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Kavli Institute for Cosmology, Cambridge

 
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Fri 29 Oct 14:00: Binary Black Hole Mergers beyond General Relativity

Tue, 26/10/2021 - 20:09
Binary Black Hole Mergers beyond General Relativity

At some length scale, Einstein’s theory of general relativity (GR) must break down and be reconciled with quantum mechanics in a quantum theory of gravity. Binary black hole mergers probe the strong field, non-linear, highly dynamical regime of gravity, and thus gravitational waves from these systems could contain beyond-GR signatures. While LIGO presently performs model-independent and parametrized tests of GR, in order to perform model-dependent tests, we must have access to numerical relativity binary black hole waveform predictions in beyond-GR theories through full inspiral, merger, and ringdown. In this talk, I will discuss our results in producing full numerical relativity waveforms in beyond-GR theories, including dynamical Chern-Simons gravity and Einstein dilaton Gauss-Bonnet gravity, and performing gravitational wave data analysis on these waveforms.

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Mon 01 Nov 13:00: Galaxy alignments in the cosmological context

Tue, 26/10/2021 - 15:48
Galaxy alignments in the cosmological context

The observed shapes and orientations of galaxies are correlated across the sky. This is known to be due to two phenomena. The first is the gravitational lensing of galaxy shapes, currently one of the major probes of dark energy. The second is the “intrinsic” alignment arising from physical interactions between galaxies and the distribution of matter in the Universe. In this talk, I will describe ongoing efforts to measure and model intrinsic alignments with multiple tools, and to mitigate their role as contaminant to the upcoming generation of gravitational lensing surveys. I will finally describe some potential applications of intrinsic alignments to cosmology.

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Fri 29 Oct 11:30: The nature of the first galaxies and reionisation: challenges in the era of SKA, Roman and JWST

Tue, 26/10/2021 - 13:42
The nature of the first galaxies and reionisation: challenges in the era of SKA, Roman and JWST

The nature of the first galaxies driving the reionisation of the intergalactic medium (IGM) and their imprint in the ionisation state of the intergalactic hydrogen gas remain outstanding questions in current astrophysics. With the upcoming launch of the James Webb Space Telescope (JWST), the Nancy Grace Roman Space Telescope (Roman), and the Square Kilometre Array (SKA), a vast amount of data will be collected that will revolutionise our understanding of the first galaxies. The number of detected early galaxies will increase greatly, and the 21cm signal from the neutral hydrogen in the IGM will probe the ionised regions continuously growing around the first galaxies in time and space. Semi-analytic models as well as semi-numerical and numerical simulations provide a great avenue to understand the characteristic signatures of galactic processes in these forthcoming galaxy and 21cm signal (IGM) observations during the Epoch of Reionisation. In this context we have developed the Astraeus framework. Astraeus contains a large (230 Mpc box) and highly resolved simulation that couples a semi-analytic model of early galaxy evolution with a semi-numerical reionisation scheme self-consistently. I will introduce this model and use it to discuss how radiative feedback from reionisation and the escape fraction of HI ionising photons from galaxies leave traces in the light emitted by the galaxies and the 21cm signal. I will end by explaining how synergising galaxy and 21cm observables can constrain the reionisation process.

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Wed 27 Oct 14:15: Proton and Nuclear Structure from the Standard Model

Tue, 26/10/2021 - 13:00
Proton and Nuclear Structure from the Standard Model

Our understanding of the structure of matter, encapsulated in the Standard Model of particle physics, is that protons, neutrons, and nuclei emerge dynamically from the interactions of underlying quark and gluon degrees of freedom. I will describe how first-principles theory calculations have given us new insights into this structure, including recent predictions of the contributions of gluons to the pressure and shear distributions in the proton, which will be measurable for the first time at the planned Electron-Ion Collider. I will also discuss studies of light nuclei which provide insights relevant to long-baseline neutrino experiments seeking to constrain the neutrino masses and mixing parameters, searches for evidence of the Majorana nature of neutrinos through neutrinoless double beta decay, and dark matter direct detection experiments. Finally, I will explain how provably exact machine learning algorithms are providing new possibilities in this field.

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Thu 28 Oct 16:00: A very high accretion rate active galaxy case study and a new large sample

Tue, 26/10/2021 - 12:05
A very high accretion rate active galaxy case study and a new large sample

Observational studies of active galactic nuclei (AGN) are pursued in various ways eg. statistical studies of many 10,000’s, smaller samples with multi-frequency data, and extremely detailed investigations of single objects. The results are then discussed and interpreted within a framework of models and general theories. I will describe two such on-going studies on behalf of myself and my collaborators. One is a new case study of an AGN with a very high accretion rate. The other is a more general study based on a new X-ray/optical selected sample of nearly 800 AGN .

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Thu 02 Dec 16:00: AI for Astronomy in the SKA Era

Mon, 25/10/2021 - 15:05
AI for Astronomy in the SKA Era

The expected volume of data from the new generation of scientific facilities such as the Square Kilometre Array (SKA) has motivated the expanded use of semi-automatic and automatic machine learning algorithms for scientific discovery in astronomy. In this field, the robust and systematic use of machine learning faces a number of specific challenges including a paucity of labelled data for training – paradoxically, although we have too much data, we don’t have enough, a clear understanding of the effect of biases introduced due to observational and intrinsic astrophysical selection effects in the training data, and motivating a quantitative statistical representation of outcomes from decisive AI applications. In this seminar I will discuss the motivations and potential for using AI solutions in astronomy, with particular reference to radio astronomy and the SKA , and how the extreme data rates of next generation instrumentation are driving automation in scientific analysis. I will also talk about the inherent biases that AI methods can introduce, why astronomy data may be particularly susceptible to these problems and discuss some of the potential methods for quantifying, understanding and mitigating the effect of these biases.

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Tue 26 Oct 13:00: (Exo)planetary Atmospheres in 3D

Fri, 22/10/2021 - 15:47
(Exo)planetary Atmospheres in 3D

The challenge of characterising exoplanets to both guide expensive observational campaigns and interpret observational data is a significant one given the complexity of planetary climates, and the breadth of the parameter space. I will present the work of the Exeter Exoplanet Theory Group (EETG) in building a hierarchy of tools, joining study of planets ranging from hot gas giants, to terrestrial planets and Earth. I will briefly explain the development approach, featuring a real-time, knowledge exchange and co-development framework with the Met Office.

I will then focus on a few key results from our scientific applications, exploring the impact of wind-driven chemical kinetics, and clouds, for Hot Jupiters. Then exploring the importance of clouds and convection for terrestrial exoplanets, before finishing with (time allowing) an outline of efforts to explore life-climate interaction.

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Wed 27 Oct 13:45: Life after death: evidence of dry minor-merger driven growth of massive quiescent galaxies

Thu, 21/10/2021 - 10:44
Life after death: evidence of dry minor-merger driven growth of massive quiescent galaxies

The average size of quiescent galaxies grows with cosmic time due to both population effects as well as evolution of individual galaxies. Theoretically, individual evolution is thought to occur through a large number of minor dry mergers, necessary to reproduce the kinematic properties of galaxies. This hypothesis is difficult to test with photometric surveys, but new, large and ultra-deep spectroscopic surveys of the early Universe enable us, for the first time, to investigate the kinematic signatures of minor mergers. I report on current work leveraging this new data to gain insight into structural evolution of galaxies after quiescence.

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Wed 27 Oct 13:15: Spectroscopic studies of star-forming galaxies in the Epoch of Reionisation

Thu, 21/10/2021 - 10:26
Spectroscopic studies of star-forming galaxies in the Epoch of Reionisation

In this talk, I will firstly present a spectroscopic case study of a 30× lensed galaxy at z=5. Detections of the C IV and [Ne III ] lines allow us to constrain the origin of the hard radiation field, the ionisation parameter, and the metallicity, while observed Mg II emission might prove a key tracer of escaping ionising radiation for JWST . Before JWST , however, we can already spectroscopically probe galaxies in the Epoch of Reionisation (EoR) with ALMA , whose recent detections of the far-infrared [CII] 158 μm and [OIII] 88 μm emission lines have opened a new observational window for studying galaxies at the highest redshift. In this talk, I will furthermore present new [OIII] 88 μm observations of four galaxies at z=7 recently detected by ALMA in [CII], allowing a multi-wavelength comparison combined with new deep HST images of the rest-frame UV. The [OIII] emission, corresponding to diffuse, highly ionised gas, and [CII] emission, tracing neutral gas and photon dissociation regions, allow some of the first explorations of the interstellar medium in the EoR.

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Fri 22 Oct 13:30: Revisiting mode stability for Kerr(-dS) black holes

Thu, 21/10/2021 - 10:09
Revisiting mode stability for Kerr(-dS) black holes

The Teukolsky master equations are a family of PDEs describing the linear behavior of perturbations of the Kerr black hole family, of which the wave equation is a particular case. As a first essential step towards stability, Whiting showed in 1989 that the Teukolsky equation on subextremal Kerr admits no exponentially growing modes.

In this talk, we review Whiting’s classical proof and a recent adaptation thereof to the extremal Kerr case. We also present a new approach to mode stability, based on uncovering hidden spectral symmetries in the Teukolsky equations. Part of this talk is based on joint work with Marc Casals (CBPF/UCD).

