Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative cosmological constant in the dark sector?   We consider the possibility that the dark sector of our Universe contains a
negative cosmological constant dubbed $\lambda$. For such models to be viable,
the dark sector should contain an additional component responsible for the
late-time accelerated expansion rate ($X$). We explore the departure of the
expansion history of these models from the concordance $\Lambda$ Cold Dark
Matter model. For a large class of our models the accelerated expansion is
transient with a nontrivial dependence on the model parameters. All models with
$w_X>-1$ will eventually contract and we derive an analytical expression for
the scale factor $a(t)$ in the neighborhood of its maximal value. We find also
the scale factor for models ending in a Big Rip in the regime where dustlike
matter density is negligible compared to $\lambda$. We address further the
viability of such models, in particular when a high $H_0$ is taken into
account. While we find no decisive evidence for a nonzero $\lambda$, the best
models are obtained with a phantom behavior on redshifts $z\gtrsim 1$ with a
higher evidence for nonzero $\lambda$. An observed value for $h$ substantially
higher than $0.70$ would be a decisive test of their viability.

32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex