# Titles and abstracts [7-10 December 2020]

Name | Talk Title & Abstract |
---|---|

Kyungjin Ahn | Two-Stage Reionization in the Era of Planck and EDGES |

The large-scale polarization anisotropy of CMB observed by Planck placed constraints on the history of reionization. Its non-parametric constraint weakly favors two-stage reionization, composed of the early slow rise and the late rapid rise of the global ionized fraction. I will show that such two-stage reionization can be naturally explained if both minihalos and more massive, atomic-cooling halos are considered in a self-consistent way. Star formation inside minihalos are strongly self-regulated in the early universe, driving the early, slow-ionization phase, while star formation inside atomic-cooling halos are unsuppressed, driving the late, rapid-ionization phase. The good agreement of the resulting polarization anisotropy of such models with the Planck observation casts a serious challenge to the already problematic 21cm observation by the EDGES, because the predicted 21cm background is even more discrepant from the EDGES-claimed signal. He will show how much LibeBIRD, a future CMB telescope with cosmic-variance limited sensitivity on polarization measurement, will tighten the reionization constraint, and the related prospect of future 21cm observations. | |

Stephen Appleby | Screening the vacuum energy with degenerate field equations |

Horndeski scalar tensor gravity models can be used to dynamically self tune the cosmological constant, effectively de-gravitating it. In this talk I show how this mechanism works, by introducing simple degenerate, Minkowski vacuum states. I explain how the models evade Weinberg’s no go theorem, and some of the properties of the vacuum states. Some open problems are highlighted. | |

Marek Biesiada | Strong lensing of gravitational waves - new opportunities for multimessenger astronomy |

Direct detections of gravitational waves (GW) opened a new era of GW astronomy. Successful GW detection and observations of coalescing binary neutron star (NS-NS) system across a spectrum of electromagnetic waves (EM) elevated multimessenger astronomy to the next stage. Future generations of GW detectors on the ground and in the space will yield a significant statistics of such events reaching up to redshift z=5 and even deeper. Non-negligible ammount of such events has a chance of being strongly lensed. I will summarize and discuss new opportunities emerging from future detections of lensed GW signals. Wave phenomena concerning lensed GW signals, like diffraction fringes and beat patterns will be presented. | |

Gianluca Calcagni | Dark energy in multifractional spacetimes |

We study the possibility to obtain cosmological late-time acceleration from a geometry changing with the scale, in particular, in the so-called multi-fractional theories with q-derivatives and with weighted derivatives. In the theory with $q$-derivatives, the luminosity distance is the same as in general relativity and, therefore, geometry cannot act as dark energy. In the theory with weighted derivatives, geometry alone is able to sustain a late-time acceleration phase without fine tuning, while being compatible with structure-formation and big-bang nucleosynthesis bounds. This suggests to extend the theory, in a natural way, from just small-scale to also large-scale modifications of gravity. Surprisingly, the Hausdorff dimension of spacetime is constrained to be close to the topological dimension 4. Promoting this finding to a principle, we conclude that present-day acceleration can be regarded as the effect of a new restoration law for spacetime geometry. Based on arXiv:2004.02896. | |

Shuo Cao | Ultra compact structure in radio quasars：a new type of standard rulers in the Universe |

Ultra-compact structure in radio sources (especially in quasars that can be observed up to very high redshifts), with milliarcsecond angular sizes measured by very-long-baseline interferometry (VLBI), is becoming an important astrophysical tool for probing both cosmology and the physical properties of AGN.We present a newly compiled data set of 120 milliarcsec. compact radio sources representing intermediate-luminosity quasars covering the redshift range 0.46 < z < 2.76 and check the possibility of using these sources as independent cosmological probes. These quasars observed at 2.29 GHz show negligible dependence on redshifts and intrinsic luminosity, and thus represent a fixed comoving-length of standard ruler.Our results demonstrate that the method extensively investigated in our work on observational radio quasar data can be used to effectively derive cosmological information. | |

Kiwoon Choi | Axion coupling hierarchies from axion landscape |

There are a variety of well-motivated hierarchies among the low energy axion couplings. I will provide an overview of those axion coupling hierarchies and discuss some model building efforts to generate such hierarchical axion couplings in low energy effective theory. | |

Ki-Young Choi | Searching for boosted dark matter by cosmic rays |

The dark matter in our Galaxy can be scattered by the high energy cosmic rays and get boosted. I will talk about the possibility to detect this relativistic dark matter in the underground dark matter detectors. Especially, he will show the constraint on the model of extra U(1) gauge meditation, called Z-prime model. | |

Eoin O Colgain | Testing string theory with late-time cosmology |

Prominent string theorists have recently made the bold conjecture that de Sitter is precluded in quantum gravity. Thus, the Universe is not big enough for the so-called \"de Sitter Swampland conjecture\" and Lambda-CDM. We live in exciting times and appear to have ring-side seat to an enthralling showdown. | |

Antonio De Felice | Weakening gravity for dark matter in a type-II minimally modified gravity |

I will discuss a proposition for a new cosmological framework in which the strength of the gravitational force acted on dark matter at late time can be weaker than that on the standard matter fields without introducing extra gravitational degrees of freedom. The framework integrates dark matter into a type-II minimally modified gravity that was recently proposed as a dark energy mimicker. The idea that makes such a framework possible consists of coupling a dark matter Lagrangian and a cosmological constant to the metric in a canonically transformed frame of general relativity (GR). On imposing a gauge fixing constraint, which explicitly breaks the temporal diffeomorphism invariance, we keep the number of gravitational degrees of freedom to be two, as in GR. We then make the inverse canonical transformation to bring the theory back to the original frame, where one can add the standard matter fields. This framework contains two free functions of time which specify the generating functional of the above mentioned canonical transformation and which are then used in order to realize desired time evolutions of both the Hubble expansion rate H(z) and the effective gravitational constant for dark matter G_eff(z). The aim of this paper is therefore to provide a new framework to address the two puzzles present in today's cosmology, i.e. the H_0 tension and the S_8 tension, simultaneously. When the dark matter is cold in this framework, we dub the corresponding cosmological model the V Canonical Cold Dark Matter (VCCDM), as the cosmological constant Λ in the standard ΛCDM is replaced by a function V(ϕ) of an auxiliary field ϕ and the CDM is minimally coupled to the metric in a canonically transformed frame. | |

Claudia de Rham | The Speed of Gravity |

The recent direct detection of gravitational waves marks the beginning of a new era for physics and astronomy with an opportunity the probe gravity at its most fundamental level and have already been used to successfully constrain or rule out many effective field theories relevant for cosmology. I will discuss the strengths and limitations of these constraints and explore other complementary approaches in segregating between various effective field theories. | |

Richard Easther | TBA |

Tomohiro Harada | Primordial black holes: mass and spin |

Recently, primordial black holes have attracted intensive attention in the fields of cosmology and gravitational waves. We discuss primordial black holes formed as results of gravitational collapse of primordial perturbations in the radiation-dominated phase of the universe. We find that the mass of primordial black holes is approximately given by the mass within the cosmological horizon when the scale of interest enters the horizon, while the standard deviation of their spins depends on the amplitude of the perturbation and therefore the probability of their formation. | |

Ho Seong Hwang | Dark Matter Distribution in Galaxy Clusters traced by Galaxies in the Real and Simulated Universe |

Sungwook E. Hong | Revealing the Local Cosmic Web by Deep Learning |

80% of the matter in the Universe is in the form of dark matter that comprises the skeleton of the large-scale structure called the Cosmic Web. As the Cosmic Web dictates the motion of all matters in galaxies and inter-galactic media through gravity, knowing the distribution of dark matter is essential for studying the large-scale structure. However, as dominated by dark matter and warm-hot inter-galactic media, both of which are hard to trace, the detailed structure of the Cosmic Web is unknown. Here we show that we can reconstruct the Cosmic Web from the galaxy distribution using the convolutional-neural-network based deep-learning algorithm. We find the mapping between the position and velocity of galaxies and the Cosmic Web using the results of the state-of-the-art cosmological galaxy simulations, Illustris-TNG. We confirm the mapping by applying it to the EAGLE simulation. Finally, using the local galaxy sample from Cosmicflows-3, we find the dark-matter map in the local Universe. We anticipate that the local dark-matter map will illuminate the studies of nature of dark matter and the formation and evolution of the Local Group. High-resolution simulations and precise distance measurements to local galaxies will improve the accuracy of the dark-matter map. | |

Kiyotomo ICHIKI | Cosmology with CMB Quadrupoles |

Scattering of cosmic microwave background (CMB) radiation in galaxy clusters induces polarization signals according to the quadrupole anisotropy in the photon distribution at the location of clusters. This `remote quadrupole' derived from the measurements of the induced polarization in galaxy clusters provides an opportunity to reconstruct primordial fluctuations on large scales. Here we discuss that comparing the CMB quadrupoles predicted by these reconstructed primordial fluctuations and the direct measurements done by the CMB satellites may enable us to test dark energy beyond cosmic variance limits. | |

Kenji Kadota | The dark matter annihilation in the presence of primordial blackholes |

I will discuss the possibility where the annihilation of dark matter (DM) is boosted in the presence of the primordial black holes (PBHs) which constitute a sub-component of the whole dark matter. | |

Ryotaro KASE | TBD |

TBD | |

Tsutomu Kobayashi | Nanohertz gravitational waves from NEC violation in the early universe |

In this talk I will show that nHz gravitational waves relevant to pulsar timing array experiments (such as NANOGrav) can be generated from quantum fluctuations in the early universe with null energy condition (NEC) violation. To evade the constraint from Big Bang nucleosynthesis, the NEC-violating phase is connected to a subsequent short slow-roll inflationary phase which ends with standard reheating, and thereby the high frequency part of the spectrum is reduced. An explicit model is constructed within the cubic Horndeski theory which allows for stable violation of the NEC. | |

Jihn E. Kim | Chiral Universe |

I will review on chiral theories, emphasizing why they arise and how they work in particle physics at the electroweak scale and in cosmological evolution. | |

Rampei Kimura | New graviton mass and non-minimal coupling |

We propose new massive gravity theories with 5 dynamical degrees of freedom. We evade uniqueness theorems regarding the form of the kinetic and potential terms by adopting the generalized massive gravity framework, where a global translation invariance is broken. By exploiting the rotation symmetry in the field space, we determine two novel classes of theories. The first one is an extension of generalized massive gravity with a non-minimal coupling. On the other hand, the second theory produces a mass term that is different from de Rham, Gabadadze, Tolley construction and trivially has 5 degrees of freedom. Both theories allows for stable cosmological solutions without infinite strong coupling, which are free of ghost and gradient instabilities. | |

Kazuya Koyama | Perturbation Theory for BAO reconstructed fields |

We derive the one-loop perturbative formula of the redshift-space matter power spectrum after density field reconstruction in the Zeldovich approximation. We find that the reconstruction reduces the amplitudes of nonlinear one-loop perturbative terms significantly by partially erasing the nonlinear mode coupling between density and velocity fields. In comparison with N-body simulations, we find that both the monopole and quadrupole spectra of reconstructed matter density fields agree with the one-loop perturbation theory up to higher wave number than those before reconstruction. We also explore the covariance of redshift-space matter power spectra. We derive perturbative formula of the covariance at the tree-level order and find that the amplitude of the off-diagonal components from the trispectrum decreases by reconstruction. We demonstrate that the error of the growth rate estimated from the monopole and quadrupole components of the redshift-space matter power spectra significantly improves by reconstruction. | |

Sachiko Kuroyanagi | Gravitational waves from non-local Starobinsky inflation |

Inflation generically predicts a gravitational wave background originating from quantum fluctuations of the space-time metric. In my talk, I will discuss gravitational waves in non-local Starobinsky inflation model, which could predict a blue-tilted spectrum. We find that commonly-used slow-roll parametrization is not valid to describe the entire shape of the spectrum. In order to predict the gravitational wave amplitude at interferometer experiment scales, we utilize full expression of the primordial tensor spectrum and show how it deviates from the prediction by approximated forms. Finally, we discuss the detectability by future experiments. | |

David Langlois | Dark energy in DHOST theories |

In this talk, I will first present the general framework of Degenerate Higher-Order Scalar-Tensor (DHOST) theories, which includes and extends Horndeski and Beyond Horndeski theories. I will then discuss some cosmological aspects, in particular the background evolution and the dynamics of linear cosmological perturbations in these models. | |

Hyung Mok Lee | TBD |

Hyun Min Lee | Sigma models for Higgs inflation and their consequences |

Higgs Inflation and some specific models of this scenario knowns as Sigma models. I will discuss about features and charachteristics of these models in my presentation and discussion. | |

Benjamin L'Huillier | Model-independent tests of Gravity with the large-scale structure |

