Gravitational waves from inflation

The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power-spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio $r$ and tensor spectral index $n_{\rm T}$. In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.Comment: 85 pages, 4 tables, 9 figures; table 2 added, references added; matches published versio

Observables from inflation: gravitational waves and magnetic fields

The inflationary paradigm represents a fascinating and elegant way of explaining crucial cosmological phenomena; moreover it is remarkably in agreement with current cosmological observations. However we are still blind to many aspects of the physics encoded in such a process and an unequivocal probe of such a mechanism is still lacking. On the other hand inflation suggests the solution to current open cosmological questions, as the observation of magnetic fields in the intergalactic medium. In order to investigate in depth the inflationary mechanism, one possibility is offered by the new era of gravitational wave detectors. In the first part of the thesis we focus on this aspect of the inflationary epoch. Any inflationary model predicts the production of a stochastic gravitational wave background (tensor modes) due to quantum fluctuations of the gravitational field. Moreover, in some scenarios, the presence of additional fields besides the inflaton and the gravitational field gives rise to efficient sources of gravitational waves, activating the so-called classical production. Inflationary gravitational wave signals turn out to represent a unique and exciting window on the origin and evolution of the universe, and a possibility of investigating the underlying theory of gravity. We point out the significant role of primordial gravitational waves in testing the inflationary mechanism itself and in constraining many aspects of the inflationary physics, exploiting the validity/violation of an inflationary consistency relation. Being inflationary gravitational waves a promising way of exploring many aspects of the physics of the early universe, we provide an updated picture of the current status and the observational prospects of inflationary tensor modes, with a particular focus on the possibility of a direct gravitational wave detection offered by current and upcoming laser interferometer detectors. Then we perform a dedicated forecast analysis of the capabilities of the LISA (Laser Interferometer Space Antenna) experiment in probing the inflationary physics. In particular, the capabilities of LISA in measuring a stochastic gravitational wave background are presented. Furthermore, we calculate the gravitational wave signal expected at the LISA frequencies for a number of selected inflationary models. We collect and re-elaborate current limits on the present time gravitational wave spectral energy density, and the sensitivity curves of LISA and other experiments, in order to outline current and expected constraints on the parameter space of the selected inflationary models. The results we find show the efficiency of the method, suggesting an exciting direction in order to investigate inflationary physics and a validation of the significant science that can be done by an experiment as LISA. In the second part of the thesis another interesting aspect of the inflationary mechanism is considered, i.e. the possibility of a significant magnetogenesis. Gamma-ray observations from blazars point out the presence of magnetic fields in the intergalactic medium, where no charged plasma are present. This fact suggests a primordial origin of such fields. Interestingly, the inflationary mechanism provides a fascinating way of explaining the presence of magnetic fields at cosmological scales. In a dedicated section, the main models of inflationary magnetogenesis are outlined. A common aspect of these models is the associated overproduction of curvature and tensor perturbations with respect to single-field slow-roll inflation. In general, observational constraints obtained by CMB measurements on such quantities lead to relevant restrictions on the associated production of magnetic fields. Other limits are provided by keeping under control the backreaction of the electromagnetic fields. In particular, we consider the case proposed from Caprini, where a magnetogenesis mechanism able to explain current gamma-ray observations and to start the galactic dynamo takes place. We calculate the correction to the scalar spectrum and bispectrum (the latter related to primordial non-gaussianities) with respect to single-field slow-roll inflation generated in such a scenario. We find that the strongest constraints on the model originate from the non-observation of a scalar bispectrum of CMB anisotropies. Nevertheless, we found that even when those stringent constraints are taken into consideration, that scenario provides a robust explanation of the observed magnetic fields for a reasonably high energy scale of inflation

Influence of Hashimoto thyroiditis on the development of thyroid nodules and cancer in children and adolescents

