New Types of Accessible Environmental Influence on Neutrino Oscillation
نویسندگان
چکیده
To describe possible effects of medium, besides the hamiltonian introduced by Mikheev, Smirnov and Wolfenstein (MSW), in principle, there may exist new terms in the evolution equation for the neutrino oscillation due to the environment. Considering a two-energy-level quantum system: ν1 − ν2, two-species neutrino system which is embedded in a matter environment, we solve the neutrino evolution equation precisely with the possible extra terms, especially, those cause alternations between pure and mixed states of the neutrino quantum system. We obtain some remarkable features for the neutrino oscillations, which are different from that of MSW and accessible to be observed in solar neutrino observation and/or in the planned long-baseline neutrino experiments. PACS: 14.60Pq, 03.65Bz, 05.75.-b To solve the solar neutrino deficit problem [1], there have been many models which all assume neutrinos to be massive [2]. And it has been realized that the solar medium influence on the neutrino oscillation may be crucial to solving the problem. Due to the influence of the solar medium, the behavior of oscillation can be drastically modified and there can be a resonance in matter if sin θm ∼ 1, even though the mixing angle in vacuum θv is very small. This is the wellknown Mikheev-Smirnov-Wolfenstein (MSW) mechanism [3, 4]. Besides the solar matter effect, the Earth matter effect may also play a certain role in the neutrino oscillation problem, i.e. the recently reported atmospheric neutrino puzzle[5] could be attributed to the medium effects either. The key point of the oscillation scenario may be illustrated by a two-level quantum system (νe, νμ) or (ν1, ν2). The former are eigenstates of weak-interaction and the later are that of mass matrix respectively. In the scenario, the relevant quantities derived from quantum field theory are transformed into a Hamiltonian of quantum mechanics (QM). The species of neutrino produced by nuclear reactions is νe which can be decomposed with respect to the basis of ν1 and ν2. Thus, without the medium effects, its evolution is |νe(t) >= cos θve |ν1 > +sin θve |ν2 >, (1) where θv is the mixing angle in vacuum and E1, E2 are energies of ν1 and ν2. As neutrinos are light, we have Ei ≈ k +m 2 i /2k (i = 1, 2), k = |k| and k is the three-momentum of the neutrinos. When MSW medium-effects are taken into account, the Hamiltonian should be modified from H to H ′ as H = k + ( m1 2k 0 0 m2 2k ) =⇒ H ′ = k + ( m1 2k −GNe cos θv −GNe sin θv cos θv −GNe sin θv cos θv m2 2k −GNe sin θv )
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تاریخ انتشار 1997