Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theoretical Methods for Giant Resonances   The Random Phase Approximation (RPA) and its variations and extensions are,
without any doubt, the most widely used tools to describe Giant Resonances
within a microscopic theory. In this chapter, we will start by discussing how
RPA comes out naturally if one seeks a state with a harmonic time dependence in
the space of one particle-one hole excitations on top of the ground state. It
will be also shown that RPA is the simplest approach in which a ``collective''
state emerges. These are basic arguments that appear in other textbooks but are
also unavoidable as a starting point for further discussions. In the rest of
the chapter, we will give emphasis to developments that have taken place in the
last decades: alternatives to RPA like the Finite Amplitude Method (FAM),
state-of-the-art calculations with well-established Energy Density Functionals
(EDFs), and progress in {\em ab initio} calculations. We will discuss
extensions of RPA using as a red thread the various enlargements of the one
particle-one hole model space. The importance of the continuum, and the
exclusive observables like the decay products of Giant Resonances, will be also
touched upon.

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The categories of this paper are: stat
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph
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The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
5
The categories of this paper are: gr-qc