The ten-parameter, quadratic Poincaré gauge theory of gravity is a plausible alternative to general relativity. We show that the rich background cosmology of the gauge theory is described by a ...noncanonical biscalar-tensor theory in the Jordan frame: the metrical analogue. This provides a unified framework for future investigation by the broader community. For many parameter choices, the noncanonical term reduces to a Cuscuton field of the form √|Xϕϕ|. The Einstein–Cartan–Kibble–Sciama theory maps to a pure quadratic cuscuton, whereas the teleparallel theory maps to the Einstein–Hilbert Lagrangian. We apply the metrical analogue to novel unitary and power-counting-renormalizable cases of Poincaré gauge theory. These theories support the concordance Λ CDM background cosmology up to an optional, effective dark radiation component, we explain this behavior in terms of a stalled cuscuton. We also obtain two dark energy solutions from one of these cases: accelerated expansion from a negative bare cosmological constant whose magnitude is screened, and emergent dark energy to replace vanishing bare cosmological constant in Λ CDM.
It was recently found that, when linearized in the absence of matter, 58 cases of the general gravitational theory with quadratic curvature and torsion are (i) free from ghosts and tachyons and (ii) ...power-counting renormalizable. We inspect the nonlinear Hamiltonian structure of the eight cases whose primary constraints do not depend on the curvature tensor. We confirm the particle spectra and unitarity of all these theories in the linear regime. We uncover qualitative dynamical changes in the nonlinear regimes of all eight cases, suggesting at least a broken gauge symmetry, and possibly the activation of negative kinetic energy spin-parity sectors and acausal behavior. Two of the cases propagate a pair of massless modes at the linear level, and were interesting as candidate theories of gravity. However, we identify these modes with vector excitations, rather than the tensor polarizations of the graviton. Moreover, we show that these theories do not support a viable cosmological background.
A method is presented for Bayesian model selection without explicitly computing evidences, by using a combined likelihood and introducing an integer model selection parameter n so that Bayes factors, ...or more generally posterior odds ratios, may be read off directly from the posterior of n. If the total number of models under consideration is specified a priori, the full joint parameter space (θ, n) of the models is of fixed dimensionality and can be explored using standard Markov chain Monte Carlo (MCMC) or nested sampling methods, without the need for reversible jump MCMC techniques. The posterior on n is then obtained by straightforward marginalization. We demonstrate the efficacy of our approach by application to several toy models. We then apply it to constraining the dark energy equation of state using a free-form reconstruction technique. We show that Λ cold dark matter is significantly favoured over all extensions, including the simple w(z) = constant model.
We make a case for setting initial conditions for inflation at the Planck epoch in the kinetically dominated regime. For inflationary potentials with a plateau or a hill, i.e., potentials that are ...bounded from above within a certain region of interest, we cannot claim complete ignorance of the energy distribution between kinetic and potential energy, and equipartition of energy at the Planck epoch becomes questionable. We analyze different classes of potentials in phase space and quantify the fraction of the Planck surface that is kinetically dominated. Considering bounded potentials with very small amplitudes as favored by current data and restricting ourselves to the domains of phase space that are of interest to cosmic inflation, we find that initial conditions of the inflaton field should be set in the kinetically dominated regime regardless of any choice of prior.
We present a novel approach for setting initial conditions on the mode functions of the Mukhanov-Sasaki equation. These conditions are motivated by minimization of the renormalized stress-energy ...tensor and are valid for setting a vacuum state even in a context where the spacetime is changing rapidly. Moreover, these alternative conditions are potentially observationally distinguishable. We apply this to the kinetically dominated universe and compare with the more traditional approach.
ABSTRACT
Maximally Smooth Functions (MSFs) are a form of constrained functions in which there are no inflection points or zero crossings in high-order derivatives. Consequently, they have ...applications to signal recovery in experiments where signals of interest are expected to be non-smooth features masked by larger smooth signals or foregrounds. They can also act as a powerful tool for diagnosing the presence of systematics. The constrained nature of MSFs makes fitting these functions a non-trivial task. We introduce maxsmooth, an open-source package that uses quadratic programming to rapidly fit MSFs. We demonstrate the efficiency and reliability of maxsmooth by comparison to commonly used fitting routines and show that we can reduce the fitting time by approximately two orders of magnitude. We introduce and implement with maxsmooth Partially Smooth Functions, which are useful for describing elements of non-smooth structure in foregrounds. This work has been motivated by the problem of foreground modelling in 21-cm cosmology. We discuss applications of maxsmooth to 21-cm cosmology and highlight this with examples using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) and the Large-aperture Experiment to Detect the Dark Ages (LEDA) experiments. We demonstrate the presence of a sinusoidal systematic in the EDGES data with a log-evidence difference of 86.19 ± 0.12 when compared to a pure foreground fit. MSFs are applied to data from LEDA for the first time in this paper and we identify the presence of sinusoidal systematics. maxsmooth is pip installable and available for download at https://github.com/htjb/maxsmooth.
ABSTRACT
Detection of millikelvin-level signals from the ‘Cosmic Dawn’ requires an unprecedented level of sensitivity and systematic calibration. We report the theory behind a novel calibration ...algorithm developed from the formalism introduced by the EDGES collaboration for use in 21-cm experiments. Improvements over previous approaches are provided through the incorporation of a Bayesian framework and machine learning techniques such as the use of Bayesian evidence to determine the level of frequency variation of calibration parameters that is supported by the data, the consideration of correlation between calibration parameters when determining their values, and the use of a conjugate-prior based approach that results in a fast algorithm for application in the field. In self-consistency tests using empirical data models of varying complexity, our methodology is used to calibrate a 50 Ω ambient-temperature load. The RMS error between the calibration solution and the measured temperature of the load is 8 mK, well within the 1 σ noise level. Whilst the methods described here are more applicable to global 21-cm experiments, they can easily be adapted and applied to other applications, including telescopes such as HERA and the SKA.
ABSTRACT
Cosmic rays generated by supernovae carry away a significant portion of the lifetime energy emission of their parent star, making them a plausible mechanism for heating the early universe ...intergalactic medium (IGM). Following a review of the existing literature on cosmic ray heating, we develop a flexible model of this heating mechanism for use in 3D seminumerical 21-cm signal simulations and conduct the first investigations of the signatures it imprints on the 21-cm power spectrum and tomographic maps. We find that cosmic ray heating of the IGM is short-ranged, leading to heating clustered around star-forming sites, and a sharp contrast between heated regions of 21-cm emission and unheated regions of absorption. This contrast results in greater small-scale power for cosmic ray heated scenarios compared to what is found for X-ray heating, thus suggesting a way to test the nature of IGM heating with future 21-cm observations. Finally, we find an unexpectedly rich thermal history in models where cosmic rays can only escape efficiently from low-mass haloes, such as in scenarios where these energetic particles originate from population III star supernovae remnants. The interplay of heating and the Lyman–Werner feedback in these models can produce a local peak in the IGM kinetic temperature and, for a limited parameter range, a flattened absorption trough in the global 21-cm signal.
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