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Kavli Institute for Cosmology, Cambridge

 
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Mon 20 Jun 13:00: Small-Scale Structure in Vector Dark Matter Zoom link: https://zoom.us/j/91709058845.

Wed, 15/06/2022 - 09:46
Small-Scale Structure in Vector Dark Matter

Can we figure out the spin of dark matter from astrophysical observations? I will talk about new phenomenology of light vector dark matter including (i) a new class of polarized vector solitons (ii) interference patterns in density (iii) intrinsic spin. These effects lead to signals in astrophysics and direct detection that can potentially distinguish vector dark matter from their scalar counterpart (via substructure in halos, gravitational waves and electromagnetic signatures). Time permitting, I will discuss preliminary results for different formation mechanisms for vector dark matter and solitons, and also generalize to include non-gravitational interactions.

Zoom link: https://zoom.us/j/91709058845.

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Fri 17 Jun 13:00: Black tsunamis and naked singularities

Mon, 13/06/2022 - 09:46
Black tsunamis and naked singularities

We study the evolution of the Gregory-Laflamme instability for black strings in global AdS spacetime, and investigate the CFT dual of the formation of a bulk naked singularity. Using an effective theory in the large D limit, we uncover a rich variety of dynamical behaviour, depending on the thickness of the string and on initial perturbations. These include: large inflows of horizon generators from the asymptotic boundary (a `black tsunami’); a pinch-off of the horizon that likely reveals a naked singularity; and competition between these two behaviours, such as a nakedly singular pinch-off that subsequently gets covered by a black tsunami. The holographic dual describes different patterns of heat flow due to the Hawking radiation of two black holes placed at the antipodes of a spherical universe. We also present a model that describes, in any D, the burst in the holographic stress-energy tensor when the signal from a bulk self-similar naked singularity reaches the boundary. The model shows that the shear components of the boundary stress diverge in finite time, while the energy density and pressures from the burst vanish.

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Fri 22 Jul 11:30: Title to be confirmed

Fri, 10/06/2022 - 14:46
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Fri 22 Jul 11:30: Title to be confirmed

Fri, 10/06/2022 - 14:46
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Fri 22 Jul 11:30: Title to be confirmed

Fri, 10/06/2022 - 14:46
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Fri 10 Jun 13:15: Evidence of planet engulfment in post-main sequence stars

Fri, 10/06/2022 - 12:17
Evidence of planet engulfment in post-main sequence stars

The post-main sequence stellar evolution can have catastrophic consequences for orbiting planets. With the expansion of the star’s envelope during the red giant branch, some exoplanets are likely engulfed, producing changes in the surface chemical composition of the star. There are no clear chemical signatures that are unequivocally associated with this event, but enhancement of light elements that should be depleted on the surface of red giants can be considered indicators of engulfment. In this talk, I will discuss lithium as a signature of accretion of substellar companions in red giant branch stars. Although identifying individual engulfment events during the red giant evolutionary phase can be complicated, the death of a low-mass star provides new opportunities to study engulfment. Metals in the atmosphere of white dwarfs are signs of accretion of smaller planetary bodies. Thus, I will also show how these polluted white dwarfs offer a novel means to study the composition of rocky exoplanets and understand if they retain the same composition as the material from which they formed.

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Tue 14 Jun 13:00: Understanding the stars in our search for another Earth

Thu, 09/06/2022 - 15:38
Understanding the stars in our search for another Earth

To understand exoplanetary systems, we can study their mass-radius relationship or lack thereof. The HARPS -N Collaboration has been leading the efforts to fill and interpret the mass-radius diagram of small planets by combining space photometry, Gaia astrometry and radial velocities. Determining a precise as-well-as accurate planet mass can only be determined with well-sampled, stable, and precise observations combined with advanced computational efforts and new extraction and processing techniques. The biggest challenge remains the stellar activity processes, mimicking and hiding planetary signals. With the HARPS -N Collaboration, we have been studying the Sun-as-a-star for 6 years, providing a dataset where we truly have no planetary signals and can study stellar behaviour in more detail. In this talk, I will give an overview on the leading efforts of our collaboration to fill the mass-radius diagram, an insight in new LSD -based processing techniques, and the behaviour over time of the standard activity indicators using Solar data.

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Mon 13 Jun 13:00: Effects and uses of CMB lensing Zoom link: https://zoom.us/j/99304579109

Thu, 09/06/2022 - 12:48
Effects and uses of CMB lensing

Large-scale structure gravitationally lenses the cosmic microwave background, producing magnification, shear and rotation effects. I describe some useful and surprising effects of this, including new optimized measurements from Planck PR4 maps, lensing biases induced via masking, and how the small rotation effect may be observable using forthcoming CMB observations.

Zoom link: https://zoom.us/j/99304579109

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Thu 16 Jun 16:00: Stopping the Stars from Twinkling: monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications

Wed, 08/06/2022 - 14:50
Stopping the Stars from Twinkling: monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications

Turbulence in the Earth’s atmosphere can limit the precision of ground-based optical telescopes, both in terms of the angular resolution and the time-resolved photometry. I will present the progress in monitoring, modelling and mitigating atmospheric turbulence for astronomy and other applications. We have successfully developed a new turbulence monitor capable of operating continuously 24-hours a day, enabling support for both solar and night-time activities but also feeding into turbulence forecasting tools. The combination of these facilities allows us to model the propagation of light through the Earth’s atmosphere anywhere in the world. This is useful to select new sites, develop new instruments and optimise scheduling for existing observatories. I will also highlight the synergies between astronomical instrumentation and other exciting applications such as free-space optical communications and satellite tracking; areas where technical research staff can transfer their skills to make a significant impact in these emerging fields.

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Wed 08 Jun 13:45: Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

Mon, 06/06/2022 - 14:35
Robustness of Molecular Detections Using High-Resolution Transmission Spectroscopy

In recent years, high-resolution transmission spectroscopy has emerged as one of the most successful techniques for detecting chemicals in transiting exoplanetary atmospheres. Despite many molecular detections to date, concerns have been raised about robustness when removing telluric and stellar features from the observed spectra, a step known as detrending. A robust detrending method has yet to be agreed upon, leaving previous detections inconsistent and sometimes irreproducible. We examine how overfitting detrending parameters can falsely amplify detection significances, and propose a robust methodology to select these parameters without introducing bias. To do this, we use CARMENES observations of the hot Jupiter HD189733b as a case study to investigate the robustness of different detrending optimisations. We find that selecting detrending parameters by optimising the difference between a signal-injected cross-correlation function and the observed cross-correlation function is robust against noise and spurious signals. On the other hand, optimising without this subtraction, as is often done, can induce spurious peaks and inflate detection significances. We reproduce previous detections with decreased significances reflecting more robust detrending. Our findings provide a robust framework for future homogeneous molecular surveys of exoplanetary atmospheres using high-resolution transmission spectroscopy.

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Mon 06 Jun 13:00: Surprising Dark Implications of a Supersymmetric Gravity Sector Zoom link: https://stonybrook.zoom.us/j/2816482971?pwd=TWpaN1hpd2laZzNxcGVJSkVGUVFDUT09.

Mon, 06/06/2022 - 11:32
Surprising Dark Implications of a Supersymmetric Gravity Sector

This talk explores surprises that emerge as consequences of accidental approximate scale invariances combined with a relatively supersymmetric gravity sector, both of which are argued to be robust consequences of UV physics (like string theory). Taken together these can be more than the sum of their parts, and suggest the low-energy world around us should consist of non-supersymmetric particle physics coupled to a rich dark sector built from supersymmetric gravity. A core prediction is that all particle masses arise proportional to the vev, v, of a dilaton field with the pattern where Standard Model masses, M, neutrino masses, m, and the Planck mass satisfy Mp/M \sim M/m \sim v, suggesting v is order 1e15. The framework also predicts the scalar potential for v, and this has both AdS and dS solutions without any need for problematic uplifting. The potential arises as a function of log v and so can give exponentially large values for v using only input parameters of order 70. Tantalizingly, at its minimum the potential evaluates to the fourth power of an energy E = (weak scale squared)/(Planck mass) that scales with v in the same way as a famous phenomenologically successful numerology. The prefactor is somewhat model-dependent, but in the known examples predicts the potential at its minimum to be suppressed by two powers of v (and five powers of log v), relative to the supersymmetry breaking scale in particle physics. For supersymmetry broken at 100 TeV this predicts a dark energy density of 1e(-91) in Planck units: not yet nailing the Dark Energy density—1e(-120)—but at least taping it down better than usual. Preliminary phenomenological implications are drawn assuming this framework eventually succeeds in further pushing down the minimum of V, and include intriguing cosmologies that (for free) seem to dynamically implement a recent proposal for resolving the Hubble tension (by modifying the electron mass around recombination).

Zoom link: https://stonybrook.zoom.us/j/2816482971?pwd=TWpaN1hpd2laZzNxcGVJSkVGUVFDUT09.

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Mon 06 Jun 13:00: Surprising Dark Implications of a Supersymmetric Gravity Sector Zoom link: https://zoom.us/j/93878540116.