General Relativity (GR) is a pillar of the concordance cosmological model, and as such, needs to be tested. The large scale structure of the Universe is a powerful laboratory to test GR. Model-independent methods allow tests that are unbiased towards a particular model, and as such, can act as a litmus test or detect potential systematics in the data. In this talk, I will show how to reconstruct model-independently the growth history from redshift-space distortion data and obtain the expansion history, and provide constraints on the matter density and the amplitude of the fluctuations. | |

Kei-ichi MAEDA | General Relativity vs Modified Gravity |

General relativity is one of the most successful theories. There are many experimental and observational tests to confirm it. On the other hand, we have also several mysteries in nature, which may be related to gravitational phenomena. It is why there are so many modified gravity theories now. In my talk, I will stress the advantage of use of the Einstein equations even when we discuss some modified gravity theory. | |

Sabino Matarrese | From the Cosmic Microwave Background to the Stochastic Gravitational-Wave Background and back: what we can learn about cosmology and theories of gravity |

Recent theoretical advances in our understanding of the Stochastic Gravitational-Wave Background (SGWB) - both of primordial and astrophysical origin - have shown several similarities with the Cosmic Microwave Background. I will review various aspects of this direction of research, focusing on anisotropy, non-Gaussanity and sensitivity to some particle physics parameters, which make the expected future detection of the SGWB and its anisotropies a true goldmine of modern cosmology and fundamental physics. | |

Shuntaro Mizuno | Blue-tilted Primordial Gravitational Waves from Massive Gravity |

Since the first direct observation of gravitational waves, the importance of the gravitational waves have been recognized in various fields of astrophysics. Especially, the primordial gravitational waves include very important information of the very early universe. For example, in the standard scenario, the amplitude of primordial gravitational waves is related with the Hubble expansion rate during inflation. Therefore, if they are detected in the near future, it is helpful to specify the new physics behind inflation. However, since the primordial gravitational waves are red-tilted, where the amplitude becomes smaller on smaller scales in the standard scenario, if they cannot be detected on the CMB scale through polarization experiments, they cannot be detected on the scales of interferometers or pulsar timing arrays, which are much smaller than the CMB scale. On the other hand, recently, we proposed a model that produces blue-tilted primordial gravitational waves, where the amplitude becomes larger on smaller scales based on a kind of massive gravity. With this model, it is possible for the primordial gravitational waves to be detected by the interferometers or pulsar timing arrays, even though they are not detected by the CMB. In this presentation, based on the two papers (arXiv:1808.02381 [gr-qc] and arXiv:1909.07563 [astro-ph.CO]), I will explain how the model produces the blue-tilted and enhanced primordial gravitational waves within the context of a consistent theory, and discuss how to distinguish the primordial gravitational waves produced by our model from the ones produced by other models. | |

Hitoshi Murayama | Baryogenesis and gravitational wave |

Shinji Mukohyama | Minimalism in modified gravity |

TBA | |

Minji Oh | Study on fiber assignment with DESI end-to-end (E2E) 1% survey mock and Pairwise-Inverse-Probability (PIP) weight |

Dark Energy Spectroscopic Instrument (DESI) is aiming to locate about 35 million galaxies over 14,000 deg2 for the purpose of studying dark energy. It will assign robotic fibers on the pre-selected targets from the image survey, which cause fiber assignment bias on the measurement of galaxy clustering. DESI E2E survey mock targeting 1% of the survey footprint can be a good data to study this effect and see if PIP weight, which is one of the approaches to correct this effect, can recover the original clustering information on galaxy distribution. | |

Nobuyoshi Ohta | Towards the determination of the dimension of the critical surface in asymptotically safe gravity |

I will discuss recent work on Higher Derivative Gravity within the Functional Renormalization Group approach. The new beta functions are obtained on a general background and go beyond previously studied approximations. The presence of a nontrivial Newtonian coupling induces, in addition to the free fixed point of the one-loop approximation, also two nontrivial fixed points, of which one has the right signs to be free from tachyons. Our results are consistent with earlier suggestions that the dimension of the critical surface for pure gravity is three. | |

Changbom Park | Horizon Run 5 Cosmological Simulation and Morphology of the First Galaxies |

The well-known galaxy morphology and background density relation at low redshifts almost disappears at z~1, where more than 80% of galaxies are late types. A natural question to ask is what is the morphology of the first galaxies. Do galaxies form with disk morphology? We address this question using the latest large cosmological gravity/hydrodynamics simulation, the Horizon Run 5. The HR5 followed the non-linear evolution of dark matter and gas within 1049x144x144cMpc3 with 1pkpc resolution. We found evidence that the initial morphology of the first galaxies is dominantly spheroid before z=6 but is disk after z=6. The physics behind this phenomenon is under inspection by using the initial conditions and merger history of the first galaxies. | |

Seong Chan Park | Spontaneous Leptogenesis in Higgs inflation |

I will propose a scenario of spontaneous leptogenesis in Higgs inflation with help from two additional operators: the Weinberg operator (Dim 5) and the derivative coupling of the Higgs field and the current of lepton number (Dim 6). The former is responsible for lepton number violation and the latter induces chemical potential for lepton number. The period of rapidly changing Higgs field, naturally realized in Higgs inflation during the reheating, allows large enhancement in the produced asymmetry in lepton number, which is eventually converted into baryon asymmetry of the universe. This scenario is compatible with high reheating temperature of Higgs inflation model. | |

David Parkinson | Cosmology with SKA and future radio surveys |

Cristiano Sabiu | Tests Beyond LCDM with a Deep Gravitational Lensing Survey |

I report on tests of extended models beyond LCDM using observational data from the Deep Lens Survey (DLS). Utilizing the complimentary statistics of galaxy clustering, galaxy-galaxy lensing and cosmic shear we are able to break parameter degeneracies allowing us to place constraints on modified gravity, dark energy and the sum of neutrino masses. | |

Nobuyuki Sakai | Can we distinguish exotic gravitating objects by observation? |

To identify observationally exotic gravitating objects such as wormholes, braneworld blackholes and boson stars, we theoretically investigate their microlensing phenomena and shadows. | |

Misao Sasaki | Primordial Black Holes and Gravitational Waves |

Primordial black holes (PBHs) may abundantly exist in the universe today. I discuss that PBHs may even be the cold dark matter of the universe, and their existence may be tested by observation of the cosmological gravitational wave background associated with PBHs. | |

Hee-Jong Seo | Reconstructing the primordial universe from galaxy surveys |

I will present progress on two essential aspects of reconstructing primordial cosmological information from the late time observed Universe. One is reconstructing the primordial clustering information from the gravitational nonlinear growth and peculiar velocity field by improving and investigating the density field reconstruction and the second is reconstructing the primordial information from observational systematics, by better mitigating the systematic effects using a Deep-Learning based method. | |

Hisaaki Shinkai | Gravitational wave and test of general relativity |

I summarize the observations by LIGO-Virgo-KAGRA collaboration, and review the status of the tests of general relativity using GW events. If time allowed, I introduce my original effort for detecting the ring-down signals of black hole using auto-regressive method. | |

Tetsuya Shiromizu | TBA |

TBA | |

Alexei Starobinsky | Beyond the simplest inflationary models with scale-free perturbation spectra |

At the present state-of-the-art, the simplest inflationary models, based either on scalar fields in General Relativity or on modified f(R) gravity, which produce the best fit to all existing obsrvational data, require one, maximum two dimensionless parameters taken from observations only. They predict scale-free and close to scale-invariant power spectra of primordial scalar perturbations and gravitational waves generated during inflation. In one-parametric models, including the original R+R^2 one (Starobinsky 1980), the definite prediction for the tensor-to-scalar ratio r=3(1-n_s)^2 = 0.004 follows. The simplest viable model in GR remains the two-parametric T-model where r is of the order of (1-n_s)^2. However, future observations, in particular discovery of primordial black holes, may require a non-scale-free primordial scalar power spectrum with local peaks and troughs. I discuss mechanisms to produce such features including the recently proposed one which arise in many-field inflation with a large non-minimal kinetic term of an inflaton field leaving inflation before its end. In this case, in addition to PBHs, small-scale secondary gravitational waves are generated, too. | |

Takahiro Tanaka | Using Gravitational Waves to Constrain Gravity Theory |

I will report our latest results on the analyses of gravitational waves focusing on testing gravity. Our interest is in how to connect the latest development of theoretical understanding of modified gravity to the actual gravitational wave data analysis. | |

Yuko Urakawa | Signature of axion dark matter through gravitational messenger |

Axion like particle is a compelling candidate of dark matter. Furthermore, exploring axion like particles (ALPs) provides a unique window to explore beyond standard model physics such as string theory. To identify an ALP as dark matter, we need to look for a unique signal which enables us to distinguish it from other dark matter candidates. In this talk, I will explain new methods to detect the imprint of ALPs through gravitational messenger, including observations of nHz gravitational waves with circular polarization. | |

Eleonora Di Valentino | Anomalies and tensions in cosmology |

The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have provided strong confirmation of the LCDM model of structure formation. However, there are a few statistically significant tensions with other cosmological probes and anomalies in the data that can indicate failure of the LCDM model. The most famous ones are the Hubble constant and the S8 parameter tensions, the Alens anomaly and a curvature of the Universe. I will show these tensions, together with some interesting extended cosmological scenarios, that could alleviate these anomalies. | |

David Wands | Stochastic inflation and the primordial black holes |

I will discuss recent work studying large fluctuations in the density field arising from quantum diffusion during inflation. Non-perturbative fluctuations on super-Hubble scales can be described using the stochastic delta-N approach. This has applications to primordial black holes and the abundance of other collapsed objects on the early universe. | |

Yuting Wang | Anisotropic clustering analysis of galaxy redshift surveys: the Multi-tracer technique and a PCA approach |

Galaxy redshift surveys can provide important information for dark energy studies primarily through the probes of baryon acoustic oscillations (BAO) and redshift space distortions (RSD). In this talk, I will present the multi-tracer clustering analysis using eBOSS DR16 luminous red galaxy and emission line galaxy samples, and latest cosmological implication. I will also talk about the new method of anisotropic clustering analysis based on a PCA approach, and its application to BOSS DR12. | |

Jun'ichi Yokoyama | Inflation in mixed Higgs and R^2 model |

The original Higgs inflation and Starobinsky's curvature square inflation are both highly consistent with the current observations of CMB. Combining these two models yield a two field inflation model with a nontrivial dynamics in the reheating stage. We discuss various aspects of this model. | |

Gong-Bo Zhao | Cosmological Implications of the eBOSS DR16 observations |

I will discuss about the most recent results of the eBOSS-DR-16 observations and SDSS-IV collaboration. | |

Satadru Bag | Be It Unresolved: Measuring Time Delays from Lensed Supernovae |

Jeff Hodgson | Cosmological QUOKKA |

We present the early results of the QUOKKAS, including a new measurement of H0. | |

Ryan E Keeley | Model Independent Statistics in Cosmology |

In this talk, I will discuss a few different techniques to reconstruct different cosmological functions, such as the primordial power spectrum and the expansion history. These model independent techniques ar useful because they can discover surprising results in a way that nested modeling cannot. | |

Hanwool Koo | Cosmology with Type Ia supernovae: Searching for systematics and model independent reconstructions |

We analyze the Joint Light-curve Analysis (JLA) Type Ia supernovae (SN Ia) compilation implementing the non-parametric iterative smoothing method. We explore the SN Ia light-curve hyperparameter space and find no dark energy model dependence nor redshift evolution of the hyperparameters. We also analyze the more recent Pantheon SN Ia compilation to search for possible deviations from the expectations of the concordance ΛCDM model. We demonstrate that the redshift binned best fit parameter values oscillate about their full dataset best fit values with considerably large amplitudes. At the redshifts below z≈0.5, we show that such oscillations can only occur in 4 to 5% of the simulations. This might be a hint for some behavior beyond the predictions of the concordance model or a possible additional systematic in the data. In addition, we develop a non-parametric approach using the distribution of likelihoods from the iterative smoothing method. It determines consistency of a model and the data without comparison with another model. Simulating future WFIRST-like data, we show how confidently we can distinguish different dark energy models using this approach. | |

Benedict Kalus | TBD |

TBD | |

Aleksandra Piórkowska-Kurpas | DECIGO AND B-DECIGO: FORECAST FOR DETECTION AND LENSING RATE OF INSPIRALLING DOUBLE COMPACT OBJECTS |

