Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Higher time derivatives, stability and Fermi Statistics   We show that statistics is crucial for the instability problem derived from
higher time derivatives. In fact, and contrary to previous statements, we check
that when dealing with Fermi systems, the Hamiltonian is well bounded and the
quantum states are normalizable. Although, ghost states are still present, they
do not affect unitarity under certain conditions. We first analyze a quantum
oscillator involving Grassman variables and then we generalize it to a Dirac
field. Finally, we discuss some physical implications

24
The categories of this paper are: dg-ga
3
The categories of this paper are: physics
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat