Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How to interpret the spectral density of the Keldysh nonequilibrium
  Green's function   This paper is devoted to the study and interpretation of the spectral
function $\mathbf{A}(\omega, T)$ of the Keldysh nonequilibrium Green's
function. The spatial diagonal of the spectral function is often interpreted as
a time-dependent local density of states. We show that this object can take
negative values implying that a simple probability interpretation as a
time-dependent density of states is not possible. The same issue also occurs
for the Wigner function $P(x,p)$ where it is solved by taking the uncertainty
principle into account. We follow the same path and incorporate the time-energy
uncertainty relation to define a convoluted spectral function that allows for a
probability interpretation. The usefulness of this quantity as a interpretative
tool is demonstrated by visualizing the charge dynamics in a quantum dot
coupled to superconducting leads.

16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics