arXiv subjects

Salvatore Samuele Sirletti

Publications and source records attributed to Salvatore Samuele Sirletti.

3 recordsLinked to original sources

arXiv2025

Stellar Objects From Quantum Gravity

This paper explores the theoretical implications of quantum gravity by analyzing compact stellar objects, presenting three distinct models that serve as alternatives to traditional black holes. These models are characterized by their extreme compactness and incorporation of a quantum core, successfully avoiding the curvature singularities typically associated with classical general relativity. Central to these models is the noncommutative parameter, which plays a crucial role in determining stellar properties and enables the exploration of various astrophysical regimes. While pure Planckian effects pose significant challenges for observational detection, our findings suggest that lower energy scales may reveal exotic stellar objects with Earth and Sun-like masses that lack classical counterparts, potentially providing the first experimental evidence of non-classical gravity. We propose that the metrics derived in this study can be tested against known neutron stars, offering promising avenues for future research aimed at understanding the interplay between quantum effects in gravity and stellar evolution, ultimately enhancing our comprehension of the universe's fundamental properties.

gr-qc↗

arXiv2025

Separating the Inseparable: Constraining Arbitrary Primordial Bispectra with Cosmic Microwave Background Data

To efficiently probe primordial non-Gaussianity using Cosmic Microwave Background (CMB) data, we require theoretical predictions that are factorizable, \textit{i.e.}\ those whose kinematic dependence can be separated. This property does not hold for many models, hindering their application to data. In this work, we introduce a general framework for constructing separable approximations to primordial bispectra, enabling direct CMB constraints on arbitrary models including those computed using numerical tools. In contrast to other approaches such as modal decompositions, we learn the basis functions directly from the data, allowing high-fidelity representations with just a handful of terms. This is practically implemented using machine-learning techniques, utilizing neural network basis functions and a loss function designed to mimic the CMB cosine similarity. We validate our pipeline using a variety of input bispectra, demonstrating that the approximations are $>99.5\%$ correlated with the truth with just three terms. By incorporating the neural basis into the \textsc{PolySpec} code, we derive KSW-type CMB estimators, which reproduce local- and equilateral-type non-Gaussianity to within $0.1σ$. As a proof-of-concept, we constrain two inflationary bispectra from the `cosmological collider' scenario; these feature an additional strongly-mixed particle sector and cannot be computed analytically. By combining the numerical predictions from \textsc{CosmoFlow} with our factorizable approach (with just three terms), we place novel constraints on the collider models using \textit{Planck} PR4 data, finding no detection of non-Gaussianity. Our method facilitates detailed studies of the inflationary paradigm, connecting modern theoretical tools with high-resolution observational data.

astro-ph.CO↗

arXiv2025

Third-order corrections to the slow-roll expansion: calculation and constraints with Planck, ACT, SPT, and BICEP/Keck

We investigate the primordial power spectra (PPS) of scalar and tensor perturbations, derived through the slow-roll approximation. By solving the Mukhanov-Sasaki equation and the tensor perturbation equation with Green's function techniques, we extend the PPS calculations to third-order corrections, providing a comprehensive perturbative expansion in terms of slow-roll parameters. We investigate the accuracy of the analytic predictions with the numerical solutions of the perturbation equations for a selection of single-field slow-roll inflationary models. We derive the constraints on the Hubble flow functions $ε_i$ from Planck, ACT, SPT, and BICEP/Keck data. We find an upper bound $ε_1 \lesssim 0.002$ at 95\% CL dominated by BICEP/Keck data and robust to all the different combination of datasets. We derive the constraint $ε_2 \simeq 0.031 \pm 0.004$ at 68\% confidence level (CL) from the combination of Planck data and late-time probes such as baryon acoustic oscillations, redshift space distortions, and supernovae data at first order in the slow-roll expansion. The uncertainty on $ε_2$ gets larger including second- and third-order corrections, allowing for a non-vanishing running and running of the running respectively, leading to $ε_2 \simeq 0.034 \pm 0.007$ at 68\% CL. We find $ε_3 \simeq 0.1 \pm 0.4$ at 95\% CL both at second and at third order in the slow-roll expansion of the spectra. $ε_4$ remains always unconstrained. The combination of Planck and SPT data leads to slightly tighter constraints on $ε_2$ and $ε_3$. On the contrary, the combination of Planck data with ACT measurements, which point to higher values of the scalar spectral index compared to Planck findings, leads to shifts in the means and maximum likelihood values for $ε_2$ and $ε_3$.

astro-ph.CO↗