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Kiana Salehi (Perimeter Institute/University of Waterloo)7/15/24, 3:45 PMContributed Talk
There are now multiple direct probes of the region near black hole horizons, including direct imaging with the Event Horizon Telescope (EHT). As a result, it is now of considerable interest to identify what aspects of the underlying spacetime are constrained by these observations. For this purpose, we present a new formulation of an existing broad class of integrable, axisymmetric,...
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Cora Uhlemann (Universität Bielefeld)7/15/24, 4:00 PMContributed Talk
Gravitational collapse shaped the cosmic large-scale structure and created a plethora of different density environments. For optimally probing gravity with galaxy surveys like Euclid and Rubin LSST, we need to dissect different density environments that are lumped together in traditional two-point statistics. I will explain how the one-point probability distribution of dark matter densities...
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Dr Kazufumi Takahashi (Yukawa Institute for Theoretical Physics, Kyoto University)7/15/24, 4:15 PMContributed Talk
Invertible disformal transformations are a useful tool to investigate ghost-free scalar-tensor theories. By performing a higher-derivative generalization of the invertible disformal transformation on Horndeski theories, we construct a novel class of ghost-free scalar-tensor theories, which we dub generalized disformal Horndeski theories. In the talk, I will clarify the basic idea for...
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Brayden Hull (UWaterloo & PI)7/15/24, 4:30 PMContributed Talk
Classical energy conditions are used to provide restrictions on the matter fields present in the stress-energy tensor to avoid possible unphysical spacetimes. These classical energy conditions are imperative to the singularity theorems of Hawking and Penrose. However, we know that spacetime breaks down near said singularities and a quantum theory of gravity is needed. One insight into this...
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Prof. Stoytcho Yazadjiev (Sofia University)7/15/24, 4:45 PMContributed Talk
In my talk I will discuss the black hole spontaneous scalarization in scalar-Gauss-Bonnet gravity. Some of the basic ideas, results and astrophysical consequences will be presented.
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I will also discuss a new fully non-linear dynamical mechanism for the formation of scalarized black holes which is different from the spontaneous scalarization. -
Jibril BEN ACHOUR (Arnold Sommerfeld Center (Germany) / ENS de Lyon (France))7/16/24, 2:15 PMContributed Talk
Exploring the structure of compact objects in modified theories of gravity is mandatory to parametrize the possible deviations w.r.t general relativity and confront these theories to the current and future observations. While important efforts have been devoted to understand the phenomenology of stars and black holes, it is still a challenging task to provide new exact analytical solutions...
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David Shlivko (Princeton University)7/16/24, 2:30 PMContributed Talk
Observational constraints on time-varying dark energy are commonly presented in terms of the two CPL parameters $w_0$ and $w_a$. Recent observations favor a sector of this parameter space in which $w_0 > -1$ and $w_0 + w_a < -1$, suggesting that the equation of state underwent a transition from violating the null energy condition (NEC) at early times to obeying it at late times. In this talk,...
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Taillte May (Perimeter Institute)7/16/24, 2:45 PMContributed Talk
Gravitational waves from black hole binary mergers can tell us a lot about the physics of the system. At the late part of the graviational wave signal, GR predicts the presence of characteristic frequencies (called quasinormal modes) in the signal. Measuring multiple quasinormal modes is a strong consistency test for GR.
Here we probe the regime where a signal can be described entirely by...
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Dr Hugo Roussille (École Normale Supérieure de Lyon)7/16/24, 3:00 PMContributed Talk
The non-linear dynamics of gravitational wave propagation in spacetime can contain drastic new phenomenology that is absent from the linearised theory. In this talk, I will probe the non-linear radiative regime of Horndeski gravity by making use of disformal field redefinition. I will discuss how disformal transformations alter the properties of congruences of geodesics and in particular how...
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Conner Dailey (UWaterloo & PI)7/16/24, 3:15 PMPoster
Recently, there has been much interest in black hole echoes, based on the idea that there may be some mechanism (e.g., from quantum gravity) that waves/fields falling into a black hole could partially reflect off of an interface before reaching the horizon. There does not seem to be a good understanding of how to properly model a reflecting surface in numerical relativity, as the vast majority...
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Ms Minahil Adil Butt (SISSA)7/17/24, 2:15 PMContributed Talk
We present a comprehensive joint analysis of two distinct methodologies for measuring the masses of galaxy clusters: hydrostatic measurements and caustic techniques. We show that by including cluster-specific assumptions obtained from hydrostatic measurements in the caustic method, the potential mass bias between these approaches can be significantly reduced. While this may appear to diminish...
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Dr Matteo Cataneo (University of Bonn)7/17/24, 2:30 PMContributed Talk
I will introduce mochi_class, a refined version of the popular Einstein-Boltzmann solver hi_class optimised for calculations within Horndeski's gravity framework. Thanks to (i) a re-parametrisation of Horndeski functions, (ii) a numerically stable quasi-static approximation, and (iii) support for time-dependent inputs, mochi_class enhances hi_class capabilities and nicely complements other...
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Jessica Muir (Perimeter Institute)7/17/24, 2:45 PMContributed Talk
Measurements of the large-scale distribution of matter in the Universe are one of our primary tools for testing the predictions of general relativity on cosmological scales. I will describe how we pursue this using data from galaxy imaging surveys, focusing on Dark Energy Survey galaxy clustering and weak lensing analyses as an example. I will highlight results from the DES Year 3 analysis...
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Mr Yunfei Wen (California Institute of Technology)7/17/24, 3:00 PMContributed Talk
We present a model that modifies general relativity on cosmological scales, specifically by having a 'glitch' in the gravitational constant between the cosmological (super-horizon) and Newtonian (sub-horizon) regimes. This gives a single-parameter extension to the standard ΛCDM model, which is equivalent to adding a dark energy component, but where the energy density of this component can have...
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Hanyu Zhang7/17/24, 3:15 PMContributed Talk
We present key cosmological findings from the Dark Energy Spectroscopic Instrument (DESI)’s first year baryon acoustic oscillations (BAO) measurements. DESI's BAO provide robust measurements of the transverse comoving distance and Hubble rate across seven redshift bins, spanning a redshift range of 0.1 < z < 4.2. DESI BAO data alone align well with the flat ΛCDM model with Ωm=0.295±0.015....
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Mr Amirhossein Dehghanizadeh (The University of Waterloo)7/18/24, 2:15 PMContributed Talk
Finding a complete explanation for cosmological evolution in its very early stages (about 13 billion years ago) can significantly advance our understanding of physics. Over the past few decades, several models have been proposed, with the majority falling into a category called inflationary universes, where the universe experiences rapid exponential expansion. Despite numerous achievements of...
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Dr Pedro Fernandes (Southern Denmark University)7/18/24, 2:30 PMContributed Talk
In this talk I will review the topic of 4D Einstein-Gauss-Bonnet gravity, which has been the subject of considerable interest over the past years. I will discuss the mathematical complexities involved in implementing this idea, and review recent attempts at constructing well-defined, self-consistent theories that enact it, and their relation to Horndeski gravity. I then move on to consider the...
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Dr Sergio Sevillano (Durham University)7/18/24, 2:45 PMContributed Talk
The ability to represent perturbative expansions of interacting quantum field theories in terms of simple diagrammatic rules has revolutionized calculations in particle physics. However, in the case of extended theories of gravity, deriving this set of rules requires linearization of gravity perturbation of the scalar fields and multiple field redefinitions making this process very...
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Jury Radkovski (Perimeter Institute, McMaster University)7/18/24, 3:00 PMPoster
We study the high-energy limit of projectable Ho\v rava gravity using on-shell graviton scattering amplitudes. We compute the tree-level amplitudes using symbolic computer algebra and analyze their properties in the case of collisions with zero total momentum. The amplitudes grow with collision energy in the way consistent with tree-level unitarity. We discuss their angular dependence and...
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Sergey Sibiryakov (McMaster U. & Perimeter Inst.)7/18/24, 3:15 PMContributed Talk
I’ll review the models of quantum gravity postulating invariance with respect to anisotropic (Lifshitz) scaling in the deep ultraviolet domain. At low energies they reduce to scalar-tensor gravity, with a timelike gradient of the scalar field breaking local Lorentz invariance. The models come in two versions differing by the dynamics in the scalar sector. The first, projectable, model has been...
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