number violating parameters set the mass scale of the active neutrinos, the efficiency of leptogenesis through a small mass splitting between pairs of sterile fermions as well as the mass scale of a sterile neutrino dark matter candidate. We provide an improved pa…
Matter Flavor Conversion Mediated by Pseudo-Sterile States as the Possible Origin of Neutrino Oscillation Anomalies
Karlsruher Institut für Technologie (KIT)（卡尔斯鲁厄理工学院）；Dipartimento Interateneo di Fisica “Michelangelo Merlin,”（米开朗基罗·梅林跨大学物理系）；Istituto Nazionale di Fisica Nucleare, Sezione di Bari（意大利国家核物理研究所巴里分部）
We study the fit of cosmological models with two additional free parameters $N_\mathrm{eff}$ and $ξ_e$ in addition to the parameters of $Λ$CDM. We introduce extra radiation components such as hot axions or sterile neutrinos in addition to the energy density of neutrinos with large neutrino degeneracy. Then, a larger $N_\mathrm{eff}$ is allowed without spoiling Big Bang Nucleosynthesis (BBN), as positive neutrino degeneracy $ξ_e$ could improve BBN fit. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae (SNeIa), it can be seen that the Hubble tension…
Gallium and short baseline reactor neutrino experiments indicate a short-distance anomalous disappearance of electron antineutrinos which, if interpreted in terms of neutrino oscillations, would lead to a sterile neutrino mass inconsistent with standard cosmological models. This anomaly is difficult to measure at 1 km baseline experiments because its disappearance effects are degenerate with that of theta_13. The flux normalization independent measurement of theta_13 at Daya Bay breaks this degeneracy, allowing an unambiguous differentiation of 1-3 neutrino oscillations and the anomalous disap…
In a previous paper [Phys. Rev. D 83, 113013 (2011)] we have shown that the solar sector data (solar and KamLAND) are sensitive to the parameter theta_14, encoding the admixture of the electron neutrino with a fourth (essentially) sterile mass eigenstate. In that work we evidenced that such data prefer a non-zero value of theta_14 and that such a preference is completely degenerate with that of non-zero theta_13. In this report we show how the evidence of theta_13 > 0, recently emerged from global neutrino data analyses, lifts such a degeneracy and disfavors the case of sterile neutrino mixing…
Low-scale seesaw variants protected by lepton number symmetry provide a natural explanation of the smallness of neutrino masses but, unlike their higher-scale counterparts, with potentially testable phenomenology. The approximate lepton number symmetry arranges the heavy neutrinos in pseudo-Dirac pairs, which might be accessible at collider or even beam dump experiments if their mass is low enough and their mixing with the active neutrinos sufficiently large. Despite their pseudo-Dirac nature, their small mass splittings may lead to oscillations that prevent the cancellation of their potential…
