Regular Seminar Roberto Emparan (ICREA, Barcelona)
The cosmic censorship conjecture raises the question of whether classical gravitational dynamics can drive a low-energy configuration into an accessible regime of quantum gravity, with Planck-scale curvatures and energy densities visible by distant observers. I will present evidence that cosmic censorhip is violated in the quintessential phenomenon of General Relativity: the collision and merger of two black holes. It only requires a sufficient total angular momentum in a collision in high enough number of dimensions. Nevertheless, I will argue that even if cosmic censorship is violated in this and in some other know instances, its spirit remains unchallenged: classical relativity describes the physics seen by observers outside the black holes accurately, with only minimal quantum input that does not entail macroscopic disruptions.
Regular Seminar Kostya Trachenko (QMUL)
room G O Jones 610
Understanding most basic thermodynamic properties of liquids such as energy and heat capacity turned out to be a long-standing problem in physics . Landau&Lifshitz textbook states that no general formulas can be derived for liquid thermodynamic functions because the interactions are both strong and system-specific. Phrased differently, liquids have no small parameter. Recent results have opened a new way to understand liquid thermodynamics on the basis of collective modes (phonons) as is done in the solid state theory. There are important differences between phonons in solids and liquids, and we have recently started to understand and quantify this difference. One striking difference is the emergence of a gap in the liquid phonon spectrum in the reciprocal space . This brings an interesting question of what kind of field theory describes this gap. We recently proposed a two-field Lagrangian which accounts for dissipation and predicts the gap in momentum space . The dissipative and mass terms compete by promoting gaps in k-space and energy, respectively (when bare mass is close to the field hopping frequency, both gaps close and the dissipative term annihilates the bare mass.) I will also discuss the recent attempt to canonically quantize this theory where I attempted to describe quantum dissipation which has been of interest recently. The Hamiltonian is quantized in terms of particles and antiparticles as in the complex scalar field theory and has the energy spectrum with the gap in momentum space. Finally, I will discuss the emergence of ultraviolet and infrared cutoffs in this theory due to dissipation.  K. Trachenko and V. V. Brazhkin, Collective modes and thermodynamics of the liquid state, Reports on Progress in Physics 79, 016502 (2016).  C. Yang, M. T. Dove, V. V. Brazhkin and K. Trachenko, Physical Review Letters 118, 215502 (2017).  K. Trachenko, Physical Review E 96, 062134 (2017).