Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Viscous Cosmologies   We probe into universes filled with Quark Gluon Plasma with non-zero
viscosities. In particular, we study the evolution of a universe with non-zero
shear viscosity motivated by the theoretical result of a non-vanishing shear
viscosity in the Quark Gluon Plasma due to quantum-mechanical effects. We first
review the consequences of a non-zero bulk viscosity and show explicitly the
non-singular nature of the bulk-viscosity-universe by calculating the
cosmological scale factor $R(t)$ which goes to zero only asymptotically. We
further extend the model of bulk viscosity to include a Cosmological Constant.
We contrast the previous results with the cosmology of universes with non-zero
shear viscosity. We first clarify under which conditions shear viscosity terms
are compatible with the Friedmann-Lama\^itre-Robertson-Walker metric. To this
end we use a version of the energy-momentum tensor from the
M\"uller-Isreal-Stewart theory which leads to causal Navier-Stoke equations. We
then derive the corresponding Friedmann equations and show under which
conditions the universe emerges non-singular.

12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci