Conference Summary presented by Joe Silk.
Speakers
Monday
Luciano Pietronero
30 Years of Fractal Universe debate: Status and Perspectives
About 30 years ago there was a prestigious conference at Princeton organized by Neil Turok with title: Critical Dialogues in Cosmology. The idea was to have exciting debates on the most important controversial topics in the field. The first debate was on the large scale structure of the universe, homogeneous or fractal. It was between Marc Davis (and Jim Peebles) and me. At that time the correlation length for galaxies, identifying the crossover to homogeneity, was supposed to be 5 Mpc but, curiously, for galaxy-clusters it was 25 Mpc. My argument was that these values did not refer to the real correlation properties, but were simply a fraction of the sample size, because the system consisted of a Fractal structure all the way through the sample (for details see Ref.). In fact the cluster sample was precisely 5 times deeper than the galaxy one, so this view also resolved this puzzling discrepancy, because clusters after all consist of galaxies and the idea that they become homogeneous at different scales is conceptually inconsistent. This debate was certified by a bet which is officially reported in the proceedings (see Ref.). According to D&P these two values, 5 and 25, should have been confirmed by future deeper distributions. I predicted instead that they would slide with the depth of the distributions because they have no real physical meaning, since the real properties are fractal correlations up to the sample limits. Today, even the most conservative people, would agree that the long sought homogeneity is not observable at least up to 100Mpc, and the preliminary results from DESI galaxies show fractal correlations up to the sample limits of 400 Mpc, so nobody talks any
more about 5 and 25. In addition the evidence for larger and larger superclusters and voids is continuously growing. Therefore the bet is over and we can safely conclude that the visible universe consists of a grandiose Fractal structure which should be considered as the basis for any realistic theory. What about the Cosmological Principle? Already Mandelbrot pointed out that one has just to be a bit more subtle and consider the “Conditional CP”. This implies that all points of the fractal structure (galaxies) are statistically similar and the conditional average density decays similarly from each of them. The occupied massive points are, however, statistically different from the voids, but this asymmetry is certainly physically acceptable. So, in some sense, one can say that in a Fractal “everybody is at the center of the universe”. We cannot use any more the Friedmann metric but, in this perspective, we could resort to the Lemaitre-Tolman-Bondi metric, which is probably a reasonable starting point. We conjecture that this more realistic consideration of the real properties of the observable universe could resolve a number of present puzzles and possibly reduce the need of so much dark matter and dark energy. Hopefully this will lead to the evolution of the present “dark age” of cosmology into a more brilliant situation.
L. Pietronero et al, On the Fractal Structure of the Visible Universe, in Critical Dialogues in
Cosmology, Ed. by Neil Turok, World Scientific p. 27 (1997)
Eleonora Di Valentino
Cracks in the Standard Cosmological Model: Anomalies, Tensions, and Hints of New Physics
The ΛCDM model has long served as the standard paradigm in cosmology, offering a remarkably successful description of the Universe’s evolution. Yet, as observational precision continues to improve, persistent tensions have emerged across a range of probes, including the well-known Hubble constant discrepancy. While individual datasets may each align with ΛCDM, their collective interpretation reveals significant discordances that challenge the model’s internal consistency. In this talk, I will review the most prominent tensions in modern cosmology and assess their implications. I will present recent results pointing to hints of dynamical dark energy and interactions within the dark sector. I will also reflect on the growing influence of methodological choices, such as dataset selection and model assumptions, in shaping our cosmological conclusions.
Alexia Lopez
A Giant Ring on the Sky
We present the discovery of `A Giant Ring on the Sky’, which is a ring-like ultra-large large-scale structure (uLSS) that appears to extend from the previously-reported Giant Arc (Lopez et al. 2022). The Giant Ring (GR) is an almost contiguous, overdense filament of MgII absorbers which appears as a Giant Ring, approximately 1Gpc across, from our line of sight.
Previously, the Giant Arc (GA) and the Big Ring (BR; Lopez et al 2024) were reported in the literature as uLSS discoveries that are very interesting for cosmology due to their huge sizes, their close cosmological proximity to each other, and their curious ring-like morphologies.
Following this, there were hints that the GA could extend into a GR (Lopez et al. 2025), which was investigated further.
There is now substantial evidence to support the reality of a GR: different observational methods affirm the presence of an overdense filament encompassed by underdense void regions, and multiple statistical tests confirms a >3 sigma detection of a GR.
The method of discovery is as described by Lopez et al. (2022) and Lopez et al. (2024), but here we are using a hybrid high-confidence sample of MgII absorbers from pairing the MgII-absorber catalogues from Anand et al. (2021) with our own MgII-absorber catalogue, restricted to the SDSS DR16Q quasars (Lyke et al. 2020).
The Giant Ring was discovered in the same field, and at the same redshift as the two previously-reported uLSSs making this third discovery an even bigger curiosity for cosmology. Nested rings (such as the BR and GR) seem unlikely to occur in a FLRW homogeneous universe, so perhaps the explanation for these structures lies beyond standard cosmology; in either case, it could be productive to follow the hints that these structures are providing.
Roger Penrose
Dark Matter in CCC and Lopez Galactic Rings
It is proposed that in the Conformal Cyclic Cosmology picture (CCC), dark matter is a form of gravity consisting of roughly Planck-mass spin-2 neutral particles. These particles would decay, with a half-life of some 10 11 years, into graviton pairs. In the CCC picture these gravitons continue from the previous aeon into the current aeon to provide a graviton background.
In the previous aeon galactic clusters will have eventually become completely dominated by huge black holes which, in the final stages, collide with one another to produce enormous bursts of gravitational waves that come through into the current aeon. These gravitational wave bursts would encounter the graviton background in our own aeon to create new dark matter. It is suggested that such newly created dark matter would provide conditions appropriate for the creation of new galaxies.
Such galaxy formations would appear to us to occur in circular arrangements, and it is proposed that this might well be the source of the rings observed by Alexia Lopez, using techniques developed by Roger Clowes, and others.
Tuesday
Daniel Pomarede
Discoveries of Large-Scale Structures by the Cosmicflows Program
The large scale structure of the Local Universe can be inferred from the analysis of peculiar velocities of galaxies. The Cosmicflows series of catalogues, which has now reached its 4th generation with 56000 distances and velocities, allowed the discoveries of the Laniakea Supercluster and of the Dipole Repeller, and a mapping of the local cosmic web on the scale of 0.1c. The presentation will focus on the two latest discoveries of very large scale structures: first, the South Pole Wall, a 1.4 billion light-years long filament, the heart of which is located at the celestial south pole behind heavily obscured regions. This structure is comparable to the Sloan Great Wall, at half the distance. Second, the discovery of Ho`oleilana, a shell-like structure observed in the distribution of the galaxies Cosmicflows-4 catalog, in the region covered by the SDSS-PV (Peculiar Velocities) subsample. Its diameter of 1 billion light-years suggest it could be associated with a baryon acoustic oscillation (BAO); as such, it would represent the first ever observation of an individual BAO. Finally we will present preliminary results on the mapping of the basin of attraction of the Sloan Great Wall. Our maps of the cosmic flows reveal a basin as large as 1.7 billion light-years, and possibly larger as the SGW is located on the outskirts of our data zone.
Edward Olex
Localized Detection of Baryon Acoustic Oscillation Shells in DESI DR1
I present results from a new local approach to detecting and characterizing Baryon Acoustic Oscillations (BAO) in the large-scale distribution of matter. The possibility of observing individual BAO structures in configuration space was long speculative until the Hoʻoleilana candidate (Tully et al. 2023), discovered in the Cosmicflows-4 dataset, revealed a single shell-like over-density with BAO-scale radius. That discovery raised the question of whether such features are reproducible cosmological signatures or rare fluctuations, and highlighted the need for systematic searches in much larger and deeper surveys. Our work addresses this question by exploiting the unprecedented statistical power of modern datasets to confirm the standard BAO shell and to identify individual instances with high confidence.
We apply a spherical wavelet transform (Arnalte-Mur et al. 2012) to galaxy redshift catalogs, convolving them with shell-shaped filters anchored on cluster centers identified in the DESI Legacy Surveys optical cluster catalog with combined spec- and photo-z (Wen & Han 2024), and tracing surrounding structure with spectroscopic redshifts from DESI DR1. Our analysis focuses on the best-observed regions of DR1 and on the luminous red galaxy samples LRG1 (0.4 < z < 0.6) and LRG2 (0.6 < z < 0.8), using of order 100,000 clusters as anchors for potential BAO centers. Extensive tests against dedicated mock and randomized catalogs, constructed to reproduce the observational properties of both cluster and galaxy samples while excluding BAO physics, enable us to detect the ensemble BAO shell signal in configuration space with significance greater than 5σ. Building on this validation, we assemble a catalog of individual BAO candidates, each with local significances exceeding 5σ. The resulting sample comprises roughly one thousand large-scale shell-like structures, with about five hundred candidates in each redshift bin, and statistical strength comparable to or greater than Hoʻoleilana, demonstrating that localized BAO features are a reproducible aspect of the cosmic density field rather than isolated curiosities.
Rather than replacing the traditional two-point correlation function (2PCF), our method provides a complementary, object-based description of BAO. While the 2PCF yields a volume-averaged acoustic scale, the wavelet approach delivers localized measurements of centers, radii, and radial profiles, enabling direct studies of environmental dependence, anisotropies, and redshift evolution. This localized characterization opens new possibilities for cosmological inference, including consistency tests, independent probes of H(z) and H0 from stacked and individual BAO detections, tests of large-scale homogeneity and isotropy, and improved control of systematics associated with spatial averaging.
In this talk, I will present the methodology, representative detections of both stacked and individual BAO shells, the statistical validation framework, and the implications of localized BAO measurements for future large-scale structure analyses with DESI, Euclid, 4MOST, and related surveys.
Jamie Incley
Tracing Cosmic Structure with Neutral Hydrogen after the Epoch of Reionization
The 21-cm signal produced by neutral hydrogen (HI) is a unique tracer of Large-Scale Structure (LSS) throughout cosmic history.
It is the only probe of the matter distribution during the Dark Ages, and enables insight into the astrophysics of the ionization process during the Epoch of Reionization (EoR).
After the EoR has concluded, only dense regions toward halo centres (which can self-shield from the ionizing photons) remain neutral and thus detectable in the 21-cm line. Therefore, post-EoR, the HI signal returns to being a strong (if biased) tracer of the underlying large-scale structure. From this late-time signal, we can trace structure formation across the universe for z < 6.
Recently, observations have suggested a late end to reionization at z ~ 5.3. Considering this and the effects of inhomogeneous recombination, it is likely that small patches of neutral IGM will remain during the time that halo-based HI emits significantly.
In this work, we present a semi-numerical simulation of the neutral hydrogen within halos, which is combined with the outputs from the open-source EoR code 21cmFAST to produce a robust representation of the emission from all HI sources. We make predictions on the detectability of a transition signal within future intensity mapping surveys, and investigate the effect of varying EoR astrophysics on the observed power spectrum.
Our simulations predict a drop in power of four orders of magnitude between 4 < z < 7. Assuming an inhomogeneous recombination model, we find a flattening of the power due to lingering neutral islands masking the late-time HI signal for 5 < z < 6.5.
Using SKA-Low deep survey parameters, we find HI power spectrum detectability at scales k < 1 h/Mpc for redshifts 3 < z < 7, even when using a horizon limit avoidance scheme to mitigate foregrounds. Our results suggest a sufficient SNR of the HI power spectrum tracing the underlying halos z < 5, which can be used for late-time cosmology; and that the resulting Ω_HI constraints can trace different reionization scenarios such as a decreased escape fraction. This study implies that SKA-Low intensity mapping observations for 3 < z < 7 will be an important probe to constrain reionization parameters as well as cosmological models.
Tobias Russell
Modelling the Effects of Primary Beam Heterogeneity in SKA-Mid for 21cm Cosmology
21cm Intensity mapping observes the emission from neutral hydrogen (HI) tracing the Universe’s large-scale structure, by quickly mapping out large volumes of the sky. As a precursor to the SKA, the MeerKAT telescope is conducting a single dish intensity mapping survey in the MeerKLASS project, which employs each antenna in the array individually, scanning at constant elevation back and forth in the azimuth. So far, MeerKLASS has detected the cross-correlation power spectrum at redshifts z=0.39-0.46 using the L-band and is currently conducting a large survey up to z=1. 45 in the UHF band. The full SKA-Mid AA* will incorporate the MeerKAT array alongside its new larger SKA dishes. However, one challenge in this set-up for HI intensity mapping science is the coherent incorporation of the beam effects in all stages of the analysis. The beam profile injects structure into the foregrounds, which are 3 – 5 orders of magnitude larger than the HI signal, affecting their smoothness across frequency and making their removal via techniques such as principal component analysis more difficult. In this work I present simulation-based results that demonstrate the complications dish mixing can cause for SKA-Mid intensity mapping clustering statistics. SKA-Mid intensity mapping will need to combine data from dishes of two different sizes and designs, introducing challenges due to the beam effects dependence on these factors. Detailed modelling of combined primary beam effects in foreground cleaned data for a mixed dish scenario will allow for the correction of beam structure contaminating clustering statistics, and is key to successfully combining these dishes in the SKA-Mid.
Xuelei Chen
Probing the Primordial Fluctuations with Low Frequency Radio Array on the Lunar Far Side
The primordial fluctuations in the cosmic dark ages offers a library of enormous amount of information on the largest scales of the observable Universe. This can in principle be retrieved by observation of the redshifted 21cm signal. I shall discuss the possibility of their measurement by low frequency radio arrays on the far side of the Moon. I shall present our forecast on the capability of such measurement, and also discuss the possible designs of such arrays, and the engineering challenges involved.
Andras Kovacs
Cosmic Voids as Probes of Large-Scale Structure and Cosmology
Voids trace the largest underdensities in the cosmic web and provide a powerful probe of cosmology on large scales. I will present recent results on void catalogues across multiple surveys, including DES, DESI, and Quaia quasars, alongside studies of prominent structures such as the Eridanus supervoid. We explore their observational imprints through cross-correlations with CMB lensing maps and related probes. On the theoretical side, I will highlight new work based on large suites of wCDM simulations, enabling predictions for void-induced signals such as the Integrated Sachs–Wolfe effect. These developments move beyond ΛCDM consistency tests toward using voids as quantitative tools for cosmological inference on the largest observable scales.
Francesco Sylos Labini
The Large-Scale Inhomogeneous and Anisotropic Universe
The spatial distribution of galaxies is a primary observable for testing the large-scale structure of the Universe. Yet its statistical characterization remains challenging: galaxy clustering exhibits strong inhomogeneities and contains the largest structures known in nature. A central question, debated for decades, concerns the scale at which the distribution becomes statistically homogeneous.
Addressing this issue requires statistical methods that rely on minimal assumptions and avoid biases induced by luminosity selection and finite sample size. Using conservative, assumption-light estimators, we analyze galaxy samples from the first data release of the Dark Energy Spectroscopic Instrument (DESI).
We find that the conditional average density follows a robust power-law decay and shows no evidence of a transition to homogeneity within the survey volume, up to scales of 400 Mpc/h. These results confirm and significantly extend trends previously reported in smaller redshift surveys.
Moreover, we detect statistically significant anisotropic structures that persist across the full depth of the samples, reaching scales of order thousands of megaparsecs. Such long-wavelength directional features are not expected in standard models of structure formation, which assume statistically isotropic initial conditions and predict the disappearance of coherent anisotropies beyond 100 Mpc/h.
The persistence of large-scale inhomogeneities and anisotropies therefore poses a challenge to the standard cosmological framework and may have implications for the consistency of the Friedmann–Lemaître–Robertson–Walker description, which presupposes an initially super-homogeneous and isotropic matter distribution.
GeonWoo Kang
Constraining Inflation Models with Spinning Voids
We present a powerful new diagnostics by which the running of scalar spectral index of primordial density fluctuations can be tightly and independently constrained. This new diagnostics utilizes coherent rotation of void galaxies, which can be observed as redshift asymmetry in opposite sides dichotomized by the projected spin axes of hosting voids. Comparing the numerical results from the AbacusSummit of cosmological simulations, we derive a non-parametric model for the redshift asymmetry distribution of void galaxies, which turns out to be almost universally valid for a very broad range of cosmologies including dynamic dark energy models with time-dependent equation of states as well as the LambdaCDM models with various initial conditions. We discover that the universality of this model breaks down only if the running of scalar spectral index deviates from zero, detecting a consistent trend that a more positive (negative) running yields a lower (higher) redshift asymmetry of voids than the model predictions. Given that non-standard inflations usually predict non-zero runnings of the spectral index and that the redshift asymmetry distribution of voids is a readily observable quantity, we conclude that this new diagnostics will pave another path toward understanding the true mechanism of inflation.
Maximilian von Wietersheim-Kramsta
An Analytical Model of the Non-Locality and Stochasticity of the Galaxy-Halo Connection in Spherical Projection
Galaxy positions and shapes, as tracers of the large-scale structure of the Universe, are key observables for testing cosmological models in the late Universe and into the non-linear regime. In this context, multi-scale baryonic dynamics, and their evolution over time, can have considerable effects on the galaxy-halo connection (galaxy bias). If unmodelled, residual uncertainties in the galaxy field can obstruct cosmological inference and weaken tests of extensions to $\Lambda$CDM. In two-dimensional projection along the line-of-sight, the relevant halo-level information can be incomplete or effectively marginalised over, motivating bias models that remain predictive without detailed halo-internal parameterisations.
To this end, I will present a new analytic galaxy-bias model in projection that incorporates stochasticity and non-locality already at linear order, while enforcing physicality and statistical isotropy for galaxy fields constructed from an underlying matter field on the sphere. This yields an explicit decomposition into a linear, non-local stochastic component in harmonic space and a non-linear residual. I will show how the model can be calibrated to the projected power spectrum measured in large-volume hydrodynamical simulations (FLAMINGO) to sample galaxy populations from simulated matter fields while conditioning on selected galaxy properties, such as halo mass or redshift. The model matches the two-point statistics down to the simulations’ resolution by construction, while recovering the bispectrum down to $\sim$10 Mpc for $M_{\mathrm{h}} > 10^{13} \, M_{\odot}$ up to $z \le 3$. The model better reproduces non-linearities driven by correlations between the local amplitude of the galaxy field and its phase, as well as the field’s mode coupling, than a local bias model across most scales and down to $M_{\mathrm{h}} = 10^{11} \, M_{\odot}$. This improves the robustness of joint clustering plus galaxy-galaxy lensing consistency tests of the growth of structure, helping to separate astrophysical systematics from genuine scale-dependent structure growth. Finally, I will demonstrate how this framework enables efficient field-level forward modelling of galaxy positions consistent with hydrodynamical simulations, while varying cosmological and astrophysical parameters, providing a practical route towards simulation-based inference (with a few of milliseconds per model evaluation) and principled model comparison with forthcoming surveys such as Euclid, Rubin LSST, and DESI.
Marco Bruni
Supermassive Black Hole Formation from Direct Collapse of CDM-Curvature Peaks in LCDM
The large scale structure of the Local Universe can be inferred from the analysis of peculiar velocities of galaxies. The Cosmicflows series of catalogues, which has now reached its 4th generation with 56000 distances and velocities, allowed the discoveries of the Laniakea Supercluster and of the Dipole Repeller, and a mapping of the local cosmic web on the scale of 0.1c. The presentation will focus on the two latest discoveries of very large scale structures: first, the South Pole Wall, a 1.4 billion light-years long filament, the heart of which is located at the celestial south pole behind heavily obscured regions. This structure is comparable to the Sloan Great Wall, at half the distance. Second, the discovery of Ho`oleilana, a shell-like structure observed in the distribution of the galaxies Cosmicflows-4 catalog, in the region covered by the SDSS-PV (Peculiar Velocities) subsample. Its diameter of 1 billion light-years suggest it could be associated with a baryon acoustic oscillation (BAO); as such, it would represent the first ever observation of an individual BAO. Finally we will present preliminary results on the mapping of the basin of attraction of the Sloan Great Wall. Our maps of the cosmic flows reveal a basin as large as 1.7 billion light-years, and possibly larger as the SGW is located on the outskirts of our data zone.
Olga Garcia Gallego
Constraining Cosmology with the Lyman-Alpha Forest
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). The most commonly used statistic to characterize these fluctuations is the 1D flux power spectrum. On small scales, the Lyman-alpha forest traces the properties of dark matter, encoding information on its still unknown nature. At the same time, the flux power spectrum is sensitive to complex gas dynamics arising from IGM photoheating during reionization. As such, the Lyman-alpha forest provides constraints that are complementary to other probes, such as the CMB. In this talk, I will present recent constraints on Cold+Warm Dark Matter (CWDM), in which structure growth is affected by the free-streaming of the warm component, using the Sherwood-Relics simulation suite and high signal-to-noise ratio, high-redshift spectra from UVES and HIRES spectrographs. These results highlight how small-scale features in the forest reveal fundamental aspects of both dark matter and the IGM thermal history.
Wednesday
Roya Mohayaee
Cosmic Dipole Anomaly
The cosmic dipole anomaly poses one of the most significant challenges to the cosmological principle and to our simple description of the Universe as homogeneous and isotropic, as encoded in the Friedmann metric. Measurements of the dipole from high-redshift radio sources and quasars exceed the expectation from the kinematic CMB dipole at a significance greater than 5σ and have so far withstood extensive scrutiny of potential systematic effects. I review the current observational status of the anomaly, assess the robustness of existing measurements, and discuss possible physical origins.
Indranil Banik (cancelled talk)
The Local Void Solution to the Hubble Tension
Cosmology is currently in a crisis known as the Hubble tension, the observation that redshift increases with distance about 10% faster than expected in the ΛCDM standard cosmological paradigm with parameters calibrated to fit the CMB anisotropies. A promising explanation for this is that we live near the centre of a large local underdensity or void. This is suggested by observations of source number counts across the whole electromagnetic spectrum, with near-infrared results implying that the density is about 20% below average out to 300 Mpc across 90% of the sky and most of the galaxy luminosity function (ApJ, 775, 62). Outflows from this KBC void can induce enough extra redshift to plausibly solve the Hubble tension (MNRAS, 499, 2845). I will discuss various tests of this proposal. It is possible to infer the H0 parameter from data in a narrow redshift range centred on z. Such an empirical H0(z) curve agrees quite well with expectations in the void model, which predicts a return to the CMB-derived H0 beyond the void (MNRAS, 536, 3232). This result is related to baryon acoustic oscillations (BAOs), which show a deviation from ΛCDM expectations (MNRAS, 540, 545). I will explain how the BAO observables would be affected by a local void. I will then present BAO results compiled over the last twenty years. These results fit better if the local void is included, thanks to good agreement with ΛCDM at high redshift but a persistent anomaly at lower redshift.
Sankalan Bhattacharyya
The Evolution of Fluctuations in the Cosmological Photoionizing Background
We formulate a description of large-scale fluctuations in the cosmic Ultra-Violet background, connecting ionising source phenomenology to large-scale structure observables. We will discuss potential clustering signatures in the cosmic ionising radiation field, examining the influence of source beaming and lifetime, as well as the impact of gravitational fluctuations. We shall illustrate how such a framework may be used to constrain the emission history and beaming of ionizing source populations as well as analysing potential theoretical systematics contaminating cosmological parameter inference pipelines. We have quantified the impact of such fluctuations on the HI Lyman-alpha flux redshift-space power spectrum and its spatial correlation function at redshifts of current and future survey interest. We find that large-scale photoionization rate fluctuations modify the shape of the Baryonic Acoustic Oscillation (BAO) peak in the correlation function and will illustrate that varying phenomenological astrophysical parameters leads to small distortion of the BAO position and large amplitude modulation. Therefore, we will conclude that these effects present a systematic bias to be considered when interpreting upcoming higher redshift Lyman-alpha surveys for cosmological parameter inference requiring precision measurement of the BAO position to the sub-percent level.
Robbert Scholtens
Exploring CMBs in Anisotropic Universes
In recent years, there have been increasing challenges to the cosmological principle, based on new observations of e.g. supernovae and the cosmic bulk flow. As a result, the cosmological community is speaking their concern for the cosmological principle, and from which scales onwards it should apply. In this context, there is a desire to understand more fully the properties and signatures of cosmologies not obeying the cosmological principle. In this article, we let go of the demand of cosmic isotropy, and instead assume only spatial homogeneity in our cosmological models. We follow the results of our previous works [see citations in the list of references], and here bring these together into one unified picture, with the goal of describing the signature(s) of anisotropy in anisotropic cosmological models. We first introduce the Bianchi models—a particular instance of spatially homogeneous cosmologies—and show that a metric can be constructed for them when an appropriate collection of desired Killing vector fields is supplied. Then, we give the perturbations of the Friedmann equations in such Bianchi models, in the Newtonian gauge, derived using much the same methodology as applicable to the FLRW models. We show these can be combined into one characteristic partial differential equation. Finally, we use this equation in order to simulate the CMB of a toy Bianchi V example and produce its power spectrum. We close with a discussion, and suggestions for further research.
Levon Pogosian
Sound-Horizon-Agnostic Approaches to the Hubble Tension and an Update on Primordial Magnetic Fields
The Hubble tension points to possible gaps in our understanding of physics around the epoch of recombination. A key aspect of the tension is its sensitivity to the sound horizon at decoupling, r_, whose value depends on the microphysics of recombination. It is therefore highly desirable to obtain empirical constraints on both H_0 and r_ without relying on model-dependent assumptions. I will present recent work that demonstrates how combining baryon acoustic oscillations with CMB lensing enables such sound-horizon-agnostic measurements of the Hubble constant. I will also provide an update on primordial magnetic fields as a potential mechanism for alleviating the Hubble tension.
Joe Silk
Conference Summary
Posters
Callum Bell
Daniel Alejandro Tapia Alanis
In this work, the projection of a semi-empirically constrained stellar-to-halo mass relation (SHMR) on the internal mass distributions of galaxy-halo systems is studied. To this end, the galaxies are modeled as a system consisting of a thick stellar disk, an infinitesimally thin gaseous disk, a classical bulge and a pseudobulge, all constrained by observational relations. These systems are then loaded into initial dark matter NFW haloes (in consistency with the SHMR) to which the adiabatic contraction formalism is then applied. As a result, the stellar Tully-Fisher relation (with various velocity definitions) and its scatter are predicted, as well as the dark matter fractions at different internal radii.
GeonWoo Kang
We report a numerical hint that the formations of cosmic voids may be closely linked with the mechanism through which the giant galaxies on void surfaces establish elliptical shapes, redder colors, and lower specific star formation rates (sSFR). Identifying the voids from the TNG300-1 simulations via the Void-Finder algorithm at z=0, 0.5 and 1, we explore if and how the shapes of the TNG galaxies located on void surfaces are aligned with the directions toward the void centers. Noting that only the giant void-surface galaxies with stellar masses heavier than 10^10.5 h^-1 solarmasses exhibit significant tendency of perpendicular alignments, we dichotomize them into two stellar mass-controlled samples according to their morphologies (elliptical or spiral), colors (redder or bluer), sSFR (lower or higher) and stellar ages (older or younger). It is found at all of the three redshifts that the perpendicular alignments of void-surface galaxies become stronger for the cases that they have elliptical shapes, redder colors, and lower sSFR, but showing weak dependence on the stellar ages. It is also shown that the numerical results are well described by the analytical one-parameter model developed by Lee~\cite{lee19} under the assumption of the existence of a linear scaling between the covariance matrices of galaxy shape axes and local tidal tensors. We test the robustness of alignment signals against the variation of void-finder algorithms and its feasibility against the redshift-space and projection effects. Our results lead us to speculate that the formation and expansion of voids may have an effect of stalling and quenching the giant void-surface galaxies by compressing adjacent matter and then preventing them from radial infall/accretion.
Gerry Williger
Current/Future Wide-field Multiobject Spectrographs: Prospects for LSS Studies
The Sloan Digital Sky Survey (SDSS) revolutionised astronomy with its comprehensive imaging and spectroscopic surveys. In particular, by observing quasar absorbers, it permitted the study of large scale structure (LSS) via gas content-selected galaxy haloes independent of galaxy luminosity.
The 2020s are witnessing a new generation of wide-field, multifibre spectrographs which offer a chance to advance significantly wide-field quasar absorber studies. We will review the capabilities and potential contributions to LSS studies of established wide-field spectrographs as a benchmark (SDSS, DESI, Anglo-Australian Telescope), the new facilities coming online (ESO 4MOST, Subaru Prime Focus Spectrograph) and prospects for the next 10-15 years. We will also describe plans for proposed LSS observing programmes, including the 4MOST ByCycle and Subaru Prime Focus Spectrograph Galaxy Evolution Survey.
Hao-Yang Jin
We investigate a model of quintessential inflation with a non-Abelian SU(2) gauge field, where the gauge kinetic function is modulated by the inflaton field. The backreaction onto the inflaton due to the gauge field yields a soft stiff period from the end of inflation to kination. This results in a characteristic gravitational wave spectrum that will be observable in the upcoming observations. We study the self-resonance of the gauge field, which may reheat the universe non-perturbatively.