Supersymmetry breaking from 4D string moduli

Il limite di bassa energia della Teoria delle Stringhe può dare luogo a teorie di campo effettive con supersimmetrie N=1 che rappresentano uno scenario molto promettente per la Fisica oltre il Modello Standard. Inoltre, le compattificazioni delle stringhe includono naturalmente meccanismi per la rottura spontanea della supersimmetria nel settore nascosto a causa della stabilizzazione dei moduli. I termini che rompono la simmetria nel visibile (soft supersymmetry breaking terms) sono poi generati attraverso l'interazione gravitazionale tra i moduli e il settore osservabile. La tesi è incentrata sui modelli 4D per le stringhe Type IIB all'interno del cosiddetto LARGE Volume Scenario per la stabilizzazione dei moduli. In particolare, considera compattificazioni di Calabi-Yau di tipo K3 fibrato in cui il Minimal Supersymmetric Standard Model (MSSM) è supportato su brane D7 avvolte su 4-cicli nel regime geometrico. Le correzioni di string loop al potenziale di Kaehler rivestono un ruolo cruciale per la stabilizzazione dei moduli e la rottura della supersimmetria. Inoltre, questa classe di compattificazioni di stringa si è dimostrata particolarmente appropriata per la realizzazione dell'inflazione cosmica. Dopo una discussione sulla forma della metrica di Kaehler per i campi di materia del settore visibile, la tesi determina la struttura dei soft supersymmetry breaking terms risultanti per differenti sistemazioni delle brane. Infine, analizza i principali vincoli fenomenologici sugli spettri di massa del settore nascosto e dei superpartner del Modello Standard, insieme con il requisito dell'ottenimento di una massa dell'Higgs corretta. L'esito finale indica che questa modellizzazione non permette contemporaneamente la presenza di una buona descrizione dell'inflazione e di un settore visibile dato esattamente dall'MSSM. Delle possibili vie d'uscita necessiterebbero o di un modello inflazionario differente o di una estensione minimale dell'MSSM (come il NMSSM)

A deep learning pipeline for product recognition on store shelves

Recognition of grocery products in store shelves poses peculiar challenges. Firstly, the task mandates the recognition of an extremely high number of different items, in the order of several thousands for medium-small shops, with many of them featuring small inter and intra class variability. Then, available product databases usually include just one or a few studio-quality images per product (referred to herein as reference images), whilst at test time recognition is performed on pictures displaying a portion of a shelf containing several products and taken in the store by cheap cameras (referred to as query images). Moreover, as the items on sale in a store as well as their appearance change frequently over time, a practical recognition system should handle seamlessly new products/packages. Inspired by recent advances in object detection and image retrieval, we propose to leverage on state of the art object detectors based on deep learning to obtain an initial productagnostic item detection. Then, we pursue product recognition through a similarity search between global descriptors computed on reference and cropped query images. To maximize performance, we learn an ad-hoc global descriptor by a CNN trained on reference images based on an image embedding loss. Our system is computationally expensive at training time but can perform recognition rapidly and accurately at test time

Real-time self-adaptive deep stereo

Deep convolutional neural networks trained end-to-end are the state-of-the-art methods to regress dense disparity maps from stereo pairs. These models, however, suffer from a notable decrease in accuracy when exposed to scenarios significantly different from the training set, e.g., real vs synthetic images, etc.). We argue that it is extremely unlikely to gather enough samples to achieve effective training/tuning in any target domain, thus making this setup impractical for many applications. Instead, we propose to perform unsupervised and continuous online adaptation of a deep stereo network, which allows for preserving its accuracy in any environment. However, this strategy is extremely computationally demanding and thus prevents real-time inference. We address this issue introducing a new lightweight, yet effective, deep stereo architecture, Modularly ADaptive Network (MADNet) and developing a Modular ADaptation (MAD) algorithm, which independently trains sub-portions of the network. By deploying MADNet together with MAD we introduce the first real-time self-adaptive deep stereo system enabling competitive performance on heterogeneous datasets.Comment: Accepted at CVPR2019 as oral presentation. Code Available https://github.com/CVLAB-Unibo/Real-time-self-adaptive-deep-stere

Studio e sviluppo di un sistema di interrogazione di Fiber Bragg Grating Sensors implementato tramite Array Waveguide Gratings

