43 research outputs found
Probing Parity-Violation with the Four-Point Correlation Function of BOSS Galaxies
Parity-violating physics in the early Universe can leave detectable traces in
late-time observables. Whilst vector- and tensor-type parity-violation can be
observed in the -modes of the cosmic microwave background, scalar-type
signatures are visible only in the four-point correlation function (4PCF) and
beyond. This work presents a blind test for parity-violation in the 4PCF of the
BOSS CMASS sample, considering galaxy separations in the range
. The parity-odd 4PCF contains no contributions
from standard CDM physics and can be efficiently measured using
recently developed estimators. Data are analyzed using both a non-parametric
rank test (comparing the BOSS 4PCFs to those of realistic simulations) and a
compressed analysis, with the former avoiding the assumption of a
Gaussian likelihood. These find similar results, with the rank test giving a
detection probability of (). This provides significant
evidence for parity-violation, either from cosmological sources or systematics.
We perform a number of systematic tests: although these do not reveal any
observational artefacts, we cannot exclude the possibility that our detection
is caused by the simulations not faithfully representing the statistical
properties of the BOSS data. Our measurements can be used to constrain physical
models of parity-violation. As an example, we consider a coupling between the
inflaton and a gauge field and place bounds on the latter's energy
density, which are several orders of magnitude stronger than those previously
reported. Upcoming probes such as DESI and Euclid will reveal whether our
detection of parity-violation is due to new physics, and strengthen the bounds
on a variety of models.Comment: 30 pages, 11 figures, accepted by Phys. Rev. D. Code available at
https://github.com/oliverphilcox/Parity-Odd-4PC
Optimal Estimation of the Binned Mask-Free Power Spectrum, Bispectrum, and Trispectrum on the Full Sky: Scalar Edition
We derive optimal estimators for the two-, three-, and four-point correlators
of statistically isotropic scalar fields defined on the sphere, such as the
Cosmic Microwave Background temperature fluctuations, allowing for arbitrary
(linear) masking and inpainting schemes. In each case, we give the optimal
unwindowed estimator (obtained via a maximum-likelihood prescription, with an
associated Fisher deconvolution matrix), and an idealized form, and pay close
attention to their efficient computation. For the trispectrum, we include both
parity-even and parity-odd contributions, as allowed by symmetry. The
estimators can include arbitrary weighting of the data (and remain unbiased),
but are shown to be optimal in the limit of inverse-covariance weighting and
Gaussian statistics. The normalization of the estimators is computed via Monte
Carlo methods, with the rate-limiting steps (involving spherical harmonic
transforms) scaling linearly with the number of bins. An accompanying code
package, PolyBin, implements these estimators in Python, and we demonstrate the
estimators' efficacy via a suite of validation tests.Comment: 33 pages, 10 figures, code available at
https://github.com/oliverphilcox/PolyBin. Accepted by Phys. Rev.
Do the CMB Temperature Fluctuations Conserve Parity?
Observations of the Cosmic Microwave Background (CMB) have cemented the
notion that the large-scale Universe is both statistically homogeneous and
isotropic. But is it invariant also under reflections? To probe this we require
parity-sensitive statistics: for scalar observables, the simplest is the
trispectrum. We make the first measurements of the parity-odd scalar CMB,
focusing on the large-scale () temperature anisotropies measured by
Planck. This is facilitated by new quasi-maximum-likelihood estimators for
binned correlators, which account for mask convolution and leakage between
even- and odd-parity components, and achieve ideal variances within . We perform a blind test for parity violation by comparing a
statistic from Planck to theoretical expectations, using two suites of
simulations to account for the possible likelihood non-Gaussianity and residual
foregrounds. We find consistency at the level, yielding no
evidence for novel early-Universe phenomena. The measured trispectra allow for
a wealth of new physics to be constrained; here, we use them to constrain eight
primordial models, including Ghost Inflation, Cosmological Collider scenarios,
and Chern-Simons gauge fields. We find no signatures of new physics, with a
maximal detection significance of . Our results also indicate that
the recent parity excesses seen in the BOSS galaxy survey are not primordial in
origin, given that the CMB dataset contains roughly more primordial
modes, and is far easier to interpret, given the linear physics, Gaussian
statistics, and accurate mocks. Tighter CMB constraints can be wrought by
including smaller scales and adding polarization data.Comment: 7+13 pages, 4+5 figures, accepted by Phys. Rev. Lett. Code available
at https://github.com/oliverphilcox/PolyBin/tree/main/planck_publi
Efficient Computation of -point Correlation Functions in Dimensions
We present efficient algorithms for computing the -point correlation
functions (NPCFs) of random fields in arbitrary -dimensional homogeneous and
isotropic spaces. Such statistics appear throughout the physical sciences, and
provide a natural tool to describe a range of stochastic processes. Typically,
NPCF estimators have complexity (for a data set containing
particles); their application is thus computationally infeasible unless
is small. By projecting onto a suitably-defined angular basis, we show that the
estimators can be written in separable form, with complexity
, or if evaluated
using a Fast Fourier Transform on a grid of size . Our decomposition
is built upon the -dimensional hyperspherical harmonics; these form a
complete basis on the -sphere and are intrinsically related to angular
momentum operators. Concatenation of such harmonics gives states of
definite combined angular momentum, forming a natural separable basis for the
NPCF. In particular, isotropic correlation functions require only states with
zero combined angular momentum. We provide explicit expressions for the NPCF
estimators as applied to both discrete and gridded data, and discuss a number
of applications within cosmology and fluid dynamics. The efficiency of such
estimators will allow higher-order correlators to become a standard tool in the
analysis of random fields.Comment: 12 pages, 2 figures, submitted to PNAS. Comments welcome
Testing Parity Symmetry with the Polarized Cosmic Microwave Background
New physics in the early Universe could lead to parity-violation in the late
Universe, sourcing statistics whose sign changes under point reflection. The
best constraints on such phenomena have come from the Planck temperature
fluctuations; however, this is already cosmic-variance-limited down to
relatively small scales, thus only small improvements are expected in the
future. Here, we search for signatures of parity-violation in the polarized
CMB, using the Planck PR4 - and -mode data. We perform both a
simulation-based blind test for any parity-violating signal at , and
a targeted search for primordial gauge fields (and the amplitudes of a
generic collapsed model) at . In all cases, we find no evidence for
new physics, with the model-independent test finding consistency with the
FFP10/NPIPE simulation suite at , and the gauge field test
constraining the fractional amplitude of gauge fields during inflation to be
below at confidence level for a fiducial model. The
addition of polarization data can significantly improve the constraints,
depending on the particular model of primordial physics, and the bounds will
tighten significantly with the inclusion of smaller-scale information.Comment: 15 pages, 9 figures. Submitted to Phys. Rev.
Combining Full-Shape and BAO Analyses of Galaxy Power Spectra: A 1.6% CMB-independent constraint on H0
We present cosmological constraints from a joint analysis of the pre- and
post-reconstruction galaxy power spectrum multipoles from the final data
release of the Baryon Oscillation Spectroscopic Survey (BOSS). Geometric
constraints are obtained from the positions of BAO peaks in reconstructed
spectra, analyzed in combination with the unreconstructed spectra in a
full-shape (FS) likelihood using a joint covariance matrix, giving stronger
parameter constraints than FS-only or BAO-only analyses. We introduce a new
method for obtaining constraints from reconstructed spectra based on a
correlated theoretical error, which is shown to be simple, robust, and
applicable to any flavor of density-field reconstruction. Assuming CDM
with massive neutrinos, we analyze data from two redshift bins
and obtain constraints on the Hubble
constant , using only a single prior on the current baryon density
from Big Bang Nucleosynthesis (BBN) and no knowledge of the power
spectrum slope . This gives , with the inclusion of BAO
data sharpening the measurement by , representing one of the strongest
current constraints on independent of cosmic microwave background data.
Restricting to the best-fit slope from Planck (but without additional
priors on the spectral shape), we obtain a measurement of . We find strong constraints on the
cosmological parameters from a joint analysis of the FS, BAO, and Planck data.
This sets new bounds on the sum of neutrino masses (at confidence) and the effective number of
relativistic degrees of freedom , though
contours are not appreciably narrowed by the inclusion of BAO data.Comment: 42 pages, 12 figures, accepted by JCAP, likelihoods available at
https://github.com/Michalychforever/lss_montepython (minor typo corrected