# Titles and abstracts [6-10 August 2018]

NameTalk Title & Abstract
Stephen Appleby The well-tempered Cosmological Constant
Self tuning is one of the few methods for dynamically cancelling a large cosmological constant and yet giving an accelerating universe. Its drawback is that it tends to screen all sources of energy density, including matter. We develop a model that tempers the self tuning so the dynamical scalar field still cancels an arbitrary cosmological constant, including the vacuum energy through any high energy phase transitions, without affecting the matter fields. The scalar-tensor gravitational action is simple, related to cubic Horndeski gravity, with a nonlinear derivative interaction plus a tadpole term. Applying shift symmetry and using the property of degeneracy of the field equations we find families of functions that admit de Sitter solutions with expansion rates that are independent of the magnitude of the cosmolog ical constant and preserve radiation and matter dominated phases. That is, the method can deliver a standard cosmic history including current acceleration, despite the presence of a Planck scale cosmological constant.
Shun Arai Constraints on gravitational couplings in Horndeski theory with gravitational waves
Horndeski theory is known as a framework for the explanation of the late-time cosmic acceleration, while a numerous number of models still remains unconstrained by observations. In addition to the cosmic acceleration, the Horndeski theory predicts the time variation of gravitational couplings. Thus, it is important to constrain the gravitational couplings by observations. For this purpose, we consider gravitational waves (GW) observations in the framework of Horndeski theory. In our previous work (arXiv:1711:03776), we revealed that the observable parameters in GW detections well trace the difference of the acceleration mechanisms in the Horndeski theory. In this work, we classify the models in terms of the gravitational couplings; G_light and G_matter. We numerically confirmed that the amplification of GW is more likely to happen during the acceleration epoch if we filter the models consistent with the observations of the Hubble parameter. This feature implies that the measurement of a GW observation can makes it easier to reduce the model space of the Horndeski theory. In the end, we forecast the constraints on the Horndeski theory by the planed GW detectors significantly constrain the models.
Jacobo Asorey Cosmology with Type Ia Supernova gravitational lensing
In the last decades, the use of Type Ia Supernovae (SN) as standard candles has allowed us to understand the geometry of the Universe as they help to measure the expansion rate of the Universe, especially in combination with other cosmological probes such as the study of cosmic microwave background radiation anisotropies or the study of the imprint of baryonic acoustic oscillations on the galaxy clustering. Cosmological parameter constrains obtained with type Ia SN are mainly affected by intrinsic systematic errors. But there are other systematic effects related with the correlation of the observed brightness of Supernova and the large-scale structure of the Universe such as the effect of peculiar velocities and gravitational lensing. The former is relevant for SN at low redshifts while the latter starts being relevant for SN at higher redshifts. Gravitational lensing depends on how much matter is along the trajectory of each SN light beam. In order to account for this effect, we consider a statistical approach by defining the probability distribution (PDF) that a given supernova brightness is magnified by a given amount, for a particular redshift . We will show that different theoretical approaches to define the matter density along the light trajectory hugely affect the shape and width of the PDF. This may have catastrophic effects on cosmology fits using Supernova lensing as planned for surveys such as the Dark Energy Survey or future surveys.
Gianluca Calcagni Testing quantum gravity
Takeshi Chiba Reconstructing f(R) gravity from the spectral index
We provide the procedure for reconstructing f(R) from a given scalar spectral index as a function of the e-fold number.
Inyong Cho Black Holes and Global Monopole in Closed and Open Space
Gongjun Choi Probing Decoupling in Dark Sectors with the Cosmic Microwave Background
The phase shift in the acoustic peaks in the angular power spectrum of CMB temperature and polarization anisotropy plays an important role as a probe of the nature of contribution to Neff. It can determine whether the extra species are free-streaming particles, like neutrinos, or tightly-coupled, like the photons, during eras probed by the CMB. On the other hand, some extensions of the standard model produce new relativistic particles that decouple from the primordial cosmic plasma after neutrinos, but prior to photons. In this talk, we study the signature of new relativistic species that decouple during this intermediate epoch. We shall argue that a new type of phase shift occurs in the acoustic peaks, different from the usual constant phase shift on small scales. For intermediate decoupling times, the shape and amplitude of the phase shift depends not only Neff but the redshift(zdec) at which the new species decoupled.
