A Formulation of the Log-Logistic Distribution for Fading Channel Modeling

In some scenarios, the log-logistic (LL) distribution is shown to provide the best fit to field measurements in the context of wireless channel modeling. However, a fading channel model based on the LL distribution has not been formulated yet. In this work, we introduce the L-distribution as a reformulation of the LL distribution for channel modeling purposes. We provide closed-form expressions for its PDF, CDF, and moments. Performance analysis of wireless communication systems operating under L-fading channels is exemplified, providing exact and asymptotic expressions for relevant metrics such as the outage probability and the average capacity. Finally, important practical aspects related to the use of the L-distribution for channel fitting purposes are discussed in two contexts: (i) millimeter-wave links with misaligned gain, and (ii) air–ground channels in unmanned aerial vehicle communications.European Social and Regional FundsJunta de Andalucia P18-RT-3175 UMA20-FEDERJA-002Universidad de MalagaUniversidad de Granad

Cosmology intertwined: a review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies

The standard ¿ Cold Dark Matter (¿CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant , the – tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the tension between the Planck CMB estimate of the Hubble constant and the SH0ES collaboration measurements. After showing the evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density , and the amplitude or rate of the growth of structure (). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the – tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questionsPeer ReviewedArticle signat per 202 autors/esPostprint (published version

Studying Cosmic Evolution with the XMM-Newton Distant Cluster Project

Investigating X-ray luminous galaxy clusters at high redshift (z>~1) provides a challenging but fundamental constraint on evolutionary studies of the largest virialized structures in the Universe, the baryonic matter component in form of the hot intracluster medium (ICM), their galaxy populations, and the effects of the mysterious Dark Energy. The main aim of this thesis work is to establish the observational foundation for the XMM-Newton Distant Cluster Project (XDCP). This new generation serendipitous X-ray survey is focused on the most distant galaxy clusters at z>1, based on the selection of extended X-ray sources, their identification as clusters and redshift estimation via two-band imaging, and their final spectroscopic confirmation. As a first step, I have analyzed 80 deg^2 (469 fields) of deep XMM-Newton archival X-ray data with a new pipeline processing system and selected almost 1000 extended sources as galaxy cluster candidates, 75% of which could be identified as clusters or groups at z<~0.6 using available optical data. This left about 250 candidates with typical 0.5-2.0keV X-ray fluxes of ~10^{-14} erg/s/cm^2 in need of confirmation as distant cluster sources. Therefore, I have adopted a new strategy to efficiently establish the nature of these extended X-ray sources and estimate their redshifts, based on medium deep Z- and H-band photometry and the observed Z-H `red-sequence' color of early-type cluster galaxies. To fully exploit this technique, I have designed a new near-infrared data reduction code, which was applied to the data collected for 25% of the 250 distant cluster candidates in two imaging campaigns at the 3.5m telescope at the Calar Alto Observatory. As a first main result, more than 20 X-ray luminous clusters were discovered to lie at a photometric redshift of z>~0.9. Furthermore, the new Z-H red sequence method has allowed a cluster sample study over an unprecedented redshift baseline of 0.2<~z<~1.5. From a comparison of the observed color evolution of the cluster red-sequence galaxies with model predictions, I could constrain the formation epoch of the bulk of their stellar populations as z_f=4.2+-1.1. This confirms the well-established old age of the stellar populations of early-type galaxies in clusters. The preliminary investigation of the H-band luminosity evolution of 63 brightest cluster galaxies (BCGs) over the same redshift range provides for the first time direct observational indications that the most massive cluster galaxies in the local Universe have doubled their stellar mass since z~1.5. My tentative finding that nearby BCGs have old, passively evolving stellar populations and were assembled in the last 9Gyr is in qualitative agreement with predictions from the latest numerical simulations based on the standard cold dark matter scenario of galaxy formation and evolution via hierarchical merging. The confirmation and refinement of these preliminary results will contribute to the development of a consistent picture of the cosmic evolution of galaxy populations and the large-scale structure

The Physical Properties of the Groups of Galaxies

Galaxy groups consist of a few tens of galaxies bound in a common gravitational potential and contain a significant fraction of the overall universal baryon budget. Therefore, they are key to our understanding of how the bulk of matter in the Universe accretes and forms hierarchical structures and how different sources of feedback affect their gravitational collapse. However, despite their crucial role in cosmic structure formation and evolution, galaxy groups have received less attention compared to massive clusters. This is perhaps in part due to their rarity in being observed and properly characterized. With the advent of eROSITA, many thousands of galaxy groups will be detected by X-ray, complementing optical and SZ coverage. In this Special Issue we collected and organized the latest developments in our understanding of these systems and present future prospects from both observational and theoretical points of view