Features in the early universe

We use cosmic microwave background (CMB) and large scale structure (LSS) data to test abroad and physically well-motivated class of inflationary models: those with flat tree-levelpotentials (typical in supersymmetry). The non-trivial features of the potential arisefrom radiative corrections which give a simple logarithmic dependence on theinflaton field, making the models very predictive. We also consider a modifiedscenario with new physics beyond a certain high energy cut-off showing up asnon-renormalizable operators (NRO) in the inflaton field. We find that both kinds ofmodels fit CMB and LSS data remarkably well, with very few free parameters. Besides,many of these models naturally predict a reasonable number of e-folds. A robustfeature of these scenarios is the smallness of tensor perturbations (). The NRO case can give a sizable running of the spectral index while achieving asufficient number of e-folds. We use Bayesian model comparison tools to assess the relativeperformance of the models. We believe that these scenarios can be considered as a standardphysical class of inflationary models, on a similar footing to monomial potentials.

We study the phenomenology of the beyond Horndeski class of scalar-tensor theories of gravity, which on cosmological scales can be characterised in terms of one extra function of time, βH, as well as the usual four Horndeski set of free functions. We show that βH can be directly related to the damping of the matter power spectrum on both large and small scales. We also find that the temperature power spectrum of the cosmic microwave background (CMB) is enhanced at low multipoles and the lensing potential is decreased, as a function of βH. For a particular choice of time dependence we find constraints on βH of order \U0001d4aa(1) using measurements of the temperature and polarisation of the CMB, as well as the lensing potential derived from it, combined with large scale structure data. We find that redshift space distortion measurements can play a significant role in constraining these theories. Finally, we comment on the recent constraints from the observation of an electromagnetic counterpart to a gravitational wave signal; we find that these constraints reduce the number of free parameters of the model but do not significantly change the constraints on the remaining parameters.

A promising idea to resolve the long standing Hubble tension is to postulate a new subdominant dark-energy-like component in the prerecombination Universe which is traditionally termed as the early dark energy (EDE). However, as shown in the Refs. [J. C. Hill et al., Early dark energy does not restore cosmological concordance, Phys. Rev. D 102, 043507 (2020), M. M. Ivanov et al.,Constraining early dark energy with large-scale structure, Phys. Rev. D 102, 103502 (2020).] the cosmic microwave background (CMB) and large-scale structure (LSS) data impose tight constraints on this proposal. Here, we revisit these strong bounds considering the Planck CMB temperature anisotropy data at large angular scales and the SPTPol polarization and lensing measurements. As advocated in [A. Chudaykin et al., Combined analysis of Planck and SPTPol data favors the early dark energy models, J. Cosmol. Astropart. Phys. 08 (2020) 013.] another paper, this combined data approach predicts the CMB lensing effect consistent with the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ expectation and allows one to efficiently probe both large and small angular scales. Combining Planck and SPTPol CMB data with the full-shape BOSS likelihood and information from photometric LSS surveys in the EDE analysis we found for the Hubble constant ${H}_{0}=69.79\ifmmode\pm\else\textpm\fi{}0.99\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ and for the EDE fraction ${f}_{\mathrm{EDE}}<0.094(2\ensuremath{\sigma})$. These bounds obtained without including a local distance ladder measurement of ${H}_{0}$ (SH0ES) alleviate the Hubble tension to a $2.5\ensuremath{\sigma}$ level. Including further the SH0ES data we obtain ${H}_{0}=71.81\ifmmode\pm\else\textpm\fi{}1.19\text{ }\text{ }\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ and ${f}_{\mathrm{EDE}}=0.088\ifmmode\pm\else\textpm\fi{}0.034$ in full accordance with SH0ES. We also found that a higher value of ${H}_{0}$ does not significantly deteriorate the fit to the LSS data. Overall, the EDE scenario is (though weakly) favored over $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ even after accounting for unconstrained directions in the cosmological parameter space. We conclude that the large-scale Planck temperature and SPTPol polarization measurements along with LSS data do not rule out the EDE model as a resolution of the Hubble tension. This paper underlines the importance of the CMB lensing effect for robust constraints on the EDE scenario.

The cosmic microwave background (CMB), carrying the inhomogeneous information of the very early universe, is of great significance for understanding the origin and evolution of our universe. However, observational CMB maps contain serious foreground contaminations from several sources, such as Galactic synchrotron and thermal dust emissions. Here, we build a deep convolutional neural network (CNN) to recover the tiny CMB signal from various huge foreground contaminations. Focusing on CMB temperature fluctuations, we find that the CNN model can successfully recover the CMB temperature maps with high accuracy, and that the deviation of the recovered power spectrum C ℓ is smaller than the cosmic variance at ℓ > 10. We then apply this method to the current Planck observations, and find that the recovered CMB is quite consistent with that disclosed by the Planck Collaboration, which indicates that the CNN method can provide a promising approach to the component separation of CMB observations. Furthermore, we test the CNN method with simulated CMB polarization maps based on the CMB-S4 experiment. The result shows that both the EE and BB power spectra can be recovered with high accuracy. Therefore, this method will be helpful for the detection of primordial gravitational waves in current and future CMB experiments. The CNN is designed to analyze two-dimensional images, thus this method is not only able to process full-sky maps, but also partial-sky maps. Therefore, it can also be used for other similar experiments, such as radio surveys like the Square Kilometer Array.

Constraints on inflation from cosmic microwave background and Lyman-α forest

We use the Chandra measurements of the X-ray gas mass fraction of 26 rich clusters released by Allen et al. to perform constraints on the holographic dark energy model. The constraints are consistent with those from other cosmological tests, especially with the results of a joint analysis of supernovae, cosmic microwave background, and large scale structure data. From this test, the holographic dark energy also tends to behave as a quintom-type dark energy.

In inflationary models with minimal amount of gravity waves, the primordial power spectrum of density fluctuations, $A_S^2(k)$, together with the basic cosmological parameters, completely specify the predictions for the cosmic microwave background (CMB) anisotropy and large scale structure. Here we show how we can strongly constrain both $A_S^2(k)$ and the cosmological parameters by combining the data from the Microwave Anisotropy Probe (MAP) and the galaxy redshift survey from the Sloan Digital Sky Survey (SDSS). We allow $A_S^2(k)$ to be a free function, and thus probe features in the primordial power spectrum on all scales. MAP and SDSS have scale-dependent measurement errors that decrease in opposite directions on astrophysically interesting scales; they complement each other and allow the measurement of the primordial power spectrum independent of inflationary models, giving us valuable information on physics in the early Universe, and providing clues to the correct inflationary model.

We present the constraints on inflationary parameters in a flatΛCDM universe obtained from the Wilkinson Microwave Anisotropy Probe (WMAP)three-year data release, plus smaller scale cosmic microwave background (CMB)and two large scale structure (LSS) data sets, 2dF and the Sloan Digital SkySurvey (SDSS) (treated separately). We use a Markov chain Monte Carlo (MCMC)technique combined with an analytic description of the inflationary spectra in termsof the horizon flow functions (HFF). By imposing a consistency condition forthe tensor-to-scalar ratio, we study the constraints on both single field standardinflation and on inflation with the violation of the null energy condition, whichleads to a blue spectrum for gravitational waves. For standard inflation, theconstraint on the tensor-to-scalar ratio we obtain from CMB data and 2dF05 isr0.01<0.26 at2σ confidence level. Without the consistency condition between the tensor-to-scalar ratio and thetensor slope, the constraint on the tensor amplitude is not significantly changed, but theconstraints on the HFFs are significantly relaxed. We then show that when the third HFFϵ3 is allowed to be non-zero and to be of order unity, a large negative (at2σ) value for the running of the scalar spectral index in standard inflation is found in any setof data we consider.

