39 research outputs found
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
Exploring Cosmic Origins with CORE: Survey requirements and mission design
Future observations of cosmic microwave background (CMB) polarisation havethe potential to answer some of the most fundamental questions of modernphysics and cosmology. In this paper, we list the requirements for a future CMBpolarisation survey addressing these scientific objectives, and discuss thedesign drivers of the CORE space mission proposed to ESA in answer to the "M5"call for a medium-sized mission. The rationale and options, and themethodologies used to assess the mission's performance, are of interest toother future CMB mission design studies. CORE is designed as a near-ultimateCMB polarisation mission which, for optimal complementarity with ground-basedobservations, will perform the observations that are known to be essential toCMB polarisation scienceand cannot be obtained by any other means than adedicated space mission
Exploring Cosmic Origins with CORE: Cosmological Parameters
We forecast the main cosmological parameter constraints achievable with theCORE space mission which is dedicated to mapping the polarisation of the CosmicMicrowave Background (CMB). CORE was recently submitted in response to ESA'sfifth call for medium-sized mission proposals (M5). Here we report the resultsfrom our pre-submission study of the impact of various instrumental options, inparticular the telescope size and sensitivity level, and review the great,transformative potential of the mission as proposed. Specifically, we assessthe impact on a broad range of fundamental parameters of our Universe as afunction of the expected CMB characteristics, with other papers in the seriesfocusing on controlling astrophysical and instrumental residual systematics. Inthis paper, we assume that only a few central CORE frequency channels areusable for our purpose, all others being devoted to the cleaning ofastrophysical contaminants. On the theoretical side, we assume LCDM as ourgeneral framework and quantify the improvement provided by CORE over thecurrent constraints from the Planck 2015 release. We also study the jointsensitivity of CORE and of future Baryon Acoustic Oscillation and Large ScaleStructure experiments like DESI and Euclid. Specific constraints on the physicsof inflation are presented in another paper of the series. In addition to thesix parameters of the base LCDM, which describe the matter content of aspatially flat universe with adiabatic and scalar primordial fluctuations frominflation, we derive the precision achievable on parameters like thosedescribing curvature, neutrino physics, extra light relics, primordial heliumabundance, dark matter annihilation, recombination physics, variation offundamental constants, dark energy, modified gravity, reionization and cosmicbirefringence. (ABRIDGED
The observed galaxy bispectrum from single-field inflation in the squeezed limit
Using the consistency relation in Fourier space, we derive the observed galaxy bispectrum from
single- eld in
ation in the squeezed limit, in which one of the three modes has a wavelength much
longer than the other two. This provides a non-trivial check of the full computation of the bispectrum
based on second-order cosmological perturbation theory in this limit. We show that gauge modes
need to be carefully removed in the second-order cosmological perturbations in order to calculate
the observed galaxy bispectrum in the squeezed limit. We then give an estimate of the e ective non-
Gaussianity due to general-relativistic lightcone e ects that could mimic a primordial non-Gaussian
signal
Exploring cosmic origins with CORE: Cosmological parameters
We forecast the main cosmological parameter constraints achievable with the
CORE space mission which is dedicated to mapping the polarisation of the Cosmic Microwave
Background (CMB). CORE was recently submitted in response to ESAâs fifth call for mediumsized mission proposals (M5). Here we report the results from our pre-submission study of the
impact of various instrumental options, in particular the telescope size and sensitivity level,
and review the great, transformative potential of the mission as proposed. Specifically, we
assess the impact on a broad range of fundamental parameters of our Universe as a function
of the expected CMB characteristics, with other papers in the series focusing on controlling
astrophysical and instrumental residual systematics. In this paper, we assume that only a
few central CORE frequency channels are usable for our purpose, all others being devoted
to the cleaning of astrophysical contaminants. On the theoretical side, we assume ÎCDM as
our general framework and quantify the improvement provided by CORE over the current
constraints from the Planck 2015 release. We also study the joint sensitivity of CORE and
of future Baryon Acoustic Oscillation and Large Scale Structure experiments like DESI and
Euclid. Specific constraints on the physics of inflation are presented in another paper of the
series. In addition to the six parameters of the base ÎCDM, which describe the matter content
of a spatially flat universe with adiabatic and scalar primordial fluctuations from inflation, we
derive the precision achievable on parameters like those describing curvature, neutrino physics,
extra light relics, primordial helium abundance, dark matter annihilation, recombination
physics, variation of fundamental constants, dark energy, modified gravity, reionization and
cosmic birefringence. In addition to assessing the improvement on the precision of individual
parameters, we also forecast the post-CORE overall reduction of the allowed parameter space
with figures of merit for various models increasing by as much as ⌠107 as compared to Planck
2015, and 105 with respect to Planck 2015 + future BAO measurements
Exploring cosmic origins with CORE: Survey requirements and mission design
Future observations of cosmic microwave background (CMB) polarisation have
the potential to answer some of the most fundamental questions of modern
physics and cosmology. In this paper, we list the requirements for a future CMB
polarisation survey addressing these scientific objectives, and discuss the
design drivers of the CORE space mission proposed to ESA in answer to the "M5"
call for a medium-sized mission. The rationale and options, and the
methodologies used to assess the mission's performance, are of interest to
other future CMB mission design studies. CORE is designed as a near-ultimate
CMB polarisation mission which, for optimal complementarity with ground-based
observations, will perform the observations that are known to be essential to
CMB polarisation scienceand cannot be obtained by any other means than a
dedicated space mission.Comment: 79 pages, 14 figure
Graviton non-Gaussianities and parity violation in the EFT of inflation
We study graviton non-Gaussianities in the EFT of Inflation. At leading (second) order in derivatives, the graviton bispectrum is fixed by Einstein gravity. There are only two contributions at third order. One of them breaks parity. They come from operators that directly involve the foliation: we then expect sizable non-Gaussianities in three-point functions involving both gravitons and scalars. However, we show that at leading order in slow roll the parity-odd operator does not modify these mixed correlators. We then identify the operators that can affect the graviton bispectrum at fourth order in derivatives. There are two operators that preserve parity. We show that one gives a scalar-tensor-tensor three-point function larger than the one computed in Maldacena, 2003 [1] if M2PAs/Î2 >> 1 (where Î is the scale suppressing this operator and As the amplitude of the scalar power spectrum). There are only two parity-odd operators at this order in derivatives
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Bootstrapping large graviton non-Gaussianities
Gravitational interferometers and cosmological observations of the cosmic
microwave background offer us the prospect to probe the laws of gravity in the
primordial universe. To study and interpret these datasets we need to know the
possible graviton non-Gaussianities. To this end, we derive the most general
tree-level three-point functions (bispectra) for a massless graviton to all
orders in derivatives, assuming scale invariance. Instead of working with
explicit Lagrangians, we take a bootstrap approach and obtain our results using
the recently derived constraints from unitarity, locality and the choice of
vacuum. Since we make no assumptions about de Sitter boosts, our results
capture the phenomenology of large classes of models such as the effective
field theory of inflation and solid inflation. We present formulae for the
infinite number of parity-even bispectra. Remarkably, for parity-odd bispectra,
we show that unitarity allows for only a handful of possible shapes: three for
graviton-graviton-graviton, three for scalar-graviton-graviton and one for
scalar-scalar-graviton, which we bootstrap explicitly. These parity-odd
non-Gaussianities can be large, for example in solid inflation, and therefore
constitute a concrete and well-motivated target for future observations
Compensated isocurvature perturbations in the galaxy power spectrum
We investigate the potential of the galaxy power spectrum to constrain compensated isocurvature perturbations (CIPs), primordial fluctuations in the baryon density that are compensated by fluctuations in CDM density to ensure an unperturbed total matter density. We show that CIPs contribute to the galaxy overdensity at linear order, and if they are close to scale-invariant, their effects are nearly perfectly degenerate with the local PNG parameter fNL if they correlate with the adiabatic perturbations. This degeneracy can however be broken by analyzing multiple galaxy samples with different bias parameters, or by taking CMB priors on fNL into account. Parametrizing the amplitude of the CIP power spectrum as PÏÏ = A2PRR(where PRR is the adiabatic power spectrum) we find, for a number of fiducial galaxy samples in a simplified forecast setup, that constraints on A, relative to those on fNL, of order ÏA/ÏfNL â 1â2 are achievable for CIPs correlated with adiabatic perturbations, and ÏA/ÏfNL â 5 for the uncorrelated case. These values are independent of survey volume, and suggest that current galaxy data are already able to improve significantly on the tightest existing constraints on CIPs from the CMB. Future galaxy surveys that aim to achieve ÏfNL ~ 1 have the potential to place even stronger bounds on CIPs