# Theoretical Cosmology Meetings

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Weekly meeting on theoretical cosmology research, mainly supported by our STFC consolidated grant, covering the very early universe, modified gravity, and dark energy. We meet Wednesdays from 1-2pm in DS 2.08.

Organiser: Thomas Tram

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- Andrea Maselli (Gran Sasso Science Institute) on 9th Feb 2022 1:00:pm
- Juan Carlos Hidalgo (National Autonomous University of Mexico) on 19th Jan 2022 1:00:pm
- Thomas Montandon (APC) on 15th Dec 2021 1:00:pm
- Daniel Green (UC San Diego) on 8th Dec 2021 5:00:pm
- Deanna C. Hooper (University of Helsinki) on 1st Dec 2021 1:00:pm Title: Lyman-alpha data as a probe of dark matter interactions || Abstract: || Despite its remarkable success, the standard LCDM paradigm has been challenged lately by significant tensions between different datasets. This has reinvigorated interest in beyond-LCDM models, such as dark matter interacting either with standard model particles or with an additional dark sector. These...
- Daniel G. Figueroa (IFIC, Valencia) on 24th Nov 2021 1:00:pm Title: The Universe in a Box || Abstract: || In this talk we will introduce CosmoLattice, a modern code for simulating the non-linear dynamics of interactive fields in an expanding universe. As a demonstration of its power we will solve three very different problems of early Universe dynamics: i) the number of e-folds between inflation...
- Andrew Gow (ICG) on 17th Nov 2021 1:00:pm Title: A History of the Universe in Primordial Black Holes || Abstract: || I will present a summary of the work carried out during my PhD at Sussex, focused on Primordial Black Holes, covering the details of their formation from inflationary fluctuations, the detailed shape of their mass distribution, and the possibility that they could...
- Cristian Barrera-Hinojosa (Durham) on 10th Nov 2021 1:00:pm Title: Probing the cosmological gravitomagnetic effect via weak lensing-kSZ cross-correlations || Abstract: || General relativity predicts that the rotational momentum flux of matter twists the spacetime via a vector gravitomagnetic (frame-dragging) field, which so far remains undetected in cosmology. This vector field induces an additional gravitational lensing effect; at the same time, the momentum field...
- Davide Gualdi (Barcelona) on 3rd Nov 2021 1:00:pm Title: Cosmology from the anisotropic bispectrum and trispectrum: prospects and tests on N-body simulations || Abstract: || Current and future spectroscopic surveys such as DESI and Euclid will cover an observed volume at least one order of magnitude larger than current state-of-the-art surveys. The increased signal-to-noise will allow higher-order statistics to significantly improve the constraints...
- Masato Minamitsuji (Lisbon) on 27th Oct 2021 1:00:pm Title: Frame invariance in higher-order gravitational theories || Abstract: || In the first part, we investigate whether the cosmological perturbations are invariant under general disformal transformation with the second-order covariant derivatives of the scalar field. We show that on superhorizon scales the difference in the comoving curvature perturbations between frames is given by the combination...
- Alexandre Barreira (Origins/LMU) on 20th Oct 2021 1:00:pm Title: Galaxy bias and the consequences for tests of the early Universe || Abstract: || “Galaxy bias” describes the relation between galaxies and their large-scale environment, and studying it leads not only to improved cosmological constraints using galaxy data, but invariably also to new insights about the astrophysics of the galaxy-environment connection. In this talk...
- Deaglan Bartlett (Oxford) on 13th Oct 2021 1:00:pm Title: Galactic-Scale Tests of Fundamental Physics || Abstract: || Conventional probes of fundamental physics tend to consider one of three regimes: small scales, cosmological scales or the strong-field regime. Since LCDM is known to have several galactic-scale issues and novel physics (modified gravity, non-cold dark matter etc.) can alter galactic dynamics and morphology, tests of...
- Hayley Macpherson (DAMTP) on 6th Oct 2021 1:00:pm Title: Luminosity distance and anisotropic sky-sampling at low redshifts: A numerical relativity study || Abstract: || Most cosmological data analysis today relies on the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, providing the basis of the current standard cosmological model. Within this framework, interesting tensions between our increasingly precise data and theoretical predictions are coming to light. It is...
- Caner Ünal (Ben-Gurion U) on 30th Jun 2021 1:00:pm Title: Small Scales of Inflation || Abstract: || In the first part of the talk, I will focus on probing small scales of inflation via gravitational waves. Specifically, I will discuss GWs at interferometers from particle production in axion inflation, then in the second part, I will focus on the induced GWs from enhanced density...
- Matteo Braglia (IFT Madrid) on 16th Jun 2021 1:00:pm Title: Primordial standard clocks in the CMB || Abstract: || Massive field oscillating around their minima produce specific oscillatory patterns in the density perturbations that record the time dependence of the scale factor in the primordial Universe (hence the name ‘Primordial Standard Clocks’). In this talk I present recent developments on the model building of inflationary classical primordial standard...
- Valerio De Luca (Geneva) on 9th Jun 2021 1:00:pm Title: Primordial Black Holes and Gravitational Waves || Abstract: || We discuss about the formation and evolution of primordial black holes and focus on their possible connection with the gravitational-wave events detected by the LIGO/Virgo Collaboration and the NANOGrav 12.5 yr signal.
- Fabrizio Renzi (Leiden) on 2nd Jun 2021 1:00:pm Title: Looking at the Universe through standard observables || Abstract: || Standard observables (e.g. SNIa, BAO, CMB) provide a unique and powerful way to test cosmological models and constrain cosmological parameters. However to derive bounds from these data, it is typically required to calibrate them with external information which leads, inevitably, to calibration-dependent constraints. In...
- Macarena Lagos (Columbia) on 26th May 2021 1:00:pm Title: Interacting Gravitational Waves || Abstract: || Gravitational waves (GWs) allow us to probe the content of the Universe and the behaviour of gravity on cosmological scales, through information contained in their propagation. For instance, the presence of dynamical fields interacting non-minimally with gravity may induce a non-trivial propagation of GWs, changing their propagation speed,...
- Emilio Bellini (Geneva) on 19th May 2021 1:00:pm Title: Sheer shear: weak lensing with one mode || Abstract: || The aim of this talk is to show the potential of the Karhunen-Loève (KL) decomposition in reducing the dimensionality of the data vector for cosmic shear measurements. This greatly simplifies the problem of computing covariance matrices. To do so, I shall first introduce the theoretical...
- Giulia Gubitosi (University of Naples) on 5th May 2021 1:00:pm Title: The early universe as a probe of Planck scale physics || Abstract: || The early universe is arguably the most promising laboratory where to test properties of physics at the Planck scale. I will review the current observational evidence concerning the primordial universe from a model-independent perspective, emphasising the fundamental assumptions behind the inflationary...
- Lukas Witkowski (IAP) on 21st Apr 2021 1:00:pm Title: Probing features during inflation with the stochastic gravitational wave background || Abstract: || Scalar fluctuations sourced during inflation, if sufficiently enhanced, induce a contribution to the stochastic gravitational wave background (SGWB) that can be detected by the upcoming generation of gravitational wave detectors. In this talk I will show that “features” during inflation, i.e....
- Daniel B. Thomas (QMUL) on 31st Mar 2021 1:00:pm Title: Poisson is not a red herring: Modified gravity on non-linear scales || Abstract: || Linear theory parameterisations for testing gravity in a model independent way are only valid on larger scales in the Universe. Upcoming surveys will have a lot of data on smaller, non-linear scales, so in order to test gravity in a...
- Guillermo Ballesteros (IFT, Madrid) on 24th Mar 2021 1:00:pm Title: Primordial black hole dark matter from inflation || Abstract: || I will discuss the idea that the dark matter of the universe may be composed of black holes of primordial origin. I will mostly focus on light black holes (of mass several orders of magnitude smaller than that of the Sun) whose formation could...
- Chunshan Lin (Jagiellonian U, Krakow) on 10th Mar 2021 12:00:pm Title: An effective field theory of holographic dark energy || Abstract: || The idea of the holographic dark energy was originally proposed to reconcile the breakdown of the QFT in a large volume, which gives rise to a relation between UV cut-off and IR cut-off. The vacuum energy speeds up the cosmic expansion while applying...
- Obinna Umeh (ICG) on 3rd Mar 2021 1:00:pm Title: Observables, fundamental physics and general relativistic effects || Abstract: || I will discuss the key ideas and results from some of the projects I have been involved in recently. They are: Impact of halo finite size on the clustering of the HI brightness temperature FFTLog and multipole decomposition of the 3PCF Then I will...
- Francesc Cunillera (Nottingham) on 24th Feb 2021 1:00:pm Title: EFTs for early and late time cosmology || Abstract: || In this talk we explore two different EFTs for cosmology. The Kaloper-Sorbo EFT is a model for axionic inflation derived from a duality with ever present 4-forms. A priori an infinite sum, we show that the theory can be consistently truncated and ask the...
- Lasma Alberte (Imperial College London) on 17th Feb 2021 1:00:pm Title: Positivity bounds in the presence of gravity || Abstract: || Positivity bounds for theories with massless spin-2 fields would have deep implications for UV physics and the Weak Gravity Conjecture. However, the presence of a singularity in the t-channel of the scattering amplitudes precludes the application of standard positivity bounds. I will discuss the...
- Noemi Frusciante (Lisbon) on 10th Feb 2021 1:00:pm Title: Modified Gravity after GW170817: Phenomenology and Cosmological bounds || Abstract: || The standard cosmological model, LCDM, is based on General relativity and assumes the Universe is made of a Dark energy component in the form of a cosmological constant (L). Although LCDM gives an astonishing description of the Universe, the model shows some shortcomings: the so-called cosmological constant...
- Kenta Ando (ICRR, Japan) on 3rd Feb 2021 1:00:pm Title: Power spectrum in stochastic inflation || Abstract: || The stochastic formalism of inflation can describe long-wavelength perturbations nonperturbatively. In this picture, inflaton fields coarse-grained over superhorizon scales evolve with random noises. Hence, the local duration of inflation becomes a random variable called the first-passage time, which is determined by the stochastic process. Fluctuations of...
- Cristian Barrera-Hinojosa (Durham) on 27th Jan 2021 1:00:pm Title: Twisting the ΛCDM spacetime with general-relativistic simulations || Abstract: || N-body simulations have proven essential for understanding the vorticity of dark matter in cosmic structure formation. In General Relativity, rotational matter flows give rise to a gravitomagnetic vector potential which is responsible for frame dragging. The faint signals of these effects remain a challenge...
- Wentao Luo (IPMU, Japan) on 20th Jan 2021 1:00:pm Title:Weak gravitational lensing and its applications on the constraints of dark matter properties and cosmology || Abstract: || “The beauty and clearness of the concordance cosmology, which fits most of the observational data, is at present obscured by two clouds.” This is a modified version of Lord Kelvin’s speech in 1900. The two dark clouds of...
- Jeff Kost (Sussex) on 16th Dec 2020 1:00:pm Title: Deciphering the Archaeological Record: Cosmological Imprints of Non-Minimal Dark Sectors || Abstract: || Many proposals for physics beyond the Standard Model give rise to a dark sector containing many degrees of freedom. In this talk, we discuss the cosmological implications of the non-trivial dynamics which may arise within such dark sectors, focusing on decay...
- Katy Clough (Oxford) on 9th Dec 2020 1:00:pm Title: Initial conditions for inflation || Abstract: || Inflation solves a number of problems in early universe cosmology but potentially introduces some new ones regarding how it was able to get started in the first place. In this talk I will explain these issues in the context of single field slow roll inflationary models, and discuss...
- Sunny Vagnozzi (KICC, Cambridge) on 2nd Dec 2020 1:00:pm Title: The trouble with spatial curvature || Abstract: || The latest results from the Planck satellite 2018 CMB temperature and polarization data appear to prefer a spatially closed Universe, with curvature parameter Ωk<0, at high significance: if true, this could represent a big problem for the extremely successful inflationary paradigm. In order to obtain reliable...
- Alexander Vikman (CEICO, Prague) on 25th Nov 2020 1:00:pm Title: Observing primordial magnetic fields through Dark Matter || Abstract: || Primordial magnetic fields (PMF) are often thought to be the early Universe seeds that have bloomed into what we observe today as galactic and extragalactic magnetic fields. Owing to their minuscule strength, PMF are very hard to detect in cosmological and astrophysical observations. I...
- David Stefanyszyn (DAMTP) on 18th Nov 2020 1:00:pm Title: A Boostless Bootstrap and Emergent Lorentz Symmetry || Abstract: || Scattering amplitudes are very cumbersome to compute with traditional methods, especially when spinning particles are in the spectrum. However, the bootstrap approach, that bypasses Lagrangians and gauge redundancies, has made the computation of S-matrix elements far more efficient and illuminating. The idea of the...
- Alice di Tucci (MPI Potsdam) on 11th Nov 2020 1:00:pm Title: Semiclassical path integrals and the initial conditions for inflation || Abstract: || In this talk, I will review recent progress in semi-classical gravity within the path integral approach. In this framework it is possible to go one step beyond the usual treatment of primordial fluctuations according to QFT in curved spacetime as the background...
- Charles Dalang (Geneva) on 4th Nov 2020 1:00:pm Title: Horndeski and the sirens || Abstract: || In dark-energy models where a scalar field is nonminimally coupled to the spacetime geometry, gravitational waves are expected to be supplemented with a scalar mode. Such scalar waves may interact with the standard tensor waves, thereby affecting their observed amplitude and polarization. Understanding the role of scalar...
- Pierre Auclair (APC, Paris) on 28th Oct 2020 1:00:pm Title: Constraints on cosmic strings from gravitational waves, diffuse gamma-ray background and dark matter || Abstract: || Cosmic strings are stable topological defect solutions of field theories which may have formed during phase transitions in the early Universe. The detection or non-detection of these relics can constrain the physics of very high energies and extensions of...
- Shubham Maheshwari (University of Groningen) on 14th Oct 2020 1:00:pm Title: Stable, non-singular bouncing universe with only a scalar mode || Abstract: || I consider higher derivative, UV modifications to GR. In particular, I will focus on a specific kind of string theory-inspired higher derivative gravity where one includes derivatives to all orders in the action. I will discuss how such a non-local theory of...
- Lucas Pinol (Institut d’Astrophysique de Paris, France) on 7th Oct 2020 1:00:pm Title: Observational Signatures of Multifield Inflation || Abstract: || Slow-roll single-field inflation constitutes the main paradigm of the Early Universe. But this model suffers from a number of conceptual issues that naturally lead to the consideration of multifield models of inflation with curved field space, which have recently been under scrutiny as realistic realisations of...
- Chiara Moretti ( Queen Mary University of London) on 24th Jun 2020 1:00:pm || Title: Fast generation of dark matter halo catalogs with modified gravity || Abstract: Future generations of large scale structure surveys will measure the clustering of matter with high precision, yielding tight constraints on cosmological parameters and allowing to investigate models that go beyond the standard LCDM one. To make predictions both for the standard...
- Ivonne Zavala (Swansea University) on 17th Jun 2020 1:00:pm || Title: Fat Inflatons, Large Turns and the η-problem || Abstract: I will discuss fat inflation in multifield models of inflation where all scalar fields are heavier than the Hubble scale, thus evading the so called η-problem. I will show how this is achieved in multifield inflation thanks to large turns in the field space....
- Enrico Pajer (Cambridge) on 3rd Jun 2020 1:00:pm || Title: On the symmetries of cosmological perturbations || Abstract: The space of inflationary models is vast, containing wide varieties of mechanisms, symmetries, and spectra of particles. Consequently, the space of observational signatures is similarly complex. Hence, it is natural to look for boundaries of the space of models and their signatures. In the first...
- Alexander Jenkins (KCL) on 27th May 2020 1:00:pm || Title: Probing the early and late Universe with the gravitational-wave background || Abstract: In the new era of gravitational-wave (GW) astronomy, one of the most exciting observational targets is the stochastic GW background (SGWB) — a persistent all-sky signal, sourced by incoherent GWs from many independent sources throughout cosmic history. The SGWB is particularly...
- Levon Pogosian (Simon Fraser University, Burnaby, Canada and the ICG)[web seminar] on 20th May 2020 1:00:pm Title: Relieving the Hubble tension with primordial magnetic fields || Abstract: || The standard cosmological model determined from the accurate cosmic microwave background measurements made by the Planck satellite implies a value of the Hubble constant H0 that is 4.4 standard deviations lower than the one determined from Type Ia supernovae. The Planck best fit...
- Ricardo Z. Ferreira (Nordita) on 13th May 2020 1:00:pm || Title: Outcomes of strong particle production || Abstract: In this talk I will discuss multi-field models of inflation where there are instabilities and strong particle production due to, a priori harmless, irrelevant operators. The instabilities can move the trajectory to a new multi-field attractor where the inflaton potential can be steeper thus proving an...
- Sebastien Renaux-Petel (IAP) on 6th May 2020 1:00:pm [web seminar] || Title: Inflation and Geometry || Abstract: Inflation, an era of accelerated expansion of the universe prior to the radiation phase, constitutes the paradigm of primordial cosmology. Within this paradigm, the simplest single-field slow-roll models economically explain all current data. However, the sensitivity of inflation to Planck scale physics, and the fact that...
