60 research outputs found
Interacting Dark Sector and Precision Cosmology
We consider a recently proposed model in which dark matter interacts with a
thermal background of dark radiation. Dark radiation consists of relativistic
degrees of freedom which allow larger values of the expansion rate of the
universe today to be consistent with CMB data (-problem). Scattering
between dark matter and radiation suppresses the matter power spectrum at small
scales and can explain the apparent discrepancies between CDM
predictions of the matter power spectrum and direct measurements of Large Scale
Structure LSS (-problem). We go beyond previous work in two ways: 1.
we enlarge the parameter space of our previous model and allow for an arbitrary
fraction of the dark matter to be interacting and 2. we update the data sets
used in our fits, most importantly we include LSS data with full -dependence
to explore the sensitivity of current data to the shape of the matter power
spectrum. We find that LSS data prefer models with overall suppressed matter
clustering due to dark matter - dark radiation interactions over CDM
at 3-4 . However recent weak lensing measurements of the power spectrum
are not yet precise enough to clearly distinguish two limits of the model with
different predicted shapes for the linear matter power spectrum. In two
Appendices we give a derivation of the coupled dark matter and dark radiation
perturbation equations from the Boltzmann equation in order to clarify a
confusion in the recent literature, and we derive analytic approximations to
the solutions of the perturbation equations in the two physically interesting
limits of all dark matter weakly interacting or a small fraction of dark matter
strongly interacting.Comment: 29 pages + 2 Appendices; published versio
The structure and assembly history of cluster-size haloes in Self-Interacting Dark Matter
We perform dark-matter-only simulations of 28 relaxed massive cluster-sized
haloes for Cold Dark Matter (CDM) and Self-Interacting Dark Matter (SIDM)
models, to study structural differences between the models at large radii,
where the impact of baryonic physics is expected to be very limited. We find
that the distributions for the radial profiles of the density, ellipsoidal axis
ratios, and velocity anisotropies () of the haloes differ considerably
between the models (at the level), even at of the
virial radius, if the self-scattering cross section is cm
gr. Direct comparison with observationally inferred density profiles
disfavours SIDM for cm gr, but in an intermediate
radial range ( of the virial radius), where the impact of baryonic
physics is uncertain. At this level of the cross section, we find a narrower
distribution in SIDM, clearly skewed towards isotropic orbits, with no
SIDM (90\% of CDM) haloes having at of the virial radius. We
estimate that with an observational sample of (
M) relaxed clusters, can potentially be used to put competitive
constraints on SIDM, once observational uncertainties improve by a factor of a
few. We study the suppression of the memory of halo assembly history in SIDM
clusters. For cm gr, we find that this happens
only in the central halo regions ( of the scale radius of the halo),
and only for haloes that assembled their mass within this region earlier than a
formation redshift . Otherwise, the memory of assembly remains and is
reflected in ways similar to CDM, albeit with weaker trends.Comment: 15 pages, 15 figures. Submitted to MNRAS. Revisions: added new figure
with an observational comparison of density profiles, improvements and
corrections to the section on velocity anisotropie
Self-interacting neutrinos, the Hubble parameter tension, and the Cosmic Microwave Background
We perform a comprehensive study of cosmological constraints on non-standard
neutrino self-interactions using cosmic microwave background (CMB) and baryon
acoustic oscillation data. We consider different scenarios for neutrino
self-interactions distinguished by the fraction of neutrino states allowed to
participate in self-interactions and how the relativistic energy density,
N, is allowed to vary. Specifically, we study cases in which:
all neutrino states self-interact and N varies; two species
free-stream, which we show alleviates tension with laboratory constraints,
while the energy in the additional interacting states varies; and a variable
fraction of neutrinos self-interact with either the total N
fixed to the Standard Model value or allowed to vary. In no case do we find
compelling evidence for new neutrino interactions or non-standard values of
N. In several cases we find additional modes with neutrino
decoupling occurring at lower redshifts . We do
a careful analysis to examine whether new neutrino self-interactions solve or
alleviate the so-called tension and find that, when all Planck 2018 CMB
temperature and polarization data is included, none of these examples ease the
tension more than allowing a variable N comprised of
free-streaming particles. Although we focus on neutrino interactions, these
constraints are applicable to any light relic particle.Comment: 42 pages, 6 tables, 13 figures, 12 appendix figures, comments welcom
The promising future of a robust cosmological neutrino mass measurement
We forecast the sensitivity of thirty-five different combinations of future
Cosmic Microwave Background and Large Scale Structure data sets to cosmological
parameters and to the total neutrino mass. We work under conservative
assumptions accounting for uncertainties in the modelling of systematics. In
particular, for galaxy redshift surveys, we remove the information coming from
non-linear scales. We use Bayesian parameter extraction from mock likelihoods
to avoid Fisher matrix uncertainties. Our grid of results allows for a direct
comparison between the sensitivity of different data sets. We find that future
surveys will measure the neutrino mass with high significance and will not be
substantially affected by potential parameter degeneracies between neutrino
masses, the density of relativistic relics, and a possible time-varying
equation of state of Dark Energy.Comment: 27 pages, 4 figures, 8 tables. v2: updated Euclid sensitivity
settings, matches published versio
A new method to measure the mass of galaxy clusters
The mass measurement of galaxy clusters is an important tool for the
determination of cosmological parameters describing the matter and energy
content of the Universe. However, the standard methods rely on various
assumptions about the shape or the level of equilibrium of the cluster. We
present a novel method of measuring cluster masses. It is complementary to most
of the other methods, since it only uses kinematical information from outside
the virialized cluster. Our method identifies objects, as galaxy sheets or
filaments, in the cluster outer region, and infers the cluster mass by modeling
how the massive cluster perturbs the motion of the structures from the Hubble
flow. At the same time, this technique allows to constrain the
three-dimensional orientation of the detected structures with a good accuracy.
