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Kavli Institute for Cosmology, Cambridge

 
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Mon 24 May 14:00: Tidal Sculpting of Short-Period Exoplanets

Fri, 14/05/2021 - 11:13
Tidal Sculpting of Short-Period Exoplanets

Multiple-planet systems composed of close-in super-Earth/sub-Neptune-sized planets are ubiquitous, representing a dominant outcome of planet formation. This population exhibits predictable hallmarks of architectural regularity and uniformity, such as low eccentricities and inclinations, similar orbital spacings, and intra-system correlations in planetary masses and radii. On top of this first-order structure, however, these systems also exhibit surprising anomalies that require explanation. Examples include (1) ultra-short period planets, whose extremely-irradiated orbits have been separated off from the rest of their systems; (2) planets piled up wide of mean-motion resonances; and (3) a subset of Neptune-sized planets that show signs of radius inflation. In this talk, I will propose that tidal dynamics can account for these specific anomalies and more. Specifically, I will discuss the critical role of enhanced tidal dissipation due to non-zero planetary axial tilts (obliquities), which arise by way of prevalent dynamical resonances. I will highlight strategies for testing these tidal theories and observing obliquities directly in the future.

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Fri 28 May 11:30: Title to be confirmed

Thu, 13/05/2021 - 13:33
Title to be confirmed

Abstract not available

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Mon 17 May 13:00: Cosmology with millimeter-wavelength intensity mapping: forecast and modelling

Wed, 12/05/2021 - 21:13
Cosmology with millimeter-wavelength intensity mapping: forecast and modelling

Line intensity mapping (LIM) is emerging as a powerful technique to map the cosmic large-scale structure. Measurement of spatial fluctuations in the intensity of spectral lines together with their observed frequency provide a low-resolution, 3-dimensional map of the structure over a wide range of scales and redshifts. Among various line candidate, rotational lines of carbon monoxide, CO(J->J-1), and the fine structure line of ionized carbon, [CII], are two of the most studied ones. In the first part of the talk, I will discuss the prospects of future ground-based mm-wavelength LIM surveys, capable of measuring power spectrum of CO and [CII] lines, in constraining properties of neutrinos and light relics. I will then describe the optimal instrument design and survey strategy to reach the required sensitivity. In the second part of the talk, after discussing some of the shortcomings of the existing models of line intensity power spectrum, I will present an extended halo model, which accounts for nonlineaities of dark matter and biasing relation, as well as the shot-noise contributions beyond Possion approximation. I will then show the comparison of the model predictions against simulated intensity maps.

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Fri 14 May 13:00: Nonlinear dynamics of flux compactification

Wed, 12/05/2021 - 19:17
Nonlinear dynamics of flux compactification

We study the nonlinear evolution of unstable flux compactifications, applying numerical relativity techniques to solve the Einstein equations in D dimensions coupled to a q-form field and positive cosmological constant. We show that initially homogeneous flux compactifications are unstable to dynamically forming warped compactifications. In some cases, we find that the warping process can serve as a toy-model of slow-roll inflation, while in other instances, we find solutions that eventually evolve to a singular state. Analogous to dynamical black hole horizons, we use the geometric properties of marginally trapped surfaces to characterize the lower dimensional vacua in the inhomogeneous and dynamical settings we consider. We find that lower-dimensional vacua with a lower expansion rate are dynamically favoured, and in some cases find spacetimes that undergo a period of accelerated expansion followed by contraction.

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Fri 14 May 11:30: Black holes in globular clusters

Wed, 12/05/2021 - 13:58
Black holes in globular clusters

Abstract not available

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Wed 12 May 14:00: Conformal correlators as simplex integrals in momentum space

Tue, 11/05/2021 - 20:09
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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Wed 19 May 14:15: Soliton resolution on wormholes

Tue, 11/05/2021 - 20:08
Soliton resolution on wormholes

Soliton resolution conjecture asserts that generic global-in-time solutions of nonlinear dispersive equations asymptotically resolve into a coherent structure and outgoing radiation. In my talk I will discuss two simple models, involving equivariant wave maps on wormholes, which provide an attractive testing ground for understanding this conjecture.

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Mon 14 Jun 16:00: Title to be confirmed PLEASE NOTE THE DIFFERENT START TIME OF **4 PM**!

Sun, 09/05/2021 - 20:20
Title to be confirmed

Abstract not available

PLEASE NOTE THE DIFFERENT START TIME OF **4 PM**!

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Mon 14 Jun 16:00: Title to be confirmed

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

Abstract not available

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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

TBD

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Mon 11 Oct 14:00: Title to be confirmed

Fri, 19/03/2021 - 10:11
Title to be confirmed

Abstract not available

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