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Kavli Institute for Cosmology, Cambridge

 
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Mon 14 Jun 16:00: Title to be confirmed

Sat, 08/05/2021 - 12:59
Title to be confirmed

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Wed 12 May 14:15: Conformal correlators as simplex integrals in momentum space

Thu, 06/05/2021 - 12:08
Conformal correlators as simplex integrals in momentum space

We review conformal field theory from a momentum-space perspective, motivated by applications to inflationary cosmology. Our main result is a generalised Feynman integral representation for the general scalar n-point function in any conformal field theory. This integral has the topology of an (n-1)-simplex, where the operators are inserted at the vertices of the simplex and the momenta running in between are the integration variables. The integrand then features an arbitrary function of the n(n-3)/2 conformal cross ratios that can be constructed from these integration variables. We show how this simplex representation solves the conformal Ward identities, and discuss its application to holographic theories. For contact Witten diagrams, the simplex representation can be found using a star-mesh duality from electrical circuit theory.

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Tue 18 May 13:00: Direct windows to the formation of giant planets on wide orbits

Wed, 05/05/2021 - 15:47
Direct windows to the formation of giant planets on wide orbits

High-contrast imaging surveys have revealed a population of giant planets and brown dwarfs that are orbiting at large separation from their star. The youngest of these objects (typically up to 10 Myr) show signs of ongoing formation as inferred from hydrogen emission lines and excess flux coming from a circumplanetary/substellar disk. The formation pathways and accretion processes in the planetary-mass regime remain not well understood. Therefore, characterization of these objects during their formation sheds light on the physical processes by which giant planets and possible moons around them form, and will help to distinguish between planetary and stellar-like formation scenarios. During this talk, I will present several results from our observational efforts in the study of accreting, directly imaged planets. In particular, I will discuss new constraints on the mass and radius of PDS 70 b and I will present ongoing work from an optical to mid-infrared characterization of GQ Lup B and its disk.

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Fri 07 May 11:00: Stringy corrections to the entropy of electrically charged supersymmetric black holes with AdS5×S5 asymptotics

Wed, 05/05/2021 - 11:14
Stringy corrections to the entropy of electrically charged supersymmetric black holes with AdS5×S5 asymptotics

I will discuss the recent calculation (arXiv:2007.06582) of the leading α′ corrections to the entropy of certain black holes with AdS5×S5 asymptotics, namely in the supersymmetric limit, the entropy does not receive α′ corrections. This result strengthens recent calculations that match the index of N=4 Super-Yang-Mills with the corresponding partition function in the supersymmetric limit. In the small temperature regime, the entropy corrections are concordant with the weak gravity conjecture.

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Fri 21 May 11:30: Tracing AGN feedback signatures from small to large scales across cosmic time

Wed, 05/05/2021 - 09:55
Tracing AGN feedback signatures from small to large scales across cosmic time

AGN feedback is now widely considered to be one of the main drivers in regulating the growth of massive galaxies. In my talk I will describe several efforts in our group to understand the power, reach and impact of AGN feedback processes. We find significant evidence for AGN feedback signatures even in low-luminosity AGN and we are now using molecular gas as a tracer to investigate if and how feedback may impact and quench galaxies at low redshift. At higher redshift, it appears that AGN -driven outflows can indeed suppress star formation in their hosts, consistent with the AGN having a `negative’ impact on galaxy evolution. However, both star formation and quasar activity peak at z ~ 2-3 where AGN are expected to impact the build-up of stellar mass the most and I will present recent efforts in our group to characterise feedback processes in powerful AGN on CGM scales at and near Cosmic Noon. In particular, our team recently discovered a unique population of luminous high-z quasars (ERQs) with extreme outflow properties. At the same time, more and more exotic AGN populations with extreme signatures are being discovered at that redshift. These populations are ideal to obtain a census of the overall mass and energy budget of both outflow and infall/feeding from the CGM , an essential requirement to probe the detailed and full feedback loop. Finally, I will also introduce the JWST ERS Program “Q3D” which will study the impact of three carefully selected luminous quasars on their hosts. Our program will serve as a pathfinder for JWST science investigations in IFU mode.

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Mon 10 May 13:00: Is Our Universe the Remnant of Chiral Anomaly in Inflation?

Tue, 04/05/2021 - 17:13
Is Our Universe the Remnant of Chiral Anomaly in Inflation?

Modern cosmology has been remarkably successful in describing the universe from a second after the Big Bang until today. However, its physics before that time is still much less certain. It profoundly involves particle theory beyond the Standard Model to explain long-standing puzzles: the origin of the observed matter asymmetry, and massive neutrinos, as well as the particle physics of dark matter and cosmic inflation. In this talk, I will explain that a new framework based on embedding axion-inflation in left-right symmetric gauge extensions of the SM can possibly solve and relate these seemingly unrelated mysteries of modern cosmology. The baryon asymmetry and dark matter today may be remnants of a pure quantum effect (chiral anomaly) in inflation which is the source of CP violation in inflation. As a smoking gun, this setup has robust observable signatures for the GW background to be probed by future CMB missions and laser interferometer detectors.

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Fri 14 May 14:00: Tidal dissipation in stars, with new results on the interaction between fast tides and convection

Tue, 04/05/2021 - 12:33
Tidal dissipation in stars, with new results on the interaction between fast tides and convection

I will present new results on tidal dissipation in stars and planets, mainly focussing on tides in convection zones. The interaction between tidal flows and turbulent convection is often considered important for tidal evolution of binary stars and planetary systems but its efficiency for fast tides (when the tidal frequency exceeds the convective turnover frequency) has long been controversial. I will first describe a new analysis of the energy transfer terms between tidal flows and convection that is verified by idealised Boussinesq and anelastic simulations. One result is that Reynolds stresses involving tidal flow components are unlikely to contribute to dissipation of equilibrium tides. I will then review the results of direct numerical simulations in both local and global models (that study Reynolds stresses involving correlations between convective flow components, which likely dominate the interaction), which demonstrate that convection can act like an effective viscosity which falls off quadratically with tidal frequency for fast tides. I will then present calculations studying tidal dissipation in stellar models with masses in the range 0.1-1.6 M_\odot throughout their evolution. These models incorporate turbulent viscosity acting on equilibrium tides and inertial waves in convection zones, and internal gravity waves in radiation zones. I will use these results to compute tidal quality factors following stellar evolution, and tidal evolutionary timescales, for the orbital decay of hot Jupiters, and the spin synchronization and circularization of binary stars.

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Fri 21 May 11:30: TBD

Tue, 04/05/2021 - 12:23
TBD

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Fri 07 May 13:00: Stringy corrections to the entropy of electrically charged supersymmetric black holes with AdS5×S5 asymptotics

Mon, 03/05/2021 - 13:19
Stringy corrections to the entropy of electrically charged supersymmetric black holes with AdS5×S5 asymptotics

I will discuss the recent calculation (arXiv:2007.06582) of the leading α′ corrections to the entropy of certain black holes with AdS5×S5 asymptotics, namely in the supersymmetric limit, the entropy does not receive α′ corrections. This result strengthens recent calculations that match the index of N=4 Super-Yang-Mills with the corresponding partition function in the supersymmetric limit. In the small temperature regime, the entropy corrections are concordant with the weak gravity conjecture.

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Mon 14 Jun 15:00: Title to be confirmed

Sun, 02/05/2021 - 13:51
Title to be confirmed

Abstract not available

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Wed 05 May 14:15: Gravitational-wave generation beyond General Relativity

Fri, 30/04/2021 - 13:54
Gravitational-wave generation beyond General Relativity

I will motivate why and how General Relativity can be classically extended and how the generation of gravitational waves can be modified. I will review how these differences can be perturbative or non-perturbative according to the specific theory under scrutiny, and show how non-linearities can become important in the merger of compact objects. I will discuss the future prospects of testing General relativity with next generation interferometers

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Wed 05 May 16:00: Physical models to predict the evolution of viruses and bacteria This lecture is a Livestream Event

Fri, 30/04/2021 - 13:35
Physical models to predict the evolution of viruses and bacteria

Abstract not available

This lecture is a Livestream Event

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Tue 01 Jun 15:00: Title to be confirmed

Tue, 27/04/2021 - 21:43
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Thu 06 May 16:00: SDSS-V: Pioneering Panoptic Spectroscopy

Tue, 27/04/2021 - 14:33
SDSS-V: Pioneering Panoptic Spectroscopy

I will describe the current progress within the Fifth Generation of SDSS . SDSS -V is an unprecedented all-sky spectroscopic survey of over six million objects. It is designed to decode the history of the Milky Way galaxy, trace the emergence of the chemical elements, reveal the inner workings of stars, and investigate the origin of planets. It mwill provide the most comprehensive all-sky spectroscopy to multiply the science from the Gaia, TESS and eROSITA missions. SDSS will also create a contiguous spectroscopic map of the interstellar gas in the Milky Way and nearby galaxies that is 1,000 times larger than the state of the art, uncovering the self-regulation mechanisms of galactic ecosystems. It will pioneer systematic, spectroscopic monitoring across the whole sky, revealing changes on timescales from 20 minutes to 20 years. I will highlight key areas of current scientific and technical development as well as opportunities to participate in the survey underway.

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Thu 10 Jun 16:00: Information-theoretic problems in astrophysics.

Mon, 26/04/2021 - 21:54
Information-theoretic problems in astrophysics.

If you are making a precise measurement, or if you are planning a project, or if you want to solve a hard problem in astrophysics, you want to make sure you are taking the best possible data, and also that you are getting the most out of the data you do take. I review some basic information theory in the context of astronomy, and then look at how it can be used to design good surveys, make good measurements, and get the most out of your data. I give examples from exoplanet search, stellar dynamics, and cosmology.

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Mon 17 May 13:00: Title to be confirmed

Mon, 26/04/2021 - 20:24
Title to be confirmed

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Tue 04 May 16:00: Symmetries of Black Hole Perturbation Theory

Mon, 26/04/2021 - 20:19
Symmetries of Black Hole Perturbation Theory

We present novel symmetries of perturbation theory around rotating and non-rotating black holes in general relativity, and discuss their origins and implications for gravitational-wave astronomy. This is motivated by two special aspects of black hole perturbations in four dimensions: isospectrality of quasinormal modes and the vanishing of tidal Love numbers. There turn out to be off-shell symmetries underlying both of these phenomena. One is a duality, which on shell reproduces the famous Chandrasekhar duality and therefore underlies isospectrality, and can be thought of as an extension of electric-magnetic duality to black hole backgrounds. The other is an infinite set of “ladder symmetries” relating modes of different angular momentum or spin, which imply the vanishing of Love numbers. We further discuss the geometric origins of these symmetries.

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Thu 27 May 16:00: Bridging Galaxy Evolution Across Cosmic Time With the CLASSY Survey

Mon, 26/04/2021 - 18:50
Bridging Galaxy Evolution Across Cosmic Time With the CLASSY Survey

Rest-frame far-ultraviolet (FUV) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of JWST and construction of the ELTs will soon usher in a new era, pushing the FUV spectroscopic frontier to z15-20. The success of these future endeavors hinges on a comprehensive understanding of the massive star populations and interstellar medium (ISM) gas conditions that power the observed FUV spectral features. I will present the COS Legacy Archive Spectroscopic SurveY (CLASSY) Treasury as a powerful and promising solution. CLASSY is a large HST program creating the first high-quality, high-resolution FUV spectral catalog of star-forming galaxies at z0, but which span similar properties as seen at high-z. The spectra contain a suite of emission and absorption lines that characterize the massive stellar populations that populate metal poor galaxies, the physical properties of large-scale outflows that regulate star formation, and the chemical abundance patterns of the gas and stars. CLASSY will improve the diagnostic power of the FUV lines for future JWST /ELT surveys, providing a long-lasting legacy to the astronomical community for decades to come.

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