Fri, 03/06/2022 - 10:41
Surprising Dark Implications of a Supersymmetric Gravity Sector

This talk explores surprises that emerge as consequences of accidental approximate scale invariances combined with a relatively supersymmetric gravity sector, both of which are argued to be robust consequences of UV physics (like string theory). Taken together these can be more than the sum of their parts, and suggest the low-energy world around us should consist of non-supersymmetric particle physics coupled to a rich dark sector built from supersymmetric gravity. A core prediction is that all particle masses arise proportional to the vev, v, of a dilaton field with the pattern where Standard Model masses, M, neutrino masses, m, and the Planck mass satisfy Mp/M \sim M/m \sim v, suggesting v is order 1e15. The framework also predicts the scalar potential for v, and this has both AdS and dS solutions without any need for problematic uplifting. The potential arises as a function of log v and so can give exponentially large values for v using only input parameters of order 70. Tantalizingly, at its minimum the potential evaluates to the fourth power of an energy E = (weak scale squared)/(Planck mass) that scales with v in the same way as a famous phenomenologically successful numerology. The prefactor is somewhat model-dependent, but in the known examples predicts the potential at its minimum to be suppressed by two powers of v (and five powers of log v), relative to the supersymmetry breaking scale in particle physics. For supersymmetry broken at 100 TeV this predicts a dark energy density of 1e(-91) in Planck units: not yet nailing the Dark Energy density—1e(-120)—but at least taping it down better than usual. Preliminary phenomenological implications are drawn assuming this framework eventually succeeds in further pushing down the minimum of V, and include intriguing cosmologies that (for free) seem to dynamically implement a recent proposal for resolving the Hubble tension (by modifying the electron mass around recombination).

Zoom link: https://zoom.us/j/93878540116.

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Wed 08 Jun 13:15: The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371

Wed, 01/06/2022 - 14:18
The Awakening Beast in the Seyfert 1 Galaxy KUG 1141+371

KUG 1141 +371 is a Seyfert 1 galaxy that shows a simultaneous flux increase in the optical and UV bands in the past decade. For instance, the Swift observations in 2019 show that the UVW2 flux of the AGN in KUG 1141 +371 has increased by over one order of magnitude since 2009. Meanwhile, the soft X-ray flux of KUG 1141 +371 also shows a steady increase by almost one order of magnitude from 2007 to 2019. The significant multi-wavelength luminosity change is likely due to a boost in mass accretion rate from approximately 0.6% of the Eddington limit to 3.2%, assuming a black hole mass of 100 million solar masses. I will present a detailed multi-epoch X-ray spectral analysis focusing on the variability of the X-ray continuum emission and the puzzling soft excess emission. In addition, our SED models also suggest a simultaneous increase in disc temperature and a decreasing inner disc radius along with the increasing accretion rate. Simultaneous ground-based optical observations show significant changes in the permitted line profiles and optical continuum. Finally, I will discuss the possible connection between KUG 1141 +371 and black hole transients in outburst.

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Fri 08 Jul 11:30: Title to be confirmed

Tue, 31/05/2022 - 19:33
Title to be confirmed

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Tue 07 Jun 13:00: The LIFE mission - atmospheric characterization of terrestrial exoplanets in the mid-infrared with a large space-based nulling interferometer

Tue, 31/05/2022 - 13:42
The LIFE mission - atmospheric characterization of terrestrial exoplanets in the mid-infrared with a large space-based nulling interferometer

The LIFE initiative (LIFE = Large Interferometry For Exoplanets) has the goal to develop the scientific context, the technology and a roadmap for an ambitious mid-infrared nulling interferometer space mission that will allow humankind to detect and characterize the atmospheres of hundreds of nearby extrasolar planets including dozens that are similar to Earth. Additional motivation for the initiative is provided by the outcome of ESA ’s “Voyage 2050” process and the corresponding recommendations from the ESA Senior Committee: the direct detection of the thermal emission of temperate terrestrial exoplanets was given very high scientific priority and is considered as a candidate theme for a future L-class mission. In this talk I will discuss the scientific potential and unique discovery space for a mission like LIFE , in particular for the detection of atmospheric biosignatures. Synergies with, but also advantages over future NASA flagship missions will be described and an overview of ongoing technology developments and related challenges will be provided.

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Fri 03 Jun 13:00: Asymptotic Symmetries in Higher Dimensions

Tue, 31/05/2022 - 09:43
Asymptotic Symmetries in Higher Dimensions

We will briefly review some recent developments in Asymptotic Symmetries in 6 dimensions, although the results should extend to any even dimensions. We shall mainly discuss supertranslations in non-linear General Relativity and if time permits, we will also look at superrotations. Reference: https://arxiv.org/abs/2201.07813

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