arXiv subjects

Giacomo Galloni

Publications and source records attributed to Giacomo Galloni.

8 recordsLinked to original sources

arXiv2026

CosmoForge I: A unified framework for QML power spectrum estimation and pixel-based likelihood analysis

Optimal power spectrum estimation on the largest angular scales of the cosmic microwave background relies on the Quadratic Maximum Likelihood (QML) estimator. Existing public implementations, however, each address only a subset of the problem and none combine power spectrum estimation with a self-consistent pixel-space likelihood within a single framework. We present CosmoForge, a public Python framework that unifies QML power spectrum estimation and pixel-based Gaussian likelihood evaluation for spin-0 and spin-2 fields on the sphere, with general (non-diagonal) noise covariances. The framework is split into three installable packages: CosmoCore (infrastructure), QUBE (Fisher and QML estimation), and PICSLike (pixel-space likelihood). A common interface exposes two interchangeable computation bases $-$ a harmonic basis built on the Sherman-Morrison-Woodbury identity and a direct pixel-space basis $-$ selecting whichever is cheaper for the configuration at hand. Exact algorithmic optimisations reduce the Fisher cost to $\mathcal{O}(\ell_{\rm max}^4)$ for arbitrary noise covariances, with Numba JIT compilation of the hot kernels and MPI parallelisation of the likelihood scan. CosmoForge reproduces the Planck low-$\ell$ Fortran reference implementation across both the QML and pixel-space likelihood pipelines, consistently with double-precision arithmetic. Native multipole binning and three output normalisations (deconvolved, decorrelated, window-convolved) are exposed through a single code path, and the same covariance infrastructure powers both QML estimation and likelihood evaluation. CosmoForge offers a general-purpose, modular, and validated tool for the optimal analysis of large-scale data on the sphere. It is publicly available, pip-installable, and extensible to non-CMB observables.

astro-ph.CO↗

arXiv2026

Cross-spectra likelihood for robust $τ$ constraints from all satellite polarisation data

The Thomson scattering optical depth to reionisation, $τ$, one of the six parameters of the $Λ$CDM model, is primarily constrained by the large-scale E-mode polarisation of the Cosmic Microwave Background (CMB). In this work, we present the E-mode Likelihood for Cross-Analysis (elica), a multi-frequency, harmonic-space likelihood that combines all currently available large-scale satellite polarisation data, namely the Planck LFI 70 GHz channel, the Planck HFI 100 and 143 GHz channels processed with the SRoll2 map-making algorithm, and the WMAP Ka, Q, and V bands. The likelihood is built on an extension of the Hamimeche-Lewis formalism to multi-field partial-sky observations. We validate the pipeline using 500 realistic simulations and find that retaining all cross-spectra and the WMAP-LFI auto-spectrum eliminates the significant bias present when all spectra are retained, while preserving comparable uncertainties in the recovered value of $τ$. From the low-$\ell$ E-mode power spectrum alone, we obtain $τ= 0.0575_{-0.0058}^{+0.0048}$ (68% CL). Combining elica with the Planck low-$\ell$ temperature likelihood and the CamSpec high-$\ell$ likelihood, we find $τ= 0.0581_{-0.0059}^{+0.0048}$ and $\ln(10^{10}A_{\mathrm{s}}) = 3.048_{-0.012}^{+0.011}$. Including ACT{} DR6 + Planck CMB lensing and DESI DR2 BAO measurements, we derive an upper bound on the total neutrino mass of $\sum m_ν< 0.069$ eV (95% CL). Our results, obtained through careful cross-validation of all available large-scale polarisation datasets, robustly confirm that the optical depth remains relatively low. This severely constrains the possibility of explaining, or even significantly reducing, the tension between DESI-BAO and CMB observations with a high value of $τ$. The elica likelihood is publicly available.

astro-ph.CO↗

arXiv2025

Accurate and efficient likelihood modeling for large-scale CMB data

Accurate parameter estimation from cosmic microwave background data requires reliable likelihood modeling, particularly at large angular scales where angular power spectrum estimators exhibit non-Gaussian statistics. We present a novel approach, based on the Hamimeche-Lewis formalism, that marginalizes over auto-spectra, thus reducing residual biases from noise misestimation and partial sky coverage. We validate our approach by simulating three independent CMB channels, or data splits, in a multi-field setting, comparing to the pixel-based likelihood ground truth estimates for the optical depth $τ$ and the tensor-to-scalar ratio $r$. We benchmark our method against the main power spectrum based alternatives available in the literature, showing that it outperforms all of them in terms of accuracy, while remaining fast and computationally efficient.

astro-ph.CO↗

arXiv2025

The first data-driven bounds on the quantum decoherence of inflationary gravitational waves

The (large-scale) structures we observe in the Universe are classical, but within the inflationary scenario they do originate from quantum fluctuations. This leads to the question: ''How did this quantum-to-classical transition occur?''. A potential explanation is quantum decoherence due to interactions between different fields present during inflation. The tensor modes (i.e. primordial gravitational waves) can interact with a scalar sector, causing their quantum decoherence to occur and inducing a change in the gravitational wave (GW) background. The power spectrum of these GWs can be constrained using the upper bounds found by Planck, BICEP/Keck Array, LIGO-Virgo-KAGRA, Big Bang Nucleosynthesis, and the Pulsar Timing Array detections. These impose constraints on the interaction between the fields. We find that the observational upper bounds mainly constrain scenarios with a strong interaction, especially if the interaction is also strongly time dependent. Furthermore, we find which observationally allowed scenarios have not completed decoherence by the end of inflation, thus possibly leaving quantum signatures in the GW background. Lastly, we show that, interestingly enough, there are decoherence scenarios corresponding to the signal observed by PTA experiments. This highlights the importance of the quantum decoherence effect on GWs.