It is unclear whether patients with Hashimoto thyroiditis (HT) are predisposed to develop thyroid nodules and/or thyroid cancer. The objective of our study was therefore to assess the prevalence of thyroid nodules and/or cancer in patients with HT and to look for possible prognostic factors. A retrospective survey of 904 children/adolescents with HT (709 females, 195 males) regularly followed in nine Italian centers of pediatric endocrinology was performed. Median period of follow-up was 4.5 years (1.2 to 12.8 years). We evaluated free T4, TSH, thyroid peroxidase antibody (TPOAb), thyroglobulin antibodies, and thyroid ultrasound yearly. One hundred seventy-four nodules were detected, with an annual incidence rate of 3.5%. Ten nodules were malignant (8 papillary and 2 papillary follicular variant), giving a 5.7% prevalence of cancer among patients with nodules. The severity of hypo-echogenity at ultrasound, TPOAb, and free T4 serum concentrations were predictive for the appearance of new nodules. Furthermore, a positive correlation was observed between TPOAb titer and the development of thyroid cancer. In conclusion, HT seems to influence the development of thyroid nodules, but not cancer in children and adolescents

Exploitation of large archives of ERS and ENVISAT C-band SAR data to characterize ground deformations

In the last few years, several advances have been made in the use of radar images to detect, map and monitor ground deformations. DInSAR (Differential Synthetic Aperture Radar Interferometry) and A-DInSAR/PSI (Advanced DInSAR/Persistent Scatterers Interferometry) technologies have been successfully applied in the study of deformation phenomena induced by, for example, active tectonics, volcanic activity, ground water exploitation, mining, and landslides, both at local and regional scales. In this paper, the existing European Space Agency (ESA) archives (acquired as part of the FP7-DORIS project), which were collected by the ERS-1/2 and ENVISAT satellites operating in the microwave C-band, were analyzed and exploited to understand the dynamics of landslide and subsidence phenomena. In particular, this paper presents the results obtained as part of the FP7-DORIS project to demonstrate that the full exploitation of very long deformation time series (more than 15 years) can play a key role in understanding the dynamics of natural and human-induced hazards. © 2013 by the authors

How future surgery will benefit from SARS-COV-2-related measures: a SPIGC survey conveying the perspective of Italian surgeons

COVID-19 negatively affected surgical activity, but the potential benefits resulting from adopted measures remain unclear. The aim of this study was to evaluate the change in surgical activity and potential benefit from COVID-19 measures in perspective of Italian surgeons on behalf of SPIGC. A nationwide online survey on surgical practice before, during, and after COVID-19 pandemic was conducted in March-April 2022 (NCT:05323851). Effects of COVID-19 hospital-related measures on surgical patients' management and personal professional development across surgical specialties were explored. Data on demographics, pre-operative/peri-operative/post-operative management, and professional development were collected. Outcomes were matched with the corresponding volume. Four hundred and seventy-three respondents were included in final analysis across 14 surgical specialties. Since SARS-CoV-2 pandemic, application of telematic consultations (4.1% vs. 21.6%; p < 0.0001) and diagnostic evaluations (16.4% vs. 42.2%; p < 0.0001) increased. Elective surgical activities significantly reduced and surgeons opted more frequently for conservative management with a possible indication for elective (26.3% vs. 35.7%; p < 0.0001) or urgent (20.4% vs. 38.5%; p < 0.0001) surgery. All new COVID-related measures are perceived to be maintained in the future. Surgeons' personal education online increased from 12.6% (pre-COVID) to 86.6% (post-COVID; p < 0.0001). Online educational activities are considered a beneficial effect from COVID pandemic (56.4%). COVID-19 had a great impact on surgical specialties, with significant reduction of operation volume. However, some forced changes turned out to be benefits. Isolation measures pushed the use of telemedicine and telemetric devices for outpatient practice and favored communication for educational purposes and surgeon-patient/family communication. From the Italian surgeons' perspective, COVID-related measures will continue to influence future surgical clinical practice

Science with the space-based interferometer LISA. IV: probing inflation with gravitational waves

We investigate the potential for the LISA space-based interferometer to detect the stochastic gravitational wave background produced from different mechanisms during inflation. Focusing on well-motivated scenarios, we study the resulting contributions from particle production during inflation, inflationary spectator fields with varying speed of sound, effective field theories of inflation with specific patterns of symmetry breaking and models leading to the formation of primordial black holes. The projected sensitivities of LISA are used in a model-independent way for various detector designs and configurations. We demonstrate that LISA is able to probe these well-motivated inflationary scenarios beyond the irreducible vacuum tensor modes expected from any inflationary background.Comment: 53 pages, 18 figures; v2: minor changes to match published versio

