Seminars

Abstract: We study the late-time relaxation of a neutral relativistic viscous fluid in d+1 dimensions.In the long-wavelength regime, linearized hydrodynamics predicts that the sound mode at momentum nk decays as e^{-i n^2 \omega_I t}, However, nonlinear analysis gives a decay of e^{-i n \omega_I t}. We derive a closed asymptotic attractor solution in which the frequency of the n-th harmonic locks to n times the complex frequency of the fundamental mode. The amplitude envelopes for energy current J obey a simple cascading relation,J_n=\alpha_J^{n-1}J_1^n with \alpha_J is fixed by the equation of state, the longitudinal viscosity, and the fundamental wavenumber. For conformal fluids,\alpha_J=1/8\eta k, in agreement with the holographic result of arXiv:2512.07242. The existence of the attractor shows that, even near equilibrium, field powers are not equivalent to amplitude order. 

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Abstract: In my talk I introduce quantum mechanics in moduli scape of string theory.  We will discuss the moduli space wave function, which describes a quantum particle moving in moduli space. We discuss the spectrum of the associated moduli space Laplacian, showing that in contains normalizable bounds states of positive energy and fixed values of the moduli fields in case the moduli space is compactifiable.  In addition we also include a potential, where quantum effects can result in moduli localised away from classical minima and in excited, positive energy states, even in cases where the classical potential exhibits a runaway behaviour.  Finally employing the well-known Wheeler-DeWitt equation of quantum gravity and combining it with  moduli space quantum mechanics,  we show how quantum effects can lead to an excited  de Sitter universe with a positive effective cosmological constant. 

Abstract: In this colloquium I will give a short introduction to Quantum Gravity and its realisation by String Theory. As known for some time, string theory predicts a huge landscape of vacua, seen as different effective theories at low energy. However, as it became evident during the recent years that the space of theories that cannot originate from string theories is much larger than the landscape, and hence usually dubbed as the so-called swampland. I will discuss some of the properties of the swampland scenario and how it has recently led to some predictions about dark energy, dark matter and primordial black holes. 

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