Ki-Young Choi Dark matter with low reheating temperature
Antonio De Felice Phenomenology in Minimal Theory of Massive Gravity: self accelerating and normal branch
Fabio Finelli Planck 2018 constraints on inflation
Jan Hamann Cosmological parameters after Planck 2018
I will summarise what the Planck 2018 data release tells us about the cosmological parameters. Particular emphasis will be given to internal and external tensions of this data set and their possible resolutions.
Lavinia Heisenberg Exposing modified gravity to the many facets of cosmic reality
Ho Seong Hwang HectoMAP and Horizon Run 4: Statistics of Cosmic Voids in the Real and Simulated Universe
Jaichan Hwang Fully nonlinear and exact formulation of relativistic perturbation theory
M. James Jee Studying Cosmology and Baryonic Feedback through Comprehensive Analysis of the Deep Lens Survey
Jiro Soda String axions, Flapping resonance, and GW forest
It has been claimed that axions predicted in string theory may have ascalar potential which has a much shallower potential region than the conventional cosine potential. We first show that such axions generically undergo a prominent resonance instability, which we named the flapping resonance. We study axion dynamics caused by the flapping resonance with analytic method and lattice simulation. We find that string axions in various mass ranges generate gravitational waves (GWs) with peaks at various frequencies determined by the mass scales, dubbed the GW forest. This may allow us to explore the string axiverse through future multi-frequency gravitational wave observations. We also investigate GWs produced by the axion dark matter.
Kenji Kadota Exploration for the light dark matter
A few examples for the light dark matter will be discussed with an emphasis to illustrate the complementarity between the particle physics and cosmology probes.
Alexander Kamenshchik Pauli-Zeldovich cancellation of the vacuum energy divergences, auxiliary fields and supersymmetry
We have considered the Pauli-Zeldovich mechanism for the cancellation of the ultraviolet divergences in vacuum energy. This mechanism arises because bosons and fermions give contributions of the opposite signs. In contrast with the preceding papers devoted to this topic wherein mainly free fields were studied, here we have taken their interactions into account to the lowest order of perturbation theory. We have constructed some simple toy models having particles with spin 0 and spin 1/2, where masses of the particles are equal while the interactions can be quite non-trivial.
Ryan Keeley Model independent inference of the expansion history and implications for the growth of structure
We model the expansion history of the Universe as a Gaussian Process and find constraints on the dark energy density and its low-redshift evolution using distances inferred from the Luminous Red Galaxy (LRG) and Lyman-alpha (Lyα) datasets of the Baryon Oscillation Spectroscopic Survey, supernova data from the Joint Light-curve Analysis (JLA) sample, Cosmic Microwave Background (CMB) data from the Planck satellite, and local measurement of the Hubble parameter from the Hubble Space Telescope (𝖧0). Our analysis shows that the CMB, LRG, Lyα, and JLA data are consistent with each other and with a ΛCDM cosmology, but the 𝖧0 data is inconsistent at moderate significance. Including the presence of dark radiation does not alleviate the 𝖧0 tension in our analysis. While some of these results have been noted previously, the strength here lies in that we do not assume a particular cosmological model. We calculate the growth of the gravitational potential in General Relativity corresponding to these general expansion histories and show that they are well-approximated by Ωm^0.55 given the current precision. We assess the prospects for upcoming surveys to measure deviations from ΛCDM using this model-independent approach.
Yoonbai Kim Inflation in f(R) gravity
Numerous models of f(R) gravity have been considered in various contexts. In this talk, we summarize (almost-all) the f(R) gravity models and check the patterns of inflation including their viabiity as a model of the inflationary universe.
Seoktae Koh Gravitational waves in inflation with Gauss-Bonnet coupling
Hanwool Koo Detection of the Intrinsic Spin Alignments in Isolated Spiral Pairs
An observational evidence for the intrinsic galaxy alignments in isolated spiral pairs is presented. From the catalog of the galaxy groups identified by Tempel et al. in the flux limited galaxy sample of the Sloan Digital Sky Survey Data Release 10, we select those groups consisting only of two spiral galaxies as isolated spiral pairs and investigate if and how strongly the spin axes of their two spiral members are aligned with each other. We detect a clear signal of intrinsic spin alignment in the isolated spiral pairs, which leads to the rejection of the null hypothesis at the 99.9999% confidence level via the Rayleigh test. It is also found that those isolated pairs comprising two early-type spiral galaxies exhibit the strongest signal of intrinsic spin alignment and that the strength of the alignment signal depends on the angular separation distance as well as on the luminosity ratio of the member galaxies. Using the dark matter halos consisting of only two subhalos resolved in the EAGLE hydrodynamic simulations, we repeat the same analysis but fail to find any alignment tendency between the spin angular momentum vectors of the stellar components of the subhalos, which is in tension with the observational result. A couple of possible sources of this apparent inconsistency between the observational and the numerical results are discussed.
Sachiko Kuroyanagi Anisotropies in the gravitational wave background as a probe of the cosmic string network
Pulsar timing arrays are one of the powerful methods to search for the existence of cosmic strings through detection of gravitational waves. In this talk, I will present how pulsar timing arrays can be used to search for cosmic strings and what types of information we can obtain if we detect gravitational wave background from them. In addition, I will show that we can extract more information on properties of cosmic strings by analyzing anisotropies in the gravitational wave background.
Benjamin L'Huillier Probing extensions to the concordance model with N-body simulations
Seokcheon Lee Modification of Starobinsky inflation
Starobinsky has suggested an inflation model which is obtained from the vacuum Einstein’s equations modified by the one-loop corrections due to quantized matter fields. Although the one-loop gravitational action is not known for a general FRW background, it can be obtained in a de Sitter space to give M2pR+αR2+βR2 ln(R/M2). Thus, one needs to investigate the inflationary behavior of this model compared to the Starobinsky model (i.e. β = 0). The coefficient α can be changed by varying the renormalization scale M2 and β is obtained from the quantum anomaly which is related to the numbers of quantum fields. It has been assumed that α ≫ β. We investigate the viable values of α and β based on the CMB observation. We also scrutinize the reheating process in this model.
Eric Linder A Tale of Two Accelerations
As astounding as current cosmic acceleration is, we believe there was another such epoch in the early universe. I discuss possible relations between today's acceleration and inflation, and today's and a Planck energy cosmological constant. The first uses the approach of alpha attractors, which can link Starobinsky inflation with dark energy. The second uses well tempering, an improved version of self tuning fields, for dynamical cancellation of a Planck energy cosmological constant as a solution of the original cosmological constant problem. Both give the exciting prospect of a correlation between the physics of the early and late universe.
Kei-ichi MAEDA Metric-Affine Gravity Theory and Acceleration of the Universe
We classify the metric-affine gravity theory and consider a minimally coupled scalar field. When we rewrite such a model in the form of Riemannian geometry, the effective potential is modified. As a result, a chaotic type inflation with \phi^2 potential is still consistent with the observational data. We also discuss a scalar field with Galileon symmetry in the metric-affine gravity and show the emergence of G-inflation.
Scott Melville Speed Limits for Dark Energy
Many dark energy and modified gravity models can alter the sound speed of gravitational waves, which was recently tightly constrained by the LIGO/Virgo Collaborations. However, these constraints must be interpreted with great care. The effective sound speed in these theories is controlled by how new degrees of freedom couple to metric fluctuations, and can be described using a low energy Effective Field Theory. Within such a framework, the sound speed generically runs with scale, and therefore the (cosmologically relevant) speed at the Hubble scale can be very different from the (observed) speed at binary merger scales. This has the potential to save many theories previously believed to be ruled out by the GW170817 observations.
Hayato Motohashi Constant-roll inflation
We propose a phenomenological class of inflationary models in which the assumption of inflaton slow-roll is replaced by more general, constant-roll condition. We derive general exact solution for the inflaton potential and dynamics, and show that there exists parameter region that satisfies the latest observational constraint on the scalar spectral index and the tensor-to-scalar ratio. We also consider its generalization to the case of f(R) gravity, for which we provide a simple constant-roll condition defined in the original, Jordan frame. The f(R) constant roll inflation also allows us to obtain exact solutions for the scalaron potential in the Einstein frame, the function f(R) in the parametric form and inflationary dynamics, which satisfies the observationally constraint.
Shinji Mukohyama Minimalism in modified gravity
Teppei Okumura Probing physical boundaries of dark matter halos from cosmic density and velocity fields
Changbom Park Cosmology with large-scale structures in the universe
David Parkinson Dark energy from the radio continuum
Dmitri Pogosyan Connectivity of the Cosmic Web
Cosmic connectivity and multiplicity, i.e. the number of filaments globally or locally connected to a given cluster is a natural probe of the growth of structure and in particular of the nature of dark energy. It is also a critical ingredient driving the assembly history of galaxies as it controls mass and angular momentum accretion. The connectivity of the cosmic web is investigated here via the persistent skeleton. This tool identifies topologically the set of ridges of the cosmic landscape which allows us to investigate in details how the nodes of the cosmic web are connected together. Locally, the number of filaments sticking out from a node is not equal to its number of connections. At small distance, the peak has an ellipsoidal shape so that only two filaments emerge. Further away, filaments are subdivided at bifurcation points. At the resolution of the maps, the local number of filaments is 3 on average in 2D and 4 in 3D, depending on the height of the peak. As an illustration, this connectivity is quantified in galaxy lensing convergence maps and large dark haloes catalogues. As a function of redshift and scale the mean connectivity decreases in a cosmology dependent way.
David Polarski On the phenomenology of dark energy
The growth index is one of the tools that can help in characterizing the growth of perturbations. Some results will be presented for dark energy models inside General Relativity and for models in modified gravity dark energy models.
Cristiano Sabiu Constraining Modified Gravity with the Deep Lens Survey
Varun Sahni Tracker models, cosmological reconstruction and the Phantom brane
I briefly discuss new tracker models of dark matter and dark energy which are motivated by the alpha-attractors. I also touch upon recent reconstructions of dark energy which may be supportive of the braneworld paradigm.
Misao Sasaki Scalaron as a heavy field and formation of primordial black holes
A model of two-stage inflation in which a scalar field, chi, is non-minimally coupled to Starobinsky's R2 gravity is disdussed. The scalaron in Starobinsky’ model drives the first stage of inflation, and chi drives the second. At the end of the first stage, the scalaron becomes heavy and undergoes damped oscillations. This causes enhancement and oscillatory features in the curvature perturbation power spectrum. The peak in these features may give rise to copious production of primordial black holes (PBHs). For a suitably chosen set of model parameters, these PBHs may even be identified as the CDM of the Universe.
Feng Shi Mapping the real-space distributions of galaxies in SDSS DR7
We extend the real-space mapping method developed in \\citet{Shi16} so that it can be applied to flux-limited galaxy samples. We use an ensemble of mock catalogs to demonstrate the reliability of this extension, showing that it allows for an accurate recovery of the real-space correlation functions and galaxy biases. We also demonstrate that, using an iterative method applied to intermediate scale clustering data, we can obtain an unbiased estimate of the growth rate of structure $f\\sigma_8$, which is related to the {\\bf clustering amplitude of matter}, to an accuracy of $\\sim 10\\%$. Applying this method to the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), we construct a real-space galaxy catalog spanning the redshift range $0.01 \\leq z \\leq 0.2$, which contains 584,473 galaxies in the North Galactic Cap (NGC). Using this data we, infer $\\fss$ at a median redshift $z=0.1$, which is consistent with the WMAP9 cosmology at $1\\sigma$ level. By combining this measurement with the real-space clustering of galaxies and with galaxy-galaxy weak lensing measurements for the same sets of galaxies, we are able to break the degeneracy between $f$, $\\sigma_8$ and $b$. From the SDSS DR7 data alone, we obtain the following cosmological constraints at redshift $z=0.1$: $f=$\\f , $\\sigma_8=$\\s and $b=$ \\bI, \\bII, \\bIII, \\bIV for galaxies within different absolute magnitude bins $\\rmag=[-23,0, -22.0], [-22,0, -21.0], [-21.0, -20.0]$ and $[-20.0, -19.0]$, respectively.
Alexei A. Starobinsky Cosmology in terms of principal historical epochs and new fundamental constants
The most compact and general way how cosmology and physics of the present and early Universe can be presented is achieved by listing its principal historical epochs and new fundamental constants following from cosmological observations only which are additional to those known from the Standard Model of elementary particles. According to the present paradigm of cosmology which agrees with all existing observational data, the history of the observable part of our Universe consists of 4 principal epochs: 1) primordial vacuum-like (quasi-de Sitter, or inflationary) stage; 2) radiation-dominated stage; 3) matter-dominated stage, and now we live in the period of the transition to a second vacuum-like stage which is remarkably qualitatively similar to the first one. The quantitative phenomenological description of this history is based on known principles of classical and quantum physics. However, it requires the introduction of at least 4 new fundamental constants and two kinds of matter seen through their gravitational interaction only: non-relativistic dark matter and vacuum-like dark energy (primordial and present ones). I describe these 4 constants and discuss physical theories standing beyond each of them. The remarkable analogy between the primordial dark energy which drove inflation long time ago and the present one suggests that the latter is not stable and eternal, too. Finally, I present some recent results on the pioneer R+R^2 inflationary model (1980), which has the minimal number - one - of parameters taken from observations, and related ones, including the dynamical attractor property of R^2 inflation for a wide class of scalar-tensor models and its most generic anisotropic pre-inflationary behavior which does not require causal connection inside a patch for the onset of inflation in its Cauchy evolution.
Takahiro Tanaka Testing gravity using gravitational waves
After giving some overview about the test of gravity using gravitational waves, I'll introduce the activities on gravitational wave data analysis that we are developing in Japan.
Atsushi Taruya Nonlinear structure formation in CDM cosmology
Evolution of large-scale structure in the Universe is supposed to be driven by the gravitational instability of cold dark matter (CDM). Such a system undergoes the so-called shell-crossing, i.e., the apparent divergence of density field, later followed by the multi-stream velocity flows. Describing and characterizing those features is important to test/constrain CDM cosmology. In this talk, I will present our recent progresses based on both perturbative calculation and numerical simulation.
Motonari Tonegawa Nonlinear structure formation in CDM cosmology
Shinji Tsujikawa Dark energy scenario consistent with GW170817 in theories beyond Horndeski
The Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories up to quartic order are the general scheme of scalar-tensor theories allowing the possibility for realizing the tensor propagation speed c_t equivalent to 1 on the isotropic cosmological background. We propose a dark energy model in which the late-time cosmic acceleration occurs by a simple k-essence Lagrangian analogous to the ghost condensate with cubic and quartic Galileons in the framework of GLPV theories. We show that a wide variety of the variation of the dark energy equation of state w including the entry to the region w<-1 can be realized without violating conditions for the absence of ghosts and Laplacian instabilities. The approach to the tracker equation of state w=-2 during the matter era, which is disfavored by observational data, can be avoided by the existence of a quadratic k-essence Lagrangian. We study the evolution of nonrelativistic matter perturbations for the model c_t=1 and show that the two quantities mu and Sigma, which are related to the Newtonian and weak lensing gravitational potentials respectively, are practically equivalent to each other. For the case in which the deviation of w from -1 is significant at a later cosmological epoch, the values of mu and Sigma tend to be larger at low redshifts.
Keiichi Umetsu Discovery of a New Fundamental Plane Dictating Galaxy Cluster Evolution from Gravitational Lensing
I will talk about the recent discovery (Fujita, Umetsu et al. 2018, ApJ, 857, 118 ) of a universal \"plane\" dictating dark-matter halo evolution from our gravitational lensing and X-ray observations from the CLASH survey. We show that high-mass galaxy clusters lie on a plane in the three-dimensional logarithmic space of their characteristic halo radius \"rs\", mass \"Ms\" , and X-ray temperature \"Tx\" with a very small orthogonal scatter. The tight correlation indicates that the gas temperature was determined at a specific cluster formation time, which is encoded in (rs,Ms) and that the gas was heated when the clusters were in the fast-growing phase. Intriguingly, the plane is significantly tilted with respect to the canonical virial expectation, Tx ~ Ms /rs. We show that the self-similar solution of Bertschinger (1985) for secondary infall and accretion can explain the observed relation, Tx ~ Ms^1.5 /rs^2. Numerical simulations reproduce the observed plane and its angle. This result holds independently of the gas physics implemented in the code, revealing the fundamental origin of this plane.
Maurice H.P.M. van Putten Alleviating tension in the Hubble parameter in well-posed quantum cosmology
The phase space of well-posed quantum cosmology is the two-dimensional cosmological horizon at Hubble radius c/H, where c is the velocity of light and H is the Hubble parameter. The vacuum acquires negative pressure by fluctuations below its fundamental frequency $\\omega_0 = \\sqrt{1-q}H$, away from the radiation dominated limit at deceleration parameter $q=1$. As a result, the de Sitter state ($q=-1$) is a turning point at $z_* ≃ (1/3)(1-3\\omega_m)$ close to zero, as opposed to an attractor in the distant future assumed in ΛCDM, where $\\omega_m=0.3$ is the baryon and cold dark matter content at the present epoch. This cosmological evolution is driven by $T_{ab}= \\left[ (1-q)\\pi_{ab}^− + q\\pi_{ab}^+\\right]\\rho_c$ of radiation on- and off-shell at closure density $\\rho_c$ where tr$\\pi_{ab}^+=0$ and tr$\\pi_{ab}^- = -2$. In units of km s$^{-1}$Mpc$^{-1}$, we obtain $H_0 = 74.86 \\pm 2.64$ for $T_{ab}$ from cosmological data $H(z)$ in 3.1$\\sigma$ tension with $H_0 = 66.76 \\pm 1.86$ for $\\Lambda$CDM, in complete agreement with Riess’ et al. (2018) $H_0 = 73.48 \\pm 1.66$ from local surveys in 3.7$\\sigma$ tension with $H_0 = 66.93 \\pm 0.62$ for $\\Lambda$CDM analysis of the CMB.
Yuting Wang BAO and RSD measurements with BOSS/eBOSS surveys
Galaxy redshift surveys are used to extract the signals of baryon acoustic oscillations (BAO) and redshift space distortion (RSD) by mapping the large scale structure of the Universe, and can provide key observational support for the studies of dark energy and gravity. In this talk, I will present the BAO and RSD analysis with BOSS DR12 sample and eBOSS DR14 quasar sample, and discuss the cosmological implications using these measurements.
Yvonne Wong
Jun'ichi Yokoyama Higgs field during and after inflation
Mijin Yoon Cosmology with the Deep Lens Survey using galaxy-galaxy and galaxy-mass power spectra
We present cosmological parameter constraints from the Deep Lens Survey (DLS) by the combined analysis of galaxy-galaxy and galaxy-mass power spectra. We measure galaxy-galaxy power spectra from two lens bins centered at z~0.25 and 0.55. To measure galaxy-mass power spectra we cross-correlate the galaxy shapes in two source bins centered at z~0.55 and 1.1 with the positions of galaxies in the two lens bins. In our cosmological parameter estimation, we marginalize over a baryonic feedback effect, as well as photometric redshift and shear calibration uncertainties. For a flat LCDM cosmology, we determine S_8=sigma_8(Omega_m/0.3)^0.5=0.857+-0.035, which is in an excellent agreement with the constraints from the previous DLS cosmic shear and the Planck. We also constrain the impact of the baryonic suppression on the matter power spectrum by combining our lensing measurements with the Planck and find that the AGN feedback in the current state-of-the-art simulations may not be strong enough.
Ying-li Zhang Scalaron from R2 R^2 -gravity as a Heavy Field
We study a model of inflation in which a scalar field is non-minimally coupled to Starobinsky’s R^2 gravity. The presence of the damped oscillations during the transition from the first to second stage of inflation causes enhancement and oscillation features in the power spectrum of the curvature perturbation. Assuming that the oscillations may be treated perturbatively, we calculate these features by using the δN formalism, and discuss its observational implications to primordial black hole formation.
Yi Zheng The hybrid redshift space distortion model with advanced TNS mapping formula