arXiv subjects

Luca Terenzi

Publications and source records attributed to Luca Terenzi.

18 recordsLinked to original sources

arXiv2026

FOSSIL: Thermo-mechanical architecture

FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions of the Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at the lowest achievable temperature (4.5 K), while the detector focal plane assembly operates at 50 mK. This paper presents the thermal architecture of the FOSSIL payload and instrument, from the spacecraft service module at 293 K down to the sub-kelvin detector stage. The thermal design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K cryocooler chain. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) system developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), which houses four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5~K bench via a carbon-fibre reinforced polymer (CFRP) hexapod structure with staged heat interception. We present the steady-state thermal budget across all stages, demonstrating comfortable margins at every temperature level, and discuss key thermal design drivers on the Blackbody Internal Reference (BBIR).

astro-ph.IM↗

arXiv2026

The exceptional locus of a motivic local system

To every Nori motivic local system over a smooth, connected complex algebraic variety, we associate an exceptional locus controlling the variation in the complexity of its stalks; the definition is given explicitly in terms of motivic Galois groups and Artin motives. We prove a motivic analogue of the Cattani--Deligne--Kaplan Theorem, asserting that the exceptional locus is a countable union of closed algebraic subvarieties. Moreover, we show that it is defined over any algebraically closed subfield over which the motivic local system admits a model, and stable under Galois conjugation when the latter descends to a smaller subfield. This extends and strengthens previous results by André in the pure case. We obtain a similar description for the splitting locus of the motivic weight filtration.

math.AG↗

arXiv2026

Spatial resolution for gamma ray interactions in stacks of monolithic silicon sensors

We are developing a new implementation of Compton imaging for nuclear medicine using a large volume of stacked monolithic silicon sensors. In this work we investigate how the spatial resolution is impacted by the pixel size, an important input to the design of the sensors. In general CMOS design is less challenging with larger pixels leaving more space for analog and digital electronics. On the other hand, spatial resolution is one of the key parameters that will impact the performance of the Compton imaging system. It is also important to consider the range of the recoil electron produced in Compton or photoelectric interactions, which impacts how accurately the interaction point can be estimated. The achievable resolution was evaluated with two interaction position reconstruction algorithms: one based on a Gaussian fit of the detected charge and a second based on the characteristic energy deposition along the electron track, with the former performing better at lower energies. Monte Carlo simulations were performed for 140 keV and 511 keV sources embedded in a water phantom, with pixel pitches ranging from 25 $μm$ to 250 $μm$. Energy-averaged in-plane resolution degraded from 8 $μm$ to 94 $μm$ as pixel size increased. The out-of-plane resolution was 216 $μm$ at low energies, limited by sensor thickness, and improved to 155 $μm$ at higher energies. The results suggest that pixel sizes in the order of 100 $μm$ can achieve spatial resolutions on the order of tens of micrometers.

physics.ins-det↗

arXiv2026

The IRT Telescope on board the THESEUS mission

We present the Infra-Red Telescope (IRT), which is part of the payload of the THESEUS mission, one on the three phase A candidate missions for the M7 slot of ESA (launch date 2037). The IRT is a 0.7 m class telescope with an off-axis Korsch optical design, with imaging capabilities in the 0.7-1.8 microns range over a 15 x 15 arc min field of view. The IRT also provides slit-less low resolution spectroscopy (R~400) over a limited field of view of 2 x 2 arc min, in the 0.8-1.6 microns range. The goal of the IRT is to identify the near infrared counterparts to the Gamma-Ray Bursts (GRBs) detected by the two other telescopes on board THESEUS (the XGIS and the SXI), and to measure on board its photometric redshift in near real-time. The position and the redshift will be transmitted immediately to ground to allow for deeper follow-up by the large telescopes (ELT, VLT, ...). If the source is bright enough, spectroscopy will be performed to characterize the GRB environment.

astro-ph.IM↗

arXiv2026

Status and future development of the COSMOCal Project for absolute CMB polarization calibration

Cosmic Microwave Background (CMB) polarization measurements are pushing instrumental sensitivities to levels where calibration systematics become a dominant limitation. The large dynamic range between cosmological and Galactic emission prevents future experiments from relying only on diffuse sky measurements or standard celestial calibrators. To address this challenge, the COSmological Microwave Observations Calibrator (COSMOCal) project proposes an artificial calibration source deployed as a guest payload on a geostationary satellite, scheduled for launch by the Eutelsat group by 2030. This source will provide stable, well-characterized polarized microwave signals accessible to multiple ground-based observatories. In this work, we present the status of the project, the updated development timeline, and the refined scientific and technical requirements, defined with the observatories that plan to use this calibration source. Furthermore, we investigate the interplay between instrumental systematics and component separation in the presence of complex models of interstellar dust emission. We discuss in this paper how this can impact the recovery of the primordial signal, and whether residual calibration errors can degrade the performance of foreground cleaning algorithms.

