Collections

Black hole superradiance is a fascinating process in general relativity and a unique window on ultralight particles beyond the standard model. Bosons -- such as axions and dark photons -- with Compton wavelengths comparable to size of astrophysical black holes grow exponentially to form large clouds spinning down the black hole in the process and produce monochromatic continuous gravitational wave radiation. In the era of gravitational wave astronomy and increasingly sensitive observations of astrophysical black holes and their properties superradiance of new light particles is a promising avenue to search for new physics in regimes inaccessible to terrestrial experiments. This workshop will bring together theorists data analysts and observers in particle physics gravitational wave astronomy strong gravity and high energy astrophysics to explore the signatures of black hole superradiance and to study the current and future possibilities of searching for new particles with black holes.

The goal of the workshop is to foster interaction between researchers working on the S-matrices of conventional strings and on ambitwistor strings.  The workshop will exploit synergies between the two frameworks and identify the current key questions in the fields and areas that can benefit from collaboration. The program of the workshop will be tailored to questions and problems raised by the participants in the run-up to the event. The goal is to spend most of the time on collaborative discussions in order to exchange expertise and to attempt to resolve questions during the workshop. A list of such problems can be found below and this will be extended by the participants in the run-up to the meeting. To obtain ambitwistor integrands and Bern-Carrasco-Johansson (BCJ) numerators for multiloop amplitudes and to connect with superstring worldsheet correlators. To develop fully nonlinear approaches by working on curved backgrounds both for application to AdS/CFT and to problems in perturbative gravity and gauge theory on nontrivial backgrounds. To understand the twistor and ambitwistor geometry underpinning both conventional and ambitwistor strings including the geometry of soft limits infrared structure and its links with formulations at null infinity. To explore mathematical structures behind the integrals of conventional and ambitwistor strings (positive geometries and canonical forms twisted (co)-cycle etc.)

Our universe is of astonishing simplicity: almost all physical observations can in principle be described by a few theories that have short mathematical descriptions. But there is a field of computer science which quantifies simplicity namely algorithmic information theory (AIT). In this workshop we will discuss emerging connections between AIT and physics some of which have recently shown up in fields like quantum information theory and thermodynamics. In particular AIT and physics share one goal: namely to predict future observations given previous data. In fact there exists a gold standard of prediction in AIT called Solomonoff induction which is also applied in artificial intelligence. This motivates us to look at a broader question: what is the role of induction in physics? For example can quantum states be understood as Bayesian states of belief? Can physics be understood as a computation in some sense? What is the role of the observer i.e. the agent that is supposed to perform the predictions? These and related topics will be discussed by a diverse group of researchers from different disciplines.

Foil theories sometimes called mathematically rigorous science fiction describe ways the world could have been were it not quantum mechanical. Our understanding of quantum theory has been deepened by contrasting it with these alternatives. So far observers in foil theories have only been modeled implicitly for example via the recorded probabilities of observing events. Even when multi-agent settings are considered these agents tend to be compatible in the classical sense that they could always compare their observations. Scenarios where agents and their memories are themselves modeled as physical systems within the theory (and could in particular measure each other as in Wigner's friend experiment) have not yet been considered. In this workshop we will investigate which foil theories allow for the existence of explicit observers and whether they allow for paradoxes in multi-agent settings such as those found in quantum theory. We will also investigate which interpretations of quantum theory would equally well interpret the foil theories and which interpretations are truly quantum. We will gain a deeper understanding of how this can happen by discussing appropriate definitions observers in these theories and seeing how such observers learn about their environment.