Nature of gravity from the mass profiles of galaxy clusters

My PhD Thesis focused on the derivation of constraints on modified gravity models by combining mass profiles of galaxy clusters, reconstructed through gravitational lensing and internal dynamics as traced by the motion of member galaxies. Modifications of gravity change the relation between the matter density fluctuations and the scalar potentials Phi, Psi in the metric describing the space-time of a galaxy cluster. An accurate measurement of these potentials can be used to investigate deviations from General Relativity (GR) predictions according to which Phi=Psi. Mass profiles from dynamics track only the potential Phi, while the lensing mass profiles reflect the contribution of the sum of the potentials. In the first part of the Thesis I analyse the galaxy clusters MACS J1206 and RXJ 2248 for which high-quality imaging and spectroscopic data have been obtained from the CLASH and CLASH-VLT projects. I combine previous determinations of lensing and dynamics mass profiles for the galaxy cluster MACS J1206 to constrain generic deviation from GR, parametrized by the ratio eta=Psi/Phi, under the assumptions of spherical symmetry and dynamical relaxation. I obtain eta=1.01 with 30% statistical uncertainties in the cluster outskirt at the 68% C.L., in agreement with GR and competitive with constraints from other analyses. I then implement a modified version of the MAMPOSSt procedure (Mamon+13), a method to reconstruct galaxy clusters mass profiles from dynamics by solving the Jeans' equation. I introduce a parametrization of the potential which accounts for a large variety of modified gravity models. As a case study, I determined the total mass profiles from dynamics of the aforementioned clusters in f(R) gravity, combining then the information from the lensing mass reconstruction to constrain the additional degree of freedom of the theory lambda. The larger is lambda the stronger is the departure from GR. In the case of MACSJ 1206 the kinematic+lensing analysis is in agreement with GR, lambda0.14 Mpc at 95% C.L. In order to better understand the nature of this apparent tension, in the last part of the Thesis I preform an analysis of \u39bCDM cosmological simulations of galaxy clusters aimed at investigating the impact of systematic effects. I found that 70% of clusters produce spurious detection of modified gravity when no selection criteria are applied. I then defined two observational parameters, connected to the main systematics affecting the analysis, which help in selecting the suitable clusters for the application of our method. Moreover, I predict that a dozen \u201cregular\u201d clusters with reliable mass profile reconstructions are already sufficient to obtain the tightest constraints on GR deviations reachable with our analysis. This work is particularly interesting in view of the next generation imaging and spectroscopic surveys that will provide data for hundreds of clusters

Testing Screening Mechanisms with Mass Profiles of Galaxy Clusters

We present \textsc{MG-MAMPOSSt}, a license-free code to constrain modified gravity models by reconstructing the mass profile of galaxy clusters with the kinematics of the cluster's member galaxies. We describe the main features of the code and we show the capability of the method when the kinematic information is combined with lensing data. We discuss recent results and forecasts on two classes of models currently implemented in the code, characterized by different screening mechanisms, namely, chameleon and Vainshtein screening. We further explore the impact of possible systematics in view of application to the data from upcoming surveys. This proceedings summarizes the results presented at the ALTECOSMOFUN workshop in September 2021.Comment: Proceedings of the ALTECOSMOFUN'21 conference published in Universe, Issue "Alternative Gravities and Fundamental Cosmology

The spooky ghost of vectorization

An interesting mechanism for the formation of hairy black holes occurs when a vector field, non-minimally coupled to a source term, grows from a perturbation of the vacuum black hole, \textit{aka} vectorization. Its study has, however, been lacking, in part due to the constant threat of ghost instabilities that have plagued vector fields. In this work, we show evidence that, in a generic family of extended-vector-tensor theories where the vector field is non-minimally coupled to the model's invariant (source term), a spherically symmetric, vectorized black hole always suffers from ghost instabilities. These ultimately turn the process of vectorization astrophysically unviable.Comment: 12 page

Constraining Chameleon screening using galaxy cluster dynamics

We constrain the Chameleon \textit{screening} mechanism in galaxy clusters, essentially obtaining limits on the coupling strength $\beta$ and the asymptotic value of the field $\phi_{\infty}$. For this purpose, we utilized a collection of the 9 relaxed galaxy clusters within the X-COP compilation in the redshift range of $z \le 0.1$. We implement the formalism assuming an NFW mass profile for the dark matter density and study the degeneracy present between the mass \M and the chameleon coupling with a high degree of improvement in the constraints for excluded parameter space. We recast our constrain to an upper limit on the scalaron field in \fofr sub-class of models of $|f_{R0}|\le 9.2\times 10^{-6}$, using all the nine clusters and $|f_{R0}|\le 1.2\times 10^{-5}$ using only 5 clusters with WL priors taken into account, at a $95\%$ confidence level. These bounds are consistent with existing limits in the literature and tighter than the constraints obtained with the same method by previous studies.Comment: Comments are welcom

Impact of Single Hemodialysis Treatment on immune Cell Subpopulations

: Hemodialysis (HD) is known to trigger a chronic inflammatory status, affecting the innate and acquired immune response. This study was aimed at a comparative analysis of immune cell subsets, proliferation, and apoptosis in subjects receiving chronic HD treatment with respect to a healthy control. Regardless of the dialysis filter used, we observed a reshaping of the acquired immune component both with respect to healthy patients and between the various sessions of dialysis treatment, with an impairment of CD3 cells, along with an increase in CD4 and CD8 cell populations producing pro-inflammatory factors such as IL-17 and IFN-gamma. The population of B cells, monocytes and NK cells were not impaired by the dialysis procedure. These results confirmed the high impact of the HD treatment on the patient's immune system, underlying the imbalance of T cell counterparts

Sudden Unexpected Deaths and Vaccinations during the First Two Years of Life in Italy: A Case Series Study

Background The signal of an association between vaccination in the second year of life with a hexavalent vaccine and sudden unexpected deaths (SUD) in the two days following vaccination was reported in Germany in 2003. A study to establish whether the immunisation with hexavalent vaccines increased the short term risk of SUD in infants was conducted in Italy. Methodology/Principal Findings The reference population comprises around 3 million infants vaccinated in Italy in the study period 1999–2004 (1.5 million received hexavalent vaccines). Events of SUD in infants aged 1–23 months were identified through the death certificates. Vaccination history was retrieved from immunisation registries. Association between immunisation and death was assessed adopting a case series design focusing on the risk periods 0–1, 0–7, and 0–14 days after immunisation. Among the 604 infants who died of SUD, 244 (40%) had received at least one vaccination. Four deaths occurred within two days from vaccination with the hexavalent vaccines (RR = 1.5; 95% CI 0.6 to 4.2). The RRs for the risk periods 0–7 and 0–14 were 2.0 (95% CI 1.2 to 3.5) and 1.5 (95% CI 0.9 to 2.4). The increased risk was limited to the first dose (RR = 2.2; 95% CI 1.1 to 4.4), whereas no increase was observed for the second and third doses combined. Conclusions The RRs of SUD for any vaccines and any risk periods, even when greater than 1, were almost an order of magnitude lower than the estimates in Germany. The limited increase in RRs found in Italy appears confined to the first dose and may be partly explained by a residual uncontrolled confounding effect of age

Brain Derived Neurotrophic Factor (BDNF) Expression Is Regulated by MicroRNAs miR-26a and miR-26b Allele-Specific Binding

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays an essential role in neuronal development and plasticity. MicroRNA (miRNAs) are small non-coding RNAs of about 22-nucleotides in length regulating gene expression at post-transcriptional level. In this study we explore the role of miRNAs as post-transcriptional inhibitors of BDNF and the effect of 3′UTR sequence variations on miRNAs binding capacity. Using an in silico approach we identified a group of miRNAs putatively regulating BDNF expression and binding to BDNF 3′UTR polymorphic sequences. Luciferase assays demonstrated that these miRNAs (miR-26a1/2 and miR-26b) downregulates BDNF expression and that the presence of the variant alleles of two single nucleotide polymorphisms (rs11030100 and rs11030099) mapping in BDNF 3′UTR specifically abrogates miRNAs targeting. Furthermore we found a high linkage disequilibrium rate between rs11030100, rs11030099 and the non-synonymous coding variant rs6265 (Val66Met), which modulates BDNF mRNA localization and protein intracellular trafficking. Such observation led to hypothesize that miR-26s mediated regulation could extend to rs6265 leading to an allelic imbalance with potentially functional effects, such as peptide's localization and activity-dependent secretion. Since rs6265 has been previously implicated in various neuropsychiatric disorders, we evaluated the distribution of rs11030100, rs11030099 and rs6265 both in a control and schizophrenic group, but no significant difference in allele frequencies emerged. In conclusion, in the present study we identified two novel miRNAs regulating BDNF expression and the first BDNF 3′UTR functional variants altering miRNAs-BDNF binding

Vulnerabilità sismica dell'edilizia in muratura veneta

La presente tesi analizza dapprima il Comune di Vittorio Veneto in Provincia di Treviso, quindi considera un campione più ampio, costituito da 8 comuni: Fonte, Giavera del Montello, Pederobba, Pieve di Soligo, Puos d'Alpago, Quero, Vas e Vittorio Veneto