astro-ph.IM↗

arXiv2026

A Comparison of Categories of Nori Motivic Sheaves

We show that two different possible theories of Nori motivic sheaves, introduced by Ivorra--Morel and by Ayoub, respectively, are canonically equivalent. The proof of this result, which exploits the six functor formalism systematically, is based on the Tannakian theory of motivic local systems. As a consequence, we obtain a system of realization functors of Voevodsky motivic sheaves into Nori motivic sheaves compatible with the six operations, previously constructed by Tubach using different methods.

math.AG↗

arXiv2025

Tensor structure on perverse Nori motives

Let $k$ be a field of characteristic $0$ endowed with a complex embedding $σ: k \hookrightarrow \mathbb{C}$. In this paper we complete the construction of the six functor formalism on perverse Nori motives over quasi-projective $k$-varieties, initiated by Ivorra--Morel. Our main contribution is the construction of a closed monoidal structure on the derived categories of perverse Nori motives, compatibly with the analogous structure on the underlying constructible derived categories. This is based on an alternative presentation of perverse Nori motives, related to the conjectural motivic perverse $t$-structure on Voevodsky motivic sheaves. As a consequence, we obtain well-behaved Tannakian categories of motivic local systems over smooth, geometrically connected $k$-varieties. Exploiting the relation with Voevodsky motivic sheaves in its full strength, we are able to define Chern classes in the setting of perverse Nori motives, which leads to a motivic version of the relative Hard Lefschetz Theorem.

math.AG↗

arXiv2024

Constructing monoidal structures on fibered categories via factorizations

Let $\mathcal{S}$ be a small category, and suppose that we are given two (non-full) subcategories $\mathcal{S}^{sm}$ and $\mathcal{S}^{cl}$ that generate all morphisms of $\mathcal{S}$ under composition in the same way as morphisms of quasi-projective algebraic varieties are generated by smooth morphisms and closed immersions. We show that a monoidal structure on a given $\mathcal{S}$-fibered category is completely determined by its restrictions to $\mathcal{S}^{sm}$ and $\mathcal{S}^{cl}$; in fact, any such pair of monoidal structures satisfying a natural coherence condition uniquely determines a monoidal structure over $\mathcal{S}$. The same principle applies to morphisms of $\mathcal{S}$-fibered categories and monoidality thereof. Under further assumptions on the subcategories $\mathcal{S}^{sm}$ and $\mathcal{S}^{cl}$, and with suitable restrictions on the $\mathcal{S}$-fibered categories and morphisms involved, we provide a variant of the above factorization method in which inverse images under closed immersion are partially replaced by the corresponding direct images: the latter variant is more adapted to the setting of perverse sheaves.

math.CT↗

arXiv2024

Extending monoidal structures on fibered categories via embeddings

Let $\mathcal{S}$ be a small category, and suppose that we are given a full subcategory $\mathcal{U}$ such that every object of $\mathcal{S}$ can be embedded into some object of $\mathcal{U}$ in the same way as every quasi-projective algebraic variety admits a closed embedding into a smooth one. We show that every monoidal structure on a given $\mathcal{S}$-fibered category satisfying certain natural conditions is completely determined by its restriction to $\mathcal{U}$; in fact, any monoidal structure over $\mathcal{U}$ satisfying similar natural conditions admits an essentially unique extension to the whole of $\mathcal{S}$. For instance, this allows one to recover the unit constraint on the classical constructible derived categories from the abelian categories of perverse sheaves. The same principle applies to morphisms of $\mathcal{S}$-fibered categories and monoidality thereof.

math.CT↗

arXiv2024

Tensor structures on fibered categories

Let $\mathcal{S}$ be a small category admitting binary products. We show that the whole theory of monoidal $\mathcal{S}$-fibered categories, which is customarily formulated in terms of the usual internal tensor product, can be rephrased purely in terms of the associated external tensor product. More precisely, we construct a canonical dictionary relating the classical structures and properties of the internal tensor product to analogous structures and properties of the external tensor product: this applies to associativity, commutativity, and unit constraints, to projection formulae, as well as to monoidality of morphisms between monoidal $\mathcal{S}$-fibered categories. For instance, we show how Mac Lane's classical pentagon and hexagon axioms can be stated using the external tensor product. Our results provide a satisfactory abstract framework to study monoidal structures in the setting of perverse sheaves.

