Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microscopic Studies on Two-Phonon Giant Resonances   A new class of giant resonances in nuclei, namely double giant resonances, is
discussed. They are giant resonances built on top of other giant resonances.
Investigation on their properties, together with similar studies on low-lying
two-phonon states, should give an answer on how far the harmonic picture of
boson-type excitations holds in the finite fermion systems like atomic nuclei.
  The main attention in this review is paid to double giant dipole resonances
(DGDR) which are observed in relativistic heavy ion collisions with very large
cross sections. A great experimental and theoretical effort is underway to
understand the reaction mechanism which leads to the excitation of these states
in nuclei, as well as the better microscopic understanding of their properties.
The Coulomb mechanism of the excitation of single and double giant resonances
in heavy ion collision at different projectile energies is discussed in
details. A contribution of the nuclear excitation to the total cross section of
the reaction is also considered. The Coulomb excitation of double resonances is
described within both, the second-order perturbation theory approach and in
coupled-channels calculation. The properties of single and double resonances
are considered within the phenomenologic harmonic vibrator model and
microscopic quasiparticle-RPA approach. For the last we use the
Quasiparticle-Phonon Model (QPM) the basic ideas and formalism of which are
presented. The QPM predictions of the DGDR properties (energy centroids,
widths, strength distributions, anharmonicities and excitation cross sections)
are compared to predictions of harmonic vibrator model, results of other
microscopic calculations and experimental data available.

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The categories of this paper are: hep-ph
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The categories of this paper are: comp-gas
4
The categories of this paper are: cond-mat
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
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The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
16
The categories of this paper are: stat