Participants

YITP, Japan

Effective field theory of vector-tensor theories

We investigate a systematic formulation of vector-tensor theories based on the effective field theory (EFT) approach. The input of our EFT is that the spacetime symmetry is spontaneously broken by the existence of a preferred timelike direction in accordance with the cosmological principle. This approach not only serves as a unified description of vector-tensor theories but also highlights universal differences between the scalar-tensor theories and the vector-tensor theories. Those theories are distinguished by a phenomenological function and consistency relations between the EFT coefficients. We also discuss phenomenological predictions based on the EFT formulation.

Orsay, France

Black Holes in Scalar-Tensor Theories

I will review black holes and other compact objects in scalar-tensor theories. One class of theories which allows analytic construction of solutions is related to shift-symmetric and parity-preserving scalar field. The shift-symmetry of the scalar field yields a Noether conserved current which proves extremely useful for integrating the equations of motion. Another type of symmetry is the conformal invariance of the equation of motion of the scalar field that allows to integrate equations of motion analytically in particular classes of theories. Finally, I will consider disformal transformations as a tool to obtain new non-trivial solutions in DHOST theories.

Korea Astronomy and Space Science Institute (KASI), Republic of Korea

Joint reconstructions of growth and expansion histories from Stage-IV surveys: Dark Energy beyond Lambda.

Using simulated Supernovae (SN), Baryon Acoustic Oscillations (BAO) and Redshift-Space Distortions (RSD) measurements from the next generation of (stage-IV) cosmological surveys, we jointly reconstruct the growth and expansion histories using a non-parametric technique: Gaussian Processes. Our approach only relies on few reasonable assumptions, namely:

(i) a Friedmann-Lemaître-Robertson-Walker metric

(ii) an Einstein De Sitter Universe at high-redshift.

We forecast the future surveys’ potential to accurately reconstruct the Dark Energy (DE) evolution and thus to detect any possible deviation from a cosmological constant. We generate mock data for various alternative DE models, and illustrate how our method captures the correct DE behaviour in all cases — being capable of ruling out \Lambda at more than 95% C.L.

Based on : Phys.Rev.D 106 (2022) 8, 083513

KEK/QUP, Japan

The past, present, and future of the search for primordial gravitational waves from cosmic inflation with CMB experiments in the Atacama desert and space

Searching for primordial gravitational waves (PGWs) is one of the key topics in cosmology because it must be smoking gun evidence from the creation of the universe. PGWs leave a characteristic pattern on the cosmic microwave background (CMB) in the form of B-mode polarization. Two experiments, POLARBEAR and BICEP2, announced a measurement/detection of "B-mode" signals in March 2014. POLARBEAR in the Atacama desert reported a measurement of B-modes at sub-degree scales created by gravitational lensing effects; BICEP2 on the South Pole claimed to detect primordial B-modes, but it has been confirmed that the signal is emitted from dust in our galaxy. Until now, no experiment has detected primordial B-modes yet, we are actively observing CMB polarization and developing/building future experiments.

In this talk, I will briefly explain the motivation of B-mode measurements first, then summarize the status of the measurements and POLARBEAR's achievements. Next I will show the progress of the current experiments, e.g. the Simons Array experiment. Then I'll talk with next-generation ground-based CMB experiments and how we need to optimize/design experiments in order to maximize our science outputs as well as to detect primordial B-modes. At the end of my talk, I will mention synergies between ground-based experiments and a satellite mission.

KIAS, Republic of Korea

The first direct measurement of gravitational potential decay rate and improved dark energy constraint

The integrated Sachs-Wolfe (ISW) effect probes the decay rate (DR) of large scale gravitational potential and therefore provides unique constraint on dark energy (DE). However its constraining power is degraded by the ISW measurement, which relies on cross-correlating with the large scale structure (LSS) and suffers from uncertainties in galaxy bias and matter clustering. In combination with lensing-LSS cross-correlation, DR can be isolated in a way free of uncertainties in galaxy bias and matter clustering. We applied this proposal to the combination of the DR8 galaxy catalogue of DESI imaging surveys and Planck cosmic microwave background (CMB) maps. We achieved the first DR measurement, with a total significance of $3.2\sigma$. We verified the measurements at three redshift bins ([0.2,0.4), [0.4, 0.6), [0.6,0.8]), with two LSS tracers (the "low-density points" and the conventional galaxy positions). Despite its relatively low S/N, the addition of DR significantly improves dark energy constraints, over SDSS baryon acoustic oscillation (BAO) data alone or Pantheon supernovae (SN) compilation alone. For flat wCDM cosmology, the improvement in the precision of $\Omega_m$ is a factor of 1.8 over BAO and 1.5 over SN. For the DE equation of state w, the improvement factor is 1.3 over BAO and 1.4 over SN. These improvements demonstrate DR as a useful cosmological probe, and therefore we advocate its usage in future cosmological analysis.

Naples University, Italy

Cosmological tests of gravity

The late time cosmic acceleration is one of the most puzzling phenomena in modern cosmology. Its modeling within General Relativity (GR) through the cosmological constant (L) results in the LCDM scenario. Although the latter gives a precise description of the Universe, it is known that it still contains a number of unresolved problems. These lead researchers to look for modified gravity models, for example by including additional degrees of freedom. In this talk I will present an overview about model independent tests of gravity, viability conditions and their impact on parameter estimation, modified gravity models that can challenge LCDM and solve cosmological tensions.

University College London, United Kingdom

Dark energy as a Weyl geometric effect

We consider the cosmological implications of quadratic Weyl geometric gravity in the presence of matter coupling. By expressing the square of the Weyl scalar with the help of an auxiliary scalar field, the gravitational action can be linearized, leading in the Riemann space to a conformally invariant theory with the matter Lagrangian nonminimally coupled to the Ricci scalar. The gravitational field equations of the theory are obtained, as well as the energy-momentum balance equations. The divergence of the matter energy-momentum tensor does not vanish, and an extra force, depending on the Weyl vector, and the matter Lagrangian is present in the theory. The cosmological implications of the theory are considered for the case of a flat, homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker geometry, and it turns out that the model gives a good description of the observational data for the Hubble function up to a redshift of the order of z =3.

Heidelberg University, Germany

Cosmological tensions as guiding principles

Nagoya, Japan

pSZ Cosmology

Abstract

TBA

Yonsei University, Republic of Korea

Title

Abstract

TBA

Kyushu, Japan

Graviton non-gaussianity in a-vacuum

Abstract

I will talk about the bispectrum of the tensor perturbation in the a-vacuum on de Sitter space and an intriguing result that the bispectrum may be exponentially enhanced to be detectable by observation even if the spectrum is too small to be detected.

Shaid Beheshti, Iran

Ginzburg-Landau Theory of Dark Energy and more!

Abstract

TBA

Ehwa Womans University, Republic of Korea

Binary black hole populations and gravitational-wave observations

The discovery of GW150914 shows stellar-mass black holes do merge. The coalescence (including inpisral-merge-ringdown phases) of a binary black hole (BBH) is proved to be observable via gravitational waves (GWs) with km-scale laser interferometry. The design sensitivity of advanced LIGO, Virgo, and KAGRA is optimized to observe stellar-mass BBHs in a GW frequency band between 10-2000 Hz. GW observation allows us to measure all three masses involved in the merge with impressive accuracy. Spins of the final BH is also a direct observable, which is one of the unique information extractable from GW observation. Beyond the stellar astrophysical point of view, strong cosmological implications with BBH populations have been actively suggested even before the detection of GWs. BBHs are expected to be "dark", for example, as they would lack any electromagnetic (EM) counterparts. However, the concept of 'dark siren', similar to 'standard candle' in the context of EM astronomy, is suggested as a way to use BBHs for measuring a Hubble constant. In this talk, I will give an brief overview of properties of BBH populations we learned so far, based on the GW transient catalog papers. I would also discuss their implications in astrophysics and cosmology.

KEK, Japan

Title

Abstract

TBA

Yonsei University, Republic of Korea

Evidence for strong systematic bias in supernova cosmology

Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) and the color-luminosity relation (CLR) in the type Ia SN luminosity standardization would not show zero-point offsets with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). Here we show that this correlation originates from a strong progenitor age dependence of the zero-points of the WLR and CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters x1 and c. This 4.6 sigma result is reminiscent of Baade's discovery of the zero-point variation of the Cepheid period-luminosity relation with population age, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant offsets in the WLR and CLR for the same dataset. We illustrate that the differences between the high-z and low-z SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift may well be an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is little evidence left for an accelerating universe, posing a serious question to one of the cornerstones of the concordance model.

Seoul National University (SNU), Republic of Korea

Identification of host galaxies of dark sirens

Gravitational waves without electromagnetic counterparts are called dark sirens. Because the positional accuracy of the gravitational wave sources detected by ground-based detectors are rather poor, the host galaxies of such dark sirens cannot be identified. Significant improvements become possible if detectors that are sensitive in mid-frequencies in the range 0.01 ~ 10 Hz as many of the black hole and neutron star binaries can be observed for long durations up to one year. We discuss the improvements in accuracies of the sky positions and luminosity distances to population of compact binary coalescences inferred from the GWTC-3 and show that host galaxies of some of these sources can be uniquely identified without the aid of electromagnetic radiation in proposed detectors such as AEDGE and DECIGO. The presence of the eccentricity at around 0.1 Hz can further improve the estimation of position and distance.

CERN, Switzerland

Non-Abelian Gauge Fields in Inflation, GW Background, and Origin of Matter Asymmetry

In this talk, I discuss the possible physical consequences of non-Abelian gauge fields in inflation. First, I explain that any SU(N) gauge field can acquire an isotropic and homogeneous VEV at its SU(2) subsector. This isotropic SU(2) gauge field's VEV is the attractor solution against initial anisotropies. Next, I show that this setup has a very rich phenomenology and in particular, leads to new mechanisms for the generation of primordial GWs and fermions in inflation. As a smoking gun, it generically predicts a chiral and non-Gaussian GW background testable by future CMB and laser interferometers. Finally, I present a possible realization of this setup based on embedding axion-inflation in Left-Right symmetric extensions of the SM, i.e. SU(2)_R-axion inflation. In this model, the chiral anomaly of the SU(2)_R gauge field provides a common origin for inflation, baryogenesis, and dark matter production.

KEK, Japan

The integrated perturbation theory for cosmological tensor fields

In order to extract maximal information about cosmology from the large-scale structure of the Universe, one needs to use every bit of signals that can be observed. Beyond the spatial distributions of astronomical objects such as galaxies, the spatial correlations of tensor fields, such as galaxy spins and shapes, are ones of promising sources that we can access in the era of large surveys in near future. The perturbation theory is a powerful tool to analytically describe the behaviors and evolutions of correlation statistics for a given cosmology. In this paper, we formulate a nonlinear perturbation theory of tensor fields in general, based on the existing formulation of integrated perturbation theory for the scalar-valued bias, generalizing it to include the tensor-valued bias. In order to take advantages of rotational symmetry, the formalism is constructed on the basis of irreducible decomposition of tensors, identifying physical variables which are invariant under the rotation of coordinates system. Fundamental formulations and calculational techniques, applications to some simple examples are presented.

References:

T. Matsubara, arxiv:2210.10435, arxiv:2210.11085

T. Matsubara, Phys. Rev. D 83, 083518 (2011)

T. Matsubara, Phys. Rev. D 90, 043537 (2014)

YITP, Japan

Dark Energy, Black Holes and Effective Field Theory

Abstract

TBA

IFT, Madrid

Machine Learning Inflation

We present a novel approach, using machine learning, to analytically reconstruct the inflationary potential directly from the CMB data. We also perform feature searches, and we find a dramatic improvement over traditional methods based on simple oscillatory models. Based on arXiv: 2211.XXXXX

RESCEU, Japan

Observational tests of gravity with gravitational waves

Abstract

TBA

CNRS & L2C- Montpellier University, France

The many uses of modified gravity

In cosmology, modified gravity can be used in order to accelerate the expansion, to modify the growth of perturbations. It can also be used to construct flat bouncing universes and we shall present such a model possessing remarkable mathematical and physical properties. We shall present as well some generalizations of this model.

University of Seoul, Republic of Korea

Deep Learning approaches to Large Scale Structure Cosmology

National Observatory of Athens, Greece

Alleviating H0 and σ8 tensions in modified gravity

Abstract - TBA

IPMU, Japan

Primordial Black Holes from Inflation

Abstract

TBA

Sejong University, Republic of Korea

Estimating the Hubble parameter from the late-time Universe and the BAO

Abstract

TBA

WASEDA, Japan

QFT description of particle scatterings after inflation

Inflaton field oscillation causes non-perturbative particle production, which is known as preheating. In such a background, the particle scattering processes differ from that in the Minkowski spacetime. We discuss the first-principle calculation of such processes within quantum field theory, and show a new non-perturbative particle production process, which cannot be captured by perturbative calculations in Minkowski spacetime.

Sejong University, Republic of Korea

Does the CMB constrain late-time unparticle cosmology?

Authors: Maurice van Putten, Maryam Aghaei Abchouyeh (speaker)

Unparticle cosmology gives an unconventional outlook on the dark sector of cosmology. This model derives from a finite temperature broken conformal symmetry of radiation, described by a non-radiative correction with unknown sign in energy density. This symmetry breaking has a sign ambiguity, in which corrections about the IR fixed point are normal or tachyonic. While the first has been ruled out in a recent study, the latter possesses a late-time temperature $T_c\simeq 4\,T_{CMB}$ where $T_{CMB}$ denotes the temperature of the Cosmic Microwave Background (CMB). The CMB is hereby exposed to an enormous heat bath. The age of the Universe constrained by the globular clusters, independently puts a constraint on any heat exchange from unparticles to the CMB in $\Lambda\mbox{CDM}$. Accordingly, we estimate the cross section of unparticles interactions with CMB photons to be $\sigma _{\gamma \mathcal{U}} \lesssim 10^{-40}\ \mbox{m}^2=10^{-3}\ \mbox{nb}$ which puts unparticles in late-time cosmology, if present, at the edge of the standard model.

KASI, Republic of Korea

A measurement of the Integrated Sachs-Wolfe Effect with the Rapid ASKAP Continuum Survey

The evolution of the gravitational potentials on large scales due to the accelerated expansion of the Universe is an important and independent probe of dark energy, known as the integrated Sachs-Wolfe (ISW) effect. We measure this ISW effect through cross-correlating the cosmic microwave background maps from the Planck satellite with a radio continuum galaxy distribution map from the recent Rapid ASKAP Continuum Survey (RACS). We detect a positive cross-correlation at ~2.8σ relative to the null hypothesis of no correlation. We parameterise the strength of the ISW effect through an amplitude parameter and find the constraints to be A_ISW = 0.94^{+0.42}_{-0.41}, which is consistent with the prediction of an accelerating universe within the current concordance cosmological model, ΛCDM. The credible interval on this parameter is independent of the different bias models and redshift distributions that were considered when marginalising over the nuisance parameters. We also detect a power excess in the galaxy auto-correlation angular power spectrum on large scales (ℓ≤40), and investigate possible systematic causes.

Central China Normal University, China

Validity of the unified R^2-dark energy models in F(R) gravity

Dark energy models of F(R) gravity generally suffer from the so-called singularity problem, which can be cured by adding an R^2 term. Considering the higher-curvature correction as an origin of inflation, we have a unified picture of the whole comic history from inflation to the dark energy epoch. The price is, however, that the structure of potential energy is gigantically reshaped, for which we reexamine the time-evolution at the radiation-dominant era. Though it can safely preserve the Big Bang nucleosynthesis, we suggest that the reheating dynamics should be refined

Yonsei University, Republic of Korea

Primordial Black Holes and Gravitational Waves from the Tachyonic Instability in Higgs-R^2 Inflation

Title : Abstract : The running of the Higgs self coupling may lead to numerous phenomena in early universe cosmology. In this talk I will introduce a scenario where the Higgs running induces turns in the trajectory passing a region with tachyonic mass, leading to a temporal tachyonic growth in the curvature power spectrum. This effect induced by the Higgs leaves phenomena in the form of primordial black holes and stochastic gravitational waves, where proposed GW observatories will be able to probe in the near future.

Ewha Womans University, Republic of Korea

Features in the power spectrum from resonant turns

We explore observational signatures from multi-field inflationary models with large turns in field space. We derive analytical solutions for the background and first perturbations and generalise our results to more than two fields. We find that multiple (sharp) turns can significantly enhance the power spectrum and can therefore lead to enhanced primordial black holes production.

SISSA, Italy

Planck-Scale Physics and the Peccei-Quinn inflation model

The radial direction of the Peccei–Quinn field can drive cosmic inflation, given a non-minimal coupling to gravity. This scenario has been considered to be capable of explaining inflation, the strong CP problem, and dark matter. We argue that Peccei– Quinn inflation is extremely sensitive to higher-dimensional operators. Further combining with the discussion on the axion quality required to solve the strong CP problem, we examine the validity of this scenario. We also show that a resonant amplification of the axion field is unavoidable after Peccei–Quinn inflation.

Jeju National University, Republic of Korea

Dynamical analysis in regularized 4D Einstein-Gauss-Bonnet gravity with non-minimal coupling

We investigate the regularized four-dimensional Einstein-Gauss-Bonnet (4D EGB) gravity with a non-minimal scalar coupling function, which is an extension of the regularized 4D EGB theory. By introducing non-minimal coupling to the Gauss-Bonnet term, we demonstrate the additional contribution to the dynamical equations which is otherwise absent in the dimensionally-regularized theory. Furthermore, we analyze the stability of the system by using the dynamical system approach based on fixed points. Then, we consider the time evolution to investigate the history of the universe and constraint with observational data to obtain the cosmological parameters of the model..

Waseda, Japan

Inspiral gravitational waveforms from compact binary systems in Horndeski gravity

In a subclass of Horndeski theories with the speed of gravity equivalent to that of light, we study gravitational radiation emitted during the inspiral phase of compact binary systems. We compute the waveform of scalar perturbations under a post-Newtonian expansion of energy-momentum ten- sors of point-like particles that depend on a scalar field. This scalar mode not only gives rise to breathing and longitudinal polarizations of gravitational waves, but it is also responsible for scalar gravitational radiation in addition to energy loss associated with transverse and traceless tensor polarizations. We calculate the Fourier-transformed gravitational waveform of two tensor polariza- tions under a stationary phase approximation and show that the resulting waveform reduces to the one in a parametrized post-Einsteinian (ppE) formalism. The ppE parameters are directly related to a scalar charge in the Einstein frame, whose existence is crucial to allow the deviation from Gen- eral Relativity (GR). We apply our general framework to several concrete theories and show that a new theory of spontaneous scalarization with a higher-order scalar kinetic term leaves interesting deviations from GR that can be probed by the observations of gravitational waves emitted from neutron star-black hole binaries. If the scalar mass exceeds the order of typical orbital frequencies ω ≃ 10−13 eV, which is the case for a recently proposed scalarized neutron star with a self-interacting potential, the gravitational waveform practically reduces to that in GR.

Sejong University, Republic of Korea

Cosmological QUOKKA - Quasar Observations on the KVN from Korea to Australia

Measuring distances vs redshift (more commonly known as a Hubble Diagram) is one of the most fundamental yet difficult observations that can be made in astronomy. Every time the diagram has been extended to greater and greater distances (or higher redshifts), important discoveries have been made. Most recently this was the accelerating expansion of the universe, for which the 2011 Nobel Prize was awarded. The discovery was accomplished using Type Ia supernovae, but they are based on the 'distance ladder' and can only be seen to a redshift of ~2. Active Galactic Nuclei (AGN) are unique objects as they can be seen at both low redshift (z~0) and high redshift (z~6). For this reason, they have long been sought as a distance measure with limited success. It is within this context that we are beginning the Cosmological QUOKKA project. The core assumption is that the radio variability observed is constrained by the speed of light. Multiplying the timescale of variability by the speed of light gives a linear size estimate which can then be compared against the apparent size using Very Long Baseline Interferometry (VLBI). In this presentation, I will describe the method, some early results (including a measurement of the Hubble Constant) and the details of our observational project using the Korean VLBI Network and the Mopra telescope in Australia.

Rikkyo University, Japan

Consistency of higher-order derivative couplings to matter fields

Recently, a generalized invertible disformal transformation with higher-order derivatives of scalar field has been proposed. However, matter fields coupled with gravity through this novel class of generalized disformal metric could yield Ostrogradsky ghost. Therefore, we analyze conditions for the matter couplings to be consistent, so that the Ostrogradsky ghost does not appear. In particular, we discuss possibility of removing the Ostrogradsky ghost without relying on any particular gauge such as the unitary gauge.

Waseda, Japan

Primordial black holes from Higgs inflation with a Gauss-Bonnet coupling

Primordial black Holes (PBHs) can be the origin of dark matter within the framework of standard model of particle physics. Inflation provides a mechanism for generating the seeds of PBHs in the presence of a nontrivial scalar field evolution. We study the power spectra of primordial curvature perturbations generated during Gauss-Bonnet (GB) corrected Higgs inflation in which the inflaton field not only has a nonminimal coupling to gravity but also has a GB coupling. For a specific choice of the GB coupling exhibiting a rapid change during inflation, we show that curvature perturbations are enhanced during the nontrivial scalar field evolution along an effective potential with a plateau or a bump. There are viable parameter spaces in which the seeds of PBHs are sufficiently generated, while satisfying observational constraints on primordial scalar and tensor power spectra on CMB scales.

KASI/UST, Republic of Korea

Cosmology with Method of Iterative Smoothing

Iterative Smoothing Method is a non-parametric regression approach for reconstruction of expansion history of the Universe and properties of dark energy. We can apply this method in various aspects of cosmology and astrophysics with no cosmological model assumption. We have worked on constraining SN Ia light-curve hyperparameters, searching for features in the data which can be a hint for systematics or new physics, parameter estimation and model selection. Our most recent application of the method is comparing our novel frequentist approach for model selection with conventional Bayesian evidence model selection. We show that when none of the candidate models (proposed to fit a data) is the true model, our novel frequentist approach can rule out all candidates while conventional Bayesian approach selects the least incorrect model. For more practical application of the method, our ongoing task is developing method of iterative smoothing for reconstructing the expansion history using combination of data with different natures. The method using combination of Type Ia supernova and BAO data is in preparation. We expect that the new method can be applied for cosmological studies using the real data from present and forthcoming surveys including DESI, Rubin, Roman, etc.

Rikkyo University, Japan

SU(N)-natural inflation in axisymmetric background

We study the homogeneous and anisotropic dynamics of pseudoscalar inflation coupled to an SU(N) gauge field. Each isotropic solution is characterized by the corresponding SU(2) subalgebra of the SU(N) algebra. It is shown numerically that the isotropic universe is a universal late-time attractor in the case of the SU(3) gauge field. Interestingly, we find that a transition between the two different gauge-field configurations characterized by different SU(2) subalgebras can occur during inflation. We clarify the conditions for this to occur.

Ewha Womans University, Republic of Korea

Think EFT! Applications of effective field theory to cosmology.

Effective field theories can be used to study a wide range of phenomena in cosmology. They can give us analytic control during the first stages of false vacuum decay, help us examine the consequences of theories with non-standard initial conditions in inflation, as well to analyse theories that do not propagate scalar degrees of freedom such as the Cuscaton and finally give us the tools to develop frameworks for torsion theories of gravity.

Nagoya University, Japan

Revisiting TOV Problems in F(R) Gravity

F(R) gravity is one of the hopeful modified gravity theories, and it has additional scalar d.o.f. for the gravitational field. We will revisit the effect of this scalar component in an isolated spherical star system explicitly. Especially we will focus on the scalar profile inside the star and the asymptotic region, which have not been discussed carefully in the literature.

University of Conneticut, US

Anthropic reasoning for the cosmological constant

Title: Abstract: The cosmological constant is accountable for the accelerated expansion of our Universe. However, there is a huge discrepancy regarding what the value should be. Observational data have provided a tight constraint on the cosmic star formation history from z = 8 to the present. What happens to the star formation rate beyond z=0? I will discuss the star formation rate from our suite of simulations into the future. Since the cosmological constant becomes dominant in the future of our universe, I further simulate counter-factual universes to assign anthropic weights to each universe within the multiverse setting. I will argue that using the asymptotic star formation efficiency as weights, we improve previous estimates of observers living in universes similar to ours..