In questa tesi si affronta lo studio dettagliato di un interrogatore di Fiber Bragg Grating Sensors tramite Array Waveguide Gratings controllabili in temperatura. Dopo aver risolto le problematiche ottiche e creato un set-up funzionante, viene progettata, realizzata e collaudata un'apposita scheda elettronica atta a condizionare, amplificare e campionare i segnali ottici oggetti di studio

Late-time attractors and cosmic acceleration

We prove the conditions under which scaling cosmologies are inevitable late-time attractors of multi-field multi-exponential potentials, independently of initial conditions. The advantage of such scaling cosmologies is that the time dependence of the fields and of the scale factor is known analytically, thus allowing late-time observables to be determined exactly. Expanding the earlier results of ref. arXiv:hep-th/2303.03418, here we continue the program of analytically characterizing the late-time behavior of cosmological solutions. Our results are general in that they are derived without relying on any approximation nor are they based on any assumption on the sources of the potential, such as their higher-dimensional or string-theoretic origin. We point out a number of model-independent features that follow from our analytic results, including a convex-hull criterion for cosmic acceleration. When applied to string theory, our analytic knowledge of late-time cosmological solutions enables us to single out potentials that can describe an accelerating universe from those which cannot and to quantitatively test several conjectured Swampland criteria.Comment: 26 pages (13 figures) + appendice

Accelerating universe at the end of time

We investigate whether an accelerating universe can be realized as an asymptotic late-time solution of FLRW-cosmology with multi-field multi-exponential potentials. Late-time cosmological solutions exhibit a universal behavior which enables us to bound the rate of time variation of the Hubble parameter. In string-theoretic realizations, if the dilaton remains a rolling field, our bound singles out a tension in achieving asymptotic late-time cosmic acceleration. Our findings go beyond previous no-go theorems in that they apply to arbitrary multi-exponential potentials and make no specific reference to vacuum or slow-roll solutions. We also show that if the late-time solution approaches a critical point of the dynamical system governing the cosmological evolution, the criterion for cosmic acceleration can be generally stated in terms of a directional derivative of the potential.Comment: 5 pages + appendix; v2: minor improvement

Fundamental and Phenomenological Aspects of Anti-D-Brane Supersymmetry Breaking

This dissertation focusses on the investigation of both the fundamental and the phenomenological features of non-supersymmetric string theories based on supersymmetry breaking by anti-D-branes. The study of non-supersymmetric string theories is shedding light on an important corner of the string landscape that might ultimately explain the reason why, so far, supersymmetry has not been detected in the observed universe. The first line of research aims at enriching the understanding of misaligned supersymmetry in String Theory. Misaligned supersymmetry consists in cancellations between bosonic and fermionic contributions at different energy levels in the whole string spectrum. This is interpreted as a physical mechanism that helps visualising the origin of the finiteness of string constructions, otherwise motivated based on the behaviour of the theory under modular transformations. A review is presented of how misaligned supersymmetry in closed-string theories leads to a cancellation between bosons and fermions even in non-supersymmetric scenarios. Then, it is shown that an entirely analogous cancellation can take place in non-supersymmetric open-string theories, too, by studying anti-D-branes placed on top of O-planes. These ideas are then developed via a systematic analysis of the net physical degeneracies at each energy level, studying their non-trivial cancellations and relating them to the modular properties of the partition function. Eventually, the whole concept of misaligned supersymmetry in String Theory is analysed in a mathematically rigorous way, showing the details of how the boson-fermion cancellations can take place in physical quantities, and the role of misalignment in all known 10-dimensional tachyon-free non-supersymmetric string constructions is finally discussed. The second line of research, instead, is devoted to a phenomenological investigation and description of a class of quasi-realistic non-supersymmetric vacua including anti-D-branes. In particular, it discusses model-building scenarios featuring intersecting anti-D3- and D7-branes. Effectively, supersymmetry is broken spontaneously, despite having no scale at which sparticles appear and standard supersymmetry is restored. If the branes are placed on singularities at the tip of warped throats in Calabi-Yau orientifold flux compactifications, they may give rise to quasi-realistic particle spectra, closed- and open-string moduli stabilisation with a Minkowski/de Sitter uplift, together with a geometrical origin for the scale hierarchies. A derivation is given of the low-energy effective field theory description for such scenarios, i.e. a non-linear supergravity theory for standard and constrained supermultiplets, including soft supersymmetry-breaking matter couplings. The effect of closed-string moduli stabilisation on the open-string matter sector is worked out, incorporating non-perturbative and perturbative effects, and the mass and coupling hierarchies are computed with a view towards phenomenology