astro-ph.CO↗

arXiv2024

Robust constraints on tensor perturbations from cosmological data: a comparative analysis from Bayesian and frequentist perspectives

We analyze primordial tensor perturbations using the latest cosmic microwave background and gravitational waves data, focusing on the tensor-to-scalar ratio, $r$, and the tensor spectral tilt, $n_t$. Utilizing data from Planck PR4, BICEP/Keck, and LIGO-Virgo-KAGRA, we employ both Bayesian and frequentist methods to provide robust constraints on these parameters. Our results indicate more conservative upper limits for $r$ with profile likelihoods compared to Bayesian credible intervals, highlighting the influence of prior selection and volume effects. The profile likelihood for $n_t$ shows that the current data do not provide sufficient information to derive quantitative bounds, unless extra assumptions on $r$ are used. Additionally, we conduct a 2D profile likelihood analysis of $r$ and $n_t$, indicating a closer agreement between both statistical methods for the largest values of $r$. This study not only updates our understanding of the tensor perturbations but also highlights the importance of employing both statistical methods to explore less constrained parameters, crucial for future explorations in cosmology.

astro-ph.CO↗

arXiv2023

Unraveling the CMB lack-of-correlation anomaly with the cosmological gravitational wave background

Since the very first observations, the Cosmic Microwave Background (CMB) has revealed on large-scales unexpected features known as anomalies, which challenge the standard $Λ$ cold dark matter ($Λ$CDM) cosmological model. One such anomaly is the "lack-of-correlation", where the measured two-point angular correlation function of CMB temperature anisotropies is compatible with zero, differently from the predictions of the standard model. This anomaly could indicate a deviation from the standard model, unknown systematics, or simply a rare realization of the model itself. In this study, we explore the possibility that the lack-of-correlation anomaly is a consequence of living in a rare realization of the standard model, by leveraging the potential information provided by the cosmological gravitational wave background (CGWB) detectable by future gravitational wave (GW) interferometers. We analyze both constrained and unconstrained realizations of the CGWB to investigate the extent of information that GWs can offer. To quantify the impact of the CGWB on the lack-of-correlation anomaly, we employ established estimators and introduce a new estimator that addresses the "look-elsewhere" effect. Additionally, we consider three different maximum multipoles, denoted as $\ell_{\rm max}$, to account for the anticipated capabilities of future GW detectors ($\ell_{\rm max} = 4, 6, 10$). Summarizing our findings for the case of $\ell_{\rm max} = 4$, we identify the angular range $[63^\circ - 180^\circ]$ as the region where future observations of the CGWB maximize the probability of rejecting the standard model. Furthermore, we calculate the expected significance of this observation, demonstrating that 98.81% (81.67%) of the GW realizations enhance the current significance of the anomaly when considering the full-sky (masked) Planck SMICA map as our CMB sky.

astro-ph.CO↗

arXiv2023

Updated constraints on amplitude and tilt of the tensor primordial spectrum

We have taken a comprehensive approach to update the limits on the tensor-to-scalar ratio ($r$) and the tensor spectral index ($n_t$), using 10 datasets from the BICEP/Keck Array 2015 and 2018, Planck releases 3 and 4, and LIGO-Virgo-KAGRA Collaboration. By fitting the complete $Λ$CDM+$r$+$n_t$ model with two different approaches for the tensor sector, we have not only established which method is the most reliable, but have also achieved the strongest constraint on the tensor-to-scalar ratio in current literature: $r<0.028$ and $-1.37 < n_t < 0.42$ at 95% confidence level. Furthermore, our examination of the common signal detected by the NANOGrav Collaboration further confirms that a simple power-law cannot reconcile the constraints from different datasets if the NANOGrav detection is due to a primordial inflationary gravitational wave background, as previously shown in the literature.

astro-ph.CO↗

arXiv2022

Test of the Statistical Isotropy of the Universe using Gravitational Waves

Since WMAP and Planck some anomalous features appeared in the Cosmic Microwave Background (CMB) large-angle anisotropy, the so-called anomalies. One of these is the hemispherical power asymmetry, i.e. a difference in the average power on the two hemispheres centered around (l, b) = (221, -20), which shows a relatively high level of significance. Such an anomaly could be the signature of a departure from statistical isotropy on large scales. Here we investigate the physical origin of this anomaly using the Cosmological Gravitational Wave Background (CGWB) detectable by future GW detectors. Indeed, the CGWB offers a unique window to explore the early universe and we show that it can be used in combination with CMB data to shed light on the statistical isotropy of our universe. Specifically, we study the evolution of gravitons in the presence of a modulating field in the scalar gravitational potentials accounting for the hemispherical power asymmetry and we infer the amplitude of this modulating field through a minimal variance estimator exploiting both constrained and unconstrained realizations of the CGWB. We show that the addition of the CGWB will allow an improvement in the assessment of the physical origin of the CMB power asymmetry. Accounting for the expected performances of LISA and BBO, we also show that the latter is expected to be signal-dominated on large-scales, proving that the CGWB could be the keystone to assess the significance of this anomaly.

astro-ph.CO↗