- Schöneberg, Nils (RWTH Aachen University)[Virtual meeting] on 29th Apr 2020 1:00:pm Title:Easing cosmological tensions — What works and what doesn’t? || Abstract: || Tensions between measurements in the early and the late universe could be a first hint at new physics beyond the standard model of cosmology. In particular the clustering of large scale structure and the current value of the Hubble parameter show intriguing discrepancies....
- Christopher Sean Gallagher (QMUL) on 22nd Apr 2020 1:00:pm Title:Multi-Scale Perturbation Theory for Cosmologies with Nonlinear Structure || Abstract: || Cosmological perturbation theory relies on the assumption that density contrasts are small. This assumption is valid for most of the history of the universe, but begins to break down at late times due to matter’s susceptibility to gravitational collapse. However, the post-Newtonian treatment of...
- David Wands (ICG) [Virtual meeting] on 25th Mar 2020 1:00:pm Title: Update on the KITP inflation workshop || Abstract: || Join Hangouts Meet: meet.google.com/kjg-gqzy-nco Join by phone:+1 234-719-4035
- Ilia Musco (Geneva), Webex seminar at 1:00 pm UK on 18th Mar 2020 1:00:pm || Title: Formation and Abundance of Primordial black holes || Abstract: Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of...
- Atsushi Naruko (CGP, YITP Kyoto). Now cancelled. on 4th Mar 2020 1:00:pm Title: Possible resolution of a spacetime singularity with field transformations || Abstract: || It is widely believed that classical gravity breaks down and quantum gravity is needed to deal with a singularity. In this talk, we show that there is a class of spacetime curvature singularities which can be resolved with metric and matter field...
- Scott Melville (DAMTP) on 26th Feb 2020 1:00:pm || Title: How to Constrain Inflation as an Effective Field Theorist || Abstract: Not all field theories are good theories. In particular, a good field theory Lagrangian should be stable (against quantum corrections), predictive (give well-defined transition probabilities), and UV-completable (can make sense at high energies). For Lorentz-invariant systems, we know how to build effective...
- Jacopo Fumagalli (IAP) on 19th Feb 2020 1:00:pm || Title: Hyper-non-Gaussianities, strongly non-geodesic motion and imaginary speed of sound || Abstract: || Several recent proposals to embed inﬂation into high-energy physics rely on inﬂationary dynamics characterized by a strongly non-geodesic motion. This in turn relaxes the conditions of slow-roll to allow for potentials that are steep in Planck units, a welcome feature in view...
- Guilheme Brando (Universidade Federal do Esp ́ırito Santo, Brasil and ICG) on 5th Feb 2020 1:00:pm Title: Different ways of testing Gravity || Abstract: || The LCDM concordance model poses is a minimalist description to our Universe, supported by several observable cosmological data, and is viewed as one of the many successes in Modern Cosmology. However, some discordances have arisen in recent years, which makes testing the LCDM model and General Relativity...
- Stargazing Night on 29th Jan 2020 5:30:pm Stargazing at Portsmouth Historic Dockyard
- Ryo Namba on 22nd Jan 2020 1:00:pm Title: Energy Injection into CMB from Axion-Gauge Field Dynamics || || Abstract: Measurements of the cosmic microwave background (CMB) radiation in the last half century have immensely advanced our knowledge and understanding of the history of our universe. The precision of the CMB observations has enabled us to show the blackbody nature of the spectrum of this...
- Kazufumi Takahashi (Kobe University) on 11th Dec 2019 1:00:pm || Title: Linear stability analysis of hairy black holes in degenerate higher-order scalar-tensor theories || Abstract: I talk about static spherically symmetric black hole solutions and their linear stability in the shift- and reflection-symmetric subclass of quadratic degenerate higher-order scalar-tensor (DHOST) theories. Black holes in this class of theories can support a nontrivial scalar hair,...
- Rampei Kimura (Waseda University, Japan) on 4th Dec 2019 1:00:pm Title: Constructing ghost-free boson-fermion system || Abstract: || I first talk about the coexistence system of both bosonic and fermionic degrees of freedom in the context of point particle system. Even if a Lagrangian does not include higher derivatives, fermionic ghosts generally exist. For a Lagrangian with up to first derivatives, we find the fermionic ghost-free condition in Hamiltonian...
- Sebastian Cespedes (ICTP) on 27th Nov 2019 1:00:pm || Title: Cosmological correlation functions from the Hamilton Jacobi formalism || Abstract: A better understanding of how correlations evolve during inflation is crucial if we are to extract information about the early Universe from our late-time observables. Using the Hamilton-Jacobi formalism, we review how the state of the Universe flows along cosmological time, analogous to...
- Mauro Pieroni (Imperial) on 20th Nov 2019 1:00:pm || Title: Constraining axion inflation with gravitational waves from preheating || Abstract: Models in which a pseudoscalar inflaton (axion) is coupled to the Chern-Simons density are of particular theoretical and phenomenological interest. The coupling between the inflaton and some (Abelian) gauge fields induces an instability which gives rise to a wide range of potentially observable...
- Matteo Braglia(Università di Bologna, Italy) on 6th Nov 2019 1:00:pm || Title: Cosmological implications of a non-minimally coupled scalar field: Dark Energy and perturbations from Inflation. || Abstract: I discuss the cosmological imprints of a non-minimally coupled scalar field that drives the late-time acceleration of the Universe and the time variation of the effective Newton constant. In a full covariant description, I describe the background...
- Tomberg, Eemeli S(University of Helsinki, Finland) on 30th Oct 2019 1:00:pm || Title: Higgs inflation and quantum corrections || Abstract: Higgs inflation is a model of cosmic inflation where the Higgs field of the Standard Model, coupled non-minimally to gravity, is the inflaton. At tree level, the model’s CMB predictions are well known and compatible with observations. However, when quantum corrections are added, the predictions may change....
- Students and Post-docs. on 23rd Oct 2019 1:00:pm Title: New Ideas in Cosmology 2 || Abstract:
- Post-docs and students in cosmology on 16th Oct 2019 1:00:pm Title: Radical new ideas in Cosmology || Abstract: Post-doctoral research fellows and students at the ICG will have an opportunity to discuss their work and talk about ideas they find more interesting in Cosmology without any interference from the faculty members.
- Rodrigo Maier(Rio de Janeiro State University (UERJ)) on 9th Oct 2019 1:00:pm || Title: Late-Time Acceleration in Bouncing Cosmologies || Abstract: In this talk, we are going to revisit some nonsingular cosmological models in the framework of modified gravity which can be constrained by observational data. All the models are sourced with the most appealing candidate for dark energy, namely, a cosmological constant. The simplest model refers...
- Will Handley (Cambridge) on 25th Sep 2019 1:00:pm ||Title: Curvature tension: evidence for a closed universe || Abstract: The curvature parameter tension between Planck 2018, cosmic microwave background lensing, and baryon acoustic oscillation data is measured using the suspiciousness statistic to be 2.5 to 3σ. Conclusions regarding the spatial curvature of the universe which stem from the combination of these data should therefore...
- || Sam Passaglia, KICP || (special time, 12pm!) on 18th Sep 2019 12:00:pm || Title: Does inflation produce enough primordial black holes to explain the dark matter? || Abstract: I will discuss the inflationary side of the primordial black hole dark matter story. I will show why in single-field inflation, slow-roll conditions must be violated for PBH production to occur. I will discuss the leading single-field model which...
- Shubham Maheshwari (University of Groningen, the Netherlands, Perturbations in higher derivative gravity beyond maximally symmetric spacetimes) on 21st Aug 2019 1:00:pm | Title: Perturbations in higher derivative gravity beyond maximally symmetric spacetimes | | | Abstract: | Higher derivative gravity is typically plagued by ghost-like states which spoil unitarity. In this talk, I will discuss a specific class of higher derivative gravity called Infinite Derivative Gravity (IDG), which is quadratic in curvature and characterized by form...
- Emir Gumrukcuoglu on 26th Jun 2019 1:00:pm | Title: Role of matter in modified gravity: a search for new interactions | Abstract: | In this talk, I will focus on the process of building classical gravitational theories. For a given theory, we start by defining some physical viability principles, formulate these into viability criteria, then finally develop a mathematical representation. However, these...
- Will Emond (University of Nottingham) on 19th Jun 2019 1:00:pm | Title: A Well-Tempered Cosmology | Abstract: The cosmological constant problem (CCP) has remained a persistent thorn in the side of contemporary theoretical physics. Currently lacking a reasonable resolution from the field theory sector, in recent years, much attention has been placed in finding solutions within the gravitational sector. A particular approach that has...
- George Zahariade (Arizona State) on 12th Jun 2019 1:00:pm Title: Classical-Quantum correspondence and backreaction Abstract: We map the quantum problem of a free bosonic field in a space-time dependent background into a classical problem. N degrees of freedom of a real field in the quantum theory are mapped into 2*N^2 classical simple harmonic oscillators with specific initial conditions. We discuss how this classical-quantum correspondence...
- 75th anniversary of D-Day. on 5th Jun 2019 8:30:am Possible travel disruption. Keep up to date with all the latest travel information and advice about road and car park closures for D-Day http://www.portsmouth.gov.uk/d-day75.
- Cyril Pitrou (IAP, France), Precision big bang nucleosynthesis with improved Helium-4 predictions on 22nd May 2019 1:00:pm | Title: Precision big bang nucleosynthesis with improved Helium-4 predictions | Abstract: Primordial nucleosynthesis or Big-Bang Nucleosynthesis (BBN) happens during the first 300 seconds of our Universe. It is one of the three evidences for the big-bang model, together with the cosmological expansion and the Cosmic Microwave Background (CMB). Now that the number of neutrino...
- Athena SWAN Conference on 15th May 2019 1:00:pm The University’s seventh annual Athena SWAN Conference is open to all staff, and will focus on gender equality and diversity. The conference will be opened by the Vice-Chancellor, Graham Galbraith. Register here: https://www.eventbrite.co.uk/e/gender-equality-are-we-there-yet-tickets-59103945492
- Chris Pattison (ICG) on 8th May 2019 1:00:pm | Title: Stochasic inflation beyond slow roll | Abstract: I will begin this talk by introducing the stochastic formalism for inflation. I will give some motivation for using the stochastic approach and then explain why we may want to consider situations that violate slow roll. I will explain the requirements for stochastic inflation to be...
- No talk (UK Cosmo on May 2nd) on 1st May 2019 1:00:pm
- PDR changed, still available. on 24th Apr 2019 1:30:pm
- Santiago Casas on 10th Apr 2019 1:00:pm | Title: Constraining Dark Energy and Modified Gravity with Euclid: What to do about model-independence and non-linearities? | Abstract:The standard cosmological model LCDM is still the best fit to present observations. However, theoretical motivations and the presence of mild tensions in the data, motivate us to look for further explanations to the accelerated expansion of the...
- Easter break is from April 8th to April 26th. Please note that there might be talks scheduled during the break. | on 8th Apr 2019
- April 3rd-5th: SEPnet Student Led Conference in Southampton | on 3rd Apr 2019 link
- Munshi, Dipak (UCL Space & Climate Physics, Mullard Space Science Laboratory) on 27th Mar 2019 1:00:pm Title: Squeezing cosmological information out of weak lensing bispectrum Abstract: I will discuss how to use the statistics called Integrated Bispectrum (IB) to probe the gravity-induced non-Gaussianity at the level of the bispectrum from weak lensing maps. I will discuss how to generalize the concept of the IB to spherical coordinates, and to three-dimensions (3D) using a spherical-Bessel decomposition....
- No Theoretical Cosmology Seminar on this date, because of the Quantum Optics Workshop (Vincenzo Tamma) on 20th Mar 2019
- Michael Kenna-Allison (ICG) on 13th Mar 2019 1:00:pm Title: Questioning the viability of bigravity cosmology Abstract:Bigravity is an extension of dRGT massive gravity which arises by promoting the background reference metric of dRGT massive gravity to a dynamical quantity. In the context of the low energy limit model, which is the only viable bigravity model distinguishable from GR, we study linear and non-linear perturbations...
- Pippa Cole (Sussex) on 6th Mar 2019 1:00:pm | Title: Primordial black holes and how to produce them | Abstract: Primordial black holes have had a recent surge in popularity due to the LIGO/VIRGO detections and the possibility that they could make up all or part of the dark matter. However, even if you only want to produce one primordial black hole, there...
- Sadra Jazayeri (DAMTP) on 27th Feb 2019 1:00:pm | Title: Solid Adiabatic Modes and Soft Theorems | Abstract: Cosmological observations, from the cosmic microwave background to large-scale structure, indicate that the initial condition for inhomogeneities in our universe has been adiabatic, namely, in the long wavelength limit, any perturbation in our universe locally mimics a coordinate change. I first review the concept of...
- Phil Bull(Queen Marry University of London) on 20th Feb 2019 1:00:pm Title: Fundamental physics with 21cm intensity mapping experiments Abstract: 21cm intensity mapping is a promising new method for conducting large-scale structure surveys over extremely large cosmic volumes, and out to high redshift. I will discuss some of the insights into inflation and the nature of GR and dark energy that we can hope to...
- Mu-In Park(Physics Dept., Sogang University, Seoul, Korea) on 13th Feb 2019 1:00:pm Title: On Cosmological Perturbations in Hořava Gravity Abstract: I will introduce Horava gravity which has been introduced 10 years ago as a power-counting renormalizable (quantum) gravity. As a cosmological test, I will consider cosmological perturbations to see if whether the scale invariant scalar, as well as tensor perturbations, can be obtained without introducing an...
- Developing Diversity in Physics (SEPnet Sharing Good Practice Workshop) on 5th Dec 2018 1:00:pm SEPnet Sharing Good Practice Workshop Wednesday 5 December 2018 12.00 – 17.00 University of Portsmouth University of Portsmouth Institute of Cosmology & Gravitation (ICG) is hosting a Diversity in Physics workshop on behalf of the South East Physics Network (SEPnet). As recent events have highlighted, unconscious and cultural biases continue to present challenges in addressing...
- Jessie Durk: This seminar is now cancelled. on 28th Nov 2018 1:00:pm Title: Black hole lattices as Inhomogeneous cosmological models. Abstract: The need to test whether the large-scale expansion of space is that of FLRW, or is instead modified by the presence of inhomogeneities, has lead to the homogeneity assumption in cosmology being relaxed. An interesting subset of inhomogeneous cosmologies include the black hole lattices. These are exact,...
- David Marsh (Cambridge) on 21st Nov 2018 1:00:pm ||Title: The landscape, the swampland, and cosmology || Abstract: I will critically review recent attempts to delineate the low-energy effective theories of consistent theories of quantum gravity using so-called “swampland conjectures”, and I will discuss the cosmological consequences of these conjectures. ||
- Yanchuan Cai (Edinburgh), [[ Special time&date: 12pm on a Monday]] on 19th Nov 2018 12:00:pm Title: Cosmology with the cosmic web Abstract: On large scales, the matter distribution of the Universe follows a web-like pattern, consisting of knot (cluster), filament, sheet and void. The cosmic-web is a non-Gaussian field, containing invaluable information about cosmology and astrophysics. I will summarise recent research activities in trying to extract this information, highlight opportunities...
- Chulmoon Yoo(PBH abundance from random Gaussian curvature perturbations and a local density threshold) on 14th Nov 2018 1:00:pm Title: PBH abundance from random Gaussian curvature perturbations and a local density threshold Abstract:The production rate of primordial black holes is often calculated by considering a nearly Gaussian distribution of cosmological perturbations, and assuming that black holes will form in regions where the amplitude of such perturbations exceeds a certain threshold. A threshold ζth for...
- Pedro Carrilho (Queen Mary University of London) on 7th Nov 2018 1:00:pm Title: Isocurvatures at second order and Magnetogenesis Abstract: Observations have offered strong support for the theory of Inflation, but many details of the physics of the early Universe are still unknown. An observation of primordial isocurvature modes would change our view of the early Universe and point towards multi-field inflation. In this talk, I will...
- Ryo Namba (McGill) on 31st Oct 2018 1:00:pm Title: Phenomenology of interacting gravitational waves during inflation Abstract: Detection of tensor mode fluctuations at the largest cosmological scales is often expected to provide a robust evidence of inflation and to fix the inflationary energy scale. Such direct connection is, however, applicable only when gravitational waves (GWs), the source of tensor perturbations, are effectively decoupled from other...
- Atsuhisa Ota (Utrecht University) on 24th Oct 2018 1:00:pm Title: Statistical anisotropy in CMB spectral distortions Abstract: Measurements of the cosmic microwave background (CMB) spectral y-distortion anisotropy offer a test for the statistical isotropy of the primordial density perturbations on 0.01≲ kMpc≲ 1. In this talk, I compute the 1-point ensemble averages of the y-distortion harmonic coefficients. They vanish for the statistically isotropic perturbations...
- Julian Adamek(QMUL) on 17th Oct 2018 1:00:pm Title: Relativistic effects in cosmic large-scale structure Abstract: As our advanced telescopes produce ever larger and deeper maps of our Universe we need to consider that observations are taken on our past light cone and on a spacetime geometry that is pervaded by small distortions. I will discuss how these aspects can be addressed...
- Claudio Llinares (ICG) on 10th Oct 2018 1:00:pm | Title: TBA | Abstract: TBA |
- Hassan Firouzjahi (IPM Tehran) on 12th Sep 2018 1:00:pm Title: Isotropic Vector Inflation | Abstract: In this talk we present a model of vector inflation containing a triplet of gauge field with a global O(3) symmetry. We decompose the perturbations into the adiabatic and entropy perturbations and calculate the power spectrum of curvature perturbations and the contribution from the gauge fields. |
- Teerthal Patel (Nagoya University) on 5th Sep 2018 1:00:pm Title: Primordial magnetic field generation in Axion Monodromy Inflation Abstract: Magnetic fields have known to exist on scales ranging from those of galaxies to galactic clusters and recently, in cosmological voids thus prompting the possibility that they could have been generated during inflation. The question of their origin is still open partly due to the...
- Shuntaro Mizuno (Kyoto University) on 22nd Aug 2018 1:00:pm Title: Blue-tilted Primordial Gravitational Waves from Massive Gravity Abstract: We study a theory of massive tensor gravitons which predicts blue-tilted and largely amplified primordial gravitational waves. After inflation, while their mass is significant until it diminishes to a small value, gravitons are diluted as non-relativistic matter and hence their amplitude can be substantially amplified compared...
- Vincenzo Tamma (Portsmouth) on 6th Jun 2018 1:00:pm Title: High-precision sensing based on thermal light interference beyond coherence Abstract: In the mid fifties Hanbury-Brown and Twiss (HBT) proposed to measure the angular dimension of stars by retrieving second-order interference in the absence of first-order interference. Remarkably, the HBT effect was at the heart of the development of the field of quantum optics. We...
- Likely no seminar this week (UK Cosmo in Swansea on May 23-24th) on 23rd May 2018 1:00:pm
- Peter Millington (Nottingham) on 9th May 2018 11:00:am || Title: Fifth forces, Higgs portals and broken scale invariance || || Abstract: The simplest modifications of general relativity often involve coupling additional scalar fields to the scalar curvature, resulting in conformally-coupled scalar-tensor theories. Indeed, any interacting scalar fields, including the Higgs field of the Standard Model (of particle physics), naturally obtain such non-minimal couplings...
- Vincenzo Tamma (!! Cancelled !!) on 2nd May 2018 1:00:pm Title: Second-Order Temporal Interference with Thermal Light: Interference beyond the Coherence Time Abstract: Talk to be rescheduled
- Gianmassimo Tasinato (Swansea) on 25th Apr 2018 1:00:pm || Title: Probing inflation with LISA interferometer || Abstract: TBA ||
- Seshadri Nadathur(ICG) on 28th Mar 2018 1:00:pm Title: Precise constraints on the growth rate from RSD in the void-galaxy cross-correlation Abstract: The vast increase in depth and data volume from forthcoming LSS surveys allows the use of a new tracer of the matter distribution for cosmology, cosmic voids. Void positions indicate regions of low density in which the dynamics and growth...
- Julio Fabris (UFES, Brazil) on 21st Mar 2018 1:00:pm Title: Viscous Cosmology Abstract: It is analyzed the effects of both bulk and shear viscosities on the perturbations, relevant for structure formation in late time cosmology. It is shown that shear viscosity can be as effective as the bulk viscosity on suppressing the growth of perturbations and delaying the nonlinear regime. The possible degeneracy...
- Sakine Nishi (Rikkyo University) on 14th Mar 2018 1:00:pm Title: Observational Predictions of Generalized Galilean Genesis Abstract: Inflation is a very successful scenario for the early universe. However, even an inflationary universe has a singularity in the past, and the alternative scenarios motivated by this problem have been discussed. In this talk, we focus on one of the alternative scenarios called Galilean genesis. This...
- Timothy Clifton (QMUL) on 7th Mar 2018 1:00:pm Title: Relativistic perturbation theory in the presence of non-linear structures Abstract: I will discuss the application of both post-Newtonian and cosmological perturbation theories, to describe cosmologies with non-linear structure. The formal application of both of these expansions will be discussed, as well as some of the applications. These will include the back-reaction problem and...
- Matteo Martinelli and Simone Peirone (Leiden) on 21st Feb 2018 1:00:pm Title: From agnostic to believer: theoretical conditions on phenomenological parametrizations Abstract: Recent low redshift observations highlights tensions in the measurements of cosmological parameters with CMB surveys. Although it is not ruled out that such tensions are due to some unforeseen systematic effect, it can also hint for a breakdown of the standard LCDM model. This...
- Ruxandra Bondarescu(Exploring the spacetime with frequency standards) on 14th Feb 2018 1:00:pm Title:Exploring the spacetime with atomic clocks Abstract: I will discuss frequency standards that measure changes to 1 part in 10^19 and their potential in space and on Earth. On Earth, the slow down of time due to changes in the water table, magma that reaches the upper crust or the presence of lighter material...
- Vincent Vennin(ICG and Paris) on 7th Feb 2018 1:00:pm Titlle: Quantum decoherence during inflation Abstract: Decoherence may play a role in the quantum-to-classical transition of primordial cosmological fluctuations. But if it occurs in the early Universe, the interaction with the environment that gives rise to it also changes observable predictions such as the power spectrum from inflation. I will show how this opens...
- Atsushi Naruko(Tohoku University ) on 31st Jan 2018 1:00:pm Title: Stable cosmological solutions in extended vector-tensor theory Abstract : Many cosmological observations imply the existence of dark matter and dark energy which induces the current accelerated expansion of the universe. As a possible origin of such dark energy, scalar-tensor theories draw much attention where scalar field is introduced as a driving force for the...
- Rossana Ruggeri (ICG) on 24th Jan 2018 1:00:pm Abstract: Title:
- Camille Bonvin (Geneva) :Testing gravity with relativistic effects in large-scale structure on 17th Jan 2018 1:00:pm Title: Testing gravity with relativistic effects in large-scale structure Abstract: The distribution of galaxies provides a powerful way to probe the properties of our universe. In order to exploit this observable properly it is necessary to understand what we are really measuring when we look at the large-scale structure. Since our universe is not...
- Baojiu Li(Durham) on 10th Jan 2018 1:00:pm Cancelled.
- Variable sound speed in interacting dark energy models – Mark S. Linton (ICG) on 13th Dec 2017 1:00:pm Title: Variable sound speed in interacting dark energy models— Abstract: The nature of both Dark Matter and Dark Energy remains one of the most open questions in cosmology. A priori there is no reason why these two sectors should not interact and current experimental bounds leave some parameter space to be explored. Additionally, given...
- Robert Hardwick (ICG) on 6th Dec 2017 1:00:am Title: A novel way to determine the scale of inflation— Abstract: Efforts to constrain the inflationary energy scale using the tensor-to-scalar ratio are limited by the minimum upper bound from observations. This still leaves a window of nearly 8 orders of magnitude in energy before the LHC can potentially offer complementary constraints from below. In the Feebly...
- South Coast cosmology meeting on 29th Nov 2017 1:30:pm
- Florian Niedermann (University of Nottingham) on 22nd Nov 2017 1:00:pm Title: Gravitational self-tuning of the vacuum energy: obstructions and ways around — Abstract: Gravitational models of self-tuning are those in which vacuum energy has no observable effect on spacetime curvature even though it is a priori unsuppressed below the cut-off, thereby avoiding the cosmological constant problem. According to a famous argument by Weinberg, consistent field...
- Quantum diffusion during inflation and primordial black holes – Christopher Pattison on 15th Nov 2017 1:00:pm Title: Quantum diffusion during inflation and primordial black holes– Abstract: I will explain how primordial black holes can form from perturbations seeded during inflation and how their abundance can be calculated in the framework of stochastic inflation. This formalism incorporates quantum backreaction of the small-wavelength fluctuations on the large distances dynamics of the Universe. If...
- Joseph Kennedy (Edinburgh) on 8th Nov 2017 1:00:pm —Title: Reconstructing Horndeski models from the effective field theory of dark energy —Abstract: Studying the effects of dark energy and modified gravity on cosmological scales has led to a great number of physical models being developed. The effective field theory (EFT) of dark energy allows an efficient exploration of this large model space. However, constraints...
- Hector Ramirez (IFIC, University of Valencia) on 1st Nov 2017 1:00:pm — Title: Generalized Slow-Roll approach for Horndeski inflation — Abstract: In the canonical realization of inflation, the primordial power spectra are usually computed in terms of a standard hierarchy of the slow-roll parameters, related to the inflaton potential, which are required to be small and constant. However, there exist well-motivated models whose inflationary potential exhibits...
- Introduction to our recent works by Matteo and Obinna on 25th Oct 2017 1:00:am ---Obinna--- General relativistic corrections to the galaxy bispectrum could mimic the cosmological signal from the early universe. I will describe our recent effort towards quantifying this accurately. ---Matteo--- I will describe a newly proposed phenomenological framework to account for screening mechanisms in dark energy/modified gravity models at mildly-non-linear scales.
- Katsuki Aoki (Waseda) on 18th Oct 2017 1:00:pm — Title: Massive graviton geons: self-gravitating massive gravitational waves — Abstract: We study vacuum solutions such that massive gravitons are confined in a local spacetime region by their gravitational energy in the context of the bigravity theory, which we call massive graviton geons. We find a non-spherically symmetric solution with a quadrupole configuration of the...
- Takeshi Kobayashi (SISSA) on 11th Oct 2017 1:00:pm ~~~Title: Baryons, Dark Matter, and Light Scalars ~~~Abstract:The appearance of scalar fields with small masses is ubiquitous in physics beyond the Standard Model. In this talk I will describe how such light scalars can play important roles in cosmology, especially in connection to the origin of the baryons and dark matter of our universe. With...
- Inflationary massive gravity, primordial black holes and gravitational waves on 11th Aug 2017 2:00:pm Misao Sasaki, Kyoto University
- Relativistic wide-angle galaxy bispectrum on the light-cone: All-sky analysis on 12th Jul 2017 1:00:pm Room: PO0.41 Abstract Given the important role that the galaxy bispectrum has recently acquired in cosmology and the scale and precision of forthcoming galaxy clustering observations, it is timely to derive the full expression of the large-scale bispectrum going beyond approximated treatments which neglect integrated terms or higher-order bias terms or use the Limber approximation....
- Jeremy Sakstein – “Some new mechanisms for baryogenesis” on 14th Jun 2017 1:00:pm Abstract: There is more matter than antimatter in the universe, and the origin of this asymmetry is still a mystery. The asymmetry can be generated dynamically in the early universe in a process referred to as baryogenesis, but the standard model is not able to produce the amount observed. This is one hint that there...
- South Coast Cosmology meeting in Sussex on 9th Jun 2017
- Kostas Skenderis (Southampton), “Holographic cosmology” on 31st May 2017 1:00:pm Abstract Holographic cosmology offers a novel framework for describing the very early Universe in which cosmological predictions are expressed in terms of the observables of a three dimensional quantum field theory (QFT). This framework includes conventional inflation, which is described in terms of a strongly coupled QFT, but it also allows for qualitatively new models...
- Chandrima Ganguly (DAMTP, Cambridge), “Isotropising anisotropic cyclic cosmologies” on 24th May 2017 1:00:pm Abstract: Standard models of cosmology use inflation as a mechanism to resolve the isotropy and homogeneity problem of the universe as well as the flatness problem. However, due to various well known problems with the inflationary paradigm, there has been an ongoing search for alternatives. Perhaps the most famous among these is the cyclic universe...
- No theory seminar due to university Athena-SWAN/diversity conference on 17th May 2017 1:00:pm
- Jerome Quintin (McGill, Montreal), Cosmological perturbations in a contracting universe and black hole formation on 10th May 2017 1:00:pm Abstract: Motivated by bouncing cosmology, I will describe the evolution of cosmological perturbations in a contracting universe dominated by a general hydrodynamical fluid. I will show that under certain conditions, the perturbations can grow non-linearly to a point where they can collapse into black holes, and I will describe the black holes that would result...
- Tommi Tenkanen (QMUL), “The many faces of the inflaton field” on 3rd May 2017 1:00:pm Abstract: The minimal requirements for every inflationary model are that the inflaton field gives a long enough period of exponential expansion and subsequently reheats the universe, so that thermal equilibrium is attained prior to Big Bang Nucleosynthesis. But could the inflaton be responsible for something else as well, namely the generation of dark matter or...
- No theory seminar due to MBA workshop on 26th Apr 2017 1:00:pm
- No theory seminar due to UK Cosmo on 5th Apr 2017 1:00:pm
- Florent Leclercq (ICG), Bayesian optimisation for likelihood-free cosmological inference on 29th Mar 2017 1:00:pm Abstract: I will present ongoing work about inference with generative cosmological models. I assume that only a small number of parameters are of interest, but that the process generating the data is very general: a noisy non-linear dynamical system with millions of hidden variables. The main challenge is then the intractability of the likelihood, and...
- Ryotaku Suzuki (ICG), “Large D Effective theory of Gravity” on 22nd Mar 2017 1:00:pm Abstract: Recent studies have shown that black hole dynamics have an extremely simplified limit in a sufficiently large spacetime dimension: the large ‘D’ limit. In the large D limit, black hole dynamics are described by an effective membrane theory of collective variables on the horizon, which is useful to explore a vast variety of black...
- Gerardo Adesso (Nottingham), “Robustness of quantum coherence” on 21st Mar 2017 11:00:am Abstract: Quantifying coherence is an essential endeavour for both quantum foundations and quantum technologies. I will give an overview of recent developments in the characterisation and quantification of coherence as a resource. In particular, I introduce the robustness of coherence as a mathematically rigorous and physically motivated quantifier of quantum coherence, which complies with the...
- Sophia Rachel Goldberg (QMUL, London), Cosmology on all scales: a two-parameter perturbation expansion on 15th Mar 2017 1:00:pm Abstract: We propose and construct a two-parameter perturbative expansion around a Friedmann-Lemaître-Robertson-Walker geometry that can be used to model high-order gravitational effects in the presence of nonlinear structure. This framework reduces to the weak-field and slow-motion post-Newtonian treatment of gravity in the appropriate limits, but also includes the low-amplitude large-scale fluctuations that are important for cosmological...
- Carsten van de Bruck (Sheffield), CANCELLED on 1st Mar 2017 1:00:pm
- Dipak Munshi (Sussex) CANCELLED, Constraining Modified Theories of Gravity with Large Scale Structure Formation on 1st Feb 2017 1:00:pm Modification of General Relativity can be invoked to explain the accelerated expansion of the Universe. Ongoing and future surveys (e.g. Euclid and LSST) will probe any departure from the predictions of GR in exquisite detail. In this talk I plan to introduce two novel techniques, based on large scale structure, to constrain modified gravity (MG) theories. In particular,...
- Vincent Vennin (ICG Portsmouth), Can we show that cosmological perturbations are of quantum mechanical origin? on 1st Feb 2017 1:00:pm Abstract: During inflation, quantum vacuum fluctuations are amplified and stretched to large distances, giving rise to cosmological perturbations that seed the large scale structure of our Universe. However, astronomers usually analyse the data with purely classical techniques and apparently never need to rely on the quantum formalism to understand them. So is there observational signatures...
- Pierstefano Corasaniti (Paris), cancelled on 18th Jan 2017 1:00:pm
- Kaloian Dimitrov-Lozanov (Cambridge), The equation of state after inflation on 11th Jan 2017 1:00:pm Abstract: I will talk about our recent work (arXiv:1608.01213) in which we calculate the equation of state after inflation and provide an upper bound on the duration before radiation domination by taking the nonlinear dynamics of the fragmented inflaton field into account. For the models considered, I will discuss how our work significantly reduces the...
- Takashi Hiramatsu (Rikkyo University, Japan) ”CMB bispectrum” on 7th Dec 2016 1:00:pm Abstract: We have developed a new Einstein-Boltzmann solver for CMB anisotropy to quantify the significance of the non-Gaussianity induced during the non-linear evolution of the primordial fluctuations after the last-scattering surface. In our numerical code, we implemented a 2nd-order line-of-sight formula, so-called “curve”-of-sight formula, which has been developed in our recent work in JCAP 1410 (2014) 051....
- Maciej Bilicki (Leiden), “All-sky galaxy catalogues in 3D and their applications” on 30th Nov 2016 1:00:pm Abstract: Many cosmological problems require three-dimensional all-sky galaxy catalogues reaching beyond the very local universe. As the currently deepest all-sky spectroscopic survey (2MRS) has mean z=0.03 only, such datasets at larger redshifts and covering more than 2pi sterad are available only from combining imaging surveys at different wavelengths and estimating photometric redshifts. I will present two...
- Tomohiro Fujita (Stanford University), “The new relationship between inflation and gravitational waves” on 23rd Nov 2016 12:00:pm Abstract: It is well known that the amplitude of the gravitational wave (GW) produced from the vacuum fluctuation during inflation is proportional to the energy scale of inflation. Thus the observation of the inflationary GW by CMB B-mode is expected to reveal the energy scale of new physics as well as pin down the inflation...
- Chunshan Lin, Kyoto University, “Do we have to modify gravity in the very early universe?” on 16th Nov 2016 1:00:pm by Chunshan Lin, Kyoto
- Seshadri Nadathur, ICG, “Spots on the Sky: cosmic superstructures and their ISW effect” on 9th Nov 2016 1:00:pm Abstract: In the presence of decaying potentials at late times, large rare superstructures in the universe imprint secondary temperature anisotropies on the CMB via the integrated Sachs-Wolfe effect. This effect might be measured by stacking analyses, but these have been controversial, due to a long-standing discrepancy between one such measurement and the LCDM theoretical...
- Joao Morais (University Pays Basque, Bilbao), Cosmology with 3-forms: global dynamics, phantom behaviour and cosmic doomsday on 2nd Nov 2016 1:00:pm In recent years, 3-forms have been studied both in the context of late-time dark energy and primordial inflation since they can very naturally accommodate a near cosmological-constant behaviour. However, depending on the choice of the potential, the Universe can end up either in a Minkowski or a de Sitter state, or even being lead to...
- Giovanni Cabass, La Sapienza Roma, “The observed squeezed limit of slow-roll inflation” on 26th Oct 2016 1:00:pm Maldacena’s consistency relation in single-field inflation encodes the fact that a local observer measuring the power spectrum of small-scale curvature perturbations cannot detect the presence of a long-wavelength mode at zeroth and first order in gradients: any physical effect will start quadratic in gradients of the long mode. Motivated by the possibility that future upper...
- Isabel Oldengott, Bielefeld, “Reionization and dark matter decay” on 25th Oct 2016 12:00:pm Cosmic reionization and dark matter decay can impact observations of the cosmic microwave sky in a similar way. A simultaneous study of both effects is required to constrain unstable dark matter from cosmic microwave background observations. We compare two reionization models with and without dark matter decay. We use the Planck 2015 data to constrain the effective decay...
- Johannes Noller, Oxford, “The landscape of linear cosmological perturbations” on 19th Oct 2016 1:00:pm DS 2.08
- Meet the group on 12th Oct 2016 2:00:pm
- Yves Dirian (Geneva), Observational constraints and Bayesian model comparison in non-local gravity on 5th Oct 2016 1:00:pm
- Using the post-Newtonian formalism to understand general relativity and its alternatives on cosmological scales on 28th Sep 2016 1:00:pm by Viraj Sanghai, QMUL.
- Complete Hamiltonian analysis of cosmological perturbations at all orders on 21st Sep 2016 1:00:pm by Debottam Nandi, IISER-TVM, Trivandrum, India.
- Claudio Llinares (TBC) on 13th Jul 2016 1:00:pm by Claudio Llinares, Durham.
- Eugeny Babichev on 6th Jul 2016 1:00:pm by Eugeny Babichev
- Sesh Nadathur (TBC) on 29th Jun 2016 1:00:pm by Sesh Nadathur
- Stochastic-delta N formalism and massive primordial black hole formation in hybrid inflation on 22nd Jun 2016 1:00:pm by Yuichiro Tada, Tokyo U.
- Ben Bose (TBC) on 15th Jun 2016 1:00:pm by Ben Bose
- Adam Solomon (TBC) on 8th Jun 2016 1:00:pm by Adam Solomon, Cambridge.
- Strong gravity and astrophysics with compact binaries at the dawn of gravitational-wave astronomy on 1st Jun 2016 1:00:pm by Emanuele Berti, Mississippi U.
- Cosmological Imprints of Inflationary Initial Conditions on 25th May 2016 1:00:pm by Jonathan Braden, UCL.
- PPN Formalism on 18th May 2016 1:00:pm by Jeremy Sakstein
- Thiago Carames (TBC) on 11th May 2016 1:00:pm by Thiago Carames (TBC)
- Ryotaku Suzuki (TBC) on 4th May 2016 1:00:pm by Ryotaku Suzuki
- Is there evidence for anisotropy in CMB data? on 16th Mar 2016 1:00:pm by Daniela Saadeh, UCL.
- Cosmological simulations & tests of gravity on 9th Mar 2016 1:00:pm by Sownak Bose, Durham University.
- Chiral primordial gravitational waves due to particle production on 2nd Mar 2016 1:00:pm by Ippei Obata, Kyoto University.
- Gravitational scalar-tensor theory on 24th Feb 2016 1:00:pm by Atsushi Naruko, Tokyo Institute of Technology.
- Inhomogeneous pressure conformally flat cosmologies and observations on 10th Feb 2016 1:00:pm by Mariusz Dabrowski, University of Szczecin.
- Localized features in the CMB spectra due to a transient reduction in the speed of sound on 3rd Feb 2016 1:30:pm by Jesus Torrado, University of Sussex.
- Inflation and the cosmic microwave background anomalies on 3rd Feb 2016 1:00:pm by Chris Byrnes, University of Sussex.
- General Relativity and Cosmic Structure Formation on 27th Jan 2016 1:00:pm by Julian Adamek, Observatoire de Paris.
- Probing the ISW imprint of “photo-z voids” with SDSS, Pan-STARRS1, and DES on 13th Jan 2016 1:00:pm by Andras Kovacs, Universitat Autonoma de Barcelona.
- Bosonic structure of a realistic SO(10) SUSY cosmic string on 6th Jan 2016 1:00:pm by Erwan Allys, IAP.
- Testing gravity with EG: Understanding Theoretical Uncertainty on 9th Dec 2015 1:00:pm by Danielle Leonard, Oxford University.
- Topics on generalized Galileons on 7th Dec 2015 11:00:am by Cedric Deffayet, IAP.
- Modelling the Large Scale Structure w and w/o massive neutrinos on 2nd Dec 2015 1:00:pm by Elena Massara, SISSA.
- A stiff HIGSStory of the Universe on 25th Nov 2015 1:00:pm by Daniel G. Figueroa, CERN
- The Inflationary Universe of α-attractors on 18th Nov 2015 1:00:pm by Marco Scalisi, University of Groningen.
- Cosmological constraints on Dark Matter properties on 11th Nov 2015 1:00:pm by Tommi Tenkanen, University of Helsinki.
- Dark matter at galactic scales & MOND on 4th Nov 2015 1:00:pm Luc Blanchet, IAP
- Primordial magnetogenesis with post-inflationary evolution on 14th Oct 2015 1:00:pm Ryo Namba, IPMU Tokyo
- Black Holes and Scalar Hair on 7th Oct 2015 1:00:pm Rahul Jha, University of Cambridge
- Disformal Electrodynamics on 23rd Sep 2015 1:00:pm Jack Morris, University of Sheffield
- Galileons and Black holes on 2nd Sep 2015 1:00:pm Minas Tsoukalas, Centro de Estudios Cientificos, Chile
- Lensing in McVittie metric on 2nd Sep 2015 11:00:am Oliver Piattella, UFES, Brazil
- A unified approach to dark energy on 22nd Jul 2015 1:00:pm Speaker: David Langlois
- Generic correlation between nonG and iso-pert with early universe axion on 15th Jul 2015 1:00:pm Speaker: Godfrey Leung
- CMB Non-Gaussianity as a Probe of Primordial Magnetic Fields on 8th Jul 2015 1:00:pm Speaker: Pranjal Trivedi
- Philosophy of Cosmology on 1st Jul 2015 1:00:pm Speaker: Bridget Falck
- Scalar field cosmology on 24th Jun 2015 1:00:pm Speaker: Claes Uggla
- Primordial Magnetism in CMB on 17th Jun 2015 1:00:pm Speaker: Levon Pogosian
- Vacuum Energy Sequestering on 10th Jun 2015 1:00:pm Speaker: David Stefanyszyn
- Journal club: Matthew Hull on 20th May 2015 1:00:pm arXiv:1502.02666
- Journal club: Alkistis Pourtsidou on 6th May 2015 1:00:pm arXiv:1504.05481
- Cosmology with the SKA on 22nd Apr 2015 1:00:pm Speaker: Roy Maartens
- Journal club: Cornelius Rampf on 15th Apr 2015 1:00:pm arXiv:astro-ph/0109483, arXiv:astro-ph/0304214
- Observational constraints and reconstruction of the interacting vacuum energy on 25th Mar 2015 1:00:pm Speaker: Yuting Wang
- Journal club: Bridget Falck on 11th Mar 2015 1:00:pm 2015MNRAS.448..307 and arXiv:1412.0066
- Construction, parameterisation and observational signatures of interacting dark energy models on 25th Feb 2015 1:00:pm Speaker: Alkistis Pourtsidou
- Massive Gravity on 11th Feb 2015 1:00:pm Speaker: Luigi Pilo
- Journal club: Thomas Tram on 4th Feb 2015 1:00:pm arXiv:1501.07512
- Primordial black holes: constraining the small scales in the big early universe on 28th Jan 2015 1:00:pm Speaker: Sam Young
- Perturbations and Conservation in Lemaitre-Tolman-Bondi Cosmology on 21st Jan 2015 1:00:pm Speaker: Alex Leithes
- Why recombination physics is important for Planck on 14th Jan 2015 1:00:pm Speaker: Jens Chluba
- Journal club: Gong-bo Zhao on 3rd Dec 2014 1:00:pm arXiv:1408.5435, arXiv:1309.6783
- Interpreting cosmological observations in a clumpy universe on 26th Nov 2014 1:00:pm Speaker: Pierre Fleury
- Think you can derive Einstein’s equations in less than 10 seconds? on 19th Nov 2014 1:00:pm Speaker: Jeremy Sakstein
- Constraining Primordial non-Gaussianity (PNG) from the large-scale structure on 12th Nov 2014 1:00:pm Speaker: Nina Roth
- Observing the inflationary Reheating on 5th Nov 2014 1:00:pm Speaker: Vincent Vennin
- Journal club: Jeremy Sakstein on 29th Oct 2014 1:00:pm arXiv:1409.0886
- Disformal Theories of Gravity on 22nd Oct 2014 1:00:pm Speaker: Jeremy Sakstein
- Light sterile neutrinos? on 15th Oct 2014 1:00:pm Speaker: Thomas Tram
- Cosmological simulations of scalar tensor theories for gravity beyond the static approximation on 10th Oct 2014 12:30:pm Speaker: Claudio Llinares
- Generalized tensor fluctuations and inflation on 8th Oct 2014 1:00:pm Speaker: Dario Cannone
- Astrophysical Tests of Gravity on 9th Jul 2014 1:00:pm Speaker: Jeremy Sakstein
- Confirming and questioning the standard LCDM at our local universe on 18th Jun 2014 1:00:pm Speaker: Yong-Seon Song
- Massive Gravity and Bigravity: from theory to cosmology on 4th Jun 2014 1:00:pm Speaker: Marco Crisostomi
- f(R) gravity in the Newtonian limit, and beyond… on 21st May 2014 1:00:pm Speaker: Dan Thomas
- Can the Photon Drive Dark Energy? on 7th May 2014 2:00:pm Speaker: Gianmassimo Tasinato
- Aspects of Emergence of Gravity and Geometry on 30th Apr 2014 1:00:pm Speaker: Florian Kühnel
- Boltzmann hierarchy for interacting neutrinos on 9th Apr 2014 1:00:pm Speaker: Isabel Oldengott
- Relativistic constraints for cosmological structure formation on 2nd Apr 2014 1:00:pm Speaker: Cornelius Rampf
- Horndeski Theory and its Multi-field extension on 19th Mar 2014 1:00:pm Speakers: Norihiro Tanahashi and Seiju Ohashi
- A large-N classification for inflationary models on 12th Mar 2014 1:00:pm Speaker: Ivonne Zavala
- The statistics of cosmlogical large scale peculiar velocity of dark matter particles and halos on 19th Feb 2014 1:00:pm Speaker: Yi Zheng
- Influence of heavy modes on perturbations in multiple field inflation on 12th Feb 2014 1:00:pm Speaker: Shuntaro Mizuno
- The Falsely Fat Curvaton on 22nd Jan 2014 1:00:pm Speaker: Gianmassimo Tasinato
- General scale invariance on 15th Jan 2014 1:00:pm Speaker: Minas Tsoukalas
- Extensions of f(R) gravity and their applications in cosmology on 4th Dec 2013 2:00:pm Speaker: Nicola Tamanini
- Bounded Scalar Perturbations in Bouncing Brane World Cosmologies on 27th Nov 2013 1:00:pm Speaker: Rodrigo Maier
- The ORIGAMI Structures of the Universe on 20th Nov 2013 1:00:pm Speaker: Bridget Falck
- Impact of primordial non-Gaussianity on hydrodynamical SZ simulations on 30th Oct 2013 1:00:pm Speaker: Francesco Pace
- New constraints on interacting dark energy and modified gravity models from Planck/Constraints on Dark Radiation and Dark Energy on 16th Oct 2013 1:00:pm Speaker: Valentina Salvatelli/Najla Said
- Interacting vacuum energy after Planck on 2nd Oct 2013 12:00:pm Speaker: Yuting Wang
- Initial Conditions for the Inflationary Wavefunction on 25th Sep 2013 1:00:pm Speaker: Navin Sivanandam
- Gravitational particle production and non-Gaussianity in supergravity R^2 inflation on 16th Sep 2013 12:00:pm Speaker: Yuki Watanabe
- The Regge-Wheeler equation for Schwarzschild spacetime in f(R) gravity on 12th Sep 2013 1:00:pm Speaker: Anne Marie Nzioki
- A universe filled with Black Holes on 28th Aug 2013 1:00:pm Speaker: Ken-ichi Nakao
- Disformal invariance of the Horndeski action: Theoretical aspects and an application to dark matter. on 10th Jul 2013 1:00:pm Speaker: Dario Bettoni
- Relativistic initial conditions for cosmological structure formation on 4th Jul 2013 12:00:pm Speaker: Cornelius Rampf
- Friday Coffee discussion on 28th Jun 2013 11:00:am Speaker: Everyone
- From configuration to dynamics on 26th Jun 2013 1:00:pm Speaker: Shinji Mukohyama
- Friday Coffee discussion on 21st Jun 2013 11:00:am Speaker: Everyone
- Nonlinear Resonance in Hořava-Lifshitz Bouncing Cosmologies on 19th Jun 2013 1:00:pm Speaker: Rodrigo Maier
- Friday Coffee discussion on 14th Jun 2013 11:00:am Speaker: Everyone
- The Effective Field of Dark Energy on 12th Jun 2013 1:00:pm Speaker: Jérôme Gleyzes
- Friday Coffee discussion on 7th Jun 2013 11:00:am Speaker: Everyone
- Giant Monopoles as a Dark Matter Candidate on 5th Jun 2013 1:00:pm Speaker: Jarah Evslin
- Friday Coffee discussion on 31st May 2013 11:00:am Speaker: Everyone
- Friday Coffee discussion on 24th May 2013 11:00:am Speaker: Everyone
- Entropy-Area relation in Black-Holes on 22nd May 2013 1:00:pm Speaker: Nima Khosravi
- Friday Coffee discussion on 17th May 2013 11:00:am Speaker: Everyone
- Newtonian, Relativistic and Primordial non–linear fluctuations in Lambda-CDM on 15th May 2013 1:00:pm Speaker: Carlos Hidalgo
- Friday Coffee discussion on 10th May 2013 11:00:am Speaker: Everyone
- Heavy fields, Decoupling and the Effective theory of Inflation on 8th May 2013 1:00:pm Speaker: Subodh Patil
- Friday Coffee discussion on 3rd May 2013 11:00:am Speaker: Everyone
- Friday Coffee discussion on 26th Apr 2013 11:00:am Speaker: Everyone
- Equivalence Principle Violation in Vainshtein Screened Two-Body Systems on 24th Apr 2013 1:00:pm Speaker: Kazuya Koyama
- Friday Coffee discussion on 19th Apr 2013 11:00:am Speaker: Everyone
- What do we know about the dark universe — A post-Planck report on 17th Apr 2013 1:00:pm Speaker: Gongbo Zhao
- Second Order Non-Gaussianity — SONG on 27th Mar 2013 1:00:pm Speaker: Christian Fidler
- Stacked phase-space distribution around clusters: testing gravity and modelling on 20th Mar 2013 1:00:pm Speaker: Tsz Yan Lam
- Journal club on 6th Mar 2013 1:00:pm Speaker: Daniel Thomas and Francesco Pace
- Journal club on 27th Feb 2013 1:00:pm Speaker: Gongbo Zhao
- Journal club on 20th Feb 2013 1:00:pm Speaker: Francesco Pace
- Predictions in Multifield Inflation on 13th Feb 2013 1:00:pm Speaker: Jonathan Frazer
- Structure Formation from Defect Interactions on 6th Feb 2013 1:00:pm Speaker: Furqaan Yusaf
- Non-Gaussianity in isocurvature perturbations on 30th Jan 2013 1:00:pm Speaker: Toyokazu Sekiguchi (Nagoya)
- Black Holes as Gravity Laboratories on 23rd Jan 2013 3:00:pm Speaker: Thomas Sotiriou (SISSA)

Events from before 2013 are available on our old website here.