Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time correlation functions for non-Hermitian quantum systems   We introduce a formalism for time-dependent correlation functions for systems
whose evolutions are governed by non-Hermitian Hamiltonians of general type. It
turns out that one can define two different types of time correlation
functions. Both these definitions seem to be physically consistent while
becoming equivalent only in certain cases. Moreover, when autocorrelation
functions are considered, one can introduce another function defined as the
relative difference between the two definitions. We conjecture that such a
function can be used to assess the positive semi-definiteness of the density
operator without computing its eigenvalues. We illustrate these points by
studying analytically a number of models with two energy levels.

20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn