The relation between geometry and matter in classical and quantum gravity and cosmology

The present thesis is divided into two main research areas: Classical Cosmology and (Loop) Quantum Gravity. The first part concerns cosmological models with one phantom and one scalar field, that provide the `super-accelerated' scenario not excluded by observations, thus exploring alternatives to the standard LambdaCDM scenario. The second part concerns the spinfoam approach to (Loop) Quantum Gravity, which is an attempt to provide a `sum-over-histories' formulation of gravitational quantum transition amplitudes. The research here presented focuses on the face amplitude of a generic spinfoam model for Quantum Gravity.

Early-type galaxies as probes of galaxy formation and cosmology

The goal of this thesis is to analyze the possibility of using early-type galaxies to place evolutionary and cosmological constraints, by both disentangling what is the main driver of ETGs evolution between mass and environment, and developing a technique to constrain H(z) and the cosmological parameters studying the ETGs age-redshift relation. The (U-V) rest-frame color distribution is studied as a function of mass and environment for two sample of ETGs up to z=1, extracted from the zCOSMOS survey with a new selection criterion. The color distributions and the slopes of the color-mass and color-environment relations are studied, finding a strong dependence on mass and a minor dependence on environment. The spectral analysis performed on the D4000 and Hδ features gives results validating the previous analysis. The main driver of galaxy evolution is found to be the galaxy mass, the environment playing a subdominant but non negligible role. The age distribution of ETGs is also analyzed as a function of mass, providing strong evidences supporting a downsizing scenario. The possibility of setting cosmological constraints studying the age-redshift relation is studied, discussing the relative degeneracies and model dependencies. A new approach is developed, aiming to minimize the impact of systematics on the “cosmic chronometer” method. Analyzing theoretical models, it is demonstrated that the D4000 is a feature correlated almost linearly with age at fixed metallicity, depending only minorly on the models assumed or on the SFH chosen. The analysis of a SDSS sample of ETGs shows that it is possible to use the differential D4000 evolution of the galaxies to set constraints to cosmological parameters in an almost model-independent way. Values of the Hubble constant and of the dark energy EoS parameter are found, which are not only fully compatible, but also with a comparable error budget with the latest results.

On the geometry of the spin-statistics connection in quantum mechanics

The Spin-Statistics theorem states that the statistics of a system of identical particles is determined by their spin: Particles of integer spin are Bosons (i.e. obey Bose-Einstein statistics), whereas particles of half-integer spin are Fermions (i.e. obey Fermi-Dirac statistics). Since the original proof by Fierz and Pauli, it has been known that the connection between Spin and Statistics follows from the general principles of relativistic Quantum Field Theory. In spite of this, there are different approaches to Spin-Statistics and it is not clear whether the theorem holds under assumptions that are different, and even less restrictive, than the usual ones (e.g. Lorentz-covariance). Additionally, in Quantum Mechanics there is a deep relation between indistinguishabilty and the geometry of the configuration space. This is clearly illustrated by Gibbs' paradox. Therefore, for many years efforts have been made in order to find a geometric proof of the connection between Spin and Statistics. Recently, various proposals have been put forward, in which an attempt is made to derive the Spin-Statistics connection from assumptions different from the ones used in the relativistic, quantum field theoretic proofs. Among these, there is the one due to Berry and Robbins (BR), based on the postulation of a certain single-valuedness condition, that has caused a renewed interest in the problem. In the present thesis, we consider the problem of indistinguishability in Quantum Mechanics from a geometric-algebraic point of view. An approach is developed to study configuration spaces Q having a finite fundamental group, that allows us to describe different geometric structures of Q in terms of spaces of functions on the universal cover of Q. In particular, it is shown that the space of complex continuous functions over the universal cover of Q admits a decomposition into C(Q)-submodules, labelled by the irreducible representations of the fundamental group of Q, that can be interpreted as the spaces of sections of certain flat vector bundles over Q. With this technique, various results pertaining to the problem of quantum indistinguishability are reproduced in a clear and systematic way. Our method is also used in order to give a global formulation of the BR construction. As a result of this analysis, it is found that the single-valuedness condition of BR is inconsistent. Additionally, a proposal aiming at establishing the Fermi-Bose alternative, within our approach, is made.

Dispersive wave solutions of the klein-gordon equation in cosmology

L'equazione di Klein-Gordon descrive una ampia varietà di fenomeni fisici come la propagazione delle onde in Meccanica dei Continui ed il comportamento delle particelle spinless in Meccanica Quantistica Relativistica. Recentemente, la forma dissipativa di questa equazione si è rivelata essere una legge di evoluzione fondamentale in alcuni modelli cosmologici, in particolare nell'ambito dei cosiddetti modelli di k-inflazione in presenza di campi tachionici. L'obiettivo di questo lavoro consiste nell'analizzare gli effetti del parametro dissipativo sulla dispersione nelle soluzioni dell'equazione d'onda. Saranno inoltre studiati alcuni tipici problemi al contorno di particolare interesse cosmologico per mezzo di grafici corrispondenti alle soluzioni fondamentali (Funzioni di Green).

Connection between x-ray and radio properties of cool-core galaxy clusters hosting radio mini-halos

Gli ammassi di galassie sono gli oggetti gravitazionalmente legati più grandi dell’Universo. Questi emettono principalmente in banda X tramite bremsstrahlung. Una frazione mostra anche emissione radio diffusa da parte di elettroni relativistici che spiraleggiano nel campo magnetico. Si possono classificare tre tipi di emissione: alon, relitti e mini-aloni radio (MH). I MH sono sorgenti radio su scale di ≥ 200 – 500 kpc, osservate al centro di ammassi caratterizzati dalla presenze di cool-core (CC). L’origine dei MH non è ancora chiara. Gli elettroni relativistici che emettono in banda radio hanno tempi di vita radiativi di molto inferiori a quelli necessari per diffondere sulle scale dell’emissione diffusa. Quindi non sono semplicemente iniettati dalle galassie presenti negli ammassi ed è necessario un meccanismo di accelerazione “in-situ” nell’ICM. I MH testimoniano la presenza di meccanismi che canalizzano parte del budget energetico disponibile nei CC nell’ICM.Quindi lo studio è importante per comprendere la fisica dell’ICM e l’interazione fra le componenti non termiche e termiche. I MH si formano attraverso la riaccelerazione delle particelle relativistiche ad opera della turbolenza del gas. L’origine di questa turbolenza tuttavia non è ancora ben compresa. Gli ammassi CC sono caratterizzati da un picco della brillanza X nelle regioni centrali e da un drop della temperatura verso il centro accompagnata da aumento della densità del gas. Si ritiene che questo sia dovuto al raffreddamento del gas che quindi fluisce nelle zone centrali. Recenti osservazioni in X risultan inconsistenti con il modello classico di CF, suggerendo la presenza di una sorgente di riscaldamento del gas su scale del core degli ammassi. Recentemente Zhuravleva (2014) hanno mostrato che il riscaldamento dovuto alla turbolenza prodotta dall'AGN centrale è in grado di bilanciare il processo di raffreddamento. Abbiamo assunto che la turbolenza responsabile del riscaldamento del gas è anche responsabile dell’accelerazione delle particelle nei MH. Nell’ambito di questo scenario ci si aspetta una correlazione tra la potenza del cooling flow, PCF, che è una misura del tasso di energia emessa dal gas che raffredda nei CC, e la luminosità radio, che è una frazione dell’energia della turbolenza che è canalizzata nell’accelerazione delle particelle. In questo lavoro di tesi abbiamo utilizzato il più grande campione disponibile di MH, allo scopo di studiare la connessione fra le proprietà dei MH e quelle del gas termico nei core degli ammassi che li ospitano. Abbiamo analizzato i dati di 21 ammassi e ricavato i parametri fisici all’interno del raggio di cooling e del MH. Abbiamo ricavato la correlazione fra luminosità radio, e PCF. Abbiamo trovato che le due quantità correlano in modo quasi-lineare confermando i risultati precedenti. Tale correlazione suggerisce uno stretto legame fra le proprietà del gas nei CC e l’origine dei MH.

Bianchi type II cosmology in Hořava–Lifshitz gravity

In this work a Bianchi type II space-time within the framework of projectable Horava Lifshitz gravity was investigated; the resulting field equations in the infrared limit λ = 1 were analyzed qualitatively. We have found the analytical solutions for a toy model in which only the higher curvature terms cubic in the spatial Ricci tensor are considered. The resulting behavior is still described by a transition among two Kasner epochs, but we have found a different transformation law of the Kasner exponents with respect to the one of Einstein's general relativity.

Interfering with the connection between the nucleus and the cytoskeleton affects nuclear rotation, mechanotransduction and myogenesis

Mechanical stress controls a broad range of cellular functions. The cytoskeleton is physically connected to the extracellular matrix via integrin receptors, and to the nuclear lamina by the LINC complex that spans both nuclear membranes. We asked here how disruption of this direct link from the cytoskeleton to nuclear chromatin affects mechanotransduction. Fibroblasts grown on flexible silicone membranes reacted to cyclic stretch by nuclear rotation. This rotation was abolished by inhibition of actomyosin contraction as well as by overexpression of dominant-negative versions of nesprin or sun proteins that form the LINC complex. In an in vitro model of muscle differentiation, cyclic strain inhibits differentiation and induces proliferation of C2C12 myoblasts. Interference with the LINC complex in these cells abrogated their stretch-induced proliferation, while stretch increased p38 MAPK and NFkappaB phosphorylation and the transcript levels of myogenic transcription factors MyoD and myogenin. We found that the physical link from the cytoskeleton to the nuclear lamina is crucial for correct mechanotransduction, and that disruption of the LINC complex perturbs the mechanical control of cell differentiation.

Coffee inhibits the reactivation of glucocorticoids by 11beta-hydroxysteroid dehydrogenase type 1: a glucocorticoid connection in the anti-diabetic action of coffee?

Recent epidemiological studies demonstrated a beneficial effect of coffee consumption for the prevention of type 2 diabetes, however, the underlying mechanisms remained unknown. We demonstrate that coffee extract, corresponding to an Italian Espresso, inhibits recombinant and endogenous 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activity. The inhibitory component is heat-stable with considerable polarity. Coffee extract blocked 11beta-HSD1-dependent cortisol formation, prevented the subsequent nuclear translocation of the glucocorticoid receptor and abolished glucocorticoid-induced expression of the key gluconeogenic enzyme phosphoenolpyruvate carboxykinase. We suggest that at least part of the anti-diabetic effects of coffee consumption is due to inhibition of 11beta-HSD1-dependent glucocorticoid reactivation.