Colloquia Archive 2024

The problem of infrared divergences in gauge-theory scattering amplitudes is as old as quantum field theory, and has been 'solved’ many times, with increasing degrees of sophistication. Perhaps surprisingly, it is still at the forefront of current research, both in view of new theoretical developments, and for phenomenological applications. I ...

Cosmology represents our window on the most fundamental principles in physics, being the energies of the processes in the primordial universe 10 order of magnitude higher than the ones at the LHC and tantalizingly close to the Planck scale. In this talk, I will stress how ideas coming from different ...

The Standard Model of Particle Physics, encapsulating the vast majority of our understanding of the fundamental nature of our Universe, is at its core a gauge theory. Much of the richness of its phenomenology can be traced back to the complicated interplay of its various gauged interactions. While massive theoretical ...

The average quantum physicist on the street would say that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under combined matrix transposition and complex conjugation) in order to guarantee that the energy eigenvalues are real and that time evolution is unitary. However, the Hamiltonian H=p^2+ix^3, which ...

Field theory has been one of the most successful methods for the characterisation of many-body systems for many decades. Different flavours of field theory, in particular the response-field formalism and Doi-Peliti field theory, have different advantages, with the latter maintaining particle entity by construction. The particulate nature of the degrees ...

Neutron stars are among the densest objects in the Universe, and the collision of two neutron stars ranks as one of the most energetic events known. The groundbreaking multimessenger detection of gravitational waves and electromagnetic signals from such a collision marked a revolution in astronomy, yielding profound insights into fundamental ...

One of the major aims of lattice QCD (LQCD) is to understand, from the known underlying theory, QCD, the spectrum and properties of hadrons—strongly interacting particles composed of quarks and gluons. Historically, a semi-quantitative understanding of the lightest hadrons was obtained using the quark model, in which the complicated ...

This talk reviews some aspects of the "angular momentum problem" in general relativity as well as of old and new results in the search for covariant and supertranslation-invariant formulas for the flux of angular momentum and other Lorentz charges in asymptotically flat spacetimes. It addresses in particular three problems with ...

Elucidating the nature of dark matter, dark energy, and dynamics of the early universe stand as major challenges of modern cosmology and particle physics. I will present a new program of addressing these challenges with galaxy surveys. This program builds on particle physics tools that have allowed me to achieve ...

We trace the origin of the dark matter, dark energy and quantum gravity problems to the extrapolation of the standard Newton-Einstein wisdom to beyond its solar system origins. We show that this same solar system wisdom can be obtained from the conformal gravity theory, with its extrapolation leading to a ...

A black hole is characterised by the fact that nothing can escape - this feature, of a boundary of information that can be accessed from that which cannot, is more general than the spacetime boundary of the event horizon. Horizons can occur in a wide range of physical situations, many of ...

The question of what fundamentally is has never been straightforward in physics, yet there had always been a tentative answer for both theoretical and practical purposes. Everything shifted about a century ago with the advent of quantum mechanics, which challenged our traditional understanding of existence as suddenly we can also ...

The story I am presenting revolves around a strange and unfamiliar to most people geometric construction, which encodes a metric on a manifold into a collection of differential forms on the same manifold. There are many known examples, in diverse dimensions. In three dimensions this coincides with the encoding of ...

I will use a real-time general relativistic Black Hole Flight Similator to show what really happens inside astronomically realistic black holes. The inner horizon of a rotating black hole is the most violent place in the Universe, easily reaching and surpassing energy densities attained in the Big Bang. What does ...

The gravitational-wave signals from merging binary systems carry unique information about the internal structure of compact objects. This is of key interest for neutron stars, whose material is compressed by strong gravity to supra-nuclear densities where novel phases of matter emerge. I will discuss examples of recent progress in the ...

The interiors of Kerr or Reissner-Nordström black holes have "inner" horizons which enclose their singularity and delineate the domain of predictability of all equations of wave equation type -- including the Einstein equations themselves. However, these inner horizons are often classically dynamically unstable and get turned into some sort of singularity ...

I will review recent progress on quantifying complexity of quantum states and operators. After introducing some of the interesting complexity measures, I will discuss what can be learnt from these new tools in quantum many-body systems and quantum field theories.

Ultra-intense laser interactions with matter give us a route to produce some of the most extreme conditions on earth. When these lasers are focused onto solid material, the electric fields associated with the laser are so strong that the atoms in the material become readily ionised to create plasma. These ...

In 1986, Kardar, Parisi and Zhang introduced a model equation for a growing surface, in the form of a nonlinear partial differential equation with noise[1]. In the original paper they applied a dynamical renormalization group analysis to demonstrate its universal nature, which is one of the first identified non-equilibrium ...