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Agius, D., Essig, R., Gaggero, D., Scarcella, F., Suczewski, G., & Valli, M. (2024). Feedback in the dark: a critical examination of CMB bounds on primordial black holes. J. Cosmol. Astropart. Phys., 07(7), 003–36pp.
Abstract: If present in the early universe, primordial black holes (PBHs) would have accreted matter and emitted high-energy photons, altering the statistical properties of the Cosmic Microwave Background (CMB). This mechanism has been used to constrain the fraction of dark matter that is in the form of PBHs to be much smaller than unity for PBH masses well above one solar mass. Moreover, the presence of dense dark matter mini -halos around the PBHs has been used to set even more stringent constraints, as these would boost the accretion rates. In this work, we critically revisit CMB constraints on PBHs taking into account the role of the local ionization of the gas around them. We discuss how the local increase in temperature around PBHs can prevent the dark matter mini -halos from strongly enhancing the accretion process, in some cases significantly weakening previously derived CMB constraints. We explore in detail the key ingredients of the CMB bound and derive a conservative limit on the cosmological abundance of massive PBHs.
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Andreotti, M. et al, Cervera-Villanueva, A., Garcia-Peris, M. a., Martin-Albo, J., Querol, M., Rocabado, J., et al. (2024). Cryogenic characterization of Hamamatsu HWB MPPCs for the DUNE photon detection system. J. Instrum., 19(1), T01007–27pp.
Abstract: The Deep Underground Neutrino Experiment (DUNE) is a next generation experiment aimed to study neutrino oscillation. Its long-baseline configuration will exploit a Near Detector (ND) and a Far Detector (FD) located at a distance of similar to 1300 km. The FD will consist of four Liquid Argon Time Projection Chamber (LAr TPC) modules. A Photon Detection System (PDS) will be used to detect the scintillation light produced inside the detector after neutrino interactions. The PDS will be based on light collectors coupled to Silicon Photomultipliers (SiPMs). Different photosensor technologies have been proposed and produced in order to identify the best samples to fullfill the experiment requirements. In this paper, we present the procedure and results of a validation campaign for the Hole Wire Bonding (HWB) MPPCs samples produced by Hamamatsu Photonics K.K. (HPK) for the DUNE experiment, referring to them as 'SiPMs'. The protocol for a characterization at cryogenic temperature (77 K) is reported. We present the down-selection criteria and the results obtained during the selection campaign undertaken, along with a study of the main sources of noise of the SiPMs including the investigation of a newly observed phenomenon in this field.
Keywords: Cryogenic detectors; Photon detectors for UV, visible and IR photons (solid-state); Photon detectors for UV, visible and IR photons (solid-state) (PIN diodes, APDs, Si-PMTs, G-APDs, CCDs, EBCCDs, EMCCDs, CMOS imagers, etc)
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Archidiacono, M., Gariazzo, S., Giunti, C., Hannestad, S., & Tram, T. (2020). Sterile neutrino self-interactions: H-0 tension and short-baseline anomalies. J. Cosmol. Astropart. Phys., 12(12), 029–20pp.
Abstract: Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples to a new light pseudoscalar degree of freedom. Consistently with previous analyses, we find that the model provides a good fit to all cosmological data and allows the high value of H-0 measured in the local universe to be consistent with measurements of the cosmic microwave background. However, new high l polarisation data constrain the sterile neutrino mass to be less than approximately 1 eV in this scenario. Finally, we combine the cosmological bounds on the pseudoscalar model with a Bayesian inference analysis of SBL data and conclude that only a sterile mass in narrow ranges around 1 eV remains consistent with both cosmology and SBL data.
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Babeluk, M. et al, & Marinas, C. (2023). CMOS MAPS upgrade for the Belle II Vertex Detector. Nucl. Instrum. Methods Phys. Res. A, 1048, 168015–5pp.
Abstract: The success of the Belle II experiment in Japan relies on the very high instantaneous luminosity, close to 6x1035 cm-2 s-1, expected from the SuperKEKB collider. The corresponding beam conditions at such luminosity levels generate large rates of background particles and creates stringent constraints on the vertex detector, adding to the physics requirements. Current prospects for the occupancy rates in the present vertex detector (VXD) at full luminosity fall close to the acceptable limits and bear large uncertainties. In this context, the Belle II collaboration is considering the possibility to install an upgraded VXD system around 2027 to provide a sufficient safety margin with respect to the expected background rate and possibly enhance tracking and vertexing performance. The VTX collaboration has started the design of a fully pixelated VXD, called VTX, based on fast and highly granular Depleted Monolithic Active Pixel Sensors (DMAPS) integrated on light support structures. The two main technical features of the VTX proposal are the usage of a single sensor type over all the layers of the system and the overall material budget below 2% of radiation length, compared to the current VXD which has two different sensor technologies and about 3% of radiation length. A dedicated sensor (OBELIX), taylored to the specific needs of Belle II, is under development, evolving from the existing TJ-Monopix2 sensor. The time-stamping precision below 100 ns will allow all VTX layers to take part in the track finding strategy contrary to the current situation. The first two detection layers are designed according to a self-supported all-silicon ladder concept, where 4 contiguous sensors are diced out of a wafer, thinned and interconnected with post-processed redistribution layers. The outermost detection layers follow a more conventional approach with a cold plate and carbon fibre support structure, and light flex cables interconnecting the sensors. This document will review the context, technical details and development status of the proposed Belle II VTX.
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Babeluk, M. et al, Lacasta, C., Marinas, C., Mazorra de Cos, J., & Vobbilisetti, V. (2024). The OBELIX chip for the Belle II VTX upgrade. Nucl. Instrum. Methods Phys. Res. A, 1067, 169659–3pp.
Abstract: The OBELIX depleted monolithic active CMOS pixel sensor (DMAPS) is currently developed for the upgrade of the vertex detector of the Belle II experiment located at Tsukuba/Japan. The pixel matrix of OBELIX is inherited from the TJ-Monopix2 chip, but the periphery includes additional features to improve performance and allow the integration into a larger detector system. The new features include a trigger unit to process trigger signals, a precision timing module and a possibility to transmit low granularity hit information with low latency to contribute to the Belle II trigger. Additionally, low dropout voltage regulators and an ADC to monitor power consumption and substrate temperature is developed. This paper will focus on the trigger contribution capabilities of the OBELIX chip.
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Barenboim, G., Chen, J. Z., Hannestad, S., Oldengott, I. M., Tram, T., & Wong, Y. Y. Y. (2021). Invisible neutrino decay in precision cosmology. J. Cosmol. Astropart. Phys., 03(3), 087–53pp.
Abstract: We revisit the topic of invisible neutrino decay in the precision cosmological context, via a first-principles approach to understanding the cosmic microwave background and large-scale structure phenomenology of such a non-standard physics scenario. Assuming an effective Lagrangian in which a heavier standard-model neutrino nu(H) couples to a lighter one nu(l) and a massless scalar particle phi via a Yukawa interaction, we derive from first principles the complete set of Boltzmann equations, at both the spatially homogeneous and the firstorder inhomogeneous levels, for the phase space densities of nu(H), nu(l), and phi in the presence of the relevant decay and inverse decay processes. With this set of equations in hand, we perform a critical survey of recent works on cosmological invisible neutrino decay in both limits of decay while nu(H) is ultra-relativistic and non-relativistic. Our two main findings are: (i) in the non-relativistic limit, the effective equations of motion used to describe perturbations in the neutrino-scalar system in the existing literature formally violate momentum conservation and gauge invariance, and (ii) in the ultra-relativistic limit, exponential damping of the anisotropic stress does not occur at the commonly-used rate Gamma(T) = (1/tau(0))( m(nu H)/E-nu H)(3), but at a rate similar to (1/ tau(0))(m(nu H)/E-nu H)(5). Both results are model-independent. The impact of the former finding on the cosmology of invisible neutrino decay is likely small. The latter, however, implies a significant revision of the cosmological limit on the neutrino lifetime tau(0) from tau(old)(0) greater than or similar to 1.2 x 10(9) s (m(nu H)/50 meV)(3) to tau(0) greater than or similar to (4 x 10(5) -> 4 x 10(6)) s (m(nu H)/50 meV)(5).
