Cosmological Observations Research Articles

A complete framework for cosmological emulation and inference with CosmoPower

Abstract We present a coherent, re-usable python framework building on the CosmoPower emulator code for high-accuracy calculations of cosmological observables with Einstein-Boltzmann codes. For detailed statistical analyses, such codes require high computing power, making parameter space exploration costly, especially for beyond-ΛCDM analyses. Machine learning-enabled emulators of Einstein-Boltzmann codes are becoming an increasingly popular solution to this problem. To enable generation, sharing and use of emulators for inference, we define standards for robustly describing, packaging and distributing them. We present software for easily performing these tasks in an automated and replicable manner and provide examples and guidelines for generating emulators and wrappers for using them in popular cosmological inference codes. We demonstrate our framework with a suite of high-accuracy emulators for the CAMB code’s calculations of CMB Cℓ, P(k), background evolution, and derived parameter quantities. We show these emulators are accurate enough for analysing both ΛCDM and a set of extension models (Neff, ∑mν, w0wa) with stage-IV observatories, recovering the original high-accuracy spectra to tolerances well within the cosmic variance uncertainties. We show our emulators also recover cosmological parameters in a simulated cosmic-variance limited experiment, finding results well within 0.1σ of the input cosmology, while requiring ≲ 1/50 of the evaluation time.

Majorana CP violating phases

The two Majorana CP-violating phases can not be determined by experiments on neutrino oscillations. It is difficult even almost impossible to measure two Majorana CP-violating phases since they are only sensitive to lepton-number-violating processes. One must take some assumption on the structure of neutrino mass matrix and their flavor mixing mechanism hidden behind in phenomenological models in order to determine Majorana CP-violating phases. Two models on the symmetry of the neutrino mass matrix are proposed in this paper. The Majorana CP-violating phases and the effective Majorana neutrino mass mee are computed in the two models. Using data in experiments on neutrino oscillations and using the limit of the absolute neutrino mass scale which is from cosmological observations, the numerical values of the Majorana CP-violating phases and the effective Majorana neutrino mass mee are obtained.

Everything hot everywhere all at once: neutrinos and hot dark matter as a single effective species

Observational cosmology is rapidly closing in on a measurement of the sum Mν of neutrino masses, at least in the simplest cosmologies, while opening the door to probes of non-standard hot dark matter (HDM) models. By extending the method of effective distributions, we show that any collection of HDM species, with arbitrary masses, temperatures, and distribution functions, including massive neutrinos, may be represented as a single effective HDM species. Implementing this method in the FlowsForTheMasses non-linear perturbation theory for free-streaming particles, we study non-standard HDM models that contain thermal QCD axions or generic bosons in addition to standard neutrinos, as well as non-standard neutrino models wherein either the distribution function of the neutrinos or their temperature is changed. Along the way, we substantially improve the accuracy of this perturbation theory at low masses, bringing it into agreement with the high-resolution TianNu neutrino N-body simulation to ≈ 2% at k = 0.1 h/Mpc and to ≤ 21% over the range k ≤ 1 h/Mpc. We accurately reproduce the results of simulations including axions and neutrinos of multiple masses. Studying the differences between the normal, inverted, and degenerate neutrino mass orderings on their non-linear power, we quantify the error in the common approximation of degenerate masses. We release our code publicly at http://github.com/upadhye/FlowsForTheMassesII.

Chasing cosmic inflation: constraints for inflationary models and reheating insights

We investigate the impact of different choice of prior's range for the reheating epoch on cosmic inflation parameter inferencein light of cosmic microwave background (CMB) anisotropy measurements from the Planck 2018 legacy releasein combination with BICEP/Keck Array 2018 data and additional late-time cosmological observations such as uncalibratedType Ia supernovae from the Pantheon catalogue, baryon acoustic oscillations and redshift space distortionsfrom SDSS/BOSS/eBOSS.Here, we explore in particular the implications for the combination of reheating and inflationary-model parameter spaceconsidering R+R 2 inflation and a broad class of α-attractor and D-brane models.Propagating the uncertainties due to an unknown reheating phase, these inflationary models completely cover the n s-r parameter space allowed by Planck and BICEP/Keck dataand represent good targets for future CMB and large-scale structure experiments.We perform a Bayesian model comparison of inflationary models, taking into account the reheating uncertaintiesassuming a conservative but accurate modelling of inflationary predictions.R+R 2 inflation, T-model α-attractor inflation for n=1, E-model α-attractor inflation for n=1/2,and KKLT inflation for p=5 are the better performing models, with none being preferred at a statistically significant level.

Non-Parametric Reconstruction of Cosmological Observables Using Gaussian Processes Regression

The current accelerated expansion of the Universe remains one of the most intriguing topics in modern cosmology, driving the search for innovative statistical techniques. Recent advancements in machine learning have significantly enhanced its application across various scientific fields, including physics, and particularly cosmology, where data analysis plays a crucial role in problem-solving. In this work, a non-parametric regression method with Gaussian processes is presented along with several applications to reconstruct some cosmological observables, such as the deceleration parameter and the dark energy equation of state, in order to contribute some information that helps to clarify the behavior of the Universe. It was found that the results are consistent with λCDM and the predicted value of the Hubble parameter at redshift zero is H0=68.798±6.340(1σ)kms−1Mpc−1.

CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations. II. Constraining cosmology and astrophysical processes with early- and late-type galaxies

Physical processes can influence the formation and evolution of galaxies in diverse ways. It is essential to validate their incorporation into cosmological simulations by testing them against real data encompassing various types of galaxies and spanning a broad spectrum of masses and galaxy properties. For these reasons, in this second paper of the CASCO series, we compare the structural properties and dark matter content of early-type galaxies taken from the camels IllustrisTNG cosmological simulations to three different observational datasets (SPIDER and MaNGA DynPop), to constrain the value of cosmological and astrophysical feedback parameters, and we compare the results with those obtained comparing the simulation expectations with late-type galaxies. We consider the size-mass, internal DM fraction-mass, and internal DM mass-stellar mass relations for all the simulations, and search for the best-fit simulation for each set of observations. For SPIDER, we find values for the cosmological parameters in line with both the literature and the results obtained from the comparison between simulations and late-type galaxies; results for the supernovae feedback parameters are instead opposite with respect to the previous results based on late-type galaxies. For we find similar values as from SPIDER for the cosmological parameters, but we find values for the supernovae feedback parameters more in line with what we found for late-type galaxies. From MaNGA DynPop, we find extreme values for the cosmological parameters, while the supernovae feedback parameters are consistent with results. When considering the full MaNGA DynPop sample, including both late- and early-type galaxies, no single simulation can reproduce the full variety in the observational datasets. The constraints depend strongly on the specific properties of each observational trend, making it difficult to find a simulation matching all galaxy types, indicating the existence of limitations in the ability of simulations in reproducing the observations.

Prospects for searching for sterile neutrinos with gravitational wave and γ-ray burst joint observations

Abstract Sterile neutrinos can influence the evolution of the universe, and thus cosmological observations can be used to detect them. Future gravitational wave (GW) observations can precisely measure absolute cosmological distances, helping to break parameter degeneracies generated by traditional cosmological observations. This advancement can lead to much tighter constraints on sterile neutrino parameters. This work provides a preliminary forecast for detecting sterile neutrinos using third-generation GW detectors in combination with future short γ-ray burst observations from a THESEUS-like telescope, an approach not previously explored in the literature. Both massless and massive sterile neutrinos are considered within the ΛCDM cosmology. We find that using GW data can greatly enhance the detection capability for massless sterile neutrinos, reaching 3σ level. For massive sterile neutrinos, GW data can also greatly assist in improving the parameter constraints, but it seems that effective detection is still not feasible.

Cosmological amplitudes in power-law FRW universe

The correlators of large-scale fluctuations belong to the most important observables in modern cosmology. Recently, there have been considerable efforts in analytically understanding the cosmological correlators and the related wavefunction coefficients, which we collectively call cosmological amplitudes. In this work, we provide a set of simple rules to directly write down analytical answers for arbitrary tree-level amplitudes of conformal scalars with time-dependent interactions in power-law FRW universe. With the recently proposed family-tree decomposition method, we identify an over-complete set of multivariate hypergeometric functions, called family trees, to which all tree-level conformal scalar amplitudes can be easily reduced. Our method yields series expansions and monodromies of family trees in various kinematic limits, together with a large number of functional identities. The family trees are in a sense generalizations of polylogarithms and do reduce to polylogarithmic expressions for the cubic coupling in inflationary limit. We further show that all family trees can be decomposed into linear chains by taking shuffle products of all subfamilies, with which we find simple connection between bulk time integrals and boundary energy integrals.

Efficient compression of redshift-space distortion data for late-time modified gravity models

Current cosmological observations allow for deviations from the standard growth of large-scale structures in the universe. These deviations could indicate modifications to General Relativity on cosmological scales or suggest the dynamical nature of dark energy. It is important to characterize these departures in a model-independent manner to understand their significance objectively and explore their fundamental causes more generically across a wider spectrum of theories and models. In this paper, we compress the information from redshift-space distortion data into 2–3 parameters μ i , which control the ratio between the effective gravitational coupling in Poisson's equation and Newton's constant in several redshift bins in the late universe. We test the efficiency of this compression using mock final-year data from the Dark Energy Spectroscopic Instrument (DESI) and considering three different models within the class of effective field theories of dark energy. The constraints on the parameters of these models, obtained from both the direct fit to the data and the projection of the compressed parameters onto the parameters of the models, are fully consistent, demonstrating the method's good performance. Then, we apply it to current data and find hints of a suppressed matter growth in the universe at ∼ 2.7σ C.L., in full accordance with previous works in the literature. Finally, we perform a forecast with DESI data and show that the uncertainties on the parameters μ 1 at z < 1 and μ 2 at 1 < z < 3 are expected to decrease by approximately 40% and 20%, respectively, compared to those obtained with current data. Additionally, we project these forecasted constraints onto the parameters of the aforesaid models.

There and Back Again: Mapping and Factorizing Cosmological Observables.

Cosmological correlators encode invaluable information about the wave function of the primordial Universe. In this Letter we present a duality between correlators and wave function coefficients that is valid to all orders in the loop expansion and manifests itself as a Z_{4} symmetry. To demonstrate the power of the duality, we derive a correlator-to-correlator factorization formula for the parity-odd part of cosmological correlators that relates n-point observables to lower-point ones via a series of diagrammatic cuts. These relations serve as the first example of physically testable cutting rules as they involve observables defined for arbitrary physical kinematics. We further show how the duality allows us to translate the cosmological optical theorem for wave function coefficients into statements about cosmological correlators.

Inflationary dynamics of Mutated Hilltop inflation in Einstein–Gauss–Bonnet Gravity under new slow-roll approximations with generalized reheating

The advancement in the observational cosmology of the early universe such as Cosmic Microwave Background (CMB) observations, puts severe constraints on the inflationary models. Many inflationary models have been ruled out by CMB, nevertheless the models ruled out in standard cold inflationary scenarios can be resurrected in modified gravity models. In this regard we examine the dynamics of inflation within the framework of Einstein–Gauss–Bonnet (EGB) Gravity using the new slow-roll approximation methods proposed in Pozdeeva et al. (2024). We consider the Mutated Hilltop inflation model (Pal et al., 2010; Pinhero and Pal, 2019) due to its origin from super-gravity, a naturally perfect choice to study the impact of EGB on inflationary observables such as tensor-to-scalar ratio (r) and scalar spectral index (ns). The period of reheating following the inflationary phase is also examined, and for the Planck’18 permitted values of ns, constraints on the reheating temperature (Tre) are computed for various equations of states during reheating (ωre).

Quantum Gravity without Quantization

Objective: An alternative way to construct a quantum model of gravity is described in this paper, not by quantizing the classical model, but by introducing a graviton background, which has a low temperature, but strongly interacts with any particle. Methods: Gravity in this case is the effect of screening the background of gravitons by bodies; several additional effects appear when photons or bodies move through the background. Results: Using Planck's formula for the graviton spectrum and taking into account the pairing effect for some of the gravitons, Newton's constant can be calculated and the magnitudes of the additional effects can be estimated. Conclusion: These small additional effects can be important for cosmology since they allow to describe the results of cosmological observations without dark energy.

Global embedding of fiber inflation in a perturbative large volume scenario

We present a global embedding of the fiber inflation model in a perturbative large volume scenario (LVS) in which the inflationary potential is induced via a combination of string-loop corrections and higher derivative F4 effects. The minimal fiber inflation model developed in the standard LVS generically faces some strong bounds on the inflaton field range arising from the Kähler cone constraints, which subsequently creates a challenge for realizing the cosmological observables while consistently respecting the underlying supergravity approximations. The main attractive feature of this proposal is to naturally alleviate this issue by embedding fiber inflation in perturbative LVS. Published by the American Physical Society 2024

Bubble velocities and oscillon precursors in first-order phase transitions

Metastable ‘false’ vacuum states are an important feature of the Standard Model of particle physics and many theories beyond it. Describing the dynamics of a phase transition out of a false vacuum via the nucleation of bubbles is essential for understanding the cosmology of vacuum decay and the full spectrum of observables. In this paper, we study vacuum decay by numerically evolving ensembles of field theories in 1+1 dimensions from a metastable state. We demonstrate that for an initial Bose-Einstein distribution of fluctuations, bubbles form with a Gaussian spread of center-of-mass velocities and that bubble nucleation events are preceded by an oscillon — a long-lived, time-dependent, pseudo-stable configuration of the field. Defining an effective temperature from the long-wavelength amplitude of fluctuations in the ensemble of simulations, we find good agreement between theoretical finite temperature predictions and empirical measurements of the decay rate, velocity distribution and critical bubble solution. We comment on the generalization of our results and the implications for cosmological observables.

Extended uncertainty principle and equation of state for dark energy

The modification of Heisenberg's uncertainty principle (HUP), is considered valuable in modern theoretical physics due to its implications on quantum gravity effects. In this paper, we attempted to derive an equation of state for dark energy, using the extended uncertainty principle (EUP) which includes a defined maximum length. We then compared this novel equation with the equations of state obtained from cosmological observations. The observational constraints on dark energy equation of states and the second law of thermodynamics suggest that the EUP parameter sign with maximum length must change.

Irreducible cosmological backgrounds of a real scalar with a broken symmetry

We explore the irreducible cosmological implications of a singlet real scalar field. Our focus is on theories with an approximate and spontaneously broken Z2 symmetry where quasistable domain walls can form at early times. This seemingly simple framework bears a wealth of phenomenological implications that can be tackled by means of different cosmological and astrophysical probes. We elucidate the connection between domain wall dynamics and the production of dark matter and gravitational waves. In particular, we identify three main benchmark scenarios. The gravitational wave signal observed by pulsar timing arrays can be generated by the domain walls if the mass of the singlet is ms∼PeV. For lower masses, but with ms≳10 GeV, scalars produced in the annihilation of the domain walls can be dark matter with a distinctive feature in their power spectrum. Finally, the thermal bath provides an unavoidable source of unstable scalars via the freeze-in mechanism whose subsequent decays can be tested by their imprints on cosmological and terrestrial observables. Published by the American Physical Society 2024

Measuring the speed of light with cosmological observations: current constraints and forecasts

We measure the speed of light with current observations, such as Type Ia Supernova, galaxy ages, radial BAO mode, as well as simulations of forthcoming redshift surveys and gravitational waves as standard sirens. By means of a Gaussian Process reconstruction, we find that the precision of such measurements can be improved from roughly 6% and to about 2–2.5% when the gravitational wave simulations are considered, and to 1.5–2% when redshift survey are included in the analysis as well. This result demonstrates that we will be able to perform a cosmological measurement of a fundamental physical constant with significantly improved precision, which will help us underpinning if its value is truly consistent with local measurements, as predicted by the standard model of Cosmology.

Absolute Reference for Microwave Polarization Experiments. The COSMOCal Project and its Proof of Concept

Context. The cosmic microwave background (CMB), a remnant of the Big Bang, provides unparalleled insights into the primordial universe, its energy content, and the origin of cosmic structures. The success of forthcoming terrestrial and space experiments hinges on meticulously calibrated data. Specifically, the ability to achieve an absolute calibration of the polarization angles with a precision of <0.°1 is crucial to identify the signatures of primordial gravitational waves and cosmic birefringence within the CMB polarization. Aims. We introduce the COSmological Microwave Observations Calibrator project, designed to deploy a polarized source in space for calibrating microwave frequency observations. The project aims to integrate microwave polarization observations from small and large telescopes, ground-based and in space, into a unified scale, enhancing the effectiveness of each observatory and allowing robust combination of data. Methods. To demonstrate the feasibility and confirm the observational approach of our project, we developed a prototype instrument that operates in the atmospheric window centered at 260 GHz, specifically tailored for use with the NIKA2 camera at the IRAM 30 m telescope. Results. We present the instrument components and their laboratory characterization. The results of tests performed with the fully assembled prototype using a Kinetic Inductance Detectors-based instrument, similar concept of NIKA2, are also reported. Conclusions. This study paves the way for an observing campaign using the IRAM 30 m telescope and contributes to the development of a space-based instrument.

Extending MGCAMB tests of gravity to nonlinear scales

Modified Growth with CAMB (MGCAMB) is a patch for the Einstein-Boltzmann solver CAMB for cosmological tests of gravity. Until now, MGCAMB was limited to scales well-described by linear perturbation theory. In this work, we extend the framework with a phenomenological model that can capture nonlinear corrections in a broad range of modified gravity theories. The extension employs the publicly available halo model reaction code ReACT, developed for modeling the nonlinear corrections to cosmological observables in extensions of the ΛCDM model. The nonlinear extension makes it possible to use a wider range of data from large scale structure surveys, without applying a linear scale cut. We demonstrate that, with the 3×2pt Dark Energy Survey data, we achieve a stronger constraint on the linear phenomenological functions μ and Σ, after marginalzing over the additional nonlinear parameter p 1, compared to the case without the nonlinear extension and using a linear cut. The new version of MGCAMB is now forked with CAMB on GitHub allowing for compatibility with future upgrades.

Non-parametric reconstruction of the fine structure constant with galaxy clusters

Testing possible variations in fundamental constants of nature is a crucial endeavor in observational cosmology. This paper investigates potential cosmological variations in the fine structure constant (α) through a non-parametric approach, using galaxy cluster observations as the primary cosmological probe. We employ two methodologies based on galaxy cluster gas mass fraction measurements derived from X-ray and Sunyaev–Zeldovich observations, along with luminosity distances from type Ia supernovae. We also explore how different values of the Hubble constant (H0) impact the variation of α across cosmic history. When using the Planck satellite’s H0 observations, a constant α is ruled out at approximately the 3σ confidence level for z≲0.5. Conversely, employing local estimates of H0 restores agreement with a constant α.