The research activity of the Institute of Physics covers five main domains:
- Quantum Science and Technology
- Condensed Matter Physics
- Biophysics and complex systems
- Particle and astrophysics
- Physics for energy
Directed polymers in random media (DPRM) is a simple lattice model in the Kardar-Parisi-Zhang (KPZ) universality class for stochastic surface growth. The model considers configurations of a directed path traversing a random energy landscape, and can be simulated in polynomial time through a transfer matrix formulation. As a possible application, we examine the expansion of biological populations into new territory using methods from DPRM, and model the stochastic spatial wandering of both genetic lineages and the boundaries between genetically segregated sectors. Laboratory experiments on microbial range expansions have shown that this stochastic wandering, transverse to the front, is superdiffusive due to the front's growing roughness, implying much faster loss of genetic diversity than predicted by simple flat front diffusive models. We study the evolutionary consequences of this superdiffusive wandering by computing coalescence statistics for pairs of individuals separated at the front, and exploring how environmental heterogeneities can locally suppress fluctuations.
By: Yun Chu
The building blocks of quantum observables are collections of asymptotic series in the coupling constant, corresponding to perturbative and non-perturbative sectors. According to the theory of resurgence, these series are related to each other in a non-trivial way, and these relations are encoded in the so-called Stokes automorphisms of the theory. In this seminar we put forward the idea that knowledge of these automorphisms and of the classical limit might make it possible to solve the quantum theory at all values of the coupling. We show how this program can be implemented in detail in quantum mechanics with polynomial potentials.
In this case, the solution takes the form of a set of coupled integral equations of the TBA type, which generalizes the famous ODE/IM correspondence. This implementation uses ideas about BPS states and their wall-crossing in supersymmetric gauge theories
By: Marcos Marino
The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups (i.e. PhD & Postdocs either directly funded by the NCCR, or as a matching contribution). The EPFL community interested in MARVEL research topics is very welcome to attend.
Each seminar consists of two 25-minute presentations, followed by time for discussion.
Pizza will be served at 11:45 in the MED hall (floor 0) and you are also cordially invited after the seminar at 13:30 for coffee and dessert to continue the discussion with the speakers.
Unified theory of thermal transport in crystals and glasses
To bend or not to bend? The dilemma of the double bond
By: Michele Simoncelli (EPFL, THEOS) & Michele Pizzochero (EPFL, C3MP)
In its most intuitive form, natural selection predicts the survival of the fittest - competition and conflict between individual organisms. But cooperation is widespread in nature, from microbes to humans. I am interested in understanding the emergence and stability of cooperation and competition, and when each is predicted to arise. I will start by briefly presenting work from my PhD where we used robots to study the evolution of communication. I will then switch model systems and talk about interactions in single species of bacteria, then multi-species bacterial communities.
Here, I will focus in more detail on our latest research using theory and experiments to study a four-species bacterial ecosystem capable of degrading liquid pollutants. We show that positive interactions that resemble cooperation are highly environment-dependent. I will then finish with an overview of ongoing projects in my group.
By: Prof. Sara Mitri, Département de Microbiologie Fondamentale, Université de Lausanne
In the last years, several groups have described the yielding phenomenon in the deformation of amorphous materials from a statistical physics point of view. To that end, coarse-grained approaches to amorphous solids were introduced, the so-called elasto-plastic models (EPM) .
In this talk, I will focus on the statistics of avalanches produced by the characteristic stick-slip behavior close to the yielding transition, enquiring into its common properties among different EPM proposals. I will present in particular the less studied case of EPMs with stress-dependent transition rates for local yielding , which help us to see how "dynamical" exponents -those related to the driving speed- may depend on the model details while universality stands more robust for "static" critical exponents.
On the way, the current understanding of yielding from mean-field descriptions and comparison with the depinning transition of a driven elastic line in random media, will be briefly discussed. If time permits, I will further comment on the the strain-rate dependence  and inertial effects  on the statistics of avalanches as we depart, respectively, from the usually addressed quasistatic and overdamped limits.
 Deformation and flow of amorphous solids: a review of mesoscale elastoplastic models
A. Nicolas, E.E. Ferrero, K. Martens, J.-L. Barrat
Rev. Mod. Phys. 90, 045006 (2018)
 Static and dynamic critical exponents for elastoplastic models of amorphous solids
E.E. Ferrero and E.A. Jagla, (unpublished).
 Driving Rate Dependence of Avalanche Statistics and Shapes at the Yielding Transition
C. Liu, E.E. Ferrero, F. Puosi, J.-L. Barrat, and K. Martens
Phys. Rev. Lett. 116, 065501 (2016)
 Inertia and universality of avalanche statistics: The case of slowly deformed amorphous solids
K. Karimi, E.E. Ferrero, J.-L. Barrat
Phys. Rev. E 95, 013003 (2017)
By: Ezequiel Ferrero