I will discuss string theory compactifications where a large number of moduli is stabilized by fluxes. I will present a conjecture which rules out the stabilization of all complex-structure moduli in F-theory at a generic point in moduli space by fluxes that satisfy the tadpole cancellation condition. Evidence for this conjecture comes from K3xK3 compactifications. Using evolutionary algorithms we found that moduli stabilization needs fluxes whose charge is slightly smaller than 1/2 of the number of moduli and larger than what is allowed by tadpole cancellation. I will furthermore comment on possible implications on de Sitter vacua obtained by antibrane uplift in long warped throats.

The dark photon is a massive hypothetical particle that interacts with the Standard Model by kinetically mixing with the visible photon. Due to the similarities with the electromagnetic signals generated by axions, several bounds on dark photon signals are simply reinterpretations of historical bounds set by axion haloscopes. However, the dark photon has a property that the axion does not: an intrinsic polarisation. Due to the rotation of the Earth, accurately accounting for this polarisation is nontrivial, and highly experiment-dependent. In this talk I will argue that if one does account for this polarisation, and the rotation of the Earth, experimental sensitivity to the dark photon’s kinetic mixing parameter can be improved by over an order of magnitude. I will then detail the strategies that would need to be taken to properly optimise a dark photon search.

Two-dimensional (2D) materials can be combined into complex heterostructures by stacking them with controlled twisted angles. Twisted layers of 2Ds present a modified band structure due to the presence of an induced Moiré pattern in their electronic structures. This field of research, commonly known as Twistronics, has blossomed recently due to the discovery of exotic states of matter in twisted bilayer graphene devices
However, this field of electronics offers many other lines of research, yet to be studied, with multiple applications and possible new effects. Our ongoing line of research focuses on the study of the appearance of exotic electronic states in heterostructures based on encapsulated graphene monolayer between two ultrathin layers of hexagonal boron nitride (hBN) by controlling the relative angle between the graphene and them.
In our latest devices, the three different layers are aligned with a commensurate pattern of the natural edges far away from the magic angle. Multiple alignment possibilities could happen following this procedure due to the two different crystalline directions of graphene and hBN, zigzag and armchair. By combining different optical and electrical measurements we can determine their exact relative alignment.
Low temperature electrical characterisation has determined, by local measurements, a high-quality sample with a sizeable mobility. The valley and spin degenerations are broken, and multiple plateaus appear when a magnetic field is applied. However, the most remarkable results of this device are not obtained with local measurements.
Magnetotransport measurements on this device have revealed an intriguing non-local electrical signal, with a chiral flavour, when small external magnetic fields are applied. The non-local signal in graphene is widely studied and different effects causing it can be found in the literature. However, very few effects can explain this chirality in the results.
There is no doubt that the study of different alignments among 2D materials opens many new possibilities in Twistronics, which could include a better understanding of anomalous superconductivity, paving the way for new methods to obtain materials with novel quantum properties. In addition to their undoubted fundamental interest, these materials may also enable new quantum technologies that constitute a technological breakthrough.

Three dimensional conformal field theories (CFTs) describe important critical physics in the real world. In the past few years much progress has been made in 3D CFTs using the conformal bootstrap. In particular, using numerical bootstrap, the critical exponents of the 3D Ising, Super-Ising, O(2), O(3) CFTs have been determined precisely with rigorous error bars, while using analytic bootstrap, the information of the leading twist operators at large spins can be computed analytically. The two bootstrap approaches are sensitive to different regions of the spectrum and complement each other. In this talk, I will first give a general review of the numerical bootstrap and analytic bootstrap. Then I will discuss how to combine the numerical bootstrap with the analytic lightcone bootstrap, i.e. a hybrid bootstrap method. As a result, the bootstrap prediction for the actual CFT can be significantly improved.

Photonic metamaterials with advanced optical and thermal functionalities have capability of active light manipulation and dynamic tuning nanoscale thermal transport. There is a constant need of functional metamaterials with (a) an excellent spectral selectivity for thermophotovoltaics and thermoelectric systems, (b) an efficient self-adaptivity for energy conversion and cooling, and (c) an ultrahigh and tunable rectification ratio for thermal management and logic devices. My research is to conduct a fundamental study of multifunctional metamaterials with tunable wavelength selectivity, self-adaptive feature, and strong thermal switching performance while taking the advantages of the scattering of multi-species nanoparticle inclusions, phase transition, and reconfigurable structures. This seminar aims to enlighten how to fundamentally explore the multifunctionalities of metamaterials and dynamic tuning of radiative thermal transport which are attributed to highly effective, thermally stable, sharply switching, phase-transition metamaterials.

Embryonic tissues are striking examples of complex viscoelastic active fluids that self-organize into highly organized structures. Studying quantitatively the complex feedback-loop between tissue rheological properties, gene expression and morphogenetic flows requires a perturbative approach, which is challenging to adopt on a developing embryo, in particular in mammals that develop in utero. Mouse embryonic stem cells can self-organize in 3D embryonic organoids called Gastruloids sharing similarities with their in vivo counterparts. Recent studies have shown that they generate in few days structures similar genetically and morphologically with organs such as the neural tube or the heart.

The first major morphogenesis step for Gastruloids (early symmetry breaking) occurs between 72h and 96h after aggregation: they transform from a spherical cell aggregate with all cells expressing a rather homogeneous gene expression to an elongated tissue displaying an antero-posterior axis associated with strong cell differentiation heterogeneities.

In this talk, I will present in a first part our current understanding on the biophysical mechanism of Gastruloids early symmetry breaking, combining 3D live microscopy of collective cell flows and physical modeling of tissue phase separation due to heterogeneities in cell populations interfacial tensions. In a second part, I will present a method combining microfluidic aspirations of 3D cells aggregates with two-photon microscopy to force embryonic stem cells aggregates to flow through constrictions while imaging the tissue response at the cellular scale (i.e. cell deformations and rearrangements). I will finally discuss how this method could be extended to study spatial heterogeneities in tissue rheological properties emerging during embryonic patterning.

Three-dimensional N =4 supersymmetric field theories admit a natural class of chiral half-BPS boundary conditions that preserve N = (0, 4) supersymmetry. While such boundary conditions are not compatible with topological twists, deformations that define boundary conditions for the topological theories were recently introduced by Costello and Gaiotto. Not all N = (0, 4) boundary conditions admit such deformations. We revisit this construction, working directly in the setting of the holomorphically twisted theory and viewing the topological twists as further deformations. Properties of the construction are explained both purely in the context of holomorphic field theory and also by engineering the holomorphic theory on the worldvolume of a D-brane. Our brane engineering approach combines the intersecting brane configurations of Hanany–Witten with recent work of Costello and Li on twisted supergravity. The latter approach allows to realize holomorphically and topologically twisted field theories directly as worldvolume theories in deformed supergravity backgrounds, and we make extensive use of this.

The possibility of probing the existence of beyond the Standard Model physics via precision measurements is of renewed importance given the current lack of signs of new particles being produced at the LHC.

One of the most important quantities in that regard is the mass of the W boson. Advanced theoretical predictions and sophisticated experimental techniques are required for measuring M_W at LHC with the precision required to provide meaningful BSM bounds.

At the same time, in order to properly compare the experimental determination with the theoretical predictions, it is important to estimate properly the uncertainties affecting the experimental value as extracted with the current setup.

In this talk I will at first present an overview of the most important theoretical uncertainties affecting the LHC determination, focusing on bottom-related effects and PDF uncertainties, while in a second part of the talk I will show an explicit example of how M_W can be used to probe indirectly supersymmetric scenarios in light of the current experimental constraints and the muon g-2 anomaly.