Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dynamics of a Two-Level System Coupled to Ohmic Bath: A Perturbation
  Approach   The physics of a two-level system coupled to Ohmic bath is studied by means
of the perturbation approach based on a unitary transformation. Our main
results are: The coherence-incoherence transition is at $\alpha_c={1\over
2}[1+\Delta_r/\omega_c]$; for $\alpha<\alpha_c$ the dynamical quantity
$P(t)=\cos(\omega_0 t)\exp(-\gamma t)$; the sussceptibility
$\chi^{\prime\prime}(\omega)/\omega$ is of a double peak structure for
$\alpha<\alpha_c$ and the Shiba's relation is exactly satisfied; at the
transition point $\alpha=\alpha_c$ the real time correlation function
$C(t)\approx -1/\gamma^2_c t^2$ in the long time limit.

34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga