480 research outputs found
Pulsar timing array observations as possible hints for nonsingular cosmology
Recent pulsar timing array (PTA) experiments have reported strong evidence of
the stochastic gravitational wave background (SGWB). If interpreted as
primordial gravitational waves (GWs), the signal favors a strongly blue-tilted
spectrum. Consequently, the nonsingular cosmology, which is able to predict a
strongly blue-tilted GW spectrum with on certain scales, offers
a potential explanation for the observed SGWB signal. In this paper, we present
a Genesis-inflation model capable of explaining the SGWB signal observed by the
PTA collaborations while also overcoming the initial singularity problem
associated with the inflationary cosmology. Furthermore, our model predicts
distinctive features in the SGWB spectrum, which might be examined by
forthcoming space-based gravitational wave experiments.Comment: 20 pages, 8 figures; references added, published in EPJ
Alleviating both and tensions: early dark energy lifts the CMB-lockdown on ultralight axion
The existence of ultralight axion (ULA) with mass is not favored by the CMB observations in the standard
CDM model. We show that the inclusion of early dark energy (EDE) will
lift the CMB-lockdown on such ULA, and possibly other forms of dark matter
beyond cold dark matter. By performing Monte Carlo Markov Chain analysis, it is
found that, as opposed to CDM, the AdS-EDE cosmology (with an Anti-de
Sitter phase around recombination) now allows the existence of axion with mass
eV and predicts of the matter in our Universe to be such ULA,
which can also help alleviating the tension in EDE.Comment: 13 pages + appendix, 10 figures; matched accepted version in pl
Towards hybrid inflation with in light of Hubble tension and primordial gravitational waves
Recently, it has been found that complete resolution of the Hubble tension
might point to a scale-invariant Harrison-Zeldovich spectrum of primordial
scalar perturbation, i.e. for km/s/Mpc. We show that for
well-known slow-roll models, if inflation ends by a waterfall instability with
respect to another field in the field space while inflaton is still at a deep
slow-roll region, can be lifted to . A surprise of our result is
that with pre-recombination early dark energy, chaotic inflation,
ruled out by Planck+BICEP/Keck in standard CDM, can be revived, which
is now well within testable region of upcoming cosmic microwave background
B-mode experiments.Comment: 12 pages, 3 figures; v2 reference adde
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