Video Library

Fractional quantum hall states with nu = p/q  have a characteristic geometry  defined by the electric quadrupole moment of the neutral composite boson that is formed by "flux attachment" of q "flux quanta" (guiding-center orbitals) to p charged particles.    This characterizes the  "Hall viscosity".    For FQHE states described by a conformal field theory with a Euclidean metric  g_ab, the quadrupole moment is proportional to the "guiding-center spin" of the composite boson and the inverse metric.       The geometry gives rise to dipole moments at external edges or internal "orbital

The symmetric Kugel-Khomskii can be seen as a minimal model describing the interactions between spin and orbital degrees of freedom in certain transition-metal oxides with orbital degeneracy, and it is equivalent to the SU(4) Heisenberg model of four-color fermionic atoms. We present simulation results for this model on various two-dimensional lattices obtained with infinite projected-entangled pair states (iPEPS), an efficient variational tensor-network ansatz for two dimensional wave functions in the thermodynamic limit.

Effective field
theory techniques allow reliable quantum calculations in general relativity at
low energy. After a review of these techniques, I will discuss the attempts to
define the gravitational corrections to running gauge couplings and to the
couplings of gravity itself. I will also describe an attempt to understand the
relation between the effective field theory and Asymptotic Safety in the region
where they overlap.

In the last few years several interesting phenomena associated to the interaction between massive black holes and fundamental bosonic fields have been discovered. I present a selection of them, including superradiance instabilities of spin-0, spin-1 and spin-2 fields, floating orbits in extreme-mass ratio inspirals and black-hole spontaneous scalarization. The theoretical potential of these effects
as almost-model-independent smoking guns for exotic particles and modified gravity, as well as their limitations in realistic astrophysical scenarios, are discussed.