Causality and momentum conservation from relative locality

Theories with a curved momentum space, which became recently of interest in the quantum-gravity literature, can in general violate many apparently robust aspects of our current description of the laws of physics, including relativistic invariance, locality, causality and global momentum conservation. We here explore some aspects of the particularly severe pathologies arising in generic theories with curved momentum space for what concerns causality and momentum conservation. However, we also report results suggesting that when momentum space is maximally symmetric, and the theory is formulated (DSR-)relativistically, with the associated relativity of spacetime locality, momentum is globally conserved and there is no violation of causality.Comment: 20 pages, 6 figures, latex (V2: minor editing

Fenomenologia di gravità quantistica: dimensione termale dello spaziotempo quantistico, causalità e conservazione del momento dalla località relativa

The original results presented in this thesis regard two very common topics of discussion in the quantum gravity debate: the dynamical dimensional reduction of spacetime and locality in quantum gravity regime. The dimensionality of quantum spacetime is often understood in terms of the spectral dimension; here, a different notion of dimensionality, the thermal dimension, is proposed. I discuss its physical properties in relation to those of the spectral dimension through the study of specific models of quantum gravity, including preliminary results obtained in the case of models with relative locality. I show that, in those cases where the spectral dimension has puzzling properties, the thermal dimension gives a different and more meaningful picture. The statistical mechanics developed to define the thermal dimension is applied also to the study of the production of primordial cosmological perturbations assuming a running Newton constant and Rainbow gravity. Concerning locality, I study in particular the theory of Relative Locality, a theoretical framework in which different observers may describe the same event as being local or non-local, depending whether it happens in the origin of their reference frame or far away from it, respectively. I show that requiring that locality is relative is enough to guarantee the objectivity of cause-effect relation in chains of events, the absence of causality-violating loops and processes violating the law of conservation of momentum.I risultati originali presentati in questa tesi riguardano due argomenti di discussione molto comuni nel dibattito sulla gravità quantistica: la riduzione dimensionale dinamica dello spaziotempo e la località nel regime di gravità quantistica. La dimensionalità dello spaziotempo quantistico viene spesso descritta in termini della dimensione spettrale; qui viene proposta una nuova nozione di dimensione, la dimensione termale. Discuto le sue proprietà fisiche in relazione a quelle della dimensione spettrale attraverso lo studio di modelli specifici di gravità quantistica, comprendendo anche risultati preliminari ottenuti nel caso di modelli con località relativa. Mostro che , in quei casi in cui la dimensione spettrale ha proprietà bizzarre, la dimensione termale fornisce un quadro diverso e più significativo. La meccanica statistica costruita per definire la dimensione termale è applicata anche allo studio della produzione delle perturbazioni cosmologiche primordiali, assumendo che costante di Newton dipenda dall'energia e la gravità "Rainbow". Per quanto riguarda la località, studio in particolare la teoria delle Località Relativa, un paradigma teorico in cui diversi osservatori possono descrivere uno stesso evento come locale o non locale, a seconda se questo avviene nell'origine del loro sistema di riferimento o lontano dall'origine, rispettivamente. Mostro che richiedere che la località sia relativa è sufficiente a garantire l'oggettività della relazione di causa-effetto in catene di eventi, l'assenza di processi che violano la causalità e di processi che violano la conservazione del momento

On the auxetic behaviour of metamaterials with re-entrant cell structures

In the present paper a two dimensional plate, made by structural straight elements and showing an auxetic behaviour, is considered. Theoretical, experimental and numerical analyses for the characterisation of its mechanical properties are presented and compared. The main geometrical parameters of an elementary cell affecting the deformation behaviour are highlighted, with emphasis to the negative values of the Poisson’s ratio

Neutrino search from {\gamma}-ray bursts during the prompt and X-ray afterglow phases using 10 years of IceCube public data

Neutrino emission from gamma-ray bursts (GRBs) has been sought for a long time, and stringent limits on the most accredited GRB emission models have been obtained from IceCube. Multi-wavelength GRB observations of the last decades improved our knowledge of the GRB emission parameters, such as the Lorentz factor and the luminosity, which can vary from one GRB to another by several orders of magnitude. Empirical correlations among such parameters have been identified during the prompt phase, with direct implications on GRB models. In this work, we use the PSLab open-access code, developed for IceCube data analyses, to search for individual neutrino emission from the prompt and afterglow phases of selected GRBs, and for stacking emission from the ensemble of such GRBs. For the afterglow phase, we focus in particular on GRBs with X-ray flares and plateaus. While past stacking searches assumed the same GRB fluence at Earth, we present a stacking scheme based on physically motivated GRB weights. Moreover, we conceive a new methodology for the prompt phase that uses the empirical correlations to infer the GRB luminosity and Lorentz factor, when redshift measurements are not available. We do not observe any significant neutrino excess. Hence, we set constraints on the GRB neutrino fluxes and on relevant GRB parameters, including the magnetic field in the jet. Notably, the baryon loading is found to be <10 for typical GRB prompts, thus disfavoring a baryonic-dominated origin of the GRB ejecta.Comment: Submitted for publication to A&A. Comments are welcom

Detecting VHE prompt emission from binary neutron-star mergers: ET and CTA synergies

The current generation of very-high-energy $gamma-$ray (VHE; E above 30 GeV) detectors (MAGIC and H.E.S.S.) have recently demonstrated the ability to detect the afterglow emission of GRBs. However, the GRB prompt emission, typically observed in the 10 keV-10 MeV band, has so far remained undetected at higher energies. Here, we investigate the perspectives of multi-messenger observations to detect the prompt emission of short GRBs in VHE. Considering binary neutron star mergers as progenitors of short GRBs, we evaluate the joint detection efficiency of the Cherenkov Telescope Array (CTA) observing in synergy with the third generation of gravitational wave detectors, such as the Einstein Telescope (ET) and Cosmic Explorer (CE). In particular, we evaluate the expected capabilities to detect and localize gravitational wave events in the inspiral phase and to provide an early warning alert able to drive the VHE search. We compute the amount of possible joint detections by considering several observational strategies, and demonstrate that the sensitivities of CTA make the detection of the VHE emission possible even if it is several orders fainter than the one observed at 10 keV-10 MeV. We discuss the results in terms of possible scenarios of production of VHE photons from binary neutron star mergers by considering GRB prompt and afterglow emissions

Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts

γ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (10 − 10 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the AHEAD2020 project (Grant agreement n. 871158). G. Ghir. acknowledges the support from the ASI-Nustar Grant (1.05.04.95). M.B., P.D., and G.G. acknowledge support from PRIN-MIUR 2017 (Grant 20179ZF5KS). G.O. acknowledges financial contribution from the agreement ASI-INAF n.2017-14-H.0. S.A. acknowledges the PRIN-INAF “Towards the SKA and CTA era: discovery, localization, and physics of transient sources” and the ERC Consolidator Grant “MAGNESIA” (nr. 817661). M.G.B. and P.D. acknowledge ASI Grant I/004/11/3. O.S.S. acknowledges the INAF-Prin 2017 (1.05.01.88.06) and the Italian Ministry for University and Research Grant “FIGARO” (1.05.06.13) for support. G.O. and S.R. are thankful to INAF—Osservatorio Astronomico di Brera for kind hospitality during the completion of this work. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester

Spectral index-flux relation for investigating the origins of steep decay in γ\gamma-ray bursts

$\gamma$-ray bursts (GRBs) are short-lived transients releasing a large amount of energy ($10^{51}-10^{53}$ erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star's death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.Comment: Published in Nature Communication

Association of nutritional glycaemic indices with global DNA methylation patterns: results from the Moli-sani cohort

Background: High dietary glycaemic index (GI) and load (GL) have been associated with increased risk of various cardiometabolic conditions. Among the molecular potential mechanisms underlying this relationship, DNA methylation has been studied, but a direct link between high GI and/or GL of diet and global DNA methylation levels has not been proved yet. We analyzed the associations between GI and GL and global DNA methylation patterns within an Italian population. Results: Genomic DNA methylation (5mC) and hydroxymethylation (5hmC) levels were measured in 1080 buffy coat samples from participants of the Moli-sani study (mean(SD) = 54.9(11.5) years; 52% women) via ELISA. A 188-item Food Frequency Questionnaire was used to assess food intake and dietary GI and GL for each participant were calculated. Multiple linear regressions were used to investigate the associations between dietary GI and GL and global 5mC and 5hmC levels, as well as the proportion of effect explained by metabolic and inflammatory markers. We found negative associations of GI with both 5mC (β (SE) = - 0.073 (0.027), p = 0.007) and 5hmC (- 0.084 (0.030), p = 0.006), and of GL with 5mC (- 0.14 (0.060), p = 0.014). Circulating biomarkers did not explain the above-mentioned associations. Gender interaction analyses revealed a significant association of the gender-x-GL interaction with 5mC levels, with men showing an inverse association three times as negative as in women (interaction β (SE) = - 0.16 (0.06), p = 0.005). Conclusions: Our findings suggest that global DNA methylation and hydroxymethylation patterns represent a biomarker of carbohydrate intake. Based on the differential association of GL with 5mC between men and women, further gender-based separate approaches are warranted

WATZON: the Italian network of ecohydrology and critical zone observatories

The Italian initiative WATZON (WATer mixing in the critical ZONe) is a network of instrumented sites, bringing together six pre-existing long-term research observatories monitoring different compartments of the Critical Zone - the Earth's permeable near-surface layer from the tops of the trees to the bottom of the groundwater. These observatories cover different climatic and physiographic characteristics over the country, providing information over a climate and eco-hydrologic transect connecting the Mediterranean to the Alps. With specific initial scientific questions, monitoring strategies, databases, and modeling activities, the WATZON observatories and sites is well representative of the heterogeneity of the critical zone and of the scientific communities studying it. Despite this diversity, all WATZON sites share a common eco-hydrologic monitoring and modelling program with three main objectives: 1) assessing the description of water mixing process across the critical zone by using integrated high-resolution isotopic, geophysical and hydrometeorological measurements from point to catchment scale, under different physiographic conditions and climate forcing; 2) testing water exchange mechanisms between subsurface reservoirs and vegetation, and assessing ecohydrological dynamics in different environments by coupling the high-resolution data set from different critical zone study sites of the initiative with advanced ecohydrological models at multiple spatial scales; 3) developing a process-based conceptual framework of ecohydrological processes in the critical zone to translate scientific knowledge into evidence to support policy and management decisions concerning water and land use in forested and agricultural ecosystems. This work provides an overview of the WATZON network, its objectives, scientific questions, and data management, with a specific focus on existing initiatives for linking data and models based on WATZON data