@misc{10481/91499,
year = {2023},
month = {3},
url = {https://hdl.handle.net/10481/91499},
abstract = {We construct globally hyperbolic spacetimes such that each slice {t=t0​} of the universal time t is a model space of constant curvature k(t0​) which may not only vary with t0​∈R but also change its sign. The metric is smooth and slightly different to FLRW spacetimes, namely, g=−dt2+dr2+Sk(t)2​(r)gSn−1​, where gSn−1​ is the metric of the standard sphere, Sk(t)​(r)=sin(k(t)
​r)/k(t)
​ when k(t)≥0 and Sk(t)​(r)=sinh(−k(t)
​r)/−k(t)

​ when k(t)≤0.

In the open case, the t-slices are (non-compact) Cauchy hypersurfaces of curvature k(t)≤0, thus homeomorphic to Rn; a typical example is k(t)=−t2 (i.e., Sk(t)​(r)=sinh(tr)/t). In the closed case, k(t)>0 somewhere, a slight extension of the class shows how the topology of the t-slices changes. This makes at least one comoving observer to disappear in finite time t showing some similarities with an inflationary expansion. Anyway, the spacetime is foliated by Cauchy hypersurfaces homeomorphic to spheres, not all of them t-slices.},
organization = {A-FQM-494-UGR18 (Junta de Andalucía/
FEDER)},
organization = {PID2020-116126GB-I00 (MCIN/ AEI/10.13039/501100011033)},
organization = {IMAG/ María de Maeztu, CEX2020-001105-MCIN/ AEI/ 10.13039/
501100011033},
publisher = {EMS Press},
keywords = {Cosmological models},
keywords = {Space topology change},
keywords = {Constant curvature},
title = {A class of cosmological models with spatially constant sign-changing curvature},
doi = {10.4171/PM/2099},
author = {Sánchez Caja, Miguel},
}