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Barenboim, G., Fernandez-Martinez, E., Mena, O., & Verde, L. (2010). The dark side of curvature. J. Cosmol. Astropart. Phys., 03(3), 008–17pp.
Abstract: Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d(A)(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Omega(k) in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d(A)(z) up to sufficiently high redshifts z similar to 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z) – Omega(k) degeneracy.
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Belle II VTX Collaboration(Babeluk, M. et al)., Marinas, C., & Mazorra de Cos, J. (2024). The DMAPS upgrade of the Belle II vertex detector. Nucl. Instrum. Methods Phys. Res. A, 1064, 169428–5pp.
Abstract: The Belle II experiment at KEK in Japan considers an upgrade for the vertex detector system in line with the accelerator upgrade for higher luminosity at long shutdown 2 planned for 2028. One proposal for the upgrade of the vertex detector called VTX aims to improve background robustness and reduce occupancy using small and fast pixels. VTX accommodates the OBELIX depleted monolithic active CMOS pixel sensor (DMAPS) on all five proposed layers. OBELIX is specifically developed for the VTX application and based on the TJ-Monopix2 chip initially developed to meet the requirements of the outer layers of the ATLAS inner tracker (ITk). This paper will review recent tests of the TJ-Monopix2 chip as well as various design aspects of the OBELIX-1 chip currently under development.
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Bertolez-Martinez, T., Esteban, I., Hajjar, R., Mena, O., & Salvado, J. (2025). Origin of cosmological neutrino mass bounds: background versus perturbations. J. Cosmol. Astropart. Phys., 06(6), 058–37pp.
Abstract: The cosmological upper bound on the total neutrino mass is the dominant limit on this fundamental parameter. Recent observations soon to be improved have strongly tightened it, approaching the lower limit set by oscillation data. Understanding its physical origin, robustness, and model-independence becomes pressing. Here, we explicitly separate for the first time the two distinct cosmological neutrino-mass effects: the impact on background evolution, related to the energy in neutrino masses; and the “kinematic” impact on perturbations, related to neutrino free-streaming. We scrutinize how they affect CMB anisotropies, introducing two effective masses enclosing background ( mBackg. nu ) and perturbations ( mPert. nu) effects. We analyze CMB data, finding that the neutrino-mass bound is mostly a background measurement, i.e., how the neutrino energy density evolves with time. The bound on the “kinematic” variable mPert. nu is largely relaxed, mPert. nu <0.8 eV. This work thus adds clarity to the physical origin of the cosmological neutrino-mass bound, which is mostly a measurement of the neutrino equation of state, providing also hints to evade such a bound.
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Boudagga, R. et al, Lacasta, C., Marinas, C., Mazorra de Cos, J., Molina-Bueno, L., & Vobbilisetti, V. (2025). Upgrade of the Belle II vertex detector with depleted monolithic CMOS active sensors. Nucl. Instrum. Methods Phys. Res. A, 1080, 170677–4pp.
Abstract: The Belle II experiment at the SuperKEKB collider in Japan, which currently holds the world luminosity record for electron-positron collisions, plans to upgrade its vertex detector (VXD) to operate at a target luminosity of 6 x 1035 cm-2s-1. A new pixelated vertex detector (VTX) is under development, utilizing a monolithic CMOS pixel sensor named OBELIX (Optimized BELle II pIXel). The VTX design incorporates 5-6 layers with a total material budget below 2.5% X0. All layers will employ the OBELIX, adapted from the TJ-Monopix2 sensor initially designed for the ATLAS Inner Tracker (ITk) upgrade. The OBELIX sensor, designed using a 180 nm CMOS process, features an enhanced pixel matrix and additional functionalities compared to its predecessor. Laboratory tests and test beam characterization results on irradiated and unirradiated TJ-Monopix2 sensors have yielded promising results, confirming the key performance parameters for the OBELIX design. This paper reviews the overall design of the VTX and the OBELIX sensor and presents the latest results of the in-beam characterization of the TJ-Monopix2.
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