Swampland conjectures set up criteria, what kind of effective quantum field theories can or cannot originate from quantum gravity, and provide at the same time intriguing new relations between the ultraviolett cutoff and certain infrared quantities of the effective field theory.
In particular, augmented with the smallness of the dark energy in the universe and other experimental observations, swampland arguments predict the existence of a dark dimension of micron size.
In the talk I will give an introduction to the dark dimension scenario and its possible consequences in particles physics and cosmology, namely for the scale of supersymmetry breaking and primordial black holes as dark matter candidates.

Compactifications with torsion of the Heterotic string preserving minimal supersymmetry in four dimensions can be obtained as orbifolds of principal two-torus bundles over a K3 surface. We consider a two-dimensional worldsheet description of these backgrounds as gauged linear sigma-models (GLSMs) with (0,2) supersymmetry. Such a formulation provides a useful framework in order to address the resolution of singular orbifold geometries. We investigate the constraints imposed by discrete symmetries on the corresponding torsional GLSMs. In particular, the principal T^2 connection over K3 is inherited from (0,2) vector multiplets. As these vectors gauge global scaling symmetries of products of projective spaces, the corresponding K3 geometry is naturally realized as an algebraic hypersurface in such a product (or as a branched cover of it). I will outline the general construction and give explicit constructions for K3 automorphisms of order two and three.

While performing its function in cells, DNA is subject to a considerable amount of mechanical deformations due to the interactions with other bio-molecules and to thermal fluctuations. To understand the functioning and properties of DNA, it is important to understand its mechanics, a task which involves modeling and experiments. In this talk I will give a general overview of our present understanding of DNA physical properties and of DNA-protein interactions, highlighting some recent results and future challenges.

I introduce the problem of realizing de Sitter vacua in string theory which in principle consists of two steps. First, one establishes a scale separated AdS vacuum which is usually done with KKLT or the LVS. Then, the minimum is uplifted to a positive value. I will revisit a famous way of uplifting which relies on using anti-D3-branes in a warped throat. Then, I discuss how alpha' corrections affect the meta-stability of anti-branes in a warped throat, and the resulting implications for phenomenology. Thereby, we will discover how alpha' corrections to anti-branes suggest a novel uplifting mechanism.

During the past decade the semileptonic b->sll decays have shown consistent deviations from the standard model predictions. Up to the last year the Lepton flavour universality (LFU) ratios RK and RK* showed hints of LFU Violation, however after the recent update from LHCb, this hints of LFUV have suddenly disappeared. We discuss the current status of these decays, after this radical change, showing that a strong case for LFU new physics (NP) not only still exists but also thanks to this update a substantial enhancement of the consistency of experimental data has been achieved. Furthermore, the array of NP patterns that appeared in previous data has been reduced to a clear single candidate, which however sees hadronic contamination. In this context we discuss the directions that can be taken to clearly distinguish NP from hadronic contributions in an agnostic way.

The strong CP problem, i.e. the unexplained absence of CP violation in strong interactions, can be solved by theories which spontaneously break spacetime parity. Those usually have few additional parameters and are therefore very predictive, but their landscape remains quite unexplored. I will present a construction based on a complete mirror copy of the standard model, linked to our world by colored portal fields. Those induce the partial spontaneous breaking of the color groups and yield a vanishing theta angle at low energies. The loop contributions to the latter are well under control. Although the model contains the heavy vectorlike fermions typical of parity models, the lightest BSM fields could be colored (pseudo-Goldstone) bosons.

Systems driven out of thermal equilibrium can form spontaneously complex structured spatial and spatio-temporal states via self-organization, even if the drive is homogeneous in space and constant in time. Broad-area vertical-cavity surface-emitting lasers (VCSELs) emerged as a highly controllable and versatile tool to investigate this interesting nonlinear laser dynamics as they are semiconductor lasers with very short (about 1 µm) but broad (about 200 µm diameter) microcavities. The high circular symmetry of VCSELs also allows for the polarization degrees of freedom to be self-organized. I will present investigations on the spontaneous appearance of vector vortex beams in a VCSEL with frequency-selective feedback with a radial, spiral and hyperbolic polarization structure and their interpretation as high order vectorial solitons. Vector vortex beams are an example of “fully structured light”, i.e. light beams with spatially inhomogeneous intensity and polarization distribution, usually created by specialized linear beam shaping devices. I will also review some results on mode-locking of laser cavity solitons, i.e. the possibility of spontaneous pulsations due to operating on multiple longitudinal modes. This might pave a path to “light bullets”, i.e. light self-localized in all three dimensions.

Evidence of spin memory for spin polarized pumping in the photoluminescence of quantum dot vertical-gain structures is presented. This opens the path to vertical-external cavity lasers with polarization control via pumping (“spin-VECSELs”).

The cortex is a thin layer located beneath the membrane of animal cells. It governs important cell mechanical properties, including cell shape. It is composed of a dense network of actin filaments and actin-binding proteins, in particular myosin motors. Myosins generate active stresses in the actin network and make it behave as an active material. The spatiotemporal organization of the cortex is tightly coupled to that of signaling molecules, in particular Rho GTPases. Indeed, the interaction between actin, myosin and Rho GTPases can give rise to self-organized patterns. Thus far, studies have focused on spatially extended patterns, like actin polymerization waves. However, spatially localized patterns are also observed in the cortex, whereby isolated spots enriched in actin, myosin and signaling molecules play a role in crucial processes, including cancer invasion. What is the origin of such isolated structures? We use a simple physical theory to show that they can emerge from the coupling between active cortical mechanics and signaling reactions, through an instability called "slanted snaking". Beyond single cells, our theory could also explain the origin of spatially localized, mechanochemical cues in tissue morphogenesis.

Please contact J. Palmeri (L2C) for the webinar link

Interaction between micro- and nano- particles and lipid membranes controls processes such as endocytosis, drug delivery and microbial infections. Dramatic changes in particle motion and membrane properties can be observed when a particle approaches a membrane. A shape transition of the membrane may occur to accommodate the particle, and partial or complete particle wrapping by the membrane takes place as a function of the energy of adhesion, membrane tension and bending. Furthermore, the interaction between a hard particle and a soft membrane may lead to complex dynamics when the system is driven out of equilibrium. Here, I will present experiments showing complex dynamics such as the physics of particle wrapping by a membrane, the transport of vesicles by active particles, and the orbital motion of active colloids around vesicles. Recent optical tweezers experiments on particle penetration inside giant vesicles will be presented and discussed in the limit of a vanishing adhesion energy [1]. In a wide range of experimental conditions, we have observed that a self-propelled Janus colloid is able to perform orbital motion around a giant vesicle remaining in a non-wrapped state [2]. Still, the active particle is able to impart a force of the order of 0.01 pN on the vesicle, which is however too small to trigger membrane wrapping. By applying external forces in the 1-100 pN range, we were able to observe membrane wrapping of bare and Janus colloids by a giant vesicle, which leads to the transport of vesicle by an active colloid [3]. References: - [1] F. Fessler, V Sharma, P Muller, A Stocco. (2023) Entry of Microparticles into Giant Lipid Vesicles by Optical Tweezers, https://arxiv.org/abs/2301.02504 (accepted in PRE).
- [2] V Sharma, E Azar, AP Schroder, CM Marques, A Stocco. (2021) Active colloids orbiting giant vesicles, Soft Matter.
- [3] V Sharma, CM Marques, A Stocco. (2022) Driven Engulfment of Janus Particles by Giant Vesicles in and out of thermal equilibrium, Nanomaterials.