Observables from inflation: gravitational waves and magnetic fields

The inflationary paradigm represents a fascinating and elegant way of explaining crucial cosmological phenomena; moreover it is remarkably in agreement with current cosmological observations. However we are still blind to many aspects of the physics encoded in such a process and an unequivocal probe of such a mechanism is still lacking. On the other hand inflation suggests the solution to current open cosmological questions, as the observation of magnetic fields in the intergalactic medium. In order to investigate in depth the inflationary mechanism, one possibility is offered by the new era of gravitational wave detectors. In the first part of the thesis we focus on this aspect of the inflationary epoch. Any inflationary model predicts the production of a stochastic gravitational wave background (tensor modes) due to quantum fluctuations of the gravitational field. Moreover, in some scenarios, the presence of additional fields besides the inflaton and the gravitational field gives rise to efficient sources of gravitational waves, activating the so-called classical production. Inflationary gravitational wave signals turn out to represent a unique and exciting window on the origin and evolution of the universe, and a possibility of investigating the underlying theory of gravity. We point out the significant role of primordial gravitational waves in testing the inflationary mechanism itself and in constraining many aspects of the inflationary physics, exploiting the validity/violation of an inflationary consistency relation. Being inflationary gravitational waves a promising way of exploring many aspects of the physics of the early universe, we provide an updated picture of the current status and the observational prospects of inflationary tensor modes, with a particular focus on the possibility of a direct gravitational wave detection offered by current and upcoming laser interferometer detectors. Then we perform a dedicated forecast analysis of the capabilities of the LISA (Laser Interferometer Space Antenna) experiment in probing the inflationary physics. In particular, the capabilities of LISA in measuring a stochastic gravitational wave background are presented. Furthermore, we calculate the gravitational wave signal expected at the LISA frequencies for a number of selected inflationary models. We collect and re-elaborate current limits on the present time gravitational wave spectral energy density, and the sensitivity curves of LISA and other experiments, in order to outline current and expected constraints on the parameter space of the selected inflationary models. The results we find show the efficiency of the method, suggesting an exciting direction in order to investigate inflationary physics and a validation of the significant science that can be done by an experiment as LISA. In the second part of the thesis another interesting aspect of the inflationary mechanism is considered, i.e. the possibility of a significant magnetogenesis. Gamma-ray observations from blazars point out the presence of magnetic fields in the intergalactic medium, where no charged plasma are present. This fact suggests a primordial origin of such fields. Interestingly, the inflationary mechanism provides a fascinating way of explaining the presence of magnetic fields at cosmological scales. In a dedicated section, the main models of inflationary magnetogenesis are outlined. A common aspect of these models is the associated overproduction of curvature and tensor perturbations with respect to single-field slow-roll inflation. In general, observational constraints obtained by CMB measurements on such quantities lead to relevant restrictions on the associated production of magnetic fields. Other limits are provided by keeping under control the backreaction of the electromagnetic fields. In particular, we consider the case proposed from Caprini, where a magnetogenesis mechanism able to explain current gamma-ray observations and to start the galactic dynamo takes place. We calculate the correction to the scalar spectrum and bispectrum (the latter related to primordial non-gaussianities) with respect to single-field slow-roll inflation generated in such a scenario. We find that the strongest constraints on the model originate from the non-observation of a scalar bispectrum of CMB anisotropies. Nevertheless, we found that even when those stringent constraints are taken into consideration, that scenario provides a robust explanation of the observed magnetic fields for a reasonably high energy scale of inflation.Il paradigma inflazionario rappresenta una modo affascinante ed elegante di spiegare alcuni cruciali fenomeni cosmologici; inoltre risulta in notevole accordo con le attuali osservazioni cosmologiche. Tuttavia, diversi aspetti della fisica di tale processo risultano ancora oscuri e una prova inequivocabile di tale meccanismo è ancora assente. Dall'altro lato, il meccanismo inflazionario si presenta come soluzione di problemi cosmologici ancora aperti, come l'osservazione di campi magnetici nel mezzo intergalattico. Per studiare in profondità il meccanismo inflazionario, una possibilità è offerta dalla nuova epoca di esperimenti per l'osservazione di onde gravitazionali. La prima parte della tesi è focalizzata su tale aspetto della fisica inflazionaria. Ciascun modello inflazionario predice la produzione di un fondo stocastico di onde gravitazionali (modo tensoriali) dovuti alle fluttuazioni quantistiche del campo gravitazionale. Inoltre, in alcuni scenari, la presenza di ulteriori campi oltre all'inflatone e al campo gravitazionale, genera efficaci sorgenti di onde gravitazionali, attivando la produzione classica. Il segnale di onde gravitazionali inflazionarie si rivela essere una unica e interessante finestra sull'origine e l'evoluzione dell'universo, e la possibilità di investigare la sottostante teoria della gravità. Nella tesi è mostrato il ruolo significativo delle onde gravitazionali primordiali nel testare il meccanismo inflazionario in sè e nel provare diversi aspetti della fisica inflazionaria, sfruttando la validità/violazione di una relazione di consistenza. Essendo le onde gravitazionali inflazionarie, un modo promettente di esplorare diversi aspetto della fisica dell'universo primordiale, è inoltre fornito un quadro aggiornato dello stato attuale e delle prospettive di osservazione dei modi tensoriali inflazionari, con una focalizzazione particolare sulla possibilità di osservazione diretta offerta dagli interferometri laser. Successivamente, sono esposte delle previsioni sulle possibilità offerte dell'interferometro spaziale LISA rispetto al testare la fisica inflazionaria. Nella seconda parte della tesi viene descritto un altro aspetto interessante della fisica inflazionaria, ovvero la possibilità di una significativa magnetogenesi. Le osservazioni di raggi gamma dai blazars indicano la presenza di campi magnetici nel mezzo intergalattico, dove non è presente plasma carico. Questo fatto suggerisce un'origine primordiale di tali campi magnetici. E' interessante notare che il meccanismo inflazionario fornisce un affascinante modo di spiegare la presenza di campi magnetici a scale cosmologiche. In una sezione dedicata, sono mostrati i principali modelli di magnetogenesi inflazionaria. Un aspetto comune di tale modelli è una sovra produzione di perturbazioni di curvatura e tensoriali, rispetto al modello inflazionario di single-field slow-roll. In generale, i limiti osservativi ottenuti da misurazioni di CMB su tali quantità comportano restrizioni significative sulla produzione di campi magnetici associata. Altri limiti sono imposti dal controllo della backreaction dei campi elettromagnetici. In particolare, nella tesi viene considerato il modello proposto da Caprini, in cui ha luogo una magnetogenesi in grado di spiegare le attuali osservazioni dei raggi gamma e di dare inizio al processo di dynamo galattica. Viene calcolata la correzione allo spettro e bispettro degli scalari rispetto al caso di single-field slow-roll, in tale scenario. Il risultato mostra come le restrizioni più forti siano dovute alla non osservazione di un bispettro degli scalari nelle anisotropie della CMB. Ciò nonostante, si conclude che anche quando tali restrizioni vengono prese in considerazione, lo scenario inflazioanrio in esame fornisce una robusta spiegazione dei campi magnetici osservati per una ragionevolmente alta scala di energia dell'inflazione

Inflationary magnetogenesis with added helicity: constraints from non-gaussianities

International audienceIn previous work (Caprini and Sorbo 2014 J. Cosmol. Astropart. Phys. JCAP10(2014)056), two of us have proposed a model of inflationary magnetogenesis based on a rolling auxiliary field able both to account for the magnetic fields inferred by the (non) observation of gamma-rays from blazars, and to start the galactic dynamo, without incurring in any strong coupling or strong backreaction regime. Here we evaluate the correction to the scalar spectrum and bispectrum with respect to single-field slow-roll inflation generated in that scenario. The strongest constraints on the model originate from the non-observation of a scalar bispectrum. Nevertheless, even when those constraints are taken into consideration, the scenario can successfully account for the observed magnetic fields as long as the energy scale of inflation is smaller than GeV, under some conditions on the slow roll of the auxiliary scalar field