The first direct detection of gravitational wave signal (GW150914) registered by aLIGO detectors opened up a new branch of science - gravitational wave (GW) astronomy. Success of the ground-based interferometric detectors revived the interest in broadening of deca- to kilo-Hertz range of GW spectrum to lower frequencies (lower than 1 Hz) inaccessible from the ground due to seismic noise. In particular, it is expected that a new generation of space mission LISA will have robust strain senstivity level at frequencies bewteen 0.1 mHz – 100 mHz over a science lifetime of a least 4 years. The remaining deci-Hertz part of GW spectrum is the target of the planned Japanese space-borne GW detector - DECihertz Interferometer Gravitational Wave Observatory (DECIGO and currently proposed smaller scale version B-DECIGO). The point is that DECIGO/B-DECIGO would be able to detect inspiralling double compact objects (DCO) – main targets to LIGO/Virgo, KAGRA or next generation ET, long time (weeks to years) before they enter the hecto-Hertz band accessible from the ground. Moreover, the joint detection with DECIGO/B-DECIGO and ground-based detectors like ET would greatly improve parametr estimation of the binaries. In this talk I will present the forecast for the detection rates of inspiralling DCOs and the unresolved confusion noise from these sources in DECIGO and B-DECIGO detectors, with using, for the first time, the population synthesis intrinsic inspiral rates of NS-NS, BH-NS and BH-BH systems. I will also show estimates of the expected gravitational lensing rates of such sources for DECIGO and B-DECIGO. Taking into account that considerable part of these events would be detectable by ground-based GW observatories the added value of DECIGO/B-DECIGO could be substantial. DECIGO will be able to register 5-50 lensed NS-NS inspirals and up to O(100) BH-BH inspirals. On the contrary, predictions for the B-DECIGO are more pessimistic: only the lensed BH-BH systems could be observed at the rate of about 50 per year. More interesting cases of NS-NS and BH-NS systems, where electromagnetic counterpart would be expected are negligible. | |

Beatriz Elizaga Navascués | Non-oscillating power spectra in (Loop) Quantum Cosmology |

In this talk we present an analytical characterization of the general conditions that a choice of vacuum state for the cosmological perturbations must satisfy to lead to a power spectrum with no scale-dependent oscillations over time. In particular, we pay special attention to the case of cosmological backgrounds governed by effective Loop Quantum Cosmology and in which the Einsteinian branch after the bounce suffers a pre-inflationary period of deccelerated expansion. This is the case more often studied in the literature because of the physical interest of the resulting predictions. In this context, we argue that non-oscillating power spectra are optimal to gain observational access to those regimes near the bounce where Loop Quantum Cosmology effects are non-negligible. In addition, we show that non-oscillatory spectra can be consistently obtained when the evolution of the perturbations is ruled by the equations derived in a loop quantization approach. Moreover, in the ultraviolet regime of short wavelength scales we prove that there exists a unique asymptotic expansion of the power spectrum that displays no scale-dependent oscillations over time. This expansion picks out the natural Poincare and Bunch Davies vacua in Minkowski and de Sitter spacetimes, respectively, and provides an appealing candidate for the choice of a vacuum for the perturbations in Loop Quantum Cosmology based on physical motivations. | |

Christoph Saulder | Peculiar velocities as a cosmological probe |

There ongoing efforts to increase the number of galaxies for which we can measure peculiar motions. While the scatter in galaxy scaling relations is with about 20% relatively large, when compared to primary distance indicators, we are able to much larger samples with more consistent sampling over a large area of the sky. With the fundamental plane, we can currently obtain redshift-independent distances to over 100 000 galaxies, primarily within the SDSS footprint-print. In the near future, this area and as well as the numbers will increase with DESI in the North and Taipan in the South. This new data will help to improve our constraints on cosmology, in particular f sigma8. | |

Junsup Shim | Identification of Cosmic Voids as the Cluster Counterpart |

We present a new void definition that connects voids with clusters, the high-density counterpart. We use a pair of $\Lambda$CDM simulations whose initial density fields are sign inverted versions to each other and study the relation between the effective void volume and the corresponding cluster mass. Massive cluster halos ($10^{13}\Msun$) are identified in one simulation at $z=0$ by linking dark matter particles. The corresponding void to each cluster is defined in the other simulation as the region occupied by the member particles of the cluster. We find a universal functional form of density profiles at z=0 and 1. We also find a power-law relation between the void effective radius and the corresponding cluster mass. Exploiting these findings, we identify cluster-counterpart voids directly from a density field without using the pair information by utilizing three parameters such as the smoothing scale, density threshold, and minimum core fraction. We identified voids corresponding to clusters more massive than $3\times10^{14}\Msun$ at approximately 70--74 \% level of completeness and reliability. Our results suggest that we can detect voids comparable to clusters of a particular mass-scale. | |

Shinji Tsujikawa | TBD |

Valeri Vardanyan | Multi-field dark energy: cosmic acceleration on a steep potential |

TBD |