arXiv subjects

Ali Rida Khalife

Publications and source records attributed to Ali Rida Khalife.

8 recordsLinked to original sources

arXiv2026

Boosting the optical depth to Thomson scattering with primordial black hole evaporation at high redshift

BAO and CMB data are somewhat discrepant when interpreted in the context of $Λ$cdm, discrepancies that show up as a `matter density deficit' and as a `CMB lensing excess'. One possible resolution is an increased optical depth to scattering off of free electrons in the post-recombination universe, $τ$, a possibility raised by Sailer et al. 2025 and Jhaveri et al. 2025. Since Planck measurements of the low-$\ell$ polarization `reionization bump' already constrain $τ$ from standard stellar-driven reionization at $z<10$, we investigate additional optical depth sourced by transient or partial reionization at higher redshift from exotic processes. For specificity, we explore the impact of Hawking radiation from a monochromatic spectrum of primordial black holes, retaining the high-$\ell$ $TT/TE/EE$ data that constrain such histories and varying the reionization redshift jointly. We find that the CMB data do not significantly prefer these additional signals: the boost is at most $Δτ\simeq 0.008$, well short of the $Δτ\simeq 0.03$ that would completely eliminate the moderate discrepancy. The matter density deficit and the lensing excess are not significantly eased: we explain why, tracing it to compensation from the reionization redshift and the residual PBH signal at $\ell > 30$.

astro-ph.CO↗

arXiv2026

The Status of Gravitational Vector Perturbations with Recent CMB Data

We present new constraints on gravitational vector perturbations ($\mathcal{V}$-modes) using Cosmic Microwave Background (CMB) data, including temperature and $E$-mode polarization from SPT-3G D1, ACT-DR6, and $Planck$, as well as $B$-mode data from BICEP/Keck and SPTpol, which provide the strongest constraints on $\mathcal{V}$-modes. We consider three initial conditions (ICs) that source $\mathcal{V}$-modes: neutrino isocurvature (ISO), neutrino octupole (OCT), and a sourced mode (SMD) generated by an anisotropic stress before matter-radiation equality. We also consider including tensor modes along with $\mathcal{V}$-modes for each of these ICs. Combining all datasets, we obtain 95\% confidence level upper limits of $r_\mathrm{v} < 1.3\times10^{-4}$ (ISO), $r_\mathrm{v} < 6.8$ (OCT), and $r_\mathrm{v} < 4.2$ (SMD), with slightly tighter bounds when tensors are included, at a pivot scale $k_p\ =\ 0.05$ Mpc$^{-1}$. Interestingly, for SMD without tensors, using SPTpol $B$-modes alone yields $r_\mathrm{v} = 4.7 \pm 2.1$, consistent with zero at $2.2σ$. Similar result is found for SMD when including tensor perturbations. No statistically significant deviation from $Λ$CDM is found. However, $\mathcal{V}$-modes are not fully excluded by current $B$-mode data and should be considered when interpreting primordial signals.

astro-ph.CO↗

arXiv2026

Disentangling cosmic distance tensions with early and late dark energy

Recent cosmological data reveal tension between parameters inferred from measurements of the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), and supernovae (SN) under $Λ$CDM. Typical dynamical dark energy parameterizations (such as $w_0w_a$) that seek to jointly resolve these tensions have an equation of state parameter that crosses into the phantom regime, leading to potential instabilities for physical models. We show that the BAO (early-time) and SN (late-time) sides of the tension can instead be treated independently. Early dark energy (EDE) can reduce the tension between CMB-BAO data by changing the calibration of the sound horizon at the drag epoch $r_d$, with a $Δχ^2 = -{9.4}$ relative to $Λ$CDM, raising $H_0$ to 70.87 $\rm km s^{-1}Mpc^{-1}$. EDE alone cannot bring consistency between CMB, BAO, and SN data, but combining with a thawing-quintessence component of dark energy reduces tensions between the three datasets, with $Δχ^2=-12.6$ relative to $Λ$CDM without a phantom component, vs. $Δχ^2=-15.8$ for $w_0 w_a$ with one. We consider different SN datasets, using the most recent DES Dovekie catalog as our default while assessing differences with the original DESY5 and Pantheon+ catalogs. While the significance of adding thawing quintessence changes, the EDE solution to the CMB-BAO tension remains nearly unaffected. Moreover, though we do not include direct Hubble constant measurements in these $Δχ^2$ values, the EDE solution reduces the Hubble tension with the Local Distance Network value from $7σ$ in $Λ$CDM to $2-3σ$ depending on the SN dataset, nominally the equivalent of an extra $Δχ^2 \sim -40$ or more.

astro-ph.CO↗

arXiv2025

Resurrecting Gravitational Vector Modes and their Magnetogenesis

We revisit the presence of primordial gravitational vector modes (V-modes) and their sourcing of primordial magnetic fields (PMF), i.e. magnetogenesis. As the adiabatic vector mode generically decays with expansion, we consider exotic initial conditions which circumvent this issue and lead to observational imprints. The first initial condition is an isocurvature mode between photons and neutrinos vorticities, and the second one is a non-trivial initial condition on the neutrino octupole. Both types of conditions sustain a constant vector mode on super Hubble scales at early times. We also consider a third scenario in which the adiabatic vector modes are rapidly sourced, at a given early but finite time, by an exotic component which develops an anisotropic stress. We find the best fitting parameters in these three cases to CMB and BAO data. We compare the resulting $B$-mode spectra of the CMB to data from BICEP/Keck and SPTpol. We find that none of the proposed initial conditions can produce large enough PMFs to seed every type of magnetic fields observed. However, V-modes are still consistent with the data and ought to be constrained for a better understanding of the primordial Universe before its hot big-bang phase.