KASI, Republic of Korea

Born to run: Inflationary Dynamics and Observational Constraints

The model of cosmological slow-roll inflation predicts a spectrum of adiabatic Gaussian density perturbations, with a spectral index close to one and very small running of that index (10^-3). It also predicts a spectrum of primordial gravitational waves. While the density fluctuations have been measured by the CMB and large-scale surveys, the gravitational waves have not been detected in the CMB polarisation. In this talk I show how that if the limit on the gravitational wave amplitude gets small enough, then slow-roll generically predicts a larger running of the density power spectrum. This running will be detectable by a combination of future all-sky surveys such as DESI, SPHEREx and CHIME, by 2030.

Institute of Theoretical Physics, Chinese Academy of Sciences, China

Starobinsky Model Revisited

We revisit the enhancement of the power spectrum in Starobinsky's linear potential model. We find that the modulated oscillations with period π gives an extra enhancement of ~2.6, which is important in generating the primordial black holes. We also compare this model to the constant-roll inflation, and briefly discuss the non-Gaussianity in both cases.

KASI, Republic of Korea

The Halo Occupation Distribution of HI Galaxies

The next generation of galaxy surveys will provide more precise measurements of galaxy clustering than have previously been possible. The 21 cm radio signals that are emitted from neutral atomic hydrogen (H I) gas will be detected by large-area radio surveys such as the Widefield Australian Square Kilometre Array (SKA) Pathfinder L-band Legacy All-sky Blind Survey and SKA, and deliver galaxy positions and velocities that can be used to measure galaxy clustering statistics. However, to harness this information to improve our cosmological understanding and learn about the physics of dark matter and dark energy, we need to accurately model the manner in which galaxies detected in H I trace the underlying matter distribution of the universe. For this purpose, we develop a new H I-based halo occupation distribution (HOD) model, which makes predictions for the number of galaxies present in dark matter halos conditional on their H I mass. The parameterized HOD model is fit and validated using the DARK SAGE semi-analytic model, where we show that the HOD parameters can be modeled by simple linear and quadratic functions of the H I mass. However, we also find that the clustering predicted by the HOD depends sensitively on the radial distributions of the H I galaxies within their host dark matter halos, which does not follow the Navarro-Frenk-White profile in the DARK SAGE simulation. As such, this work enables-for the first time-a simple prescription for placing galaxies of different H I masses within dark matter halos in a way that is able to reproduce the H I mass-dependent galaxy clustering and H I mass function simultaneously and without requiring knowledge of the optical properties of the galaxies. Further efforts are required to demonstrate that this model can be used to produce large ensembles of mock galaxy catalogs for upcoming surveys.

KASI, Republic of Korea

Probing the primordial universe with CMB power spectrum and bispectrum

I present two of our recent works on the early universe using Planck’s CMB temperature and polarisation data. The first concerns a free-form reconstruction of the primordial power spectrum. We further develop the Modified Richardson-Lucy (MRL) algorithm to include polarisation data and introduce a novel regularisation term which reduces noise fitting. The reconstructed spectrum has some notable features that improve the fit to each of TT, TE and EE data, whilst being statistically consistent with a simple power-law of ΛCDM. The second work is on a novel CMB bispectrum estimator, named CMB-BEst, for probing primordial non-Gaussianity. CMB-BEst is computationally efficient and suitable for studying oscillatory bispectrum shapes, such as those predicted from feature and resonance-type inflation models. We conclude with some future prospects for upcoming CMB surveys.

Chung-Ang University, Republic of Korea

Reheating and Dark Matter Freeze-in in the Higgs-R^2 Inflation Model

We study the post-inflationary dynamics for reheating and freeze-in dark matter in the Higgs-R^2 inflation model. Taking the perturbative approach for reheating, we determine the evolution of the temperature for radiation bath produced during reheating and determine the maximum and reheating temperatures of the Universe. Adopting a singlet scalar dark matter with a conformal non-minimal coupling and a vanishing Higgs-portal coupling, we discuss the freeze-in production of dark matter both from the non-thermal scattering during reheating and the thermal scattering after reheating. We find that thermal scattering is dominant for dark matter production in our model due to the high reheating temperature. The reheating temperature in our model is determined dominantly by the Higgs condensate to be up to about 10^14 GeV and dark matter with masses up to about 10^9 GeV can be produced with a correct relic density.

Reference: https://arxiv.org/abs/2202.13063

APCTP, Republic of Korea

The evidence of special early dark energy from BBN

TBA