Kavli Affiliate: Kent Irwin
| First 5 Authors: Erminia Calabrese, J. Colin Hill, Hidde T. Jense, Adrien La Posta, Irene Abril-Cabezas
| Summary:
We use new cosmic microwave background (CMB) primary temperature and
polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT)
Data Release 6 (DR6) to test foundational assumptions of the standard
cosmological model and set constraints on extensions to it. We derive
constraints from the ACT DR6 power spectra alone, as well as in combination
with legacy data from Planck. To break geometric degeneracies, we include ACT
and Planck CMB lensing data and baryon acoustic oscillation data from DESI
Year-1, and further add supernovae measurements from Pantheon+ for models that
affect the late-time expansion history. We verify the near-scale-invariance
(running of the spectral index $d n_s/dln k = 0.0062 pm 0.0052$) and
adiabaticity of the primordial perturbations. Neutrino properties are
consistent with Standard Model predictions: we find no evidence for new light,
relativistic species that are free-streaming ($N_{rm eff} = 2.86 pm 0.13$,
which combined with external BBN data becomes $N_{rm eff} = 2.89 pm 0.11$),
for non-zero neutrino masses ($sum m_nu < 0.082$ eV at 95% CL), or for
neutrino self-interactions. We also find no evidence for self-interacting dark
radiation ($N_{rm idr} < 0.134$), early-universe variation of fundamental
constants, early dark energy, primordial magnetic fields, or modified
recombination. Our data are consistent with standard BBN, the FIRAS-inferred
CMB temperature, a dark matter component that is collisionless and with only a
small fraction allowed as axion-like particles, a cosmological constant, and
the late-time growth rate predicted by general relativity. We find no
statistically significant preference for a departure from the baseline
$Lambda$CDM model. In general, models introduced to increase the Hubble
constant or to decrease the amplitude of density fluctuations inferred from the
primary CMB are not favored by our data.
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