We study 2-field inflation models based on the ``large-volume'' flux compactification of type IIB string theory. The role of the inflaton is played by a K\"ahler modulus $\ensuremath{\tau}$ corresponding to a 4-cycle volume and its axionic partner $\ensuremath{\theta}$. The freedom associated with the choice of Calabi-Yau manifold and the nonperturbative effects defining the potential $V(\ensuremath{\tau},\ensuremath{\theta})$ and kinetic parameters of the moduli brings an unavoidable statistical element to theory prior probabilities within the low-energy landscape. The further randomness of $(\ensuremath{\tau},\ensuremath{\theta})$ initial conditions allows for a large ensemble of trajectories. Features in the ensemble of histories include ``roulette trajectories,'' with long-lasting inflations in the direction of the rolling axion, enhanced in the number of e-foldings over those restricted to lie in the $\ensuremath{\tau}$-trough. Asymptotic flatness of the potential makes possible an eternal stochastic self-reproducing inflation. A wide variety of potentials and inflaton trajectories agree with the cosmic microwave background and large scale structure data. In particular, the observed scalar tilt with weak or no running can be achieved in spite of a nearly critical de Sitter deceleration parameter and consequently a low gravity wave power relative to the scalar curvature power.

The current available Cosmic Microwave Background (CMB) data show an anomalously low value of the CMB temperature fluctuations at large angular scales (ℓ < 40). This lack of power is not explained by the minimal ΛCDM model, and one of the possible mechanisms explored in the literature to address this problem is the presence of features in the primordial power spectrum (PPS) motivated by the early universe physics. In this paper, we analyse a set of cutoff inflationary PPS models using a Bayesian model comparison approach in light of the latest CMB data from the Planck Collaboration. Our results show that the standard power-law parameterisation is preferred over all models considered in the analysis, which motivates the search for alternative explanations for the observed lack of power in the CMB anisotropy spectrum.

Traditionally, inflationary models are analyzed in terms of parameters such as the scalar spectral index ${n}_{s}$ and the tensor to scalar ratio $r$, while dark energy models are studied in terms of the equation of state parameter $w$. Motivated by the fact that both deal with periods of accelerated expansion, we study the evolution of $w$ during inflation, in order to derive observational constraints on its value during an earlier epoch likely dominated by a dynamic form of dark energy. We find that the cosmic microwave background and large-scale structure data is consistent with ${w}_{\mathrm{inflation}}=\ensuremath{-}1$ and provides an upper limit of $1+w\ensuremath{\lesssim}0.02$. Nonetheless, an exact de Sitter expansion with a constant $w=\ensuremath{-}1$ is disfavored since this would result in ${n}_{s}=1$.

The polarization of the cosmic microwave background (CMB) provides a plethora of information about the early universe. Most notably, gravitational waves from the Inflationary epoch (the leading explanation of the origin of the universe) create a unique CMB polarization [Formula: see text]-mode signal. An unambiguous detection of the Inflationary [Formula: see text]-mode signal would be a window into the physics of the universe as it was [Formula: see text][Formula: see text]s after the Big Bang, at energy scales many orders of magnitude larger than what the LHC can produce. However, there are several instrumental and astrophysical sources that can obfuscate the Inflationary [Formula: see text]-mode signal. One of the most difficult parameters to calibrate for CMB telescopes is the absolute orientation of the antenna’s polarization sensitive axis. A miscalibration of the polarization orientation rotates the much brighter [Formula: see text]-mode signal, producing a false [Formula: see text]-mode signal. The current best uncertainty on polarization orientation in the CMB community is [Formula: see text], set from extrapolating IRAM measurements of the Crab Nebula supernova remnant at 90 GHz to 150 GHz, where the CMB signals peak. This accuracy is not sufficient to convincingly detect [Formula: see text]-modes predicted by currently allowable models of Inflation. We suggest to precisely measure the Crab Nebula’s polarization, which can be calibrated absolutely to [Formula: see text] from measurements of the polarized emission of Mars, and use these data to calibrate current and upcoming CMB experiments. In addition to Inflationary [Formula: see text]-modes, more precise calibration will allow us to better constrain the sum of the neutrino masses and set limits on exotic physics such as parity violation through cosmic polarization rotation.

