145 research outputs found
First CMB Constraints on Direction-Dependent Cosmological Birefringence from WMAP-7
A Chern-Simons coupling of a new scalar field to electromagnetism may give
rise to cosmological birefringence, a rotation of the linear polarization of
electromagnetic waves as they propagate over cosmological distances. Prior work
has sought this rotation, assuming the rotation angle to be uniform across the
sky, by looking for the parity-violating TB and EB correlations a uniform
rotation produces in the CMB temperature/polarization. However, if the scalar
field that gives rise to cosmological birefringence has spatial fluctuations,
then the rotation angle may vary across the sky. Here we search for
direction-dependent cosmological birefringence in the WMAP-7 data. We report
the first CMB constraint on the rotation-angle power spectrum for multipoles
between L = 0 and L = 512. We also obtain a 68% confidence-level upper limit of
1 degree on the square root of the quadrupole of a scale-invariant
rotation-angle power spectrum.Comment: 14 pages, 12 figures, 4 tables; accepted to PR
New probe of magnetic fields in the prereionization epoch. I. Formalism
We propose a method of measuring extremely weak magnetic fields in the
intergalactic medium prior to and during the epoch of cosmic reionization. The
method utilizes the Larmor precession of spin-polarized neutral hydrogen in the
triplet state of the hyperfine transition. This precession leads to a
systematic change in the brightness temperature fluctuations of the 21-cm line
from the high-redshift universe, and thus the statistics of these fluctuations
encode information about the magnetic field the atoms are immersed in. The
method is most suited to probing fields that are coherent on large scales; in
this paper, we consider a homogenous magnetic field over the scale of the 21-cm
fluctuations. Due to the long lifetime of the triplet state of the 21-cm
transition, this technique is naturally sensitive to extremely weak field
strengths, of order G at a reference redshift of (or
G if scaled to the present day). Therefore, this might open up the
possibility of probing primordial magnetic fields just prior to reionization.
If the magnetic fields are much stronger, it is still possible to use this
method to infer their direction, and place a lower limit on their strength. In
this paper (Paper I in a series on this effect), we perform detailed
calculations of the microphysics behind this effect, and take into account all
the processes that affect the hyperfine transition, including radiative decays,
collisions, and optical pumping by Lyman- photons. We conclude with an
analytic formula for the brightness temperature of linear-regime fluctuations
in the presence of a magnetic field, and discuss its limiting behavior for weak
and strong fields.Comment: 26 pages, 4 figures, updated to match published versio
Tension in the Context of Dark Matter-Baryon Scattering
We explore the concordance of cosmological data in the context of dark matter
(DM) that interacts with baryons. Using the effective theory of large-scale
structure, we perform the first analysis of galaxy clustering data for this
scenario and find a mild preference for velocity-independent
DM-baryon scattering, assuming 10% of DM is interacting. Our results indicate
that a broad power suppression on small scales is a generic feature that may
help resolve tension between cosmological data sets. The validity of this
interacting DM model will be critically tested with incoming survey data.Comment: 21 pages, 10 figures, submitted to PR
Self-Interacting Neutrinos in Light of Large-Scale Structure Data
We explore a self-interacting neutrino cosmology in which neutrinos
experience a delayed onset of free streaming. Using the effective field theory
of large-scale structure (LSS), we perform the first combined likelihood
analysis of BOSS full-shape galaxy clustering, weak lensing, and Lyman-
forest measurements, together with the cosmic microwave background (CMB)
temperature and polarization anisotropy data from Planck, in search for
evidence of neutrino self-interactions. In agreement with previous results, we
find a bimodal posterior distribution for the effective strength of neutrino
self-interaction, showing that a vanishingly small interaction and a relatively
strong interaction are both consistent with cosmological data, providing fits
of nearly equal quality. We find that strong self-interactions in the neutrino
sector can alleviate the tension while maintaining a good fit to the LSS
data. Our results may have implications for particle model-building and ongoing
neutrino oscillation experiments, and motivate further exploration of particle
interactions that can generate a delay in neutrino free-streaming. We discuss
sensitivity of the upcoming galaxy surveys to ruling out neutrino
self-interaction at the level consistent with the current data.Comment: 14 pages, 4 figures, comments are welcom
Dark matter direct detection from new interactions in models with spin-two mediators
We consider models where a massive spin-two resonance acts as the mediator between Dark Matter (DM) and the SM particles through the energy-momentum tensor. We examine the effective theory for fermion, vector and scalar DM generated in these models and find novel types of DM-SM interaction never considered before. We identify the effective interactions between DM and the SM quarks when the mediator is integrated out, and match them to the gravitational form factors relevant for spin-independent DM-nucleon scattering. We also discuss the interplay between DM relic density conditions, direct detection bounds and collider searches for the spin-two mediator
