In presence unless otherwise noted
Winter term 2024/25:
14:15, Philosophenweg 12, Room 105 or online
Geodesic congruences, Raychaudhuri equation and Black Hole area theorem
Summer term 2024:
14:15, Philosophenweg 12, Room 105 or online
Title: Testing Relativistic Corrections on Large Scale Structure
Winter term 2023/24:
14:15, Philosophenweg 12, Room 105 or online
Title: Model-independent test on the cosmological Poisson equation
Abstract: In this talk I will present how one can test the cosmological Poisson equation by requiring only the validity of three main assumptions: the energy-momentum conservation equations of matter, the equivalence principle, and the cosmological principle. We first point out that one can only measure the combination ${\mathcal M}\equiv \Omega_m^{(0)}\mu$, where $\mu$ quantifies the deviation of the Poisson equation from the standard one and $\Omega_m^{(0)}$ is the fraction of matter density at present. Then we employ a recent model-independent forecast for the growth rate $f(z)$ and the expansion rate $E(z)$ to obtain constraints on ${\mathcal M}$ for a survey that approximates a combination of the Dark Energy Spectroscopic Instrument and Euclid. We find that ${\mathcal M}$ can be measured only to within 20-30% up to $z=1.5$. We also project our constraints on some parametrizations of ${\mathcal M}$ proposed in literature, while still maintaining model-independence for the background expansion, the power spectrum shape, and the non-linear corrections. As expected, we find much weaker model-independent constraints than found so far for such models. This means that the cosmological Poisson equation remains quite open to various alternative gravity and dark energy models.
Title: On UV completion of Higgs inflation in Palatini formalism
Abstract: I will investigate UV completion of Higgs inflation in the Palatini formalism. It is known that the cutoff scales for the perturbative unitarity become much smaller than the Planck scale to be consistent with CMB observations. Expecting that the low cutoff scales originate in the curvature of a field-space spanned by the Higgs fields, I consider embedding the curved field-space into a higher dimensional flat space and apply this procedure to the Palatini-Higgs scenario. I will show that, while the new field introduced in this way successfully flattens the field-space, the new field can not uplift the cutoff up to the Planck scale. I will also compare the result with vanilla Higgs inflation.
Summer term 2023:
14:15, Philosophenweg 12, Room 105
Title: Detecting anomalies with Machine Learning
In recent years, Machine Learning techniques have proven to be powerful tools for data analysis both inside and outside of physics. The ability to model high-dimensional spaces through expressive functions parameterized by neural networks has enabled new solutions for complex problems. These tools are general and highly portable to other fields. In this talk, I will introduce the concept of anomaly searches and detection. Anomaly detection was initially introduced in computer science and has been constantly developed in particle physics, offering enhanced sensitivity for model-agnostic searches. I will present a density-based approach for the detection of Out-Of-Distribution (OOD) events, leveraging Auto-Encoders and Energy-Based Models for unsupervised training and improved likelihood interpretation. I will demonstrate the strength and weaknesses of the methodology with proof-of-concept results on LHC data, including top tagging, semi-visible jet detection, and applications for online triggering.
Title: Unbiased cosmology from biased tracers
Abstract: I will introduce the role played by symmetries in the perturbative expansion of the large-scale structure (LSS). In particular, I will describe how to establish which of the coefficients, usually referred as bias parameters, of the perturbation theory kernels are dictated by symmetries and which not. This approach is especially relevant for non-standard models that respect the same symmetries as ΛCDM and where perturbation theory at higher orders has not been exhaustively explored, such as dark energy and modified gravity scenarios. I will describe how to use this approach to perform general model-independent analysis based only on symmetry principles for realistic surveys. The bias parameters are usually treated as unknown nuisance parameters as they can depend on complex galaxy formation and evolution physics and the assembly history (assembly bias). I will show how to use the semi-analytic code Galacticus to study the assembly bias for the primordial non-Gaussian bias. I will show the dependence of this parameter on observable galaxy properties, such as the (g-r) color or the H\alpha emission line luminosity. This is relevant since theoretical motivated priors on the non.ì-Gaussian parameter would possibly allow for a detection of primordial non-Gaussianities, giving us more insight on the very first moment of our Universe.
Title: Testing modified gravity with Galactic observables
Abstract: We explore the potential of Milky Way observables, specifically the rotation curve and line of sight accelerations, as discriminators between modified and Newtonian gravity. Our investigation primarily centers around the Horndeski class of modified theories of gravity.
Title：Model-independent forecasting of modified gravity
Title: PHOTON RINGS IN KERR DE SITTER SPACETIME
Abstract: Recently, the Event Horizon Telescope (EHT) collaboration has provided interferometric observations of the black holes M87 and Sagittarius A∗ (SgrA∗ ) at the center of the galaxies Messier 87 and Milky Way, respectively, thus providing valuable insights into the emission structure on horizon scales. Calculations within the framework of General Relativity (GR), show that the black hole image is not a single continual entity. Rather, it is made up of an infinite sequence of self-similar subrings converging to the critical curve. These subrings constitute the photon ring, which in itself is observable. The critical curve represents the locus on the image plane resulting from photons moving along bound orbits, and its shape follows from GR. While the shape of the critical curve is predicted by GR, it cannot be directly observed. Despite that, the photon ring demonstrates a close approximation and resemblance to the critical curve affirming its potential as a robust testing ground for GR. In this presentation, we will explore photon rings in Kerr-de Sitter (KdS) spacetime. We will commence with an in depth analysis of the general structure of photon orbits pertinent to the formation of the photon ring. We then explore analytic ray-tracing to investigate direct images, lensing rings, and photon rings for equatorial disks around black holes. The photon ring exhibits a sequence of successive images that are exponentially demagnified, rotated, and delayed in time. To comprehensively conclude our discussion, we will analyze the critical parameters responsible for governing these essential characteristics of demagnification, rotation, and delay in the consecutive subrings.
Title: A dark future for dark matter
Abstract: The origin nature of dark matter is one of the greatest puzzles in modern physics. Despite the large efforts from particle and astro physicists in the search for dark matter, after almost four decades we are still quite in the dark and we have been able only to provide partial constraints on the nature of this elusive component in our Universe. I will present the current and future prospects for the search for dark matter, and highlight the challenges that lay in front of us for the next decade or more.
Title: Partition functions and Markov-chains for inference in cosmology
Abstract: Monte Carlo Markov-chain methods are a standard tool in inference in cosmology for sampling posterior distributions. I’ll illustrate their relation to thermodynamics, in particular the sampling of the Metropolis-Hastings algorithm to a canonical partition sum. This analogy allows an efficient analytic description of non-Gaussian features, the computation of Shannon-entropies and lastly the definition of convergence criteria supplementing the Gelman-Rubin criterion. I conclude by giving an outlook on inference questions that could be addressed by the partition formalism
Title : Testing the continuity equation at cosmological scales.
Abstract : Extensions to LCDM or modified gravity theories are often considered assuming conservation of the fluid equations. Here we report progress on a project where we relax this assumption on the continuity equation along with the common modified gravity parameters, i.e. the ones modifying the Poisson and Weyl potential and try to put constraints using cosmological observables that are sensitive to their modifications.
Title: Model independent forecasting DESI vs LSST
Abstract: We will discuss briefly the necessity of another one among the many forecasts. Followed by a detailed selection of parameters, expected results and possible improvements in the future as well as difficulties concerning forecasts between DESI and LSST.
Title: “A broad introduction to accelerated expanding universes from string theory and their difficulties”
Abstract: Obtaining accelerated expanding universes from string theory remains one of the core issues of string phenomenology. In principle, accelerated expanding universes can be realized through de Sitter vacua or string-theoretic quintessence models. Without assuming a background in string theory, I will introduce the main steps to obtain accelerated expanding universes. In particular, I will address the difficulties that arise in each approach.
