Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Massless neutrino oscillations   Quantum dynamical semigroups provide a general framework for studying the
evolution of open systems. Neutrino propagation both in vacuum and in matter
can be analyzed using these techniques: they allow a consistent treatment of
non-standard, dissipative effects that can alter the pattern of neutrino
oscillations. In particular, initially massless neutrinos can give rise to a
nonvanishing flavour transition probability, involving in addition the Majorana
CP-violating mixing phase.

21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex