The Hubble tension has reached the 5$\sigma$ confidence threshold and is currently considered the biggest crisis for the LCDM standard model of cosmology. Yet, despite more than a decade of thorough search, a well motivated and simple solution to the Hubble tension has not emerged. In this talk I review the current observational status of the Hubble tension and what makes the problem of trying...
The LCDM model relies on DM (described as a pressure-less fluid) and the cosmological constant. The physics of the dark sector is otherwise not specified. In this talk I discuss models in which the dark sector consists of (at least) two scalar fields, one of which a dark matter candidate, while the other plays the role of dark energy. These fields are interacting, resulting in theories with...
In this talk, we will present a systematic comparison of statistical approaches to Baryon Acoustic Oscillation (BAO) analysis using DESI DR2 data. We evaluate different methods for handling the nuisance parameter such as marginalization, profiling, Taylor expansion, and full likelihood analysis across multiple cosmological models. We demonstrate the how different cosmological models are...
I review a model of (metastable) approximately de-Sitter inflation induced by a condensate of chiral primordial gravitational waves in the early Universe in string-inspired Chern-Simons cosmologies, with gravitational anomalies. The model maps to a running vacuum model cosmology, and has the capability of alleviating the modern era cosmological tension under some natural assumptions.
The cosmological constant problem remains one of the deepest puzzles in effective field theory and cosmology. In this talk, I will show how four-form field strengths offer model builders a valuable tool to tackle this challenge. I begin by reframing the problem using the infinite-wavelength (spacetime-averaged) trace of the gravitational equations. I then review and explore two main...
We propose a novel and natural mechanism for cosmic acceleration driven by primordial black holes (PBHs) exhibiting repulsive behavior. Using a new ``Swiss Cheese'' cosmological approach, we demonstrate that this cosmic acceleration mechanism is a general phenomenon by examining three regular black hole spacetimes - namely the Hayward, Bardeen and Dymnikova spacetimes - as well as the...
Since the very first observations, the Cosmic Microwave Background (CMB) has revealed on large scales unexpected features known as anomalies, which challenge the standard Λ cold dark matter (ΛCDM) cosmological model. One of these is the hemispherical power asymmetry, i.e. a difference in the average power on the two hemispheres centered around (l, b) = (221, −20), which shows a relatively high...
The tensions and anomalies appearing or increasing in the era of precision cosmology are due to a mismatch between the late time predictions obtained by applying the standard LCDM model (and its perturbations) to measurements at the CMB and actual measurements realized in our vicinity. Two main solutions to this issue can be considered: modifying Einstein's GR or keeping this theory and...
We are currently living through a remarkable era in cosmology and gravitational physics, characterised by an unprecedented influx of observational data. One of the most pressing challenges facing cosmologists today is to understand the mysterious cause of the Universe’s recent accelerated expansion. The leading explanations for this phenomenon involve either a dark energy component or...
We propose a quantum gravity theory that leads to a modified Friedmann equation, potentially explaining the accelerated expansion of the universe without the need for dark energy. In our approach, cosmic acceleration arises naturally from quantum gravitational effects. The resulting corrections offer a possible resolution to the Hubble Tension by modifying both early and late-time cosmic...
A remarkable observational property of optically selected, blue quasars is the tight non-linear relation between their X-ray and UV emission. Since no complete physical model is available to explain such relation, a reliable derivation of distances based on its non-linearity requires a complete and careful analysis of the sample properties, in order to rule out systematic effects such as (a) a...
I introduce quasars as new cosmological probes, leveraging the UVâX-ray luminosity relation and the Lusso & Risaliti catalog to build an extended Hubble diagram up to zâ¼7. I present joint analyses with several crucial probes as SNe Ia, BAO, DES, and CMB to test ÎCDM and dark energy models. The results show that simple model extensions fail to resolve current tensions, while interacting...
In this talk, I will present a method to directly reconstruct the matter power spectrum from linear to non-linear scales with cosmic shear. I will demonstrate that future cosmic shear surveys will be sensitive to the shape of the matter power spectrum on non-linear scales. I will show that it should be possible to distinguish between different models of baryonic feedback, and help provide a...
As wide-field surveys yield increasingly precise data, multiprobe analyses offer significant advantages. In this talk, I will discuss our recent study in which we use a previously developed framework to analyze combinations of three CMB (Planck PR3, Planck PR4, and ACT+WMAP) datasets, DESI Y1 Baryon Acoustic Oscillation (BAO) data, and a 9 Ã 2pt low-z dataset comprising KiDS-1000, BOSS DR12,...
The sign-switching cosmological constant cold dark matter ($\Lambda_{\rm s}$CDM) cosmology has emerged as a promising new paradigm, showing notable success in reconciling observational data from diverse probes and in addressing major cosmological tensions, such as the $H_0$, $S_8$, and $\gamma$ (growth index) discrepancies. The model introduces a minimal but non-trivial modification to the...
One of the important challenges in modern cosmology relates to the search for models that go beyond $\Lambda$CDM for the resolution of cosmological tensions and lead to deviations from the standard model predictions. We discuss a field theoretic approach based on a dynamical quintessence field interacting with dark matter (QCDM) which can be utilized in the analysis of Hubble tension,...
I will present research focused on measuring the peculiar (gravitational) velocities of galaxies. The goal is to achieve a three-dimensional reconstruction of the velocity field of the Local Universe, which reflects the distribution of both dark and luminous matter. This approach enables us to determine local values of fsigma_8 , H0 , and the local bulk flow, using these as key tests of the...
I present a trilogy of works exploring the possibility that primordial black holes often considered as dark matter candidates, are non-singular objects. The investigations are motivated by the expectation that a complete theory of quantum gravity should ultimately resolve curvature singularitiesâan endemic feature of the Schwarzschild and Kerr metrics typically used to describe PBHs. In the...
We investigate the cosmological dynamics of teleparallel dark energy in the presence of nonzero spatial geometry. We specifically analyze nonminimal scalar-tensor theories in the torsion-based framework by considering different scalar field potentials and examining the resulting background evolution and linear perturbations. Adopting a dynamical systems approach, we reformulate the field...
As cosmological observations reach unprecedented precision, the standard $\Lambda$CDM model is facing mounting pressure on multiple fronts. The well-known Hubble tension — a persistent $\sim 5 \sigma$ discrepancy between early- and late-universe determinations of the Hubble constant — challenges the foundations of our baseline paradigm. At the same time, recent Baryon Acoustic Oscillation...
We explore an interacting dark sector model in trace-free Einstein gravity where dark energy has a constant equation of state, w=-1, and the energy-momentum transfer potential is proportional to the cold dark matter density. Compared to the standard ÎCDM model, this scenario introduces a single additional dimensionless parameter, ε, which determines the amplitude of the transfer potential. ...
I will discuss how (non-standard) neutrino properties can address some cosmological anomalies of different nature such as the neutrino mass tension, NANOGrav, potential Deuterium problem, excess radio background, non-standard 21cm cosmological global signal. At the same time they might also contribute to ameliorate the Hubble tension. I will discuss a few models able to connect and explain...
I will introduce the axio-dilaton models of dark energy where the dilaton plays the role of quintessence and the axion induces a new way of screening long range forces. We will see that the screening properties of these models lead to early dark energy related to the axion potential and phantom crossing from the coupling of the dilaton to matter.
The Universe, as described by the standard model of Cosmology, is a vast ocean of darkness-dominated by dark matter and dark energy, with only a trace of luminous matter giving rise to the cosmic web we observe today. Yet this seemingly insubstantial fraction has shaped galaxies, clusters, and filaments across billions of years. What remains largely invisible, however, may hold the key to...
Modern physical theories rest on two foundational assumptions general covariance, which holds that the laws of physics are valid across all of space-time, and the cosmological principle, which asserts that no observer occupies a special location in the universe. Both principles can be empirically tested through astronomical spectroscopy. Tests of general covariance involve searching for...
In Yukawa cosmology, a recent discovery revealed a relationship between baryonic matter and the dark sector. The relation is described by the parameter α and the long-range interaction parameter λ - an intrinsic property of the graviton. Applying the uncertainty relation to the graviton raises a compelling question: Is there a quantum mechanical limit to the measurement precision of the Hubble...
Cosmology currently faces significant challenges due to persistent tensions between independent observational datasets. Resolving these discrepancies within a unified framework would strengthen confidence in any proposed cosmological model and may require going beyond General Relativity. One compelling alternative is Teleparallel Gravity, a torsion-based formulation of gravity that offers a...
Spacetime is foamy: it undergoes quantum fluctuations, with distance uncertainty scaling as the cube root of distances, consistent with the holographic principle - hence the name "holographic spacetime foam" (HSF) (also known as "holographic quantume foam"). HSF, in conjunction with thermodynamics, naturally demands the existence of a dark sector, the quanta of which obey infinite statistics....
Cosmological tensions have questioned the validity of the concordance model, opening avenues for new physics. One possible alternative is to model the cosmological expansion of the Universe using alternative gravitational models. In this talk, the scalar-tensor and teleparallel gravity paradigms are discussed within the context of large-scale structure formation and how the growth structure...
The inflationary paradigm remains the leading candidate for explaining the early universe's homogeneity, isotropy, and the origin of cosmic perturbations. However, its compatibility with current observational data and the persistent tensions within the ÎCDM model motivate the exploration of alternative gravitational frameworks. In this talk, we delve into the dynamics of cosmic inflation...
One of the major challenges of modern cosmology is the detection of primordial Bâmode polarization anisotropies in the CMB, a smoking gun for inflation. The B-modes is the most promising direct observational signature of the inflationary phase that is thought to have taken place in the early Universe, generating primordial perturbations, producing Standard Model elementary particles and...
In this work we propose a setup for the origin of dark matter based on spacetime with a warped extra dimension and three branes: the Planck brane, the TeV brane and a dark brane, at a (sub)-GeV scale. The Standard Model is localized in the TeV brane, thus solving the Higgs hierarchy problem, while the dark matter χ, a Dirac fermion, is localized in the dark brane. The dark matter has only...
As an implication from Quantum Gravity, the swamplandish TransâPlanckian Censorship Conjecture (TCC) prohibits eternal cosmological acceleration, a prediction that aligns naturally with the quintom-B behavior from the latest DESI DR2 data. Primarily, we implement TCC bounds within the framework of dynamical dark energy, especially in the w0waCDM parametrization and f(T), f(Q) modified...
We develop a new class of inflationary attractors which
are compatible with the recent ACT results. They are based on
fractional Kaehler potentials, $K$, for a gauge-singlet inflaton
$\sg$ which reduce, along the inflationary path, to the form
$N/(1-\sg^{q})^{p}$ with $q=1, 2$ and $0.1\leq p\leq10$. The
combination of these $K$'s with the chaotic potentials $\phi^n$
(where $n=2, 4$)...
Recently, various cosmological tensions have arisen for the standard model of cosmology. For the Hubble-constant $H_0$ tension, we have proposed a series of no-go "theorems" for possible deviations from the $\Lambda$CDM model. For the Hubble-variation $\delta H_0$ tension, we have found novel evidence for going beyond the $\Lambda$CDM model in a non-trivial manner. For the intercept $a_B$...
The inferred cosmological information is most robust when multiple probes are combined. Two of the most sensitive probes of the large-scale structure of the universe are galaxy clustering and weak lensing. I will present new cosmological results combining those two probes (in a so-called 3x2pt analysis) using DESI DR1 spectroscopic data for the galaxy clustering and weak lensing data from the...
Modern cosmological research still thoroughly debates the discrepancy between local probes and the Cosmic Microwave Background observations in the Hubble constant (\texorpdfstring{$H_0$}{H0}) measurements, ranging from 4 to 6$Ï$. In the current study, we examine this tension using the Supernovae Ia (SNe Ia) data from the Pantheon, Pantheon+ (P+), Joint Lightcurve Analysis (JLA), and Dark...
The Vera Rubin Observatories Legacy Survey of Space and Time will open an unprecedented view of our universe with the survey slated to begin this fall. I will review status and results from the Observatory thus far as well as the major cosmological probes for LSST and expectations for the constraints to come.
Baryon Acoustic Oscillations are considered one of the most powerful cosmological probes. They are generally deemed to provide distance measures independent of a specific cosmological model. At the same time the obtained distances are considered agnostic with respect to other cosmological observations. However, in current measurements, the inference is done assuming parameter values of a...
We have proposed a novel approach to investigate, in a geometrical way, the renormalization group equations for particle physics and gravity. The Stochastic gauge geometry flow hence introduced entails the breakdown of symmetries in the infrared, where the classical theory is recovered. We show several phenomenological implications for cosmology and astrophysics, QCD confinement and the...
Elliptical galaxies formed very rapidly, with the more massive ones forming faster, on a timescale shorter than a Gyr. The high metallicities of these galaxies imply them to have had significantly top-heavy galaxy-wide stellar initial mass functions. In other words, the synthesis of the heavy elements on such a short time scale in these galaxies implies them to have been 10000 times brighter...
Galaxy clusters are excellent natural laboratories to study the nature of gravity and highlight possible tensions with the LambdaCDM scenario, at the edge between cosmology and astrophysics. Cluster mass profiles, determined through different methods, provide critical information on the distribution and interplay of baryonic matter, dark sector, and gravity. I present recent results obtained...
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 ÎCDM 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...
Scalar field dark matter (SFDM) is an alternative candidate to standard dark matter models, gaining attention due to the unique effects associated with its ultra-light mass. While its dynamics have been extensively studied across different scales, its full phenomenology remains under active investigation. In particular, the role of self-interactions and their impact on structure formation are...
We face the dichotomy of an ad hoc dark Universe compatible with GR but lacking experimental confirmation and unsupported by the SM, while we witness the continuous successes of GR. The latter do not impede a multitude of rightly efforts in reformulating gravitation, also for facing suspected or known limitations in the regime of strong field and of quantum scale. Among the messengers of the...
Stage IV galaxy surveys will test the cosmological model with unprecedented precision, providing critical insights into tensions like the S8 discrepancy and probing evolving dark energy scenarios. To fully realize the potential of these surveys, forward modeling of galaxy populations offers a promising pathâenabling both accurate redshift calibration and a deeper understanding of galaxy...
We are in a golden era of cosmology, driven by increasingly precise observations and deep surveys of large-scale structure. While the ÎCDM modelâwith Einsteinâs cosmological constant Î and cold dark matterâremains successful, persistent tensions like the Hubble constant discrepancy suggest it may be incomplete. This talk explores whether general relativity is truly general. We argue...
Gravitational lensing is one of the indirect methods for detecting dark matter, allowing us to reconstruct the mass distribution of foreground objects and provide insights into their gravitational fields and dynamics, which can be used to study the properties of dark matter halos and test gravitational theories. Galaxy-galaxy lensing provides an effective approach to studying the...
Distance ladders which calibrate the luminosity of Type Ia supernovae (SNe Ia) currently provide the strongest constraints on the local value of H0. Recent studies from the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) show good consistency between measurements of SNe Ia host distances. These are calibrated to NGC 4258 using different primary distance indicators (Cepheids,...
Recent observations in Physical Cosmology have achieved a precision that not only allows for a better determination of model parameters, but also, the existence of cosmological tensions between current datasets motivates exploiting this precision to test for alternative theories that extend the particle content of the Standard Model. Theories beyond the Standard Model of particle physics...
We study the evolution of domain wall networks and their phenomenological implications in a model of a real scalar, where a Z2-symmetry is slightly broken by a potential bias. It is demonstrated that the latter triggers domain wall annihilation considerably earlier than previously thought. As a result, the energy density of gravitational waves produced by the network of biased domain walls,...
The late-time accelerated expansion of the universe remains a profound mystery, traditionally attributed to a cosmological constant or dark energy component. However, mounting observational tensions like Hubble tension have challenged the adequacy of the standard ÎCDM model and motivated alternative approaches. This study explores entropic dark energy models, which emerge from the...
In this talk, we present a higher-dimensional framework in which the curvature of compact internal space can drive an effective sign change in the 4D cosmological constant, mimicking the behavior required by phenomenological extensions of ÎCDM. A spontaneous transition in the size of the extra dimensions leads to a mirror AdS-dS shift in the external spacetime, offering a novel geometric...
Hubble H0 tension in nonlocal de Sitter gravity Branko Dragovich Institute of Physics, University of Belgrade, Belgrade, and Mathematical Institute of the Serbian Academy of Sciences and Arts, Belgrade, Serbia Email dragovich@ipb.ac.rs Abstract Despite its great success, the general theory of relativity is not the final theory of gravity. In addition to other problems,...
Ultralight Dark Matter (ULDM) has emerged as a compelling alternative to the Cold Dark Matter paradigm at small scales, naturally producing solitonic cores at the center of halos and granular structures arising from wave interference. These features lead to distinctive dynamical effects, including the random motion of the core and dynamical heating of stars in galactic systems. In this work we...
We present two fundamental theories for the early Universe: (i) the first consists in an ultraviolet completion of the inflationary paradigm, (ii) the second instead replaces inflation with quantum gravity.
The thereatical framework is for both the scenarios a nonlocal unification of gravity and matter consistent with unitarity and finiteness at quantum level.
In (i) the theory is...
Dark matter consisting of ultralight bosons can form a macroscopic Bose-Einstein condensate with distinctive observational signatures. I will discuss a two-field generalization where an axion couples to a moduli field through its kinetic term, representing the phase and radial modes of a complex scalar field. This kinetic coupling produces dramatic modifications to cosmological evolution, and...
Probes of the large scale structures can give us the much needed insight into the nature of the dark Universe. In this talk I will show the latest results from the Kilo Degree Survey (KiDS) and our prospect with the stage four survey LSST. I will focus on the 3x2pt analysis that combines weak gravitational lensing, galaxy-galaxy lensing and galaxy clustering, from its models to analysis.
In this talk I will introduce angular redshift fluctuations (ARF), a novel cosmological observable that, contrary to other standard probes that measure the counts and the shapes of galaxies, looks at the galaxies' redshifts and their fluctuations when projected under any given redshift shell. I will show ARF are found to be extremely sensitive to radial peculiar velocities, and also to the...
I will discuss the swampland distance conjecture and the Dark Dimension proposal for the cosmological constant. I will then argue on the possibility that the dark dimension obtains large size by higher dimensional inflation, relating the weakness of the actual gravitational force to the size of the observable universe. I will show that the power spectrum of primordial density fluctuations from...
Observational biases are unavoidably present in cosmological data data, and very often very difficult to asses. At the same time, we are entering the era of "big data" cosmological surveys, where data analysis has to be automatized to a large degree. While these big data will provide opportunities for unprecedentedly precise statistical measurements, task of disentangling observational biases,...
I will talk about our work where we investigate deviations from the standard adiabatic evolution of the CMB temperature, $T_{\rm CMB}(z)$, using the latest Sunyaev-Zelâdovich effect measurements and molecular line excitation data. We reconstruct the redshift evolution of $T_{\rm CMB}(z)$ in a model-independent way using Gaussian Process regression as well by chi-sq statistics. By combining...
Primordial black holes (PBHs), formed from the collapse of primordial fluctuations during the radiation-dominated era, provide a unique probe of small-scale primordial perturbations. The statistical properties of these fluctuations are crucial for determining the PBH abundance and spatial distribution. We show that even in relatively simple single-field inflation models, deviations from...
Interactions between dark matter and dark energy have been explored in a variety of contexts, with recent motivations coming from the ongoing cosmological tensions. However, many nonminimally coupled models are either strongly constrained by background observations or are phenomenological in nature. In this talk, I will present a new class of interacting Lagrangian models where scalar fields...
The origin of the high-redshift supermassive black holes (SMBHs) seen by JWST is an open puzzle in cosmology. We examine the possibility that decaying dark matter can provide the conditions necessary for the formation of these black holes. Decaying dark matter models that inject 1--13.6~eV radiation into the early universe can prevent the formation of Pop III stars by suppressing the molecular...
An analysis of a historical compilation of Hubble-Lemaaitre constant values in the last 50 years gives a chi^2 value of the dispersion with respect to the weighted average much larger than the number of points, which has an associated probability that is very low. This means that Hubble tensions were always present in the literature, due either to the underestimation of statistical error bars...
I will explain the conceptual ideas of correlation geometry underlying the theory of Causal Fermion Systems. I will explain how correlation geometry is a good candidate for a fundamental mathematical structure as it is background independent by design. This realizes Mach's dream of a purely relational description of nature.
The parameter σ8 is commonly used to quantify the amplitude of matter fluctuations at linear cosmological scales. However, its intrinsic dependence on h can introduce biases and couples the growth and Hubble tensions in an intricate way, when comparing the predictions of different models and/or datasets. For example, the bias found in models with large values of H0 is more prominent,...
Modified gravity theories, proposed to address coincidence, cosmological constant problem along with the tensions, often imply a varying Newton constant G. Observational studies usually rely on parametrizations of G, but these can produce quantities, such as the Hubble rate, that are not consistent with Einstein's equations and thus introduce arbitrariness.
We study a more consistent...
\begin{equation} S = \frac 1{16\pi G} \int (R-2\Lambda + (R-4\Lambda)\mathcal{F}(\Box)(R-4\Lambda))\sqrt{-g} \mathrm d^4 x \end{equation} was recently introduced, and a few exact cosmological solutions in flat space were presented. One of the solutions has similar properties to an interference between the radiation and the dark energy, while the other one is a nonsingular time symmetric...
The most debated crisis in cosmology today is, perhaps, the inconsistency of the estimated value of the current expansion rate of the Universe (known as the Hubble constant, H0) between different probes using high redshift and low redshift observations. Gravitational wave (GW) emitting sources, which are routinely observed nowadays through the ground-based LIGO-Virgo-KAGRA detector network,...
The stochastic dynamics of a scalar field in dS can be regarded as a non-perturbative diffusion process, to which exact distribution and correlation functions are constructed by utilising the correspondence between diffusion and Schroedinger equations. The Krein--Adler transformation of the quantum harmonic oscillator deletes several pairs of the energy levels to define quantum deficient...
In this talk I will give an overview on how the properties of dwarf galaxies have been proved to be in tension with LCDM expectations in terms of their morphology, distribution and phase-space correlation. I will then discuss the different signs of tidal disturbance that the satellite galaxies of the Milky Way present, which can not be explained if these dwarf galaxies are surrounded by a halo...
Upcoming stage 4 surveys, such as the Simons Observatory, LSST, and Euclid, are poised to measure weak gravitational lensing of the Cosmic Microwave Background (CMB) and galaxies with unprecedented precision. While the power spectrum is the standard statistic used to analyze weak lensing data, non-Gaussianity from non-linear structure growth encodes additional cosmological information in...
