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Predictive Dirac and Majorana neutrino mass textures from SU(6) grand unified theories

Zackaria Chacko, P. S. Bhupal Dev, Rabindra N. Mohapatra, and Anil Thapa
Phys. Rev. D 102, 035020 – Published 20 August 2020

Abstract

We present simple and predictive realizations of neutrino masses in theories based on the SU(6) grand unifying group. At the level of the lowest-dimension operators, this class of models predicts a skew-symmetric flavor structure for the Dirac mass term of the neutrinos. In the case that neutrinos are Dirac particles, the lowest-order prediction of this construction is then one massless neutrino and two degenerate massive neutrinos. Higher-dimensional operators suppressed by the Planck scale perturb this spectrum, allowing a good fit to the observed neutrino mass matrix. A firm prediction of this construction is an inverted neutrino mass spectrum with the lightest neutrino hierarchically lighter than the other two, so that the sum of neutrino masses lies close to the lower bound for an inverted hierarchy. In the alternate case that neutrinos are Majorana particles, the mass spectrum can be either normal or inverted. However, the lightest neutrino is once again hierarchically lighter than the other two, so that the sum of neutrino masses is predicted to lie close to the corresponding lower bound for the normal or inverted hierarchy. Near future cosmological measurements will be able to test the predictions of this scenario for the sum of neutrino masses. In the case of Majorana neutrinos that exhibit an inverted hierarchy, future neutrinoless double beta experiments can provide a complementary probe.

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  • Received 20 May 2020
  • Accepted 30 July 2020

DOI:https://doi.org/10.1103/PhysRevD.102.035020

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Particles & Fields

Authors & Affiliations

Zackaria Chacko1, P. S. Bhupal Dev2, Rabindra N. Mohapatra1, and Anil Thapa3

  • 1Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20740, USA
  • 2Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri 63130, USA
  • 3Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078, USA

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Vol. 102, Iss. 3 — 1 August 2020

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  • Figure 1
    Figure 1

    Global oscillation analysis obtained from NuFit4.1 for the case of an inverted hierarchy (IH) compared to the results from our benchmark points for the Dirac model (Fit1, Fit2, Fit3). The gray-, green-, and pink-colored contours represent the NuFit 1σ, 2σ, and 3σ CL allowed regions, respectively, while the red markers represent the NuFit best-fit values for an IH. The blue, black, and brown markers are, respectively, the predictions of the benchmark points corresponding to Fit 1, Fit 2, and Fit 3, as given in Table 4.

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  • Figure 2
    Figure 2

    Global oscillation analysis obtained from NuFit4.1 for both the normal hierarchy (NH) and inverted hierarchy (IH) compared to our benchmark models for the Majorana case (Fit 1, Fit 2, Fit 3, Fit 4). The gray-, green-, and pink-colored contours represent the NuFit 1σ, 2σ, and 3σ CL contours, respectively, in the NH case, whereas the solid, dashed, and dotted lines correspond to the 1σ, 2σ, and 3σ CL contours, respectively, for IH. The red and purple markers in each case correspond to the NuFit best-fit values for the IH and NH, respectively, while the blue, black, brown, and gray markers are the predictions of the benchmark models corresponding to Fits 1, 2, 3, and 4, respectively, as given in Table 7. In the bottom right panel, |Δm3l2| refers to the atmospheric mass-squared splitting, with l=1(2) for NH (IH).

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  • Figure 3
    Figure 3

    Model predictions for the effective Majorana mass mee as a function of sin2θ12 (left), Δm212 (right), and mi (bottom). The blue (red) points correspond to NH (IH), and the dark (light) color corresponds to the 1σ (3σ) CL for the oscillation observables. The horizontal orange band shows the sensitivity of the future 0νββ experiment nEXO at 3σ CL. The vertical blue (red) band shows the forecast 1σ limits on mi from CMB-S4 in the case of NH (IH), whereas the vertical dotted lines show the corresponding central values.

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