153 research outputs found
Limits on Neutrino-Neutrino Scattering in the Early Universe
In the standard model neutrinos are assumed to have streamed across the
Universe since they last scattered at the weak decoupling epoch when the
temperature of the standard-model plasma was ~MeV. The shear stress of
free-streaming neutrinos imprints itself gravitationally on the Cosmic
Microwave Background (CMB) and makes the CMB a sensitive probe of neutrino
scattering. Yet, the presence of nonstandard physics in the neutrino sector may
alter this standard chronology and delay neutrino free-streaming until a much
later epoch. We use observations of the CMB to constrain the strength of
neutrino self-interactions G_eff and put limits on new physics in the neutrino
sector from the early Universe. Recent measurements of the CMB at large
multipoles made by the Planck satellite and high-l experiments are critical for
probing this physics. Within the context of conventional LambdaCDM parameters
cosmological data are compatible with G_eff < 1/(56 MeV)^2 and neutrino
free-streaming might be delayed until their temperature has cooled to as low as
~25 eV. Intriguingly, we also find an alternative cosmology compatible with
cosmological data in which neutrinos scatter off each other until z~10^4 with a
preferred interaction strength in a narrow region around , where is
the Fermi constant. This distinct self-interacting neutrino cosmology is
characterized by somewhat lower values of both the scalar spectral index and
the amplitude of primordial fluctuations. While we phrase our discussion here
in terms of a specific scenario in which a late onset of neutrino
free-streaming could occur, our constraints on the neutrino visibility function
are very general.Comment: 9 Pages, 4 figures, 1 table. v2: Version accepted for publication,
enhanced discussion on neutrino interaction beyond the SM, enhanced figures,
references adde
Oscillating Bispectra and Galaxy Clustering: A Novel Probe of Inflationary Physics with Large-Scale Structure
Many models of inflation predict oscillatory features in the bispectrum of
primordial fluctuations. Since it has been shown that primordial
non-Gaussianity can lead to a scale-dependent halo bias, we investigate the
effect of oscillations in the three-point function on the clustering of
dark-matter halos. Interestingly, we find that features in the inflaton
potential such as oscillations or sharp steps get imprinted in the mass
dependence of the non-Gaussian halo bias. In this paper, we focus on models
displaying a sharp feature in the inflaton potential as well as Resonant
non-Gaussianity. In both cases, we find a strong scale dependence for the
non-Gaussian halo bias with a slope similar to that of the local model. In the
resonant case, we find that the non-Gaussian bias oscillates with halo mass, a
novel feature that is unique to this type of models. In the case of a sharp
feature in the inflaton potential, we find that the clustering of halos is
enhanced at the mass scale corresponding to the Fourier mode that exited the
horizon when the inflaton was crossing the feature in the potential. Both of
these are new effects that open the possibility of characterizing the
inflationary potential with large-scale-structure surveys. We briefly discuss
the prospects for detecting these non-Gaussian effects.Comment: 9 pages, 8 figures; v2 matching published versio
Thomson scattering: One rate to rule them all
The enduring tension between local and distant measurements of remains
unresolved. It was recently pointed out that cosmic microwave background (CMB)
and large-scale structure (LSS) observables are invariant under a uniform
rescaling of the gravitational free-fall rates of all species present and the
Thomson scattering rate between photons and electrons. We show that a unique
variation of the fine-structure constant and the electron mass can leverage this scaling transformation to reconcile the CMB and LSS data
with a broad spectrum of Hubble constant values, encompassing those inferred
from local measurements. Importantly, this study demonstrates that the
constraints on the variation of fundamental constants imposed by the specific
recombination history are not as stringent as previously assumed. Our work
highlights the critical role of the Thomson scattering rate in the existing
Hubble tension and offers a distinct avenue of exploration for particle model
builders.Comment: 19 pages + references, 5 figure
Rock 'n' Roll Solutions to the Hubble Tension
Local measurements of the Hubble parameter are increasingly in tension with
the value inferred from a CDM fit to the cosmic microwave background
(CMB) data. In this paper, we construct scenarios in which evolving scalar
fields significantly ease this tension by adding energy to the Universe around
recombination in a narrow redshift window. We identify solutions of with simple asymptotic behavior, both oscillatory (rocking) and
rolling. These are the first solutions of this kind in which the field
evolution and fluctuations are consistently implemented using the equations of
motion. Our findings differ qualitatively from those of the existing
literature, which rely upon a coarse-grained fluid description. Combining CMB
data with low-redshift measurements, the best fit model has and increases
the allowed value of from 69.2 km/s/Mpc in CDM to 72.3 km/s/Mpc
at . Future measurements of the late-time amplitude of matter
fluctuations and of the reionization history could help distinguish these
models from competing solutions.Comment: 19 pages, 9 figures + appendi
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