Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Theoretical tools for CMB physics   This review presents, in a self-consistent manner, those analytical tools
that are relevant for the analysis of the physics of CMB anisotropies generated
in different theoretical models of the early Universe. After introducing the
physical foundations of the Sachs-Wolfe effect, the origin and evolution of the
scalar, tensor and vector modes of the geometry is treated in both
gauge-invariant and gauge-dependent descriptions. Some of the recent progresses
in the theory of cosmological perturbations are scrutinized with particular
attention to their implications for the adiabatic and isocurvature paradigms,
whose description is reviewed both within conventional fluid approaches and
within the the Einstein-Boltzmann treatment. Open problems and theoretical
challenges for a unified theory of the early Universe are outlined in light of
their implications for the generation of large-scale anisotropies in the CMB
sky and in light of the generation of stochastic backgrounds of relic gravitons
between few Hz and the GHz.

18
The categories of this paper are: econ
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci