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29.09.26, 09:30
Large-scale B-mode polarization of the cosmic microwave background (CMB) is a prime target for current and future experiments in search of primordial gravitational waves (PGW). With increasingly sensitive instruments being deployed, secondary B-modes induced by the weak gravitational lensing of CMB photons are becoming an important limitation and need to be mitigated. My talk will cover the...
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29.09.26, 09:50
Galaxy cluster cosmology has proven to be a reliable probe not only for standard LCDM models, but also for testing gravity and modified physics. In this talk, I present my work on a Growth-Geometry split of the matter density parameter (Omega_m) within the context of LCDM, utilizing South Pole Telescope (SPT) and Dark Energy Survey (DES) data. By evaluating which of these two components is...
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29.09.26, 10:05
The epoch of reionisation is a key epoch in the history of our Universe, during which the first stars and galaxies formed, but it is extremely challenging to observe. Better characterisation of the EoR can reduce uncertainties on cosmological parameters like the neutrino mass. Here I describe how kSZ statistics, in particular the kSZ trispectrum and cross-correlation with CMB lensing, can be...
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29.09.26, 10:25
Recent developments in the cosmological collider programme have highlighted the possibility of probing new particle species present during inflation. In these scenarios, the inflaton couples to additional massive fields whose exchange leaves distinctive imprints in primordial correlation functions. In particular, the bispectrum exhibits characteristic momentum dependence controlled by the...
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29.09.26, 10:40
We present a self-consistent joint analysis of the thermal Sunyaev-Zel’dovich (tSZ) power spectrum and cluster number counts (CNC) in which clusters detected above a signal-to-noise (SNR) threshold are masked from the power spectrum and used instead as the CNC sample, so that the two probes act on non-overlapping halo populations. Using synthetic Planck-like data from a halo-painting pipeline,...
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29.09.26, 11:25
Ultralight axions are a well-motivated dark matter candidate whose large de Broglie wavelength suppresses the growth of structure on small scales, making cosmological observations a powerful probe of their existence. Realizing the full constraining power of current and upcoming surveys, however, requires accurate predictions of nonlinear structure formation in mixed cold dark matter–ultralight...
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29.09.26, 11:45
Parity violation provides a new probe of fundamental physics in the primordial Universe. Recent hints of parity-odd signals in large-scale structure motivate a careful connection between primordial parity-violating non-Gaussianity and late-time observables. We derive the parity-odd matter trispectrum at one-loop order, including the effects of nonlinear gravitational evolution. We then extend...
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29.09.26, 12:00
Detecting the global 21-cm signal from Cosmic Dawn and the Epoch of Reionization requires extremely precise calibration, since instrumental systematics can easily mimic or obscure the cosmological signal. In this work, we investigate the numerical stability of the Bayesian calibration pipeline used by the REACH experiment, which models receiver noise using the noise wave formalism. We identify...
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29.09.26, 12:15
We apply for the first time an alternative approach based on the Renormalization Group (RG) formalism, proposed in Rubira and Schmidt 2023, in which the bias parameters become explicitly dependent on the cut-off scale and are naturally suited for EFT-based field-level inference. Specifically, we use the Lagrangian perturbation theory forward-modeling code $\texttt{LEFTfield}$ to generate mock...
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29.09.26, 14:00
Cosmological simulations face a fundamental trade-off between volume and resolution: large boxes are representative of the real Universe, but have insufficient fidelity to model the detailed physics of galaxy formation, while high-resolution hydrodynamic simulations must be run in volumes far too small to be cosmologically representative. Zoom simulations can re-simulate small regions from a...
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29.09.26, 14:20
Source Injection produces synthetic source catalog by running the image reduction pipeline. The process replicates the complicated process from image to catalogs. The synthetic galaxies produced from source injection have similar observational systematics as real galaxies.
When a galaxy sample is selected, it occupies a continuous color space. Then galaxies within this sample may respond...
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29.09.26, 14:40
A question that has gained importance in recent years is how to maximize the cosmological information that can be extracted from observational data.
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Approaches based on summary statistics compress the data into a lower-dimensional representation, thereby losing part of the information. In contrast, the core idea of field-level inference is to use the full overdensity field, bypassing the... -
29.09.26, 14:55
Weak gravitational lensing and photometric galaxy clustering are the two pillars of large-scale-structure cosmology, and both rest on one fragile assumption: that we know the redshift distribution, $n(z)$, of our galaxy samples. In this talk I show that this assumption breaks down in subtle but consequential ways, and present forward-modelling methods to fix it. Galaxies blended in the focal...
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29.09.26, 15:40
We are leading the production of MeerKLASS on-the-fly interferometric imaging data and catalogs for the 10,000 deg2 MeerKLASS UHF survey. My group has focused on the production of continuum imaging and catalogs in UHF (and also L-band over a smaller test field). We are pursuing scientific analyses of multi-wavelength source catalogs, where each radio source is associated with an optical/NIR...
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29.09.26, 16:00
Line intensity mapping (LIM) is emerging as a powerful observational technique to study the large-scale structure across an unprecedented range of cosmic history. By measuring the integrated emission from entire galaxy populations rather than resolving individual sources, LIM complements traditional galaxy surveys and provides a unique view of the Cosmic Web from the nearby Universe to Cosmic...
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29.09.26, 16:20
X-ray binaries (XRBs) are cosmologically significant sources of heating and pre-ionisation in the early Universe, dominating the high-redshift X-ray background throughout Cosmic Dawn and the Epoch of Reionisation (EoR). Population III XRBs are a largely homogeneous population that dominate heating in minihaloes, while Population II X-ray binaries are a highly heterogeneous population, with a...
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30.09.26, 09:35
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30.09.26, 09:50
We report the first measurement of the Hubble constant 𝐻_0 using the stochastic gravitational-wave background arising from binary black hole mergers. This astrophysical background is sensitive to the expansion history of the Universe and, thus, can be used for cosmological parameter inference independently of not only electromagnetic methods, but also gravitational-wave standard siren...
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30.09.26, 10:10
Large-scale structure is a powerful probe of dark matter beyond the standard cold paradigm, since even a subdominant warm component can leave observable signatures through its free-streaming effects. In mixed dark matter cosmologies, where cold and warm components evolve jointly, these effects generate not only total density fluctuations but also relative density and velocity perturbations...
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30.09.26, 10:25
Testing the expansion history beyond the redshift range densely sampled by Type Ia supernovae requires independent distance probes with distinct astrophysical systematics. Wide-field time-domain surveys now deliver light curves for hundreds of thousands of quasars, making AGN variability a viable survey-scale distance indicator via the optical/UV variability–luminosity anti-correlation: at...
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117. Yunhe Wang - "Testing HEFT counterterm modeling of baryon feedback with Magneticum simulations"30.09.26, 10:40
Baryon feedback in galaxy-galaxy lensing (GGL) and the combination with galaxy clustering and cosmic shear (3x2pt), and its measurement in hydrodynamical simulations, are much less studied than in cosmic shear alone. Modeling baryonic feedback with counterterms in the hybrid effective field theory (HEFT) has not been tested against realistic baryonic effects from simulations.
This project...
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30.09.26, 11:25
Wide-area surveys that measure the clustering and weak lensing of galaxies are some of our most powerful cosmological probes, with Stage IV projects like the Vera C. Rubin Observatory, Euclid, and Dark Energy Spectroscopic Intrument (DESI) set to enable high-precision cosmological measurements in the coming years. Getting the most out of these surveys will rely on careful modelling of the...
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30.09.26, 11:45
This talk will briefly cover the basics of SBI before delving into methods for validating a neural network and its performance demonstrated on neural posterior estimation for cosmological parameters based on analytical simulations of galaxy cluster catalogs. Finally the talk will explain how network performance for this use-case scales with the inferred parameters and number of training...
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30.09.26, 12:00
Standard analyses of galaxy clustering rely on summary statistics such as the power spectrum and bispectrum, but extending to higher-order n-point functions quickly becomes intractable. Field-level inference (FLI) offers an alternative by forward-modeling the galaxy density field and explicitly employing the full joint posterior of the initial conditions, cosmological parameters, and bias...
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30.09.26, 14:10
False vacuum decay plays a pivotal role in the physics of the early Universe. However, we lack a satisfying theoretical understanding of this process, with existing approaches working only in imaginary (Euclidean) time, and relying on untested assumptions and approximations. In this talk, I will introduce two complementary approaches toward a real-time theory of vacuum decay: semiclassical...
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30.09.26, 14:30
Bose-Einstein condensates have been used successfully as quantum simulators for early-universe particle production. We extend this analogy to the interacting theory. To this end, we compute the leading interaction terms expected in a general experimental setup that determine the 3-point correlations. We apply them to cosmologically motivated expanding model universes, but also periodically...
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30.09.26, 14:45
Inflation offers a compelling explanation of how the primordial universe evolved into the universe well described by $\Lambda$CDM. Measuring the non-Gaussianity of primordial density fluctuations will deliver crucial insight into the more fundamental mechanism behind inflation. We forecast future constraints on local primordial non-Gaussianity ($f_{\rm NL}^{\rm loc}$) under the context of...
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30.09.26, 15:00
Cosmic strings are one-dimensional topological defects that may form in symmetry-breaking phase transitions in the early universe. While they may reach cosmological scales in length they are typically thinner than a proton. Therefore we can treat them as essentially one-dimensional when modelling their dynamics.
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If they exist we may detect them through the radiation they emit: If they form in... -
30.09.26, 15:15
Dissipative effects appear in many early-Universe scenarios, yet their universal observational signatures and systematic confrontation with data remain largely unexplored. We employ the Open Effective Field Theory of Inflation (Open EFToI) to consistently incorporate dissipative and stochastic effects while preserving scale invariance. Dissipation enhances specific interaction channels of the...
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01.10.26, 09:30
Galaxy clusters are sensitive probes of the growth of cosmic structure, but their cosmological power depends on clean samples with well-characterized selection, accurate redshifts, and controlled contamination. I will discuss recent progress and challenges in turning large samples of more than 10,000 ICM-selected candidates into well-controlled galaxy cluster catalogs using multi-wavelength...
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01.10.26, 09:50
TBC (Simons Observatory Initial Science Observations or projected-fields kSZ)
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01.10.26, 10:10
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01.10.26, 10:25
Particle production is common to many microphysical models of inflation and can imprint observable features in the cosmic microwave background (CMB) anisotropies. Based on arxiv: 2606.26823, 2509.23123, we consider a scenario in which the inflaton couples to an extremely massive field ($m_\chi \gtrsim \mathcal{O}(100 H_I)$, where $H_I$ is the inflationary Hubble scale). In this model, particle...
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01.10.26, 10:40
Galaxy clusters carry angular momentum. If the intracluster gas rotates coherently, the kinetic Sunyaev-Zeldovich (kSZ) effect imprints a dipole on the microwave sky centered on the cluster. We show that microwave maps alone can be used to reconstruct a noisy vector field tracing the projected angular momentum of the ionized gas. In this talk we introduce a simple model for coherent...
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01.10.26, 11:40
Understanding the Epoch of Reionisation remains one of the pivotal tasks of modern cosmology, embodied by one of the six base parameters of the Lambda-CDM model: the reionisation optical depth, whose Planck legacy constraint has recently been challenged in order to resolve tensions of the DESI BAO measurements with the base Lambda-CDM model. Meanwhile, next-generation telescopes such as EUCLID...
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01.10.26, 12:00
The epoch of reionisation (EoR) is one of the major phase transitions in the universe’s history as the first UV sources – expected to be hosted by dark matter halos which are end points of structure formation – ionise the neutral hydrogen left after recombination. Theoretically, we expect bubbles of ionised hydrogen centred at UV emitting galaxies to grow and intersect, eventually reionising...
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01.10.26, 12:15
The Lyman-alpha forest is a powerful cosmological probe of matter density fluctuations in the weakly non-linear regime through the high redshift and underdense intergalactic medium (IGM). On small scales, the Lyman-alpha 1D flux power spectrum is uniquely sensitive to both the properties of dark matter and the complex gas dynamics driven by IGM photoheating during reionization, offering...
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01.10.26, 14:00
TBC (LSS related)
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01.10.26, 14:20
Upcoming and ongoing large-scale structure surveys are probing the Universe across increasingly large volumes, opening a new window onto relativistic effects that become important on horizon scales. In this talk, I will discuss how these effects enter observed galaxy clustering statistics in redshift space. While the standard Kaiser contribution captures the dominant Newtonian redshift-space...
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01.10.26, 14:40
The cosmological bispectrum is a powerful probe of non-Gaussianity, sensitive to both nonlinear structure formation and primordial physics from inflation. However, measuring the bispectrum in large-scale structure surveys is computationally challenging due to its high dimensionality and observational effects.
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In this talk I present ongoing work extending the MODAL bispectrum estimator to... -
01.10.26, 14:55
Extracting precise cosmological constraints from cosmic shear observations requires accurate modeling of the non-linear matter power spectrum, which is suppressed at small scales ($k\sim$1 to 10$\,h~$Mpc$^{-1}$) due to baryonic feedback. Various hydrodynamical simulations predict different levels of matter power spectrum suppression based on the type and strength of the feedback mechanisms...
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01.10.26, 15:15
Scale-dependent bias, a result of nonlinear modulation of small-scale statistics by long-wavelength modes, is a tell-tale sign of inflationary physics. Through the squeezed-limit bispectrum, the nonlinear coupling depends on both the magnitude ratio and the relative angle between the long and short modes, the latter largely disregarded as inaccessible through two-point correlations of the...
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01.10.26, 16:00
GPUs offer a way to massively parallelise certain types of physical models, allowing us to compare more models for the same compute budget (and hence do more science) whilst avoiding the use of emulators (which must be retrained every time you modify the underlying physics). More efficient forward models also allow us to tackle higher-dimensional problems (map/field-level inference) and more...
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143. Kai Lehman: Evidence Networks with Learned References for Fast Simulation-Based Model Inference01.10.26, 16:15
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01.10.26, 16:30
One of the major frontiers for Stage IV galaxy surveys is photometric redshift estimation. For weak lensing cosmology, the required characterization of redshift distributions is an order of magnitude more precise than current state-of-the-art. Because the true population is not directly accessible to us, every photo-z method relies - implicitly or explicitly - on a prior over galaxy SEDs,...
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As cosmological datasets from Large-Scale Structure (LSS) and the Cosmic Microwave Background (CMB) grow in precision and complexity, disparities between datasets demand robust statistical methods for model comparison and tension quantification. However, calculating Bayesian evidences remains a computationally prohibitive bottleneck, limiting the rapid validation of new datasets and extended...
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The next-generation of wide-field galaxy surveys, known as Stage IV experiments, aims to investigate the "dark sector" by mapping a significant fraction of the observable Universe at unprecedented depth. In doing so, these surveys will also contribute to transform our understanding of galaxy formation and evolution. Their vast statistical power is however limited by systematic effects that...
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Recent developments in computing cosmological dressing rules have produced different formalism to compute the correlator and thus aid study of their properties. Dressing rules [2503.10598] and the spectral representation (KLF) are two such recent results being used to compute correlators. Dressing rules were derived as a way to add additional propagators to use the flat space feynman rules to...
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Fast Radio Bursts (FRBs) are very short transients bright enough to be detected at large cosmological distances. Their source is still unknown, but the radio pulse undergoes dispersion caused by free electrons associated with halos and the large-scale structure. This makes FRBs a sensitive probe of the baryon content in the Universe.
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As the dispersion depends on the frequency, the...
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