Title: Cosmology with Gravitational Wave Merger Events: Current Status and Future Challenges
Abstract: In recent years, with the LIGO-Virgo-KAGRA detector network, the catalog of Gravitational Waves (GW) merger events has grown to about 90 merger events. This brings us to the era of GW astronomy. In this talk, I will briefly discuss the techniques used to create the catalog of GW mergers (from searches to source properties estimation) and compare the results across various catalogs. I will then go on to discuss the current techniques to do cosmology with GW events and how it can help us resolve so-called Hubble tension in the future. The third generation (3G) GW detectors such as Cosmic Explorer and Einstein Telescope are expected to be operational sometime during next decade and they will be an order of magnitude more sensitive compared to the current generation detectors. We will be able to probe to low frequencies such as 3-4 Hz and can detect binary black hole merger events up to very large redshift. I will discuss the forecast of cosmological studies in the era of 3G detectors. Specifically, how the 3G detectors can help us probing large scale structure features, such as galaxy bias and baryon acoustic oscillations, solely from the GW observations, and hence provide an independent probe to cosmology. -
Winter term 22/23:
Follow-up on Bayesian statistical measures
Bayesian measures of complexity, robustness and surprise
https://arxiv.org/abs/astro-ph/0602378
https://arxiv.org/abs/1209.1897
Cancelled
Pedro Riba Mello – Surprise and Discordances
In this talk I'll show how we can use the Surprise Statistics to explore discordances between datasets. The Surprise is a tool based on the Kullback-Leibler divergence and offers a way to quantify discordance between datasets in multiple dimensions in parameter space. The Surprise statistics has an analytical solution for gaussian distributions but for the general case of a non-gaussian distribution the Surprise and its distribution needs to be evaluated numerically. We’ll analyze multiple Supernova mocks created blindly and show an implementation to evaluate the non-gaussian case for the Surprise.
Luca Amendola - Golden hats of the Bronze Age: did they have an astronomical significance?
Based on a paper published here:
https://journal.equinoxpub.com/JSA
See also this wikipedia article:
Ziad Sakr - Forecasts on LCDM extensions from Euclid primary probes
I will present some preparatory forecasts performed within the Euclid collaboration using the mission primary probes, i.e. galaxy clustering detected from spectroscopic measurements and the so called 3×2 probe or weak lensing + galaxy clustering and their cross correlations, detected from measurements of photometric redshifts, on extensions to LCDM standard cosmological model by means of the commonly used dark energy equation of state and growth index parameter but also on other more specific models of modified gravity such as f(R) or Brans-Dicke before finishing with additional forecasts on some model independent null tests.
Konstantin Meyer
Stellar streams and dark matter substructure
Christmas edition - favourite papers and Christmas quiz
Luca Amendola - Testing gravity with GWs inspiral waveforms
I will discuss a recent paper by Tsujkawa and collaborators (https://arxiv.org/abs/2209.13749) and a follow-up paper we are now working on.
Prajwal Hassan Puttasiddappa
R. Jimenez et al.: Why is zero spatial curvature special?
cancelled due to extra Cosmology Seminar
Tanmoy Modak - Probing cosmic inflation with CMB and 21cm intensity mapping
In this talk I will discuss how well one can constrain the inflationary dynamics using future CMB and 21cm data. In particular, I will show that these data would provide stringent probe to the extended Starobinsky model. In addition, I will also provide projections for the Hubble slow-roll parameters.
Discussion round on non-linear vs. linear scales in relation to the 21cm background
Ziyang Zheng - Coupled and uncoupled early dark energy, and the cosmological tensions
Some early dark energy (EDE) models with non-negligible dark energy fractions in the pre-recombination epochs are capable of alleviating the Hubble tension quite efficiently. However, there has been an intensive discussion on whether these models enhance the power of matter fluctuations and worsen the tension with the large-scale structure (LSS) measurements. In this talk I will discuss the effect of several EDE models, considering also in some cases a coupling between the dark sector, and the effect of massive neutrinos. In the best case, namely ultra-light axion-like (ULA) potential, the Hubble tension is reduced to around 2$\sigma$, and the amount of clustering at linear scale is similar to the $\Lambda$CDM with the LSS estimator $\sigma_{12}$.
Caroline Heneka - A hands-on tutorial to run your own deep neural network
Winter semester kick-off, presentation of 'Computer Vision Astrophysics' (and Cosmology)
Summer term 22:
Adrian Schirra - Non-linear perturbation theory for the large-scale structure
The increasing precision of large-scale structure surveys calls for accurate theoretical modeling. In this talk, I will present the non-linear perturbation theory, which is applicable in the weakly non-linear regime. I will calculate the one-loop corrections to the power spectrum, while taking into account redshift space distortions as well as galaxy bias. The predictions of this model can be compared to observational data with MCMC algorithms.
Martin Kärcher (Aix-Marseille Université) - Tensor-Inverse Gravity - A new Hope to Replace the Cosmological Constant?
In this talk I will present a specific kind of modified gravity model based on the idea of replacing the cosmological constant with a scalar constructed of the inverted Ricci tensor (see https://arxiv.org/pdf/2006.04209.pdf). I will introduce the model by summarizing the original article and then present our extension to other tensors. In particular we investigate if inverting the Einstein or Riemann tensor can lead to a solution to the impossible transition from matter-like to accelerated expansion as occurring in a simple case of Ricci-inverse gravity.
Martin Kärcher - Cancelled
Cancelled.
Manuel Wittner - rehearsal
Cancelled.
Cancelled.
Chiara Cecchini (University of Trento) - Primordial magnetic fields in scale-invariant inflation
Magnetic fields permeate the Universe probed so far, from planetary scales to the Intergalactic Medium. An intriguing possibility is that they are remnants of primordial fields that originated during inflation. However, the amplification of vector perturbations in an exponentially expanding universe requires the breaking of EM conformal invariance. To this end, one can introduce a time-dependent coupling I(t) between the EM tensor and a scalar field with a non-trivial dynamics. In this work, we consider inflationary magnetogenesis in a scale-invariant model of quadratic gravity (arXiv:1512.07186). After constraining the model against spectral indices measurements, we investigate the optimal functional form of the coupling I(t) to generate a nearly scale-invariant spectrum of magnetic energy density and sufficiently strong fields at the end of inflation. We conclude by discussing the main problems with such a generation mechanism and a possible way out. A purely analytical analysis has been carried out.
Alejandro Hernández Arboleda (UFES - PPGCosmo, Brazil) - Screening tests with galaxy rotation curves
Modified theories of gravity make use, in a general sense, of screening mechanisms such as Vainshtein screening, to hide the effects of their modifications to Newtonian gravity and general relativity at local scales. Although the screening mechanism is responsible for suppressing “fifth forces” in the vicinity of massive sources, it can be broken inside them. In this tunch I will discuss updates of my research dealing with vainshtein screening breaking at the scale of galaxies using rotation curves and several dark matter profiles, focusing on the numerical methods used to study them.
Pedro da Silveira Ferreira - First constraints on the intrinsic CMB dipole and our velocity with Doppler and aberration
We test the usual hypothesis that the Cosmic Microwave Background (CMB) dipole, its largest anisotropy, is due to our peculiar velocity with respect to the Hubble flow by measuring independently the Doppler and aberration effects on the CMB using Planck 2018 data. We remove the spurious contributions from the conversion of intensity into temperature and arrive at measurements which are independent from the CMB dipole itself for both temperature and polarization maps and both SMICA and NILC component-separation methods. Combining these new measurements with the dipole one we get the first constraints on the intrinsic CMB dipole. Assuming a standard dipolar lensing contribution we can put an upper limit on the intrinsic amplitude: 3.7 mK (95% CI). We estimate the peculiar velocity of the solar system without assuming a negligible intrinsic dipole contribution: v=(300+111−93) km/s with (l,b)=(276±33,51±19)∘ [SMICA], and v=(296+111−88) km/s with (l,b)=(280±33,50±20)∘ [NILC] with negligible systematic contributions. These values are consistent with the peculiar velocity hypothesis of the dipole.
In this tunch, I will discuss our previous results (https://arxiv.org/abs/2011.08385 and https://arxiv.org/abs/2107.10846), and comment a bit about our next steps.
Winter term 21/22:
Cancelled.
Raquel Fazolo - Skewness as a test of dark energy perturbations We investigate the role played by dark energy perturbations in the skewness S_3 of large-scale matter distribution. We consider a two-fluid universe composed by matter and dark energy, with perturbations in both components, and we estimate numerically the skewness of the matter density field as a function of the dark energy parameters. We characterize today's S_3 value for quintessence and phantom dark energy cosmologies as well as its dependence on the matter density parameter Ω_m0 and the dark energy sound speed c_{s}^2 with accurate numerical fitting. These fits can be used to test cosmology against future high quality data on large scale structure. (arXiv:2202.08355)
Prajwal Hassan Puttasiddappa
Higher-Derivative Screening and UV aspects
In this Tunch I would like to present some aspects of higher derivative screening mechanisms famously known as the Vainstein mechanism. First, we shall see it in the context of extended-BDLCDM, where we employ these mechanisms to screen the BD effects locally so that we reconcile observationally constrained Newton's constant G_N but still maintain BDLCDM cosmology in the cosmological scales. We will realize that higher-order derivatives do not provide a suffiently large gradient to screen BD effects locally [1]. The screening mechanism itself is a result of the domination of dynamics of higher-order operators. In the effective field theory context, we want to see to what extent we can have a predictive theory [2]. So in the second part, our concern will be on the UV aspects of these theories and their implications to macroscopic physics [3].
[1] JCAP 09 (2021) 040 (arXiv:2105.14819). [2] JCAP 11( 2014) 016 (arXiv:1405.5213). [3] JCAP 06 (2018) 039 (arXiv:1712.04019)
Nico Lorenz
Clustering of Gravitational Wave and Supernovae events: a
multitracer analysis in Luminosity Distance Space
Sarah Libanore et al.
view arXiv
Luca Amendola - Non-linear perturbation theory (part 2)
Prajwal Hassan Puttasiddappa - Cosmological Singularity in the Local analysis
Pedro da Silveira Ferreira - Rencontres de Moriond 2022 (Cosmology): Highlights and impressions
In this tunch I will briefly present some of the highlights of the Moriond 2022 Cosmology conference (the 56th edition).
Cancelled.
Luca Amendola - Non-linear perturbation theory (part 1)
Cancelled.
Cancelled.
Alejandro Hernández Arboleda (UFES - PPGCosmo, Brazil) - New test of dark matter theories with galaxy rotation curves
Scalar field theories usually predict the existence of a “fifth force” which essentially codifies the modifications to Newtonian gravity and general relativity of such theories and controls the accelerated expansion of the universe at cosmological scales. In general, these theories make use of screening mechanisms, such as Vainshtein screening, to hide the effects of their modifications at local scales and satisfy solar system tests. Although the screening mechanism is responsible for suppressing the “fifth force” in the vicinity of massive sources, it can be broken inside them. In this tunch I will discuss the results of my investigation dealing with vainshtein screening breaking at the scale of galaxies using rotation curves and several dark matter profiles, focusing on the numerical methods used to study them.
Cancelled.
David Camarena
Challenges for the statistical gravitational-wave method to measure the Hubble constant
Emery Trott, Dragan Huterer
view arXiv
Cancelled.
Rodrigo Von Marttens (Observatório Nacional, Rio de Janeiro) - Testing the consistency of the standard cosmological model
First, we perform a general test of the ΛCDM and wCDM cosmological models by comparing constraints on the geometry of the expansion history to those on the growth of structure. Specifically, we split the total matter energy density, Ω_M , and (for wCDM) dark energy equation of state, w, into two meta-parameters each: one that captures the geometry, and another that captures the growth. We constrain our split models using current cosmological data, including type Ia supernovae, baryon acoustic oscillations, redshift space distortions, gravitational lensing, and cosmic microwave background (CMB) anisotropies. We focus on two tasks: (i) constraining deviations from the standard model, captured by the difference between the geometry and growth parameters, and (ii) investigating whether the S 8 tension between the CMB and weak lensing can be translated into a tension between geometry and growth, i.e. ΔΩ_M ≠ 0, Δw ≠ 0. Lastly, we relax the conventional assumption of a minimal coupling between the DM and DE, to reconstruct a possible interaction in the dark sector in a model-independent way, using data from type Ia supernovae, cosmic chronometers and baryonic acoustic oscillations. According to our analysis, the ΛCDM model is consistent with our model-independent approach at least at 3σ CL over the entire range of redshift studied. On the other hand, our analysis shows that the current background data do not allow us to rule out the existence of an interaction in the dark sector.
Cancelled.
Cancelled.
Prajwal Hassan Puttasiddappa - Fifth force, Dark matter, and Gravitational Waves
It was shown by L.Amendola, J.Rubio, C.Wetterich (2018) that a long-range, attractive fifth force, stronger than gravity could produce primordial black holes (PBH), and along with S.Savastano (2019) they also argued that primordial dark matter halos could be formed. The model contains a beyond standard model fermion field and a scalar field which mediates the fifth force between the former. Interestingly, unlike conventional PBH which forms before nucleosynthesis, these are formed in the radiation era! According to the estimates, it is plausible that these objects constitute the entire dark matter component in the universe. With their distinctive mass range and density, we show that they fall within the sensitivity range of future gravitational wave detectors. The presentation is mainly based on the original works (arXiv: 1711.09915, 1906.05300) along with a small portion of gravitational waves (arXiv: 1706.02111, 1207.5359).
Luca Amendola
Measurements of the Hubble Constant: Tensions in Perspective
Wendy L. Freedman
view arXiv
Raquel Fazolo
A model-independent reconstruction of dark energy to very high redshift
Adam Moss, Edmund Copeland, Steven Bamford, Thomas Clarke
view arXiv
Summer term 21:
Lorenzo Pizzuti - Testing screening mechanisms with mass profiles of galaxy clusters
Testing screening mechanisms with mass profiles of galaxy clusters Abstract: Galaxy clusters constitute a powerful tool to investigate modification of gravity at cosmological scales; in particular, with the combination of cluster’s mass profiles derived with lensing and internal kinematic analyses, it is possible to constrain departures from General Relativity in a complementary way with respect to other cosmological and astrophysical probes. In this context, I will present MG-MAMPOSSt, a code to constrain modified gravity models by reconstructing the mass profile with the kinematic of cluster's member galaxies, along with recent results and forecasts on two classes of models characterized by different screening mechanisms, namely chameleon and Vainshtein screening. I will show the capability of the method when combined with lensing data as well as some criteria to control possible systematics in view of the application to the data of upcoming imaging and spectroscopic surveys.
Martin Kärcher and Manuel Wittner - There is Something Wrong in the Action…
Reasonable modified gravity theories, apart from resembling general relativity on solar system scales, must satisfy some further conditions in order to be consistent. One such condition is stability, i.e. the absence of ghosts, gradient instabilities and tachyons. In this tunch, we will elaborate on the exorcism of such ghosts; that is, using the example of the novel inverse-Ricci gravity, we will explain how to find conditions on the action level that render the theory stable. Special attention will be paid to finding a proper gauge-choice with which the analysis can be performed.
Roberto Capuzzo-Dolcetta - Violent dynamics in the Galactic nucleus
The central region of our Galaxy (as well as of most of others) is site of violent activity and constitutes an unique place to set constraints to various physical theories. In this talk I will give a short overview of the strong dynamics of stars around the Sgr A* massive object at the center of the Milky Way and present some results about an intriguing hypothesis concerning the growth of the central supermassive black hole observed in many galaxies including our Galaxy.
Ziyang Zheng - Constraints on the fraction of early dark energy in the pre- andpost-recombination epochs
Early dark energy (EDE) models present around the matter-radiation equality time $t_{eq}$ have been proposed as a promising solution to the famous $H_0$ tension (arXiv:1301.5279, arXiv:1811.04083), at the cost of increasing the large scale structure (LSS) formation processes with respect to the $\Lambda_{CDM}$ model. This issue could in principle be alleviated by introducing a non-negligible EDE component in the post-recombination era. In this work we constrain the fraction of early dark energy during the whole cosmic history, with the EDE component represented by a fluid parametrization and also a more model-independent approach based on the binning of the EDE density. We also investigate the LSS tension when studied in terms of the recently proposed $\sigma_{12}$ and $S_{12}$ parameters.
Replaced by extracurricular cosmology seminar.
Cancelled.
Guilherme Brando - Fully relativistic predictions in Horndeski gravity from standard Newtonian N-body Simulations
The N-body gauge allows the introduction of relativistic effects in Newtonian cosmological simulations. Here we extend this framework to general Horndeski gravity theories, and investigate the relativistic effects that the scalar field introduces in the matter power spectrum at intermediate and large scales. In particular, we show that the kineticity function at these scales enhances the amplitude of the signal of contributions coming from the extra degree of freedom. Using the Quasi-Static Approximation (QSA), we separate modified gravity effects into two parts: one that only affects small-scale physics, and one that is due to relativistic effects. This allows our formalism to be readily implemented in modified gravity N-body codes in a straightforward manner, e.g., relativistic effects can be included as an additional linear density field in simulations. We identify the emergence of gravity acoustic oscillations (GAOs) in the matter power spectrum at large scales, k∼10^−3−10^−2 Mpc−1. GAO features have a purely relativistic origin, coming from the dynamical nature of the scalar field. GAOs may be enhanced to detectable levels by the rapid evolution of the dark energy sound horizon in certain modified gravity models and can be seen as a new test of gravity at scales probed by future galaxy and intensity-mapping surveys.
Cancelled.
Walter Riquelme - Primordial non-Gaussianity from the angular clustering: prospects for DES
Primordial non-Gaussianity (PNG) is claimed to be a smoking gun to differentiate between the vast collection of inflationary models. The current constraints on PNG, parametrized by fNL, are obtained from the CMB, which has reached the cosmic variance limit. A promising way to look for PNG is using the Large Scale Structures (LSS) of the universe, with the potential of breaking the sigma(fNL)~1 barrier. In this talk, I will present an analysis of the methods for looking at Primordial non-Gaussianity in the Large Scale Structure of the Universe, with the main focus on the Dark Energy Survey (DES). We use the Angular Correlation Function (ACF) and show how it is modified by Primordial Non-Gaussianity via a scale-dependent bias (Dalal et al. 2008). One of the main focus of the work is on the integral constraint (IC) condition, which is found to be key to obtain unbiased PNG constraints. The IC corrects for the fact that the mean density of the Universe is measured from the observed galaxies. The methods are analyzed and optimized for two kinds of simulations: COLA mocks that follow the DES angular and redshift distribution and N-Body simulations with non-Gaussian initial conditions. With the aforementioned simulations, we focus on optimizing the methods to constraint fNL to obtain precise and unbiased results, preparing the ground for the DES Y3 data. We highlight the potential that DES and future photometric surveys could have in constraining PNG.
Jenny Wagner - Matter Matryoshkas – The emergence of self-similar cosmic structures
From galaxy clusters to star clusters structures resemble each other like Matryoshka dolls. While self-similarity establishes a unified, scale-independent description of cosmic structures, we have not fully grasped its emergence yet. Instead, heuristic functions like the Navarro-Frenk-White profile are fitted to mass densities of observed structures in the Newtonian framework. This talk shows that the fitting functions are set by the interactions generating the structure and that they represent the smoothed distribution of its constituents. Forgoing resolution and boundary effects, structure morphologies caused by gravitation in general relativity can already be found in works on self-similar inhomogeneous spacetimes from the 1970s and 80s. Thus, any structure morphology dominated by scale-free gravitational interactions is of self-similar type and can be understood in terms of fundamental principles.
Literature:
https://www.worldscientific.com/doi/epdf/10.1142/S0218271820430178
https://www.sciencedirect.com/science/article/abs/pii/0003491683900246
C. Wetterich
Cosmology from pregeometry
C. Wetterich
view arXiv
Raquel Fazolo
Evolution of hierarchical clustering in the CFHTLS-Wide since z ∼ 1
M. Wolk, H. J. McCracken, S. Colombi, J. N. Fry, M. Kilbinger, P. Hudelot, Y. Mellier and O. Ilbert
view arXiv
Cancelled.
Prajwal Hassan Puttasiddappa - “Probing Quantum Nature of Gravity”
Quantizing gravity in conventional way fails theoretically at 2 loop level for pure gravity and at 1 loop with matter. It was also argued that, possibility of detecting a single quanta of gravitation is very less due to our sensitivity limitations. On the other hand, quantum mechanics has fundamental formalism problems. Many people tried to answer these two questions together by Gravitizing Quantum Mechanics. But, could we actually see if gravity participates in quantum mechanical experiments? What are the directions in this aspect? Can we finally see the quantum nature of gravity? That too on a low energy table-top experiment? We will briefly explore the recent experimental directions.
Based on:
Tabletop experiments for quantum gravity: a user's manual
Daniel Carney, Philip C. E. Stamp and Jacob M. Taylor
view arXiv
Underground test of gravity-related wave function collapse
Sandro Donadi et al.
Nature Phys. 17 (2021) 1, 74-78
David Camarena
On the use of the local prior on the absolute magnitude of Type Ia supernovae in cosmological inference
David Camarena and Valerio Marra
view arXiv
Winter term 20/21:
Ziyang Zheng - China
Ice & Snow festival, natural landscapes, lantern festival, hot springs, cherry blossoms, Ice houses….. Welcome to my cultural tunch! I would like to introduce my hometown-the northeast of China, as well as my previous institute in southern China-USTC, have a look at the differences between northern & southern china!
Prajwal Hassan Puttasiddappa - India: Perspectives and Science Undercurrent
I will introduce you to some of India's contributions to the field of Physics and Mathematics with a jot of personal journey and inspirations. I will convey some facts about my previous university education and their research interests. The idea is to share the “Indian” perspective on nature and its phenomena.
Raquel Fazolo - Brazil
Abdolali Banihashemi - A hint from Hubble: Does H_0 tension reveal the secrets of dark energy?
In this talk we will have a brief review on H_0 tension and then we investigate, theoretically and observationally, a model in which dark energy emerges as a critical phenomenon.
Manuel Wittner - Implications of string theory on the QCD axion
The QCD axion is arguably the most prominent solution to the strong CP problem. On the other hand, string theory as a candidate for an underlying theory beyond the standard model offers a plethora of axion-like fields, one of which could indeed play the role of the QCD axion. In general, however, it seems difficult to construct stringy models that contain a QCD axion in the preferred parameter range. In this tunch I am going to elaborate on the difficulties one has to overcome when constructing stringy axion models and on the phenomenological consequences of such models for the QCD axion and the early universe.
Martin Kärcher - Riemann-Einstein-Inverse Gravity
The current FLRW-model makes use of a cosmological constant which enters the Einstein field equations in order to explain observations of an accelerated expansion of the Universe. However, the cosmological constant is not flawless and brings some issues along the way, for example, the fine-tuning problem. There exists a whole realm of alternatives to the FLRW-model, trying to fit observations without the necessity of a cosmological constant. I investigated a specific modification of General Relativity by adding a scalar to the action, build from the inversion of the Einstein tensor and the Riemann tensor (similar to this reference arxiv.org/abs/2006.04209). I carried out a linearized stability analysis for the two cases in which I searched for critical points in the accelerating regime. To wrap up the overview of the dynamical system, numerical solutions were derived.
Victor Bosca - Modelling accurately the microlensing of supernovae in a lumpy universe
Needless to say that the nature of dark matter is one of the biggest questions of modern physics. The possibility that dark matter is (at least partially) made of compact objects is a very appealing idea. One way to probe compact objects, such as primordial black holes, beyond the Solar mass is via supernova lensing. In this project we model the probability density function of microlensing magnification P(A|f), given that a fraction f of dark matter is made of compact objects. We include many effects, such as the complex distribution of dark matter in haloes, the subtle effect of lens-lens coupling and the finite size of sources.
Cristian Moreno Pulido - Renormalized ρ vac without m^4 terms
The cosmological constant (CC) term, Λ, in Einstein's equations has been for some three decades a fundamental buildingblock of the concordance or standard ΛCDM model of cosmology. Even though the model is not free of fundamental problems, they have not been circumvented by any alternative dark energy proposal either. However, an interesting alternative is that the vacuum energy is a “running quantity” in quantum field theory in curved spacetime. Several works have shown that this is option can compete with the ΛCDM with a rigid Λ term. The so-called, “running vacuum models” (RVM) are characterized by a vacuum energy density, ρvac, which is evolving with time as a series of even powers of the Hubble parameter and its time derivatives. This form has been motivated by renormalization group arguments in previous works. In this talk we show how to compute the renormalized energy-momentum tensor with the help of adiabatic regularization procedure as it has been done in arXiv/2005.03164 (Eur.Phys.J.C(2020)80:692). The final result is a RVM-like form of the vacuum energy, with ρvac(H) being a constant term plus others ∼H2 and ∼H4. Besides, it does not carry dangerous terms proportional to m4, the quartic powers of the masses of the fields, which are a well-known source of exceedingly large contributions.
Alejandro Hernandez - Palatini-type gravity and dark matter in galaxies
From the weak field limits of Palatini f(R) gravity and Eddington-inspired-Born-Infeld gravity (EiBI), we test the possibility of these theories to either replace dark matter or change the amount of dark matter in galaxies. We consider the SPARC galaxy sample. However, instead of considering individual galaxy fits, we use here a normalized missing velocity approach, as here detailed. The method is based on the data density in the plane rn × δv, where rn is the normalized galaxy radius and δv stands for the normalized difference between the observed and the baryonic circular velocity. As here discussed, this plane is useful for testing the dark matter or non-Newtonian model contribution to the rotation curve, it commonly depends on one less model parameter (due to the normalization), it reduces the dependence on baryonic details of individual galaxies (since only the average sample behavior is tested) and promptly yields the model overall behaviour: providing hints on which type of galaxies the proposed model has most difficulties on addressing; or if the proposed model is simply not compatible with observational data. For the models here tested, we show that: i) considering their theoretical basis: a. These models can enhance thin disk stability, and b. the NFW dark matter halo cannot be in general used with them, since it implies an unbounded force; ii) without any kind of dark matter, these models are in general incompatible with galaxy rotation curve data (they would require unrealistic stellar disks); iii) (expectation) if used together with a phenomenologically successful dark matter halo (the Burkert profile), the models are compatible with null or close to null non-Newtonian behaviour in galaxies; that is, we find no evidence that the non-Newtonian corrections could improve the Burkert profile success.
Raquel Fazolo
Interacting Dark Energy in a closed universe
Eleonora Di Valentino, Alessandro Melchiorri, Olga Mena, Supriya Pan, Weiqiang Yang
view arXiv
David Camarena
Two-point statistics without bins: A continuous-function generalization
of the correlation function estimator for large-scale structure
Kate Storey-Fisher, David W. Hogg
view arXiv
Summer term 20:
Adrià Gómez-Valent - Boosting MonteCarlo sampling with a non-Gaussian fit
We propose a new method, called MonteCarlo Posterior Fit, to boost the MonteCarlo sampling of likelihood (posterior) functions. The idea is to approximate the posterior function by an analytical multidimensional non-Gaussian fit. The many free parameters of this fit can be obtained by a smaller sampling than is needed to derive the full numerical posterior. In the examples that we consider, based on supernovae and cosmic microwave background data, we find that one needs an order of magnitude smaller sampling than in the standard algorithms to achieve comparable precision. This method can be applied to a variety of situations and is expected to significantly improve the performance of the MonteCarlo routines in all the cases in which sampling is very time-consuming. Finally, it can also be applied to Fisher matrix forecasts, and can help solve various limitations of the standard approach.
This discussion is based view arXiv
Winter term 19/20:
Cancelled.
Christof Wetterich - The great emptiness at the beginning of the Universe
This informal discussion concerns the proposal of the great emptiness as a possible beginning of the Universe in the infinite past of physical time. In the beginning, particles are very rare and effectively massless. Only expectation values of fields and average fluctuations characterize the lightlike vacuum of this empty Universe. Our observed inhomogeneous Universe can be extrapolated backwards to the lightlike vacuum in the infinite past, and therefore can have lasted eternally. There is no physical big bang singularity. Standard inflation models admit a primordial flat frame for which spacetime is flat in the infinite past.
This discussion is based view arXiv
David Camarena - Exploring the cosmic distance ladder
The cosmic distance ladder is one of the most powerful ways to constraint the Hubble constant at local scales. In this tunch, we will explore two novel approximations to the cosmic distance ladder assessing mainly the impact of the deceleration parameter and the role that BAO distances plays in the Hubble tension problem.
David Camarena
Cosmological model insensitivity of local H0 from the Cepheid distance ladder
S. Dhawan, D. Brout, D. Scolnic, A. Goobar, A.G. Riess, V. Miranda
view arXiv
Cancelled due to overlap with the Cosmology Seminar.
Adrià Goméz-Valent
Concerns regarding the use of black hole shadows as standard rulers
S. Vagnozzi, C. Bambi and L. Visinelli
view arXiv
Raquel Fazolo - TBA
Christmas break
Christmas break
Arvid Weyrauch - TBA (Christmas Tunch)
Raquel Fazolo
Is the Hubble diagram of quasars in tension with concordance cosmology?
Hermano Velten, Syrios Gomes
view arXiv
Luca Amendola
Challenging a Newtonian prediction through Gaia wide binaries
X. Hernandez, R. A. M. Cortés, C. Allen, R. Scarpa
view arXiv
Ana Marta Pinho
Wrapping up the decade - the discoveries and the tensions
Cancelled due to overlap with the Cosmology Seminar.
Josue Motoa Manzano (Universidad de Valle, Cali, Colombia; visitor at ITP, Universität Heidelberg) - “De Sitter symmetries and inflationary correlators in parity violating scalar-vector models”
We use conformal symmetry to constrain the shape of inflationary correlators in the presence of long-lived vector field perturbations. Applying conformal Ward identities, we derive general expressions, up to amplitudes and normalization factors, for the two and three-point correlators in the presence of vector fields mediated by the interaction f(\phi)\left(F_{\mu \nu}F^{\mu \nu}+\alpha\tilde{F}_{\mu \nu}F^{\mu \nu}\right), where f(\phi) is a suitable coupling function between the scalar and the vector field. This interaction allows for isotropy and parity symmetry breaking and is consistent with super horizon conformal symmetry.
Manuel Wittner
Trans-Planckian Censorship and Inflationary Cosmology
Alek Bedroya, Robert Brandenberger, Marilena Loverde, Cumrun Vafa
view arXiv
Leonardo Giani (UFES, Brazil; visitor at ITP, Universität Heidelberg) - “Late-times asymptotic equation of state for a class of nonlocal theories of gravity”
We investigate the behavior of the asymptotic late-times effective equation of state for a class of nonlocal theories of gravity. These theories modify the Einstein-Hilbert Lagrangian introducing terms containing negative powers of the d'Alembert operator acting on the Ricci scalar. We find that imposing vanishing initial conditions for the nonlocal content during the radiation-dominated epoch implies the same asymptotic late-times behavior for most of these models. In terms of the effective equation of state of the universe, we find that asymptotically ωeff→−1, approaching the value given by a cosmological constant. On the other hand, unlike in the case of ΛCDM, the Hubble factor is a monotonic growing function that diverges asymptotically. We argue that this behavior is not a coincidence and discuss under which conditions this is to be expected in these nonlocal models.
Based on view arXiv
Ana Marta Pinho
Planck evidence for a closed Universe and a possible crisis for cosmology
Eleonora Di Valentino, Alessandro Melchiorri and Joseph Silk
Manuel Wittner (ITP, Universität Heidelberg) - “Challenges of Stringy Quintessence: the F-term Problem”
In light of the recently proposed de Sitter-swampland conjecture, string theory seems to favor dynamic dark energy models like quintessence over a cosmological constant to drive the late time acceleration of the universe. In this talk I argue, however, that stringy quintessence models are difficult to realize as well. I elaborate on the light volume problem and identify a so called “F-term problem”: The positive energy density of standard-model SUSY breaking is higher than the depth of all known negative contributions. Resolving this issue would require new, unknown contributions to the vacuum energy and therefore necessitates further analysis.
(Based on the recent paper view arXiv )
Arvid Weyrauch
Obtaining Precision Constraints on Modified Gravity with Helioseismology
Ippocratis Saltas, Ilídio Lopes
view arXiv
Summer term 19:
Giorgio Laverda (ITP, Universität Heidelberg) - “The entropic theory of gravity”
Since its first appearance in 2010, the theory of entropic gravity has been widely debated. The interpretation of gravity as an entropic force appears to be capable of describing Newtonian gravity and general relativity. In this talk I will introduce the basic principles of the theory while highlighting the controversial points.
Canceled due to overlap with cosmology seminar.
Jakob Henrichs (ITP, Universität Heidelberg) - “Milky Way rotation curve in modified gravity”
Rotation curves of galaxies provide a strong evidence for dark matter and can be used to test modified gravity theories. In this talk I show the results of an analysis of the Milky Way rotation curve in modified gravity. I use the Horndeski Theory to derive the gravitational potential and two different dark matter models for the analysis.
Oliver Fabio Piattella
Can the quantum vacuum fluctuations really solve the cosmological constant problem?
Gabriel R. Bengochea, Gabriel León, Elias Okon, Daniel Sudarsky
view arXiv
Adrià Gòmez-Valent (ITP, Universität Heidelberg) - “Quantifying the evidence for the current speed-up of the Universe with low and intermediate-redshift data. A more model-independent approach”
According to cosmological low and intermediate-redshift data, what is the statistical evidence in favor of the current speed-up of the Universe? Although this question seems to be kind of outdated, a quick review to the many papers that address this pivotal question in the literature tells us that the answer is not obvious at all. Determining the value of the deceleration parameter in the context of particular cosmological models, concrete parametrizations of the cosmographical quantities, or even using truncated cosmographical expansions in which the truncation order is set in an ad hoc way can lead to biased estimations of the value of the deceleration parameter at present, q0, and its uncertainty. In this talk, which is based on arXiv:1810.02278, JCAP 05 (2019) 026, I present a new determination of q0 obtained with data from the Pantheon+MCT compilation of supernovae of Type Ia, cosmic chronometers and baryon acoustic oscillations. I apply the so-called Weighted Function Regression method to reconstruct q(z) more model-independently than many analyses in the literature, improving in this way the usual cosmograhical approach. We will see, for instance, that using only the first two data sets the level of evidence for the current positive acceleration of the universe is only moderate (using Jeffreys' scale and jargon), contrary to the more than 17\sigma-evidence found in the framework of the standard flat LCDM model. The level of evidence grows up to the very strong one when BAO data are also considered, giving rise to q0= -0.60 +- 0.10, with a deceleration-acceleration transition redshift at z_t = 0.80 +- 0.10. The jerk is also reconstructed, although unfortunately current data is unable to set stringent constraints to this cosmographical parameter.
Giorgio Laverda
Strong gravity signatures in the polarization of gravitational waves
S. Shankaranarayanan
view arXiv
Julius Wons
Gravitational wave standard sirens and cosmological parameter measurement
Xin Zhang
view arXiv
Arvid Weyrauch & Manuel Wittner (ITP, Universität Heidelberg) - “Cosmology, philosophically speaking” (Collective Discussions)
As researchers we tend to find answers using the scientific method. However, some questions may not have an answer but still spark a lot of different thoughts and perspectives. In this tunch, we will address some of these questions, from the nature of time to its beginning.
Leonardo Giani
Is Gravity Actually the Curvature of Spacetime?
Sebastian Bahamonde, Mir Faizal
view arXiv
Ana Marta Pinho
Black hole shadow as a standard ruler in cosmology
Oleg Yu. Tsupko, Zuhui Fan, Gennady S. Bisnovatyi-Kogan
view arXiv
Oliver Piattella (UFES, Brazil; visitor at ITP, Universität Heidelberg) - “Neutron stars masses in R^2 gravity”
We investigate the mass-radius (M-R) relation for neutron stars in f(R) = R + R^2 gravity. We adopt a spherically symmetric metric and a SLy equation of state. We stress how in f(R) gravity it is possible to define mass in many inequivalent ways which are nonetheless all equivalent in General Relativity. We investigate the role of the extra scalar degree of freedom in the definition of the masses and in the features of the M-R relation.
Adrià Gomez-Valent
Recasting H0 tension as OmegaM tension at low z
Eoin Ó Colgáin
view arXiv
Leonardo Giani
How to Hide a Cosmological Constant
S. Carlip
view arXiv
Luca Amendola (ITP, Universität Heidelberg) - “Fisher matrix for multiple tracers (1904.00673)”
I show how to obtain constraints on β, the ratio of the matter growth rate and the bias that quantifies the linear redshift-space distortions, that are independent of the cosmological model, using multiple tracers of large-scale structure. For a single tracer the uncertainties on β are constrained by the uncertainties in the amplitude and shape of the power spectrum, which is limited by cosmic variance. However, for two or more tracers this limit does not apply, since taking the ratio of power spectra cosmic variance cancels out, and in the linear (Kaiser) approximation one measures directly the quantity (1+β1μ2)2/(1+β2μ2)2, where μ is the angle of a given mode with the line of sight. I provide analytic formulae for the Fisher matrix for one and two tracers (up to quadrature) and quantify the signal-to-noise ratio needed to make effective use of the multiple-tracer technique. I also forecast the errors on β for a survey like Euclid.
Xuewen Liu
21-cm observations and warm dark matter models
Alexey Boyarsky, Dmytro Iakubovskyi, Oleg Ruchayskiy, Anton Rudakovskyi, Wessel Valkenburg
view arXiv
Ana Marta Pinho (ITP, Universität Heidelberg) - “Cosmological Information Flow”
The current state of Cosmology is a strong statistical preference for the LCDM model although with some unsolved problems. The recent data tensions raise now the doubt about the validity of the data pipeline and/or the LCDM model. Information theory provides some very useful tools that can measure the amount of information given by the data. Also these tools can be related to what it is commonly used in the literature as uncertainty measurements. In this talk I will present this on going work that tries to understand how information flows in the cosmological framework.
Ana Marta Pinho
Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM
Adam G. Riess, Stefano Casertano, Wenlong Yuan, Lucas M. Macri, Dan Scolnic
view arXiv
Manuel Wittner
Probing modified gravity in cosmic filaments
Alex Ho, Max Gronke, Bridget Falck, David F. Mota
view arXiv
Winter term 18/19:
Collective Discussions
Jiaming Zhao
The local and distant Universe: stellar ages and $H_0$
Raul Jimenez, Andrea Cimatti, Licia Verde, Michele Moresco, Benjamin Wandelt
ePrint: arXiv: 1902.07081
Ana Marta Pinho
The observable $E_g$ statistics
Basundhara Ghosh, Ruth Durrer
ePrint: arXiv: 1812.09546
Ana Marta Pinho & Manuel Wittner (ITP, Universität Heidelberg) - “Cosmology, philosophically speaking” (Collective Discussions)
As researchers we tend to find answers using the scientific method. However, some questions may not have an answer but still spark a lot of different thoughts and perspectives. In this tunch, we will address some of these questions, from infinity to the beginning of the universe as well as the anthropic principle or the nature of time and space.
Julius Wons
Using a black hole to weigh light: can the Event Horizon Telescope yield new information about the photon rest mass?
Robert P. Cameron
ePrint: arxiv 1902.02209
Jiaming Zhao
Cosmological constrains from the Hubble diagram of quasars at high redshifts
Guido Risaliti and Elizabeta Lusso
ePrint: arXiv: 1811.02590
Oliver Piattella
On the cosmological problem
Lucas Lombrasier
ePrint: arXiv: 1901.08588
Manuel Wittner (ITP, Universität Heidelberg) - “Introduction to flux compactifications and moduli stabilization”
Kaluza-Klein compactifications are the bridge between 10D string theory and our 4D world. Through the large number of possibilities of this compactified internal space, a vast landscape of string vacua arises, one of which might represent our Universe. In this talk I will introduce basic knowledge about flux compactifications and the stabilization of moduli, which are necessary steps in order to obtain realistic 4D models.
Ana Marta Pinho
Could Solar Radiation Pressure Explain 'Oumuamua's Peculiar Acceleration?
Shmuel Bialy, Abraham Loeb
ePrint: arXiv: 1810.11490
Xuewen Liu
On the road to per-cent accuracy: nonlinear reaction of the matter power spectrum to dark energy and modified gravity
Matteo Cataneo, Lucas Lombriser, Catherine Heymans, Alexander Mead, Alexandre Barreira, Sownak Bose, Baojiu Li
ePrint: arXiv: 1812.05594
Salvador Ramirez (ITP, Universität Heidelberg) - “Deser-Woodard Model and its Reconstruction Problem”
Nonlocal modifications of gravity arise when one attempts to see the effects of radiative corrections at the classical level. These corrections are often impractical, they are difficult to calculate and depend on the method used and assumptions about the source of the corrections. To overcome this we can take a top-down approach, and construct an action with nonlocal terms based on their properties. Deser-Woodard model follows this approach and constructs an action with one of the simplest nonlocal terms and an arbitrary function. We will discuss the reconstruction problem of this model and provide a method to reproduce any given background. Since the model differs with $\Lambda$CDM at the perturbation level, we can test the model with observational data.
Jiaming Zhao
KiDS+GAMA: Constraints on Horndeski gravity from combined large-scale structure probes
Alessio Spurio Mancini, Fabian Köhlinger, Benjamin Joachimi, Valeria Pettorino, Björn Malte Schäfer, Robert Reischke, Samuel Brieden, Maria Archidiacono et al.
ePrint: arXiv: 1901.03686
Julius Wons
Melanopogenesis: Dark Matter of (almost) any Mass and Baryonic Matter from the Evaporation of Primordial Black Holes weighing a Ton (or less)
Logan Morrison, Stefano Profumo, Yan Yu
ePrint: arXiv: 1812.10606
Xuewen Liu (Institute of Theoretical Physics, CAS, Peking) - Cultural Tunch
Christmas break
Christmas break
Collective Discussions
Collective Discussions
Jiaming Zhao
Cosmological parameter constraints for Horndeski scalar-tensor gravity
Johannes Noller, Andrina Nicola
ePrint: arXiv: 1811.12928
Guillem Domenèch
Early Dark Energy Can Resolve The Hubble Tension
Vivian Poulin, Tristan L. Smith, Tanvi Karwal, Marc Kamionkowski
ePrint: arXiv: 1811.04083
Collective Discussions
Julius Wons
Primordial Black Holes With Multi-Modal Mass Spectra
Bernard Carr, Florian Kuhnel
ePrint: arXiv: 1811.06532
Salvador Ramirez
Current Signs of Dynamical Dark Energy
Joan Sola Peracaula, Adria Gomez-Valent, Javier de Cruz Perez
ePrint: arXiv: 1811.03505.pdf
Julius Wons (ITP, Universität Heidelberg) - “Are primordial standard clocks really standard?”
Excited heavy fields during the creation of the primordial curvature perturbation leave oscillatory patterns in the power spectrum. These patterns can be used to distinguish between different primordial scenarios (inflation, bounce, …) and are therefore called primordial standard clocks. I will show that this is in general not true if the mass of the heavy field is time dependent or when having non-canonical kinetic terms.
Manuel Wittner
On the Cosmological Implications of the String Swampland
Prateek Agrawal, Georges Obied, Paul J. Steinhardt, Cumrun Vafa
ePrint: arXiv: 1806.09718
Stefano Savastano
The Primordial Black Hole Dark Matter - LISA Serendipity
N. Bartolo, V. De Luca, G. Franciolini, M. Peloso, A. Riotto
ePrint: arXiv: 1810.12218
Xue-Wen Liu
The End of Cosmic Growth
Eric V. Linder, David Polarski
ePrint: arXiv: 1810.10547
Public Holiday
Dario Bettoni
Dark energy after GW170817, revisited
Edmund J. Copeland, Michael Kopp, Antonio Padilla, Paul M. Saffin, Constantinos Skordis
e-Print: arXiv:1810.08239
Ana Marta Pinho
H0 Tension: Response to Riess et al arXiv:1810.03526
Tom Shanks, Lucy Hogarth, Nigel Metcalfe
e-Print: arXiv:1810.07628
Manuel Wittner (ITP, Universität Heidelberg) - Cultural Tunch
Summer term 18:
Collective Journal Club
Akshay Rana (University of Delhi, India)- “Novel ways to constrain Graviton mass and spatial curvature”
In cosmology, it always remains a topic of great interest to constrain cosmological parameters by using different approaches and observational probes to confirm their consistency. In the same direction, I will present two novel ways that can be used to limit the mass of the Graviton and the spatial curvature of the space. My talk will be focused on two different aspects of present precision cosmology,
1) Firstly, I will discuss about the graviton, which is a massless particle in GR while considered to be massive in some alternative models of GR like; Massive gravity theories. I will present a novel approach that can be used to put stringent constraints on its mass using galaxy clusters.
2) Similarly, the estimation of spatial curvature of the Universe is also one of the most fundamental issue of modern cosmology. I will discuss a model-independent approach to test the curvature of space by using statistical features of strong gravitational lensing.
Collective Journal Club
Davi C. Rodrigues(Federal University of Espirito Santo, Brazil)-“Absence of a fundamental acceleration scale in galaxies”
The Radial Acceleration Relation confirms that a nontrivial acceleration scale a0 can be found from the internal dynamics of several galaxies. The existence of such a scale is not obvious as far as the standard cosmological model is concerned, and it has been interpreted as a possible sign of modified gravity. We consider 193 high-quality disk galaxies and, using Bayesian inference, we show that the probability of existence of a fundamental acceleration is essentially zero: the null hypothesis is rejected at more than 10σ. We conclude that a0 is of emergent nature. In particular, the MOND theory, a well-known alternative to dark matter that is based on the existence of a fundamental acceleration scale, or any other theory that behaves like it at galactic scales, is ruled out as a fundamental theory for galaxies at more than 10σ.
Elena Sellentin (Geneva University)- “Objective Bayesian analysis of neutrino masses and hierarchy”
Given the precision of current neutrino data, priors still impact noticeably the constraints on neutrino masses and their hierarchy. To avoid our understanding of neutrinos being driven by prior assumptions, we construct a prior that is mathematically minimally informative. Using the constructed uninformative prior, we find that the normal hierarchy is favoured but with inconclusive posterior odds of 5.1:1. Better data is hence needed before the neutrino masses and their hierarchy can be well constrained. We find that the next decade of cosmological data should provide conclusive evidence if the normal hierarchy with negligible minimum mass is correct, and if the uncertainty in the sum of neutrino masses drops below 0.025 eV. On the other hand, if neutrinos obey the inverted hierarchy, achieving strong evidence will be difficult with the same uncertainties. Our uninformative prior was constructed from principles of the Objective Bayesian approach. The prior is called a reference prior and is minimally informative in the specific sense that the information gain after collection of data is maximized. The prior is computed for the combination of neutrino oscillation data and cosmological data and still applies if the data improve.
Collective Journal Club
Gerasimos Belegrinos (ITP, Universität Heidelberg)-“Why not two scalars? ”
Scalar-Tensor theories are arguably the largest known and most widely used models of modified gravity due to their combination of simplicity and extensive range of applications. The recent gravitational wave/ gamma ray bursts detection seems to indicate that a subclass of simplest Horndeski theories respects the constraints set on the gravitational waves speed. One way to go further is to take into account one additional scalar degree of freedom. In my work I consider to this purpose linear pertubation theory for a Biscalar-Tensor theory. The modified gravity quantities (effective gravitational constant, anisotropic stress-slip and weak lensing potential) are derived using the quasi-static approximation. In my talk I will present some of the results achieved that might have theoretical and observational interest. Finally I will present a way for testing an approximation performed while solving the modified growth rate.
Public Holiday
Caroline Heneka (SCUOLA NORMALE SUPERIORE, Pisa)-“The nature of modifications to gravity: 21cm to the rescue?”
For this tunch I will briefly review some basics of both the global 21cm signal and 21cm intensity mapping at high redshifts (of reionization and beyond). I will continue to discuss the recent measurement of the global 21cm signal by EDGES, and conclude with the prospects of measuring general modifications of gravity with intensity mapping.
Collective Journal Club
Public Holiday
Group Discussion
Collective Journal Club
arXiv 1804.04320
arXiv 1804.09206
Winter term 17/18:
Group Discussion
Jenny Wagner (ITA, Heidelberg University)-“A model-independent approach to gravitational lensing”
Strong gravitational lenses can map an extended background source to several highly distorted and magnified images. Analysing the properties of those images yields important information about the distribution of the lensing mass and the background source. Common approaches to reconstruct the source or the lensing mass distribution model the global properties of the source and the lens. They obtain a consistent description of the entire configuration by refining the model until it matches the observation to a predefined precision. We develop a new approach to infer local properties of the gravitational lens and to reconstruct the source using only the properties of the multiple images without assuming a lens or a source model. In the talk, I will introduce the method and its calibration by simulated lensing configurations, show its application to the galaxy-cluster-scale gravitational lens CL0024, and compare the resulting local lens properties to those obtained by two different lens modeling methods. As our approach relies on fewer assumptions and takes less than a second to yield results that agree to the model-based ones, it is an efficient tool for extracting local lensing properties from large data sets of forthcoming sky surveys.
Collective Journal Club
seminar by Alessandra Silvestri (Instituut Lorentz - Leiden)
Testing gravity with Large Scale Structure: the theoretical side of the challenge
See Seminars page for abstract
Collective Journal Club
Group Discussion
Collective Journal Club
Alefe Almeida(ITP, Heidelberg University)
Martin Pauly, Santiago Casas
Higgs-Dilaton Cosmology: An inflation - dark energy connection constrained by future galaxy surveys
e-Print: arXiv:1712.04956
Alessio Spurio Mancini
Testing (modified) gravity with 3D and tomographic cosmic shear
e-Print: arXiv:1801.04251
Group Discussion
Henrik Nersisyan
Quantum equivalence of f(R)-gravity and scalar-tensor-theories
Michael S. Ruf, Christian F. Steinwachs
e-Print: arXiv:1711.07486
Dario Bettoni
Vainshtein mechanism after GW170817
Marco Crisostomi, Kazuya Koyama
e-Print: arXiv:1711.06661
Adalto R. Gomes - UFMA (Brazil)- “Some results in kink-antikink scattering”
After introduced some motivations related to this topic (see for instance possible connections to bubble collisions [1]), I review some known results from kink-antikink scattering in nonintegrable models, focusing on the main aspects of the scalar field after the collision process: the formation of a bion state or inelastic scattering (1-bounce collision). The nonlinearity leads to the intriguing effect of 2-bounce collisions, observed for a range of initial velocities of the pair kink-antikink. This means that depending on the model, we can have the possibility of the formation of a structure of 2-bounce windows in velocity. Then I discuss a deformed $\phi^4$ model in (1,1) dimensions [2]. Stability analysis leads to a Schroedinger-like equation with a zero-mode and at least one vibrational (shape) mode. For small deformation and for one or two vibrational modes, the observed two-bounce windows in velocity are explained by the standard mechanism of a resonant effect between the first vibrational and the translational modes. With the increase of the deformation, the effect of the appearance of more than one vibrational mode is the gradual disappearance of the initial two-bounce windows. The total suppression of two-bounce windows even with the presence of a vibrational mode offers a counter-example of what expected from the standard mechanism [3]. I end presenting some recent results from kink-antikink scattering in a degenerate vacuum to vacuumless model [4].
[1] J. Braden, J. R. Bonda, L.Mersini-Houghtonc, “Cosmic bubble and domain wall instabilities I: parametric amplification of linear fluctuations”, JCAP03 (2015) 007.
[2] F. C. Simas, Adalto R. Gomes, K. Z. Nobrega, J.C.R.E. Oliveira, ”Suppression of two-bounce win- dows in kink-antikink collisions”, JHEP 1609 (2016) 104.
[3] D.K. Campbell, J.S. shonfeld, C.A. Wingate, “Resonance structure in kink-antikink interaction in $\phi^4$ theory”, Physica D 9 (1983) 1.
[4] F. C. Simas, Adalto R. Gomes, K. Z. Nobrega, “Degenerate vacua to vacuumless model and kink-antikink collisions”, Phys. Lett. B775 (2017) 290.
Cornelius Rampf
Solving the Vlasov equation in two spatial dimensions with the Schrödinger method
arXiv:1711.00140
Guillem Domenech
Stability of Geodesically Complete Cosmologies
arXiv:1610.04207
Lorenzo Pizzuti- “Modified gravity with galaxy cluster mass profiles: from data to simulations”
Abstract: I will provide a brief overview of my work concerning constraints on modified gravity models obtained using galaxy cluster mass profile determinations. In particular, I will present the results of a paper in which we combined the information given by the kinematics of galaxies in clusters with the information provided by lensing analyses for 2 galaxy clusters of the CLASH-CLASH\VLT collaboration to get constraints on f(R) models. In order to discuss the applicability of the proposed method in view of future imaging and spectroscopic surveys, I will further introduce my current study of cosmological simulations, aiming at estimating and calibrating the impact of systematics.
Adria Gomez-Valent
An alternative to the LCDM model: the case of scale invariance
arXiv arXiv:1701.03964
Special JC on Gravitational Waves detection
Caroline Heneka - Strong constraints on cosmological gravity from GW170817 and GRB 170817A - 1710.06394
Martin Pauly - GW170817 Falsifies Dark Matter Emulators - 1710.06168
Ana Marta Pinho - Welcome to the multi-messenger Era! Lessons from a neutron star and the landscape ahead - 1710.05931
Alessio Spurio Mancini - Dark Energy after GW170817 - 1710.05901
Summer term 17:
Martin Pauly (ITP, Heidelberg) - “Predictions of renormalized Higgs inflation”
Abstract: Higgs inflation is a model, that allows to explain inflation with the standard model degrees of freedom by introducing an additional coupling between the Higgs field and gravity. In this talk, I am going to explore the influence of the running of the standard model couplings on the observational predictions of Higgs inflation. In particular, the running of the Higgs-self-coupling and sudden changes in that coupling will be important. These sudden changes can be induced by the effective-field-theory nature of Higgs inflation. I will show that as long as the coupling stays sufficiently large in the inflationary region the predictions are insensitive to the running and become sensitive once the coupling approaches the critical point.
Caroline Heneka
Safely smoothing spacetime: backreaction in relativistic cosmological simulations
arXiv:1706.09309
Javier Rubio
Primordial Black Hole production in Critical Higgs Inflation
arXiv:1705.04861
Cornelius Rampf (ITP, Heidelberg University ) - “Shell-crossing in quasi one-dimensional flow ”
Abstract: So far exact analytic solutions to the cosmological fluid equations existed for initial data that only depend on one space variable. Exact solutions (until shell-crossing) play an important role in cosmology, not only because they are simple but because the breakdown of smooth 3D solution through the development of infinite density caustics begins generically as an almost 1D phenomenon with the formation of pancakes. I present recent work on quasi-one-dimensional (Q1D) flow that depends on all three coordinates but differs only slightly from a strictly 1D flow, thereby allowing a perturbative treatment of shell-crossing using the Euler-Poisson equations written in Lagrangian coordinates. The signature of shell-crossing is then just the vanishing of the Jacobian of the Lagrangian map, a regular perturbation problem. In essence, the problem of the first shell-crossing, which is highly singular in Eulerian coordinates, has been desingularized by switching to Lagrangian coordinates, and can then be handled by perturbation theory. All-order recursion relations are obtained for the time-Taylor coefficients of the displacement field, and it is shown that the Taylor series has an infinite radius of convergence. This allows the determination of the time and location of the first shell-crossing, which is generically shown to be taking place earlier than for the unperturbed 1D flow.
Caroline Heneka
Improving constraints on the growth rate of structure by modelling the density-velocity cross-correlation in the 6dF Galaxy Survey
arXiv:1706.05205
Santiago Casas (ITP, Heidelberg University) - “Non-linear structure formation”
Javier Rubio (ITP, Heidelberg University) - “Scale invariance: connecting inflation and dark energy”
Abstract: Inflation and dark energy share many essential properties. I will show that these two eras can be accommodated into a common framework based on scale invariance. I will discuss the phenomenological consequences of two scenarios based on i) exact scale symmetry and ii) broken scale invariance with symmetry resurgence at UV and IR fixed points.
Henrik Nersisyan
A Nonlocal Approach to the Cosmological Constant Problem
arXiv:1703.09715
Martin Pauly
Primordial black hole constraints for extended mass functions
arXiv:1705.05567
Alefe Almeida(ITP, Heidelberg University) - “ A method for evaluating models that use galaxy rotation curves to derive matter density profiles”
Abstract: There are some approaches, either based on GR or modified gravity that use galaxy rotation to derive the matter density of the corresponding galaxy. In this work, we proposed a test for evaluating them.
Kevin Wolz
Ana Marta Pinho
Stability of fundamental couplings: a global analysis
arXiv:1701.08724
Yves Dirian (Geneva University ) - “A numerical relativity scheme for cosmological simulations”
Abstract: I present a new 3+1 integration scheme which allows one to pass an adaptation of the robustness test to the cosmological context, at least in the case of General Relativity with a pressureless perfect fluid field. As an interesting by-product of this construction, a novel constraint-damping method is obtained.
Viviana Niro
Dario Bettoni
Gravitational Waves in Doubly Coupled Bigravity
arXiv:1703.08016