Topic: Friday GR Seminar

Time: Oct 22, 2021 01:30 PM London

https://maths-cam-ac-uk.zoom.us/j/99680141835?pwd=c1Y2R0YrSEZ1T0dUM3FzdENiQXJtUT09

Meeting ID: 996 8014 1835

Passcode: 635710

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Wed 10 Nov 13:00: Electron Transport, Acceleration and Loss in the Outer Radiation Belt

Wed, 20/10/2021 - 17:40
Electron Transport, Acceleration and Loss in the Outer Radiation Belt

The flux of relativistic electrons in Earth’s radiation belts is highly variable, fluctuating over orders of magnitude within hours. In particular, the flux at the outer edge of the magnetosphere may undergo rapid and sustained losses due to magnetopause motion. Forecasting the behaviour of the radiation belts is important in order to predict the risk posed to satellites by high energy particles. We use a three-dimensional diffusion model based on the Focker-Planck equation to model phase-averaged phase space electron densities to investigate the behaviour of the outer radiation belt. We investigate the accuracy of a last closed drift shell model in predicting electron fluxes near the magnetopause, with the eventual aim of using this model to replace the data-driven outer boundary of the diffusion model.

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Fri 22 Oct 13:30: Revisiting mode stability for Kerr(-dS) black holes

Wed, 20/10/2021 - 17:04
Revisiting mode stability for Kerr(-dS) black holes

The Teukolsky master equations are a family of PDEs describing the linear behavior of perturbations of the Kerr black hole family, of which the wave equation is a particular case. As a first essential step towards stability, Whiting showed in 1989 that the Teukolsky equation on subextremal Kerr admits no exponentially growing modes.

In this talk, we review Whiting’s classical proof and a recent adaptation thereof to the extremal Kerr case. We also present a new approach to mode stability, based on uncovering hidden spectral symmetries in the Teukolsky equations. Part of this talk is based on joint work with Marc Casals (CBPF/UCD).

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Wed 20 Oct 14:15: Lattice field theory in the era of quantum simulation

Wed, 20/10/2021 - 14:05
Lattice field theory in the era of quantum simulation

In order to study complex quantum many-body systems, a vigorous program has formed in recent years to take advantage of opportunities in quantum simulation and quantum computation, building upon the vision of Richard Feynman. Such activities have also started in nuclear and high-energy physics, hoping to bring new and powerful experimental and computational tools to address a range of challenging problems in strongly-interacting systems in the Standard Model. With the ultimate goal of simulating strong dynamics of quarks and gluons at the heart of the matter in and out of equilibrium, significant progress has been made in theoretical and algorithmic developments for, and hardware implementation of, a number of lattice gauge theories in recent years. In this talk, I introduce analog, digital, and hybrid analog-digital approaches to the simulation of quantum field theories, along with a few illustrative examples. I will further comment on the prospect of co-development of “quantum” tools and hardware for simulating quantum chromodynamics.

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Wed 27 Oct 14:15: TBC

Wed, 20/10/2021 - 11:47
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Mon 29 Nov 13:00: Title to be confirmed

Wed, 20/10/2021 - 11:37
Title to be confirmed

Abstract not available

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Mon 25 Oct 16:00: Nornalizing Flows for cosmology applications

Wed, 20/10/2021 - 11:35
Nornalizing Flows for cosmology applications

Normalizing Flows (NF) are bijective maps from the data to a Gaussian (normal) distribution or viceversa. In contrast to other generative models they are lossless and provide data likelihood via the Jacobian of the transformation. I will first present a novel Sliced Iterative NF (SINF), which is based on Optimal Transport theory, achieving state of the art results in density estimation for small data samples and in anomaly detection applications in high energy physics. I will discuss its applications to Bayesian Inference and to Global Optimization problems, where it enables new methods of sampling and optimization, which have the potential to accelerate standard Monte Carlo Markov Chains. In the second half of the talk I will present a Normalizing Flow for data structures with Rotational and Translational Equivariance (TRENF), which can be used for generative modeling and likelihood analysis of cosmological data. By training the data likelihood on the posterior this approach enables near optimal cosmological likelihood analysis, where information from all the data is optimally combined into a single number (likelihood) as a function of cosmological parameters. This method provides uncertainty quantification via the full posterior of cosmological parameters, which paves the way for a complete and optimal cosmological data analysis with Normalizing Flows.

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Wed 17 Nov 14:15: TBC

Tue, 19/10/2021 - 20:23
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Wed 10 Nov 14:00: TBC

Tue, 19/10/2021 - 20:17
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Wed 03 Nov 16:00: TBC

Tue, 19/10/2021 - 20:12
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