arXiv subjects

T. Trombetti

Publications and source records attributed to T. Trombetti.

10 recordsLinked to original sources

arXiv2024

Quantum Convolutional Neural Networks for the detection of Gamma-Ray Bursts in the AGILE space mission data

Quantum computing represents a cutting-edge frontier in artificial intelligence. It makes use of hybrid quantum-classical computation which tries to leverage quantum mechanic principles that allow us to use a different approach to deep learning classification problems. The work presented here falls within the context of the AGILE space mission, launched in 2007 by the Italian Space Agency. We implement different Quantum Convolutional Neural Networks (QCNN) that analyze data acquired by the instruments onboard AGILE to detect Gamma-Ray Bursts from sky maps or light curves. We use several frameworks such as TensorFlow-Quantum, Qiskit and PennyLane to simulate a quantum computer. We achieved an accuracy of 95.1% on sky maps with QCNNs, while the classical counterpart achieved 98.8% on the same data, using however hundreds of thousands more parameters.

astro-ph.HE↗

arXiv2019

Fundamental Physics with the Square Kilometre Array

The Square Kilometre Array (SKA) is a planned large radio interferometer designed to operate over a wide range of frequencies, and with an order of magnitude greater sensitivity and survey speed than any current radio telescope. The SKA will address many important topics in astronomy, ranging from planet formation to distant galaxies. However, in this work, we consider the perspective of the SKA as a facility for studying physics. We review four areas in which the SKA is expected to make major contributions to our understanding of fundamental physics: cosmic dawn and reionisation; gravity and gravitational radiation; cosmology and dark energy; and dark matter and astroparticle physics. These discussions demonstrate that the SKA will be a spectacular physics machine, which will provide many new breakthroughs and novel insights on matter, energy and spacetime.

astro-ph.CO↗

arXiv2019

Predictions for the diffuse cosmic dipole at radio frequencies from reionization imprints

The cosmological reionization can be studied in the radio through the tomographic view offered by the redshifted 21-cm line and the integrated information carried out by the diffuse free-free emission, coupled to the Comptonization distortion, relevant at higher frequencies. Current predictions span a wide range of possibilities, while the recent EDGES observations disagree with the standard models and call, if confirmed, for non-standard physical processes and/or for an early population of extragalactic sources producing a remarkable background at high redshifts almost consistent with the ARCADE 2 claim of a significant excess of CMB absolute temperature at low frequency. These signatures can be observed in global signal and fluctuations, from very large to small angular scales. The observer peculiar motion with respect to a reference frame in rest with respect to the CMB produces boosting effects in various observable quantities, remarkable at low multipoles, and particularly in the dipole, with frequency spectral behaviours depending on the monopole emission spectrum. We present a novel investigation at radio frequencies, aimed at predicting the imprints expected in the redshifted 21-cm line signal and in the diffuse free-free emission plus the Comptonization distortion for several models. Furthermore, we consider the same type of signal but expected from the cosmological radio background determining the offset for 21-cm line. The combination of these signals and their relevance in the various frequency ranges are studied. This approach, linking monopole and anisotropy analyses, can be applied on wide sky coverage surveys as well as to sets of sky patches. Relying only on the quality of interfrequency and relative data calibration, it in principle by-passes the need for precise absolute calibration, a critical point of current and future radio interferometric facilities.

astro-ph.CO↗

arXiv2019

Extragalactic astrophysics with next-generation CMB experiments

Planck, SPT and ACT surveys have clearly demonstrated that Cosmic Microwave Background (CMB) experiments, while optimised for cosmological measurements, have made important contributions to the field of extragalactic astrophysics in the last decade. Future CMB experiments have the potential to make even greater contributions. One example is the detection of high-z galaxies with extreme gravitational amplifications. The combination of flux boosting and of stretching of the images has allowed the investigation of the structure of galaxies at z ~3 with the astounding spatial resolution of about 60 pc. Another example is the detection of proto-clusters of dusty galaxies at high z when they may not yet possess the hot intergalactic medium allowing their detection in X-rays or via the Sunyaev-Zeldovich effect. Next generation CMB experiments, like PICO, CORE, CMB-Bharat from space and Simons Observatory and CMB-S4 from the ground, will discover several thousands of strongly lensed galaxies out to z~6 or more and of galaxy proto-clusters caught in the phase when their member galaxies where forming the bulk of their {stars. They will also detect tens of thousands of local dusty galaxies and thousands of radio sources at least up to z~5. Moreover they will measure the polarized emission of thousands of radio sources and of dusty galaxies at mm/sub-mm wavelengths.

astro-ph.GA↗

arXiv2019

Isotropic non-Gaussian $g_\mathrm{NL}$-like toy models that reproduce the cosmic microwave background anomalies

Based on recent observations of the cosmic microwave background (CMB), claims of statistical anomalies in the properties of the CMB fluctuations have been made. Although the statistical significance of the anomalies remains only at the $\sim2-3σ$ significance level, the fact that there are many different anomalies, several of which support a possible deviation from statistical isotropy, has motivated a search for models that provide a common mechanism to generate them. The goal of this paper is to investigate whether these anomalies could originate from non-Gaussian cosmological models, and to determine what properties these models should have. We present a simple isotropic, non-Gaussian class of toy models that can reproduce six of the most extensively studied anomalies. We compare the presence of anomalies found in simulated maps generated from the toy models and from a standard model with Gaussian fluctuations. We show that the following anomalies, as found in the Planck data, commonly occur in the toy model maps: (1) large-scale hemispherical asymmetry (large-scale dipolar modulation), (2) small-scale hemispherical asymmetry (alignment of the spatial distribution of CMB power over all scales $\ell=[2,1500]$) , (3) a strongly non-Gaussian hot or cold spot, (4) a low power spectrum amplitude for $\ell<30$, including specifically (5) a low quadrupole and an unusual alignment between the quadrupole and the octopole, and (6) parity asymmetry of the lowest multipoles. We note that this class of toy model resembles models of primordial non-Gaussianity characterised by strongly scale-dependent $g_{NL}$-like trispectra.

astro-ph.CO↗

arXiv2019

Spectral Distortions of the CMB as a Probe of Inflation, Recombination, Structure Formation and Particle Physics

Following the pioneering observations with COBE in the early 1990s, studies of the cosmic microwave background (CMB) have focused on temperature and polarization anisotropies. CMB spectral distortions - tiny departures of the CMB energy spectrum from that of a perfect blackbody - provide a second, independent probe of fundamental physics, with a reach deep into the primordial Universe. The theoretical foundation of spectral distortions has seen major advances in recent years, which highlight the immense potential of this emerging field. Spectral distortions probe a fundamental property of the Universe - its thermal history - thereby providing additional insight into processes within the cosmological standard model (CSM) as well as new physics beyond. Spectral distortions are an important tool for understanding inflation and the nature of dark matter. They shed new light on the physics of recombination and reionization, both prominent stages in the evolution of our Universe, and furnish critical information on baryonic feedback processes, in addition to probing primordial correlation functions at scales inaccessible to other tracers. In principle the range of signals is vast: many orders of magnitude of discovery space could be explored by detailed observations of the CMB energy spectrum. Several CSM signals are predicted and provide clear experimental targets, some of which are already observable with present-day technology. Confirmation of these signals would extend the reach of the CSM by orders of magnitude in physical scale as the Universe evolves from the initial stages to its present form. The absence of these signals would pose a huge theoretical challenge, immediately pointing to new physics.

astro-ph.CO↗

arXiv2018

Average fractional polarization of extragalactic sources at Planck frequencies

Recent detailed simulations have shown that an insufficiently accurate characterization of the contamination of unresolved polarized extragalactic sources can seriously bias measurements of the primordial cosmic microwave background (CMB) power spectrum if the tensor-to-scalar ratio $r\sim 0.001,$ as predicted by models currently of special interest (e.g., Starobinsky's $R^2$ and Higgs inflation). This has motivated a reanalysis of the median polarization fraction of extragalactic sources (radio-loud AGNs and dusty galaxies) using data from the \textit{Planck} polarization maps. Our approach, exploiting the intensity distribution analysis, mitigates or overcomes the most delicate aspects of earlier analyses based on stacking techniques. By means of simulations, we have shown that the residual noise bias on the median polarization fraction, $Π_{\rm median}$, of extragalactic sources is generally $\simlt 0.1\%$. For radio sources, we have found $Π_{\rm median} \simeq 2.83\%$, with no significant dependence on either frequency or flux density, in good agreement with the earlier estimate and with high-sensitivity measurements in the frequency range 5--40\,GHz. No polarization signal is detected in the case of dusty galaxies, implying 90\% confidence upper limits of $Π_{\rm dusty}\simlt 2.2\%$ at 353\,GHz and of $\simlt 3.9\%$ at 217\,GHz. The contamination of CMB polarization maps by unresolved point sources is discussed.

astro-ph.CO↗

arXiv2017

Exploring cosmic origins with CORE: effects of observer peculiar motion

We discuss the effects on the CMB, CIB, and thermal SZ effect due to the peculiar motion of an observer with respect to the CMB rest frame, which induces boosting effects. We investigate the scientific perspectives opened by future CMB space missions, focussing on the CORE proposal. The improvements in sensitivity offered by a mission like CORE, together with its high resolution over a wide frequency range, will provide a more accurate estimate of the CMB dipole. The extension of boosting effects to polarization and cross-correlations will enable a more robust determination of purely velocity-driven effects that are not degenerate with the intrinsic CMB dipole, allowing us to achieve a S/N ratio of 13; this improves on the Planck detection and essentially equals that of an ideal cosmic-variance-limited experiment up to a multipole l of 2000. Precise inter-frequency calibration will offer the opportunity to constrain or even detect CMB spectral distortions, particularly from the cosmological reionization, because of the frequency dependence of the dipole spectrum, without resorting to precise absolute calibration. The expected improvement with respect to COBE-FIRAS in the recovery of distortion parameters (in principle, a factor of several hundred for an ideal experiment with the CORE configuration) ranges from a factor of several up to about 50, depending on the quality of foreground removal and relative calibration. Even for 1% accuracy in both foreground removal and relative calibration at an angular scale of 1 deg, we find that dipole analyses for a mission like CORE will be able to improve the recovery of the CIB spectrum amplitude by a factor of 17 in comparison with current results based on FIRAS. In addition to the scientific potential of a mission like CORE for these analyses, synergies with other planned and ongoing projects are also discussed.

astro-ph.CO↗

arXiv2016

Multi-frequency polarimetry of a complete sample of PACO radio sources

We present high sensitivity polarimetric observations in 6 bands covering the 5.5-38 GHz range of a complete sample of 53 compact extragalactic radio sources brighter than 200 mJy at 20 GHz. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a 91% detection rate (at 5 sigma). Within this frequency range the spectra of about 95% of sources are well fitted by double power laws, both in total intensity and in polarisation, but the spectral shapes are generally different in the two cases. Most sources were classified as either steep- or peaked-spectrum but less than 50% have the same classification in total and in polarised intensity. No significant trends of the polarisation degree with flux density or with frequency were found. The mean variability index in total intensity of steep-spectrum sources increases with frequency for a 4-5 year lag, while no significant trend shows up for the other sources and for the 8 year lag. In polarisation, the variability index, that could be computed only for the 8 year lag, is substantially higher than in total intensity and has no significant frequency dependence.

astro-ph.GA↗

arXiv2011

The Simultaneous Medicina-Planck Experiment (SiMPlE): data acquisition, reduction and first results

The Simultaneous Medicina-{\it Planck} Experiment (SiMPlE) is aimed at observing a selected sample of 263 extragalactic and Galactic sources with the Medicina 32-m single dish radio telescope in the same epoch as the Planck satellite observations. The data acquired with a frequency coverage down to 5 GHz, also combined with Planck at frequencies above 30 GHz, will constitute a useful reference catalogue of bright sources over the whole Northern hemisphere. Furthermore, source observations performed in different epochs and comparison with other catalogues allow the investigation of source variabilities on different timescales. In this work, we describe the sample selection, the on-going data acquisition campaign, the data reduction procedures, the developed tools, and the comparison with other data-sets. We present the data at 5 and 8.3 GHz for the SiMPlE Northern Sample consisting of 79 sources with $δ\geq 45^\circ$ selected in our catalogue and observed during the first 6 months of the project. A first analysis of their spectral behaviour and long-term variability is also presented.

astro-ph.CO↗