Octant of θ_{23} in Danger with a Light Sterile Neutrino.
Present global fits of world neutrino data hint towards nonmaximal 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 as a case study. In the so-called 3+1 scheme involving three active and one sterile neutrinos, the ν_{μ}→ν_{e} transition probability probed in the LBL experiments acquires a new interference term via active-sterile oscillations. We find that this interference term can mimic a swap of the θ_{23} octant, even if one uses the information from both neutrino and antineutrino channels. As a consequence, the sensitivity to the octant of θ_{23} can be completely lost, and this may have serious implications for our understanding of neutrinos from both the experimental and theoretical perspectives.
Institute of Physics, Sachivalaya Marg, Sainik School Post, Bhubaneswar 751005, India.|Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085, India.
Sanjib Kumar
SK
Agarwalla
Institute of Physics, Sachivalaya Marg, Sainik School Post, Bhubaneswar 751005, India.|Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085, India.
Sabya Sachi
SS
Chatterjee
Dipartimento Interateneo di Fisica "Michelangelo Merlin", Via Amendola 173, 70126 Bari, Italy.|Istituto Nazionale di Fisica Nucleare, Sezione di Bari, Via Orabona 4, 70126 Bari, Italy.
Antonio
A
Palazzo