math.CT↗

arXiv2024

On the functoriality of universal abelian factorizations

In this note, we discuss several aspects of the functoriality of universal abelian factorizations associated to representations of quivers into abelian categories. After recalling the general construction of universal abelian factorizations, we review the canonical lifting procedures for exact functors and natural transformations thereof (already studied by F. Ivorra in a slightly different axiomatic framework) and we describe how these interact with general categorical constructions; for sake of simplicity, we mostly focus on the case where the quivers and representations considered are defined by actual (additive) categories and (additive) functors. We then extend these known results in two directions which have not been explored explicitly in the existing literature: on the one side, to the setting of multi-linear functors; on the other side, to the setting of abelian fibered categories. Combining these two extensions, we are able to discuss the case of monoidal structures on abelian fibered categories; the latter case has been successfully applied in the author's construction of the tensor structure on perverse Nori motives.

math.CT↗

arXiv2021

The XGIS instrument on-board THESEUS: the detection plane and on-board electronics

The X and Gamma Imaging Spectrometer instrument on-board the THESEUS mission (selected by ESA in the framework of the Cosmic Vision M5 launch opportunity, currently in phase A) is based on a detection plane composed of several thousands of single active elements. Each element comprises a 4.5x4.5x30 mm 3 CsI(Tl) scintillator bar, optically coupled at both ends to Silicon Drift Detectors (SDDs). The SDDs acts both as photodetectors for the scintillation light and as direct X-ray sensors. In this paper the design of the XGIS detection plane is reviewed, outlining the strategic choices in terms of modularity and redundancy of the system. Results on detector-electronics prototypes are also described. Moreover, the design and development of the low-noise front-end electronics is presented, emphasizing the innovative architectural design based on custom-designed Application-Specific Integrated Circuits (ASICs).

astro-ph.IM↗

arXiv2021

The XGIS imaging system onboard the THESEUS mission

Within the scientific goals of the THESEUS ESA/M5 candidate mission, a critical item is a fast (within a few s) and accurate (<15 arcmin) Gamma-Ray Burst and high-energy transient location from a few keV up to hard X-ray energy band. For that purpose, the signal multiplexing based on coded masks is the selected option to achieve this goal. This contribution is implemented by the XGIS Imaging System, based on that technique. The XGIS Imaging System has the heritage of previous payload developments: LEGRI/Minisat-01, INTEGRAL, UFFO/Lomonosov and ASIM/ISS. In particular the XGIS Imaging System is an upgrade of the ASIM system in operation since 2018 on the International Space Station. The scientific goal is similar: to detect a gamma-ray transient. But while ASIM focuses on Terrestrial Gamma-ray Flashes, THESEUS aims for the GRBs. For each of the two XGIS Cameras, the coded mask is located at 630 mm from the detector layer. The coding pattern is implemented in a Tungsten plate (1 mm thickness) providing a good multiplexing capability up to 150 keV. In that way both XGIS detector layers (based on Si and CsI detectors) have imaging capabilities at the medium - hard X-ray domain. This is an improvement achieved during the current THESEUS Phase-A. The mask is mounted on top of a collimator that provides the mechanical assembly support, as well as good cosmic X-ray background shielding. The XGIS Imaging System preliminary structural and thermal design, and the corresponding analyses, are included in this contribution, as it is a preliminary performance evaluation.

astro-ph.IM↗

arXiv2021

The X/Gamma-ray Imaging Spectrometer (XGIS) on-board THESEUS: design, main characteristics, and concept of operation