astro-ph.CO↗

arXiv2025

OLÉ -- Online Learning Emulation in Cosmology

In this work, we present OLÉ, a new online learning emulator for use in cosmological inference. The emulator relies on Gaussian Processes and Principal Component Analysis for efficient data compression and fast evaluation. Moreover, OLÉ features an automatic error estimation for optimal active sampling and online learning. All training data is computed on-the-fly, making the emulator applicable to any cosmological model or dataset. We illustrate the emulator's performance on an array of cosmological models and data sets, showing significant improvements in efficiency over similar emulators without degrading accuracy compared to standard theory codes. We find that OLÉ is able to considerably speed up the inference process, increasing the efficiency by a factor of $30-350$, including data acquisition and training. Typically the runtime of the likelihood code becomes the computational bottleneck. Furthermore, OLÉ emulators are differentiable; we demonstrate that, together with the differentiable likelihoods available in the $\texttt{candl}$ library, we can construct a gradient-based sampling method which yields an additional improvement factor of 4. OLÉ can be easily interfaced with the popular samplers $\texttt{MontePython}$ and $\texttt{Cobaya}$, and the Einstein-Boltzmann solvers $\texttt{CLASS}$ and $\texttt{CAMB}$. OLÉ is publicly available at https://github.com/svenguenther/OLE .

astro-ph.CO↗

arXiv2025

The End of Easy Phenomenology for CMB Experiments: A Case Study in the Dark Sector

The precision of Cosmic Microwave Background (CMB) experiments, specifically its lensing reconstruction, has reached the limit where non-linear corrections cannot be ignored. Neglecting these corrections results in biased constraints on cosmological parameters. In this work, we use lensing data from Planck and the South Pole Telescope third generation camera (SPT-3G) taken in 2018 to highlight the impact of these biases in two ways. First, we estimate the shifts due to ignoring non-linear corrections in $Λ$CDM. We find 0.2-0.6$σ$ shifts in the Dark Matter (DM) fraction, the Hubble constant, and the amplitude of matter fluctuations at $8 h^{-1}$ Mpc. Second, we estimate the loss in constraining power for not including data sensitive to non-linear corrections. As a case study, we consider two interacting DM models, for which such corrections are not readily available in existing CMB Boltzmann codes. The first one is DM interacting with baryons, while the second is DM interacting with Dark Radiation (DR). For the former case, when we add primary CMB data from SPT-3G 2018 observations, we find that constraints on model parameters improve by 10-20% compared to previous studies. However, we forecast a further 50% improvement on these constraints if one could include current or upcoming SPT-3G lensing data. For the case of DM interacting with DR, no meaningful constraints on the model parameters are found without including information from CMB lensing. We also highlight that the codes used to calculate non-linear corrections in $Λ$CDM, specifically HaloFit and HMCode, provide unstable results when improperly used for these extended models. These outcomes constitute a reason for caution if using CMB lensing data when constraining such models, as well as a motivation for estimating their non-linear corrections.

astro-ph.CO↗

arXiv2024

Review of Hubble tension solutions with new SH0ES and SPT-3G data

We present an updated analysis of eleven cosmological models that may help reduce the Hubble tension, which now reaches the $6σ$ level when considering the latest SH0ES measurement versus recent CMB and BAO data, assuming $Λ$CDM. Specifically, we look at five classical extensions of $Λ$CDM (with massive neutrinos, spatial curvature, free-streaming or self-interacting relativistic relics, or dynamical dark energy) and six elaborate models featuring either a time-varying electron mass, early dark energy or some non-trivial interactions in the neutrino sector triggered by a light Majoron. We improve over previous works in several ways. We include the latest data from the South Pole Telescope as well as the most recent measurement of the Hubble rate by the SH0ES collaboration. We treat the summed neutrino mass as a free parameter in most of our models, which reveals interesting degeneracies and constraints. We define additional metrics to assess the potential of a model to reduce or even solve the Hubble tension. We validate an emulator that uses active learning to train itself during each parameter inference run for any arbitrary model. We find that the time-varying electron mass and the Majoron models are now ruled out at more than $3σ$. Models with a time-varying electron mass and spatial curvature or with early dark energy reduce the tension to $1.0-2.9σ$. Nevertheless, none of the models considered in this work is favored with enough statistical significance to become the next concordance model of Cosmology.

astro-ph.CO↗

arXiv2023

Why is zero spatial curvature special?

Evidence for almost spatial flatness of the Universe has been provided from several observational probes, including the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO) from galaxy clustering data. However, other than inflation, and in this case only in the limit of infinite time, there is no strong a priori motivation for a spatially flat Universe. Using the renormalization group (RG) technique in curved spacetime, we present in this work a theoretical motivation for spatial flatness. Starting from a general spacetime, the first step of the RG, coarse-graining, gives a Friedmann-Lemaître-Robertson-Walker (FLRW) metric with a set of parameters. Then, we study the rescaling properties of the curvature parameter, and find that zero spatial curvature of the FLRW metric is singled out as the unique scale-free, non-singular background for cosmological perturbations.

astro-ph.CO↗