We use a cosmological numerical simulation to test the method. We then apply
the method to the Coma cluster, where we find two galaxy sheets, and measure
the mass of Coma to be Mvir=(9.2\pm2.4)10^{14} Msol, in good agreement with
previous measurements obtained with the standard methods.Comment: 10 pages, 12 figures, submitted to MNRA
Parameter inference with non-linear galaxy clustering: accounting for theoretical uncertainties
We implement EuclidEmulator (version 1), an emulator for the non-linear
correction of the matter power spectrum, into the MCMC forecasting code
MontePython. We compare the performance of Halofit, HMCode, and
EuclidEmulator1, both at the level of power spectrum prediction and at the
level of posterior probability distributions of the cosmological parameters,
for different cosmological models and different galaxy power spectrum wave
number cut-offs. We confirm that the choice of the power spectrum predictor has
a non-negligible effect on the computed sensitivities when doing cosmological
parameter forecasting, even for a conservative wave number cut-off of
. We find that EuclidEmulator1 is on average up to
more sensitive to the cosmological parameters than the other two codes,
with the most significant improvements being for the Hubble parameter of up to
and the equation of state of dark energy of up to , depending on
the case. In addition, we point out that the choice of the power spectrum
predictor contributes to the risk of computing a significantly biased mean
cosmology when doing parameter estimations. For the four tested scenarios we
find biases, averaged over the cosmological parameters, of between 0.5 and
2 (from below up to for individual parameters).
This paper provides a proof of concept that this risk can be mitigated by
taking a well-tailored theoretical uncertainty into account as this allows to
reduce the bias by a factor of 2 to 5, depending on the case under
consideration, while keeping posterior credibility contours small: the standard
deviations are amplified by a factor of in all cases.Comment: 22 pages, 14 figure
The Cosmology of Dark Energy Radiation
In this work, we quantify the cosmological signatures of dark energy
radiation -- a novel description of dark energy, which proposes that the
dynamical component of dark energy is comprised of a thermal bath of
relativistic particles sourced by thermal friction from a slowly rolling scalar
field. For a minimal model with particle production emerging from first
principles, we find that the abundance of radiation sourced by dark energy can
be as large as , exceeding the bounds on relic dark
radiation by three orders of magnitude. Although the background and
perturbative evolution of dark energy radiation is distinct from Quintessence,
we find that current and near-future cosmic microwave background and supernova
data will not distinguish these models of dark energy. We also find that our
constraints on all models are dominated by their impact on the expansion rate
of the Universe. Considering extensions that allow the dark radiation to
populate neutrinos, axions, and dark photons, we evaluate the direct detection
prospects of a thermal background comprised of these candidates consistent with
cosmological constraints on dark energy radiation. Our study indicates that a
resolution of is required to achieve sensitivity to
relativistic neutrinos compatible with dark energy radiation in a neutrino
capture experiment on tritium. We also find that dark matter axion experiments
lack sensitivity to a relativistic thermal axion background, even if enhanced
by dark energy radiation, and dedicated search strategies are required to probe
new parameter space. We derive constraints arising from a dark photon
background from oscillations into visible photons, and find that several orders
of magnitude of viable parameter space can be explored with planned
experimental programs such as DM Radio and LADERA.Comment: 27 pages, 16 figures, 3 table
Confronting interacting dark radiation scenarios with cosmological data
Dark radiation (DR) is generally predicted in new physics scenarios that
address fundamental puzzles of the Standard Model or tensions in the
cosmological data. Cosmological data has the sensitivity to constrain not only
the energy density of DR, but also whether it is interacting. In this paper, we
present a systematic study of five types of interacting DR (free-streaming,
fluid, decoupling, instantaneous decoupling, and recoupling DR) and their
impact on cosmological observables. We modify the Boltzmann hierarchy to
describe all these types of interacting DR under the relaxation time
approximation. We, for the first time, robustly calculate the collision terms
for recoupling scalar DR and provide a better estimation of the recoupling
transition redshift. We demonstrate the distinct features of each type of DR on
the CMB and matter power spectra. We perform MCMC scans using the Planck 2018
data and BAO data. Assuming no new physics in the SM neutrino sector, we find
no statistically significant constraints on the couplings of DR, although there
is a slight preference for a late transition redshift for instantaneous
decoupling DR around recombination, and for the fluid-like limit of all the
cases. The constraint varies marginally depending on the
type of DR.Comment: 20 pages + references, 12 figure
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