THESEUS is one of the three missions selected by ESA as fifth medium class mission (M5) candidates in its Cosmic Vision science program, currently under assessment in a phase A study with a planned launch date in 2032. THESEUS is designed to carry on-board two wide and deep sky monitoring instruments for X/gamma-ray transients detection: a wide-field soft X-ray monitor with imaging capability (Soft X-ray Imager, SXI, 0.3 - 5 keV), a hard X-ray, partially-imaging spectroscopic instrument (X and Gamma Imaging Spectrometer, XGIS, 2 keV - 10 MeV), and an optical/near-IR telescope with both imaging and spectroscopic capability (InfraRed Telescope, IRT, 0.7 - 1.8 $μ$m). The spacecraft will be capable of performing fast repointing of the IRT to the error region provided by the monitors, thus allowing it to detect and localize the transient sources down to a few arcsec accuracy, for immediate identification and redshift determination. The prime goal of the XGIS will be to detect transient sources, with monitoring timescales down to milliseconds, both independently of, or following, up SXI detections, and identify the sources performing localisation at < 15 arcmin and characterize them over a broad energy band, thus providing also unique clues to their emission physics. The XGIS system consists of two independent but identical coded mask cameras, arranged to cover 2 steradians . The XGIS will exploit an innovative technology coupling Silicon Drift Detectors (SDD) with crystal scintillator bars and a very low-noise distributed front-end electronics (ORION ASICs), which will produce a position sensitive detection plane, with a large effective area over a huge energy band (from soft X-rays to soft gamma-rays) with timing resolution down to a few $μ$s.Here is presented an overview of the XGIS instrument design, its configuration, and capabilities.

astro-ph.IM↗

arXiv2013

In-flight calibration and verification of the Planck-LFI instrument

In this paper we discuss the Planck-LFI in-flight calibration campaign. After a brief overview of the ground test campaigns, we describe in detail the calibration and performance verification (CPV) phase, carried out in space during and just after the cool-down of LFI. We discuss in detail the functionality verification, the tuning of the front-end and warm electronics, the preliminary performance assessment and the thermal susceptibility tests. The logic, sequence, goals and results of the in-flight tests are discussed. All the calibration activities were successfully carried out and the instrument response was comparable to the one observed on ground. For some channels the in-flight tuning activity allowed us to improve significantly the noise performance.

astro-ph.IM↗

arXiv2013

PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in response to the Call for White Papers for the definition of the L2 and L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1) an imager with a 3.5m mirror (cooled to 4K for high performance in the far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and (2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS instrument but over three orders of magnitude more sensitive. Highlights of the new science (beyond the obvious target of B-modes from gravity waves generated during inflation) made possible by these two instruments working in tandem include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters extending to large redshift and measuring their peculiar velocities and temperatures (through the kSZ effect and relativistic corrections to the classic y-distortion spectrum, respectively) (2) a detailed investigation into the nature of the cosmic infrared background (CIB) consisting of at present unresolved dusty high-z galaxies, where most of the star formation in the universe took place, (3) searching for distortions from the perfect CMB blackbody spectrum, which will probe a large number of otherwise inaccessible effects (e.g., energy release through decaying dark matter, the primordial power spectrum on very small scales where measurements today are impossible due to erasure from Silk damping and contamination from non-linear cascading of power from larger length scales). These are but a few of the highlights of the new science that will be made possible with PRISM.

astro-ph.CO↗

arXiv2010

Planck-LFI: Design and Performance of the 4 Kelvin Reference Load Unit

The LFI radiometers use a pseudo-correlation design where the signal from the sky is continuously compared with a stable reference signal, provided by a cryogenic reference load system. The reference unit is composed by small pyramidal horns, one for each radiometer, 22 in total, facing small absorbing targets, made of a commercial resin ECCOSORB CR (TM), cooled to approximately 4.5 K. Horns and targets are separated by a small gap to allow thermal decoupling. Target and horn design is optimized for each of the LFI bands, centered at 70, 44 and 30 GHz. Pyramidal horns are either machined inside the radiometer 20K module or connected via external electro-formed bended waveguides. The requirement of high stability of the reference signal imposed a careful design for the radiometric and thermal properties of the loads. Materials used for the manufacturing have been characterized for thermal, RF and mechanical properties. We describe in this paper the design and the performance of the reference system.

astro-ph.IM↗

arXiv2010

Planck-LFI radiometers tuning

"This paper is part of the Prelaunch status LFI papers published on JINST: http://www.iop.org/EJ/journal/-page=extra.proc5/jinst" This paper describes the Planck Low Frequency Instrument tuning activities performed through the ground test campaigns, from Unit to Satellite Levels. Tuning is key to achieve the best possible instrument performance and tuning parameters strongly depend on thermal and electrical conditions. For this reason tuning has been repeated several times during ground tests and it has been repeated in flight before starting nominal operations. The paper discusses the tuning philosophy, the activities and the obtained results, highlighting developments and changes occurred during test campaigns. The paper concludes with an overview of tuning performed during the satellite cryogenic test campaign (Summer 2008) and of the plans for the just started in-flight calibration.

astro-ph.IM↗