Searching for Pseudo-Dirac neutrinos from Astrophysical sources in IceCube data

TL;DR

This work tests the pseudo-Dirac neutrino hypothesis using IceCube IC86 PSTracks data for four astrophysical sources, comparing the standard three-flavor oscillation framework to a pseudo-Dirac scenario characterized by active-sterile mass-squared splittings $δm^2$. By modeling source fluxes with pion-decay production and performing a likelihood analysis that fits $n_s$, the spectral index γ, and $δm^2$, the authors derive exclusion regions for $δm^2$, including a stacking analysis that combines all sources. No evidence for pseudo-Dirac oscillations is found; the stacking analysis excludes $δm^2$ in the range $[2.1\times10^{-21},2.0\times10^{-16}]$ eV$^2$ (0.5 TeV–1 PeV) at $\ge 90\%$ CL, with modest extensions when lowering the energy threshold to 0.1 TeV. The study also explores data-driven background methods, yielding broader exclusions, and highlights the potential for improved bounds with additional sources and future IceCube data.

Abstract

We analyze IceCube public data from its IC86 configuration, namely PSTracks event selection, to search for pseudo-Dirac signatures in high-energy neutrinos from astrophysical sources. Neutrino flux from astrophysical sources is reduced in the pseudo-Dirac scenario due to the conversion of active-to-sterile neutrinos as compared to the neutrino oscillation scenario of only three active neutrinos over astrophysical distances. We fit IceCube data using astrophysical flux models for four point-like sources in both scenarios and constrain the active-sterile mass-square-difference in the absence of any evidence for the pseudo-Dirac scenario. We present the exclusion regions for the common mass-squared difference $δm^2$, inducing active-sterile oscillations, for all three neutrino flavors. This includes results from individual sources as well as from a stacking analysis that combines data from the four sources. Our findings indicate that the exclusion region is $δm^2 \in [2.1\times 10^{-21} - 2.0\times 10^{-16}]$ eV$^2$ with $\ge 90\%$ confidence level (CL) significance for neutrino energies ranging from 0.5 TeV to 1 PeV. When we extend the energy range down to 0.1 TeV, the exclusion region broadens to $δm^2 \in [1.1 \times 10^{-21} - 3.0\times 10^{-16}]$ eV$^2$ at $\ge 90\%$ CL.

Figures (10)

• Figure 1: Oscillation probabilities for the three active neutrinos in the pseudo-Dirac scenario with respect to the neutrino energy $E_{\nu}$ for NGC 1068, PKS 1424+240, TXS 0506+056 and NGC 4151 for different $\delta m^2$ values.
• Figure 2: Variation of oscillation probabilities for the three active neutrinos in the pseudo-Dirac scenario with respect to the $\delta m_i^2$ for $E_{\nu} = 1$ TeV, in the context of NGC 1068, PKS 1424+240, TXS 0506+056 and NGC 4151. We considered here $\delta m_1^2 = \delta m_2^2 = \delta m_3^2 = \delta m^2$. Different curves represent different survival and transition probabilities. The corresponding SM probabilities are shown as the gray lines, e.g., $P_{ee}^{\rm SM}$ is shown as the gray solid line.
• Figure 3: Contour plots of the TS scanned over the parameter $n_s$ and $\gamma$ and subtracted from the maximum TS obtained for their best-fit values ${\hat{n}}_s$ and $\hat{\gamma}$ (the quantity $\Delta {\rm TS}^\prime$ defined in Eq. (\ref{['eq:DeltaTSprime']}) represented by the color bar), have been projected in the $\gamma$-$n_s$ plane for both $\delta m^2 = 0$ (SM) and for a nonzero $\delta m^2$ value for the sources (except GB6 J1542+6129) listed in Table \ref{['tab:sources']}. The best-fit point in each case is represented with 'x' and the allowed regions with 68% and 95% C.L. are shown as solid and dashed curves, respectively. The energy-range for IceCube is considered to be 0.5 TeV - 1 PeV.
• Figure 4: The results of the statistical analysis are presented in this figure. In the left panel, the number of events with respect to $\delta m^2$ are shown for all four sources. The best-fit curves are shown in solid blue (NGC 1068), red (PKS 1424+240), green (TXS 0506+056) and orange (NGC 4151), along with their 1$\sigma$ and 2$\sigma$ regions in dark and light gray shades, respectively. In the right panel, the curves representing $\Delta$TS vs. $\delta m^2$ are shown. We have provided the constraints on $\delta m^2$ parameter at 90%, 95% and 99% C.L. from different sources individually with blue-solid (NGC 1068), red-dashed (PKS 1424+240 I), red-solid (PKS 1424+240 II), green-solid (TXS 0506+056) and orange-solid (NGC 4151) curves. Results from the stacking analysis are represented as black-dashed (includes PKS 1424+240 I) and black-solid (includes PKS 1424+240 II) curves, for the two redshift values of PKS 1424+240. The yellow and green shaded regions corresponding to the stacking analysis I and II, respectively, represent the $\delta m^2$ range excluded at $\ge 90\%$ CL. For this analysis, we considered the neutrino energy range as 0.5 TeV - 1 PeV.
• Figure 5: Data driven background: Contour plots same as Fig. \ref{['fig:contours']}. The best-fit point in each case is represented with 'x' and the allowed regions with 68% and 95% C.L. are shown as solid and dashed curves, respectively. The energy range for IceCube is considered to be 0.5 TeV - 1 PeV.