Many scenarios of physics beyond the standard model predict new light, weakly coupled degrees of freedom, populated in the early universe and remaining as cosmic relics today. Due to their high abundances, these relics can significantly affect the evolution of the universe. For instance, massless relics produce a shift $\mathrm{\ensuremath{\Delta}}{N}_{\mathrm{eff}}$ to the cosmic expectation of the effective number of active neutrinos. Massive relics, on the other hand, additionally become part of the cosmological dark matter in the later universe, though their light nature allows them to freely stream out of potential wells. This produces novel signatures in the large-scale structure (LSS) of the universe, suppressing matter fluctuations at small scales. We present the first general search for such light (but massive) relics (LiMRs) with cosmic microwave background (CMB) and LSS data, scanning the 2D parameter space of their masses ${m}_{X}$ and temperatures ${T}_{X}^{(0)}$ today. In the conservative minimum-temperature (${T}_{X}^{(0)}=0.91\text{ }\text{ }\mathrm{K}$) scenario, we rule out Weyl (and higher-spin) fermions---such as the gravitino---with ${m}_{X}\ensuremath{\ge}2.3\text{ }\text{ }\mathrm{eV}$ at 95% C.L., and set analogous limits of ${m}_{X}\ensuremath{\le}11$, 1.1, 1.6 eV for scalar, vector, and Dirac-fermion relics. This is the first search for LiMRs with joint CMB, weak-lensing, and full-shape galaxy data; we demonstrate that weak-lensing data is critical for breaking parameter degeneracies, while full-shape information presents a significant boost in constraining power relative to analyses with only baryon acoustic oscillation parameters. Under the combined strength of these datasets, our constraints are the tightest and most comprehensive to date.

We develop a new phenomenological model that addresses current tensions between observations of the early and late Universe. Our scenario features: (i) a decaying dark energy fluid (DDE), which undergoes a transition at $z \sim 5,000$, to raise today's value of the Hubble parameter -- addressing the $H_0$ tension, and (ii) an ultra-light axion (ULA), which starts oscillating at $z\gtrsim 10^4$, to suppress the matter power spectrum -- addressing the $S_8$ tension. Our Markov Chain Monte Carlo analyses show that such a Dark Sector model fits a combination of Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations, and Large Scale Structure (LSS) data slightly better than the $\Lambda$CDM model, while importantly reducing both the $H_0$ and $S_8$ tensions with late universe probes ($\lesssim 3\sigma$). Combined with measurements from cosmic shear surveys, we find that the discrepancy on $S_8$ is reduced to the $1.4\sigma$ level, and the value of $H_0$ is further raised. Adding local supernovae measurements, we find that the $H_0$ and $S_8$ tensions are reduced to the $1.4\sigma$ and $1.2\sigma$ level respectively, with a significant improvement $\Delta\chi^2\simeq -18$ compared to the $\Lambda$CDM model. With this complete dataset, the DDE and ULA are detected at $\simeq 4\sigma$ and $\simeq2\sigma$, respectively. We discuss a possible particle physics realization of this model, with a dark confining gauge sector and its associated axion, although embedding the full details within microphysics remains an urgent open question. Our scenario will be decisively probed with future CMB and LSS surveys.

We study anisotropic (patchy) screening induced by the resonant conversion of cosmic microwave background (CMB) photons into dark-sector massive vector bosons (dark photons) as they cross non-linear large scale structure (LSS). Resonant conversion takes place through the kinetic mixing of the photon with the dark photon, one of the simplest low energy extensions to the Standard Model. In the early Universe, resonant conversion can occur when the photon plasma mass, obtained as the photon propagates through the ionized interstellar and intergalactic media, matches the dark photon mass. After the epoch of reionization, resonant conversion occurs mainly in the ionized gas that occupies virialized dark matter halos, for a range of dark photon masses between 10-13 eV ≲ m A' ≲ 10-11 eV. This leads to new CMB anisotropies that are correlated with LSS, which we refer to as patchy dark screening, in analogy with anisotropies from Thomson screening. Its unique frequency dependence allows it to be distinguished from the blackbody CMB. In this paper, we use a halo model approach to predict the imprint of dark screening on the CMB temperature and polarization anisotropies, as well as their correlation with LSS. We then examine the two- and three-point correlation functions of the dark-screened CMB, as well as correlation functions between CMB and LSS observables, to project the sensitivity of future measurements to the kinetic mixing parameter and dark photon mass. We demonstrate that an analysis with existing CMB data can improve upon current constraints on the kinetic mixing parameter by two orders of magnitude with the two-point correlation functions, while data from upcoming CMB experiments and LSS surveys can further improve the reach by another order of magnitude with two- and three-point correlation functions.