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Yang, W. Q., Pan, S., Di Valentino, E., Mena, O., & Melchiorri, A. (2021). 2021-H-0 odyssey: closed, phantom and interacting dark energy cosmologies. J. Cosmol. Astropart. Phys., 10(10), 008–21pp.
Abstract: Up-to-date cosmological data analyses have shown that (sigma) a closed universe is preferred by the Planck data at more than 99% CL, and (b) interacting scenarios offer a very compelling solution to the Hubble constant tension. In light of these two recent appealing scenarios, we consider here an interacting dark matter-dark energy model with a non-zero spatial curvature component and a freely varying dark energy equation of state in both the quintessential and phantom regimes. When considering Cosmic Microwave Background data only, a phantom and closed universe can perfectly alleviate the Hubble tension, without the necessity of a coupling among the dark sectors. Accounting for other possible cosmological observations compromises the viability of this very attractive scenario as a global solution to current cosmological tensions, either by spoiling its effectiveness concerning the H-0 problem, as in the case of Supernovae Ia data, or by introducing a strong disagreement in the preferred value of the spatial curvature, as in the case of Baryon Acoustic Oscillations.
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Di Valentino, E., Gariazzo, S., Mena, O., & Vagnozzi, S. (2020). Soundness of dark energy properties. J. Cosmol. Astropart. Phys., 07(7), 045–45pp.
Abstract: Type Ia Supernovae (SNeIa) used as standardizable candles have been instrumental in the discovery of cosmic acceleration, usually attributed to some form of dark energy (DE). Recent studies have raised the issue of whether intrinsic SNeIa luminosities might evolve with redshift. While the evidence for cosmic acceleration is robust to this possible systematic, the question remains of how much the latter can affect the inferred properties of the DE component responsible for cosmic acceleration. This is the question we address in this work. We use SNeIa distance moduli measurements from the Pantheon and JLA samples. We consider models where the DE equation of state is a free parameter, either constant or time-varying, as well as models where DE and dark matter interact, and finally a model-agnostic parametrization of effects due to modified gravity (MG). When SNeIa data are combined with Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements, we find strong degeneracies between parameters governing the SNeIa systematics, the DE parameters, and the Hubble constant H-0. These degeneracies significantly broaden the DE parameter uncertainties, in some cases leading to O(sigma) shifts in the central values. However, including low-redshift Baryon Acoustic Oscillation and Cosmic Chronometer measurements, as well as CMB lensing measurements, considerably improves the previous constraints, and the only remaining effect of the examined systematic is a less than or similar to 40% broadening of the uncertainties on the DE parameters. The constraints we derive on the MG parameters are instead basically unaffected by the systematic in question. We therefore confirm the overall soundness of dark energy properties.
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Escudero, M., Ramirez, H., Boubekeur, L., Giusarma, E., & Mena, O. (2016). The present and future of the most favoured inflationary models after Planck 2015. J. Cosmol. Astropart. Phys., 02(2), 020–21pp.
Abstract: The value of the tensor-to-scalar ratio r in the region allowed by the latest Planck 2015 measurements can be associated to a large variety of inflationary models. We discuss here the potential of future Cosmic Microwave Background cosmological observations in disentangling among the possible theoretical scenarios allowed by our analyses of current Planck temperature and polarization data. Rather than focusing only on r, we focus as well on the running of the primordial power spectrum, alpha(s) and the running thereof, beta(s). If future cosmological measurements, as those from the COrE mission, confirm the current best-fit value for beta(s) greater than or similar to 10(-2) as the preferred one, it will be possible to rule-out the most favoured inflationary models.
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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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Ramirez, H., Passaglia, S., Motohashi, H., Hu, W., & Mena, O. (2018). Reconciling tensor and scalar observables in G-inflation. J. Cosmol. Astropart. Phys., 04(4), 039–20pp.
Abstract: The simple m(2)phi(2) potential as an inflationary model is coming under increasing tension with limits on the tensor-to-scalar ratio r and measurements of the scalar spectral index n(s). Cubic Galileon interactions in the context of the Horndeski action can potentially reconcile the observables. However, we show that this cannot be achieved with only a constant Galileon mass scale because the interactions turn off too slowly, leading also to gradient instabilities after inflation ends. Allowing for a more rapid transition can reconcile the observables but moderately breaks the slow-roll approximation leading to a relatively large and negative running of the tilt alpha(s) that can be of order n(s) – 1. We show that the observables on CMB and large scale structure scales can be predicted accurately using the optimized slow-roll approach instead of the traditional slow-roll expansion. Upper limits on vertical bar alpha(s)vertical bar place a lower bound of r greater than or similar to 0.005 and, conversely, a given r places a lower bound on vertical bar alpha(s)vertical bar, both of which are potentially observable with next generation CMB and large scale structure surveys.
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