Identifying the theory of dark matter with direct detection
Identifying the true theory of dark matter depends crucially on accurately characterizing interactions of dark matter (DM) with other species. In the context of DM direct detection, we present a study of the prospects for correctly identifying the low-energy effective DM-nucleus scattering operators connected to UV-complete models of DM-quark interactions. We take a census of plausible UV-complete interaction models with different low-energy leading-order DM-nuclear responses. For each model (corresponding to different spinâ, momentumâ, and velocity-dependent responses), we create a large number of realizations of recoil-energy spectra, and use Bayesian methods to investigate the probability that experiments will be able to select the correct scattering model within a broad set of competing scattering hypotheses. We conclude that agnostic analysis of a strong signal (such as Generation-2 would see if cross sections are just below the current limits) seen on xenon and germanium experiments is likely to correctly identify momentum dependence of the dominant response, ruling out models with either "heavy" or "light" mediators, and enabling downselection of allowed models. However, a unique determination of the correct UV completion will critically depend on the availability of measurements from a wider variety of nuclear targets, including iodine or fluorine. We investigate how model-selection prospects depend on the energy window available for the analysis. In addition, we discuss accuracy of the DM particle mass determination under a wide variety of scattering models, and investigate impact of the specific types of particle-physics uncertainties on prospects for model selection
Parity Violation in Graviton Non-gaussianity
We study parity violation in graviton non-gaussianity generated during
inflation. We develop a useful formalism to calculate graviton non-gaussianity.
Using this formalism, we explicitly calculate the parity violating part of the
bispectrum for primordial gravitational waves in the exact de Sitter spacetime
and prove that no parity violation appears in the non-gaussianity. We also
extend the analysis to slow-roll inflation and find that the parity violation
of the bispectrum is proportional to the slow-roll parameter. We argue that
parity violating non-gaussianity can be tested by the CMB. Our results are also
useful for calculating three-point function of the stress tensor in the
non-conformal field theory through the gravity/field theory correspondence.Comment: v2:style changed to JHEP, 21 pages, references added; v3: published
version in JHE
Spectral Distortions of the CMB as a Probe of Inflation, Recombination, Structure Formation and Particle Physics
Following the pioneering observations with COBE in the early 1990s, studies
of the cosmic microwave background (CMB) have focused on temperature and
polarization anisotropies. CMB spectral distortions - tiny departures of the
CMB energy spectrum from that of a perfect blackbody - provide a second,
independent probe of fundamental physics, with a reach deep into the primordial
Universe. The theoretical foundation of spectral distortions has seen major
advances in recent years, which highlight the immense potential of this
emerging field. Spectral distortions probe a fundamental property of the
Universe - its thermal history - thereby providing additional insight into
processes within the cosmological standard model (CSM) as well as new physics
beyond. Spectral distortions are an important tool for understanding inflation
and the nature of dark matter. They shed new light on the physics of
recombination and reionization, both prominent stages in the evolution of our
Universe, and furnish critical information on baryonic feedback processes, in
addition to probing primordial correlation functions at scales inaccessible to
other tracers. In principle the range of signals is vast: many orders of
magnitude of discovery space could be explored by detailed observations of the
CMB energy spectrum. Several CSM signals are predicted and provide clear
experimental targets, some of which are already observable with present-day
technology. Confirmation of these signals would extend the reach of the CSM by
orders of magnitude in physical scale as the Universe evolves from the initial
stages to its present form. The absence of these signals would pose a huge
theoretical challenge, immediately pointing to new physics.Comment: Astro2020 Science White Paper, 5 pages text, 13 pages in total, 3
Figures, minor update to reference
CMB-S4 Science Book, First Edition
This book lays out the scientific goals to be addressed by the
next-generation ground-based cosmic microwave background experiment, CMB-S4,
envisioned to consist of dedicated telescopes at the South Pole, the high
Chilean Atacama plateau and possibly a northern hemisphere site, all equipped
with new superconducting cameras. CMB-S4 will dramatically advance cosmological
studies by crossing critical thresholds in the search for the B-mode
polarization signature of primordial gravitational waves, in the determination
of the number and masses of the neutrinos, in the search for evidence of new
light relics, in constraining the nature of dark energy, and in testing general
relativity on large scales
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