Talks

Parity symmetry is known to be violated in the weak interaction. Do the physical laws behind the unsolved problems of modern cosmology – cosmic inflation, dark matter, and dark energy – also violate parity symmetry? In this talk, we will discuss theoretical and observational possibilities of parity violation in cosmology, a topic that has received much attention in recent years.

• Speaker: Eiichiro Komatsu (MPA Garching)
• Monday 11 March 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Inigo Zubeldia.

Add to your calendar or Include in your list

Abstract not available

• Speaker: Jean-Luc Lehners (MPI for Gravitational Physics, Potsdam)
• Monday 13 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

Add to your calendar or Include in your list

For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.

• Speaker: Stephen Taylor, Vanderbilt University
• Thursday 07 March 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, IoA (tea at 3:30 pm).
• Series: The Eddington Lectures ; organiser: .

Add to your calendar or Include in your list

CubeSats stand at the forefront of the New Space Revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications for research in astronomy. With their standardised dimensions and modular design, these Nanosatellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with a special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.

• Speaker: Dr. Dolev Bashi
• Tuesday 05 March 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Dr. Dolev Bashi.

Add to your calendar or Include in your list

General relativity (GR) exists in different formulations. They are equivalent in pure gravity but generically lead to distinct predictions once matter is included. After a brief overview of various versions of GR, I will focus on metric-affine gravity, which avoids any assumption about the vanishing of curvature, torsion, or nonmetricity. With a view toward the Standard Model, we can construct a generic model of (complex) scalar, fermionic, and gauge fields coupled to GR and derive an equivalent metric theory, which features numerous new interaction terms. There are multiple phenomenological consequences, which I will detail: an improved setting for Higgs inflation, a new (purely gravitational) production channel for fermionic dark matter, and an outlook on axion inflation.

• Speaker: Claire Rigouzzo (KCL)
• Friday 08 March 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

Add to your calendar or Include in your list

The existence of dark matter, which constitutes 85% of the matter density and 26% of the total energy density, is clearly demonstrated by cosmological observations of the Universe. And yet, very little is known about the nature of dark matter. The observations support the ‘cold dark matter’ (CDM) paradigm, in which the dark matter is a heavy particle, with little to no interactions through fundamental forces other than gravity. The cosmological and astrophysical observations of dark matter’s gravitational interaction currently provide the only robust evidence of dark matter. These observations typically rely on characterising the distribution of matter in the Universe. A dark matter particle that is lighter than the standard CDM paradigm predicts imprints a suppression of structure in the matter distribution. The exact scale where this happens is most often linked to the mass of the dark matter particle. I will present new results on the thermal relic warm dark matter constraints using the high-redshift cosmic web as traced by the Lyman-alpha forest.

• Speaker: Vid Iršič
• Wednesday 06 March 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

Add to your calendar or Include in your list

CubeSats stand at the forefront of the New Space Revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications for research in astronomy. With their standardised dimensions and modular design, these Nanosatellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with a special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.

• Speaker: Dolev Bashi
• Tuesday 05 March 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Dolev Bashi.

Add to your calendar or Include in your list

In this talk I will discuss several studies in which quantum computers have been proposed as tools for studying particle theories. The first study uses quantum annealers to implement simple scalar field theories and observe quantum tunnelling, which follows the expected analytic behaviour: for example the decay rate follows the WKB approximation. The second more recent idea uses photonic devices to implement quantum tunnelling. In principle in both of these studies we are observing non-perturbative effects, suggesting that these and similar methods may be of interest in understanding a wide range of phenomena. The talk will be pedagogical.

• Speaker: Steve Abel (IPPP)
• Wednesday 06 March 2024, 14:00-15:00
• Venue: MR2.
• Series: Theoretical Physics Colloquium; organiser: Hannah Banks.

Add to your calendar or Include in your list

Since 1963, we have known, or at least suspected, that element abundances in the solar corona and wind are different to those in the photosphere. Elements that are predominantly ionized in the photosphere and chromosphere, e.g. Fe, Si, Mg, are observed to be enhanced in abundance once transported to the corona and wind by a factor of typically 3-4, while elements that are mainly neutral are relatively unaffected. Due to the dependence on the ionization potential, this phenomenon has been dubbed the First Ionization Potential (FIP) Effect. A model capturing the FIP and effect and the various modifications to it seen in different coronal regions and the solar wind invokes ion-neutral separation by the ponderomotive force due to Alfven and magnetosonic waves propagating through the chromosphere. This acts on ions, but not neutrals, and depends on the interaction of the waves with the magnetic geometry of the solar atmosphere.

The launch of the Extreme Ultraviolet Explorer (EUVE) in 1992 afforded us the first observations of abundances in stellar coronae. This, and succeeding missions like Chandra, XMM -Newton and Suzaku, have shown that solar-like stars show a similar FIP effect, which transitions to Inverse FIP (IFIP), i.e. a coronal depletion of Fe, Si, Mg, etc., as the activity level increases.

In this presentation, I will review the theoretical basis of FIP and IFIP fractionation by the ponderomotive force. Fractionation by such means is new to solar physics and astrophysics, but is not new to science. Manipulation of atoms, molecules, biological samples, etc. by the forces due to refraction of photons from lasers, known as “optical tweezers”, has a rather long history in optical sciences, and won Nobel Prizes for Steven Chu (in 1997) and Arthur Ashkin (in 2018). Our model is a precise analog of this work, but with magnetohydrodynamic waves instead of optical photons. This connection leads to a better physical understanding of the mechanisms at work in FIP fractionated plasma.

Work supported by NASA Heliophysics Supporting Research Program (80HQTR20T0076), and by Basic Research Funds of the Office of Naval Research.

• Speaker: Martin Laming (Naval Research Laboratory, Washington DC)
• Monday 04 March 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

Add to your calendar or Include in your list

Light scalar fields are often considered as part of explanations for dark energy and dark matter. They also appear in theories in which gravity is modified on cosmological scales. If the scalar field theory has a screening mechanism, the fifth forces that the scalar mediates can be significant in the cosmological vacuum but suppressed on Earth and in the solar system. It has been claimed that current data from galaxy surveys is sufficient to exclude the possibility that these theories could be relevant on astrophysical or cosmological scales. In this talk I will consider how such scalar fields behave in galaxies, and show that they may not be excluded after all.

• Speaker: Clare Burrage (Nottingham)
• Monday 04 March 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Dr Dong-Gang Wang.

Add to your calendar or Include in your list

Cassiopeia A is the best-observed core-collapse supernova remnant in our galaxy. Analyses of the 1 Million second Chandra Very Large Project X-ray observation and the data from infrared spectroscopy by Spitzer lead to a “complete” (within the limitations of the data quality) assessment of the elemental composition of the explosion ejecta, comprising both the reverse shocked X-ray emitting plasma and the photoionized unshocked ejecta emitting primarily in the infrared. This is the first time such a detailed census of supernova ejecta has ever been accomplished. More recently, Cassiopeia A has been observed with the James Webb Space Telescope. A first look suggests that these data corroborate and extend our previous analysis. Hard X-ray observations by NUSTAR reveal the mass and location of the radioactive nucleus 44Ti and optical imaging reveals a natal kick imparted to the compact central object (presumed to be a neutron star), anti-correlated with the 44Ti location, as expected. However, X-ray imaging reveals almost “pure” Fe knots on the east limb, presumably the ashes of alpha rich freeze out, which do not correlate so well. All these observables carry information about processes at the core of the supernova and allow us (and others) to speculate about the nature of the explosion, in ways that complement conclusions drawn from the prompt observations of supernovae.

• Speaker: Martin Laming (US Naval Research Laboratory)
• Thursday 14 March 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

Add to your calendar or Include in your list

For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.

• Speaker: Dr Stephen Taylor, Vanderbilt University, Nashville, Tennessee, USA
• Thursday 07 March 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

Add to your calendar or Include in your list

Investigating the fundamental origins of Bekenstein-Hawking entropy is a profound challenge in theoretical physics. This investigation is especially relevant for anti de Sitter (AdS) black holes, where it is proposed that the entropy can be explained through the microstates of the holographic dual quantum field theory, in line with the AdS/CFT correspondence. In this talk, I will review recent advancements in deriving the Bekenstein-Hawking entropy for various supersymmetric AdS black holes across different dimensions.

• Speaker: Seyed Morteza Hosseini, Imperial College London
• Friday 01 March 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

Add to your calendar or Include in your list

CubeSats stand at the forefront of the New Space revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications of research in astronomy. With their standardised dimensions and modular design, these Nanosatellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.

• Speaker: Dolev Bashi
• Tuesday 05 March 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Dolev Bashi.

Add to your calendar or Include in your list

The Square Kilometre Array (SKA) will be the largest interferometric radio telescope to date, with unprecedented resolution and sensitivity to study various phenomena of the universe. In data processing pipelines for radio telescopes, real time calibration, such as beam former and pointing offset calibration, are crucial for obtaining high-quality interferometric data from the observations. As an example, I will discuss the design and ongoing implementation of the pointing offset calibration pipeline within SKA ’s data processing software, describing the steps carried out to integrate the pipeline into telescope execution control and data queue system, as well as outlining challenges and greater implications on the data processing algorithm and software within the radio astronomy community.

• Speaker: Dr. Ying-He Celeste Lü (Cavendish Astrophysics)
• Tuesday 27 February 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

Add to your calendar or Include in your list

Abstract not available

• Speaker: Jean-Luc Lehners (MPI for Gravitational Physics, Potsdam)
• Monday 13 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

Add to your calendar or Include in your list

The cosmic history of galaxy formation is the history of star formation writ large. While the contents of the universe are mostly invisible and interact with baryons only weakly, a wide array of physical processes affect evolution of the observable baryons. Some of the most important processes involve coupling between stellar and gaseous components, since massive stars are the primary energy source in the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium (IGM). The majority of stellar energy — including UV radiation, winds, and supernovae — is returned rapidly after a given population of stars forms, and is therefore collectively termed “star formation feedback.” Because the state of the ISM determines the star formation rate, and stellar feedback determines the ISM state, quantifying how this co-regulation works is crucial to theoretical modeling. The need to quantify feedback responses also extends to galaxy formation theory on larger scales, where galactic winds driven by feedback heat and add metals to the CGM , thereby regulating the accretion that replenishes the ISM , and where escaping stellar UV ionizes the IGM . Because the observational characterization of galaxies — both near and far — relies on emission lines and infrared continuum from gas and dust subject to photoheating and photochemistry from starlight, quantitative interpretation of observations also relies on calibration using physical models that accurately represent radiative transfer in complex environments. In this lecture, I will review current theory of the physics of feedback, showcasing results from state-of-the-art, high-resolution numerical radiation-magnetohydrodynamic simulations that directly follow multiphase ISM evolution including the effects of UV radiation, stellar winds, and supernovae. These simulations, on both scales of individual star-forming molecular clouds, and scales of galactic disks, show star formation efficiencies and rates that are consistent with detailed observations in the nearby universe, and also indicate strong sensitivity to environment. At high densities and where dust and metal abundances are high, stellar radiation does not propagate as far, and cooling rates are enhanced. As a result of the reduced effectiveness of feedback in maintaining the ISM pressure (turbulent, thermal, and magnetic), star formation rates and efficiencies are expected to increase in high-density environments. Results from suites of resolved star-forming ISM simulations have been used to calibrate new subgrid models, and incorporation of these new results in galaxy formation models may potentially significantly change predictions for star formation at high redshift.

• Speaker: Eve Ostriker (Princeton University)
• Tuesday 12 March 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy (and online - details to be sent by e-mail).
• Series: The Kavli Lectures; organiser: Steven Brereton.

Add to your calendar or Include in your list

Abstract not available

• Speaker: Claudio Zanni (INAF Turin)
• Monday 17 June 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

Add to your calendar or Include in your list

Abstract not available

• Speaker: Chris Osborne (Glasgow)
• Monday 10 June 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

Add to your calendar or Include in your list

Abstract not available

• Speaker: Ugo Lebreuilly (CEA Saclay)
• Monday 03 June 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

Add to your calendar or Include in your list