The interactions of the gravitational metric with other spin-2 fields are strongly constrained by the absence of the so called ghost instabilities in the theory. Although the study of such ghost free interactions are well motivated theoretically, their construction and even the question of their existence have been long standing problems. I will motivate the study of such theories and then...
One of the most remarkable possibilities of General Relativity concerns gravitational collapse to black holes, leaving behind a geometry with light rings, ergoregions and horizons. These peculiarities are responsible for uniqueness properties and energy extraction mechanisms that turn black holes into ideal laboratories of strong gravity, of particle physics (yes!) and of possible...
Neutron star mergers are related to a large number of (astro-)physical questions. For example, they had long been suspected to produce gravitational waves, gamma ray bursts and -by some- to produce heavy "rapid neutron capture" elements. While overall convincing, all these conjectures were only based on indirect, often theoretical arguments and none was proven by direct observations. The...
Two neutron stars merge somewhere in the Universe approximately every 10 to 1000 seconds, creating violent explosions potentially observable in gravitational waves and across the electromagnetic spectrum. The transformative coincident gravitational-wave and electromagnetic observations of the binary neutron star merger GW170817 gave invaluable insights into these cataclysmic collisions. And...
In spite of its fragile elegance, General Relativity (GR) is subject to scrutiny due to several factors, such as observational evidence such as "dark matter" and "dark energy", along with theoretical challenges like inevitable singularities and the enigma of black-hole information loss. In alternative gravity theories, the macroscopic properties of neutron stars (NSs) such as mass, radius,...
Relativistic magnetized jets are common features of Active Galactic Nuclei (AGNs), that feature multi-timescale variability and a non-thermal spectrum ranging from radio to gamma-raysThese highly magnetized jets are prone to undergo several Magneto-hydrodynamic (MHD) instabilities during their propagation in space and could trigger jet radiation and particle acceleration. In this work, we...
An overview of how the scientific field of transients such as supernovae has been transformed over the past 15 years, i.e. since the start of the OKC. Focus will be on the large sky surveys iPTF and ZTF, with possible detours to neutrino and gravitational wave counterparts and maybe an outlook for LSST.
High-energy cosmic-ray electrons and positrons cool rapidly as they propagate through the Galaxy, due to synchrotron interactions with magnetic fields and inverse-Compton scattering interactions with photons of the interstellar radiation field. Typically, these energy losses have been modelled as a continuous process. However, inverse-Compton scattering is a stochastic process, characterised...
I will present the effect of dark matter annihilation on the formation of Jovian planets. We show that dark matter heat injections can slow or halt Kelvin-Helmholtz contraction, preventing the accretion of hydrogen and helium onto the solid core. The existence of Jupiter in our solar system can therefore be used to infer constraints on dark matter with relatively strong interaction cross...
In the context of neutrino oscillations, the wave packet representation of propagating neutrinos has emerged as an indispensable tool for deriving the transition probabilities. Conventionally in these analyses, the neutrino wave packet is assumed to be a Gaussian profile. However, it remains unclear to what extent results depend on the assumption of Gaussianity, since (i) the assumption...
The quantization of gravity is widely believed to result in gravitons -- particles of discrete energy that form gravitational waves. But their detection has so far been considered impossible. Here we show that signatures of single gravitons can be observed in laboratory experiments. We show that stimulated and spontaneous single-graviton processes can become relevant for massive quantum...
Traditional numerical simulations employing gravitational softening are unable to resolve the small-scale dynamics and gravitational wave emission from supermassive black hole binaries. Instead, the parsec-scale dynamics is typically modelled by postprocessing the simulations using either semi-analytic methods based on orbit-averaged equations or by resimulating the core regions of the merged...
Detailed measurements of the cosmic microwave background during the last three decades have revolutionized our understanding of the Big Bang and the evolution of structure in the universe. These advances have been made possible through a close collaboration between instrumentalists, theorists and data analysts. As the signal-to-noise ratio of available data increases, it becomes more and more...
Cunning instrument design is at the core of most successful endeavors in experimental physics. In this talk, I will describe hardware efforts at the OKC motivated by our desire to address fundamental questions in cosmology and astroparticle physics. The talk will cover some of the fun (and not-so-fun) challenges associated with designing tunable plasmonic resonators and broadband absorbers for...
In the context of perturbative quantum field theory (QFT), the addition of quadratic-curvature invariants to the Einstein-Hilbert action makes it possible to achieve strict renormalizability in four dimensions. However, this theory exhibits unusual features due to an additional massive spin-2 ghost particle. In this talk, we are going to argue that despite the presence of the ghost and...
Standard Model neutrinos decoupled from the primordial plasma about one second after the big bang and have been free-streaming through the cosmos ever since. This leaves a subtle imprint in the baryon acoustic oscillations as observed in the cosmic microwave background (CMB) and large-scale structure (LSS) of the universe. Through careful theoretical considerations of the underlying physics...
The kinetic Sunyaev-Zel'dovich effect (kSZ) is induced by the scattering of Cosmic Microwave Background (CMB) photons with a medium of free electrons that possess a non-zero bulk velocity. These scatterings alter the small-scale CMB temperature anisotropies, which correlate with the growth of ionising regions during the Epoch of Reionization (EoR). Hence, the kSZ observations can be merged...
If relativistic gravitation has a quantum description, it must be meaningful to consider a spacetime metric in a quantum superposition. But how might such a superposition be described, and how could observers detect it? I will present an operational framework for studying “superpositions of spacetimes” via indirect measurements, on particles residing in such spacetime. After presenting the...
Last year, the supernova cosmology team at the Oskar Klein Centre made an exciting discovery. With the Zwicky Transient Facility, we observed a supernova which was gravitationally lensed by a massive galaxy, resulting in four images of the same object. The lensed supernova, baptised ‘SN Zwicky’, points to a poorly understood population of low-mass lens galaxies. Gravitationally lensed...
Strongly lensed supernovae are excellent, independent probes to measure the Hubble constant and weigh in on the Hubble tension. In my talk I will discuss the time delay measurements for the first resolved strongly lensed Type Ia supernova, iPTF16geu. I will also review spectroscopic observations of SN Zwicky, the first lensed supernova discovered by Zwicky Transient Facility, including JWST...
Historically the most popular dark matter candidates have been new elementary particles, such as WIMPs and axions. However Primordial Black Holes (PBHs), black holes formed from over-densities in the early Universe, are another possibility. The discovery of gravitational waves from mergers of ~10 Solar mass black hole binaries by LIGO-Virgo has generated a surge in interest in PBH dark matter....
Unveiling the origin of the coalescing binaries detected via gravitational waves (GW) is challenging, notably if no multi-wavelength counterpart is detected. One important diagnostic tool is the coalescing binary distribution with respect to the large scale structures (LSS) of the universe, which we quantify via the cross-correlation of galaxy catalogs with GW ones. By using both existing and...
Primordial black holes (PBHs), produced in the early universe, can be responsible for many phenomena, ranging from dark matter to gravitational waves. In this work, we introduce a scenario where the Standard Model Higgs running induces features in the inflationary potential motivated by Higgs inflation. We identify that a near-inflection point or a tachyonic instability can develop in the...
Primordial non-Gaussianity is a powerful tool to discriminate between models of inflation by probing the dynamics and field content of the very early Universe. In this talk I will show that theories of inflation with multiple, rapidly turning fields can generate large, potentially observable amounts of non-Gaussianity. I will discuss a novel, analytical formula for bispectrum generated from...
The detection of a binary neutron star merger in 2017 through both gravitational waves and electromagnetic emission opened a new era of multimessenger astronomy. During the merger, several mechanisms like the Kelvin-Helmholtz instability, the winding up effect and the MRI, can amplify the initial magnetic field in the remnant to be powerful enoguh for launching a jet, with an associated short...
The epoch of reionisation marks the emergence of the first galaxies that emit light into the intergalactic medium, leading to the ionisation and heating of the Universe. This phase is a forefront area in astrophysics. While our current understanding relies on theoretical models of early galaxy formation within the standard cold dark matter (CDM) cosmology, recent observations, including early...
The talk will cover some of the lessons we learned from 15 years of the observations of the Fermi LAT satellite and what we hope to learn with the upcoming Cherenkov Telescope array.
Cosmological tensions have recieved much attention in recent years, with the community debating the significance (or lack thereof) of the difference in parameter inferences of $H_0$, $S_8$ or $\Omega_K$ between supernovae, CMB, weak lensing and BAO datasets. Bayesian methods for quantifying tensions across high-dimensional datasets have been developed to robustly determine hidden levels of...
Ultralight bosons are a prominent type of axion-like dark matter. These particles may form clouds around black holes through the superradiance process. The remaining system with a boson cloud around a black hole is often called a gravitational atom due to the similarities to the electron cloud of a hydrogen atom. In this talk I will discuss one of the first non-perturbative explorations of...
The rapid development of detector technology, including these sensitive to gravitational waves and neutrinos, has brought us to the gate of an era where we will be able to observe transient events as they unfold throughout a large fraction of the Universe. The availability of these data floods requires new systems for data processing and the consistent application of modern statistical methods...
Advanced data analysis and machine learning techniques are increasingly required to optimally exploit large experimental or observational data sets to answer fundamental physics, astrophysics, and cosmology research questions. In recent years, OKC members' coherent efforts have created a thriving community of computational physicists and data analysts, culminating in the recent establishment...
This is a story about how breakthroughs in machine learning over the past 15 years have borne a paradigm shift in how to do data analysis in Astronomy, enabling impactful science that was previously out-of-reach.
The dynamics of galaxy evolution leaves its mark on the distribution of galaxy properties in the Universe. Studying the joint distribution of galaxy characteristics (mass,...
In this talk we tackle two open and pressing questions for the academic community:
1) Is spacetime emergent and if so can this be tested in a laboratory setting?
2) Is it possible to be an active and engaged researcher after leaving Academia?
We present initial hints that both questions have a positive answer!
