# Titles and abstracts [4-8 April 2016]

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

Frederico Arroja | Mimetic Horndeski Gravity | |

Amir Aghamousa | Time delay estimation of strong lens systems | |

Takeshi Chiba | Planck Constraints on the Variation of the Gravitational Constant | We report the constraint on the time variation of the gravitational constant by the analysis of the Planck data. |

Ki-Young Choi | TBA | |

Antonio De Felice | Phenomenology of minimal theory of massive gravity | We investigate the minimal theory of massive gravity (MTMG) recently introduced. After reviewing the original construction based on its Hamiltonian in the vielbein formalism, we reformulate it in terms of its Lagrangian in both the vielbein and the metric formalisms. It then becomes obvious that, unlike previous attempts in the literature, not only the potential but also the kinetic structure of the action is modified from the de Rham-Gabadadze-Tolley (dRGT) massive gravity theory. We confirm that the number of physical degrees of freedom in MTMG is two at fully nonlinear level. This proves the absence of various possible pathologies such as superluminality, acausality and strong coupling. Afterwards, we discuss the phenomenology of MTMG in the presence of a dust fluid. We find that on a flat homogeneous and isotropic background we have two branches. One of them (self-accelerating branch) naturally leads to acceleration without the genuine cosmological constant or dark energy. For this branch both the scalar and the vector modes behave exactly as in general relativity (GR). The phenomenology of this branch differs from GR in the tensor modes sector, as the tensor modes acquire a non-zero mass. Hence, MTMG serves as a stable nonlinear completion of the self-accelerating cosmological solution found originally in dRGT theory. The other branch (normal branch) has a dynamics which depends on the time-dependent fiducial metric. For the normal branch, the scalar mode sector, even though as in GR only one scalar mode is present (due to the dust fluid), differs from the one in GR, and, in general, structure formation will follow a different phenomenology. The tensor modes will be massive, whereas the vector modes, for both branches, will have the same phenomenology as in GR. |

Jinn-ouk Gong | Relativistic non-linear perturbation in a $\Lambda$CDM universe | |

Jan Hamann | Hunting for features in the primordial power spectrum | |

Lavinia Heisenberg | TBA | |

Ho Seong Hwang | A Cosmological Test with Large-scale Structures at Intermediate Redshifts | |

Kiyotomo Ichiki | Relationship between the CMB, SZ Cluster Counts, and Local Hubble Parameter Measurements in a Simple Void Model | The discrepancy between the amplitudes of matter fluctuations inferred from Sunyaev-Zel\'dovich cluster number counts, the primary temperature, and the polarization anisotropies of the cosmic microwave background (CMB) measured by the Planck satellite can be reconciled if the local universe is embedded in an under-dense region as shown by Lee, 2014. Here using a simple void model assuming the open Friedmann-Robertson-Walker geometry and a Markov Chain Monte Carlo technique, we investigate how deep the local under-dense region needs to be to resolve this discrepancy. Such local void, if exists, predicts the local Hubble parameter value that is different from the global Hubble constant. We derive the posterior distribution of the local Hubble parameter from a joint fitting of the Planck CMB data and SZ cluster number counts assuming the simple void model. We show that the predicted local Hubble parameter value is in better agreement with direct local Hubble parameter measurements, indicating that the local void model may provide a consistent solution to the cluster number counts and Hubble parameter discrepancies. |

Ryotaro Kase | Conical singularities and the Vainshtein screening in full GLPV theories | In Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, it is known that the conical singularity arises at the center of a spherically symmetric body ($r=0$) in the case where the parameter $\\alpha_{{\\rm H}4}$ characterizing the deviation from the Horndeski Lagrangian $L_4$ approaches a non-zero constant as $r \\to 0$. We derive spherically symmetric solutions around the center in full GLPV theories and show that the GLPV Lagrangian $L_5$ does not modify the divergent property of the Ricci scalar $R$ induced by the non-zero $\\alpha_{{\\rm H}4}$. Provided that $\\alpha_{{\\rm H}4}=0$, curvature scalar quantities can remain finite at $r=0$ even in the presence of $L_5$ beyond the Horndeski domain. For the theories in which the scalar field $\\phi$ is directly coupled to $R$, we also obtain spherically symmetric solutions inside/outside the body to study whether the fifth force mediated by $\\phi$ can be screened by non-linear field self-interactions. We find that there is one specific model of GLPV theories in which the effect of $L_5$ vanishes in the equations of motion. We also show that, depending on the sign of a $L_5$-dependent term in the field equation, the model can be compatible with solar-system constraints under the Vainshtein mechanism or it is plagued by the problem of a divergence of the field derivative in high-density regions. |

Sergey V. Ketov | Search for Dark Energy in IIA strings compactified on rigid CY manifolds | I report about our recent results in the search for de-Sitter vacua in the type-IIA superstrings compactified on rigid Calabi-Yau spaces. |

Naoya Kitajima | Revisiting CDM isocurvature perturbations in the curvaton scenario | |

Seyen Kouwn | Massive Photon and Dark Energy | We investigate cosmology of massive electrodynamics and explore the possibility whether massive photon could provide an explanation of the dark energy. The action is given by the scalar-vector-tensor theory of gravity which is obtained by non-minimal coupling of the massive Stueckelberg QED with gravity and its cosmological consequences are studied by paying a particular attention to the role of photon mass. We find that the theory allows cosmological evolution where the radiation- and matter-dominated epochs are followed by a long period of virtually constant dark energy that closely mimics ΛCDM model and the main source of the current acceleration is provided by the nonvanishing photon mass governed by the relation Λ~m^2. A detailed numerical analysis shows that the nonvanishing photon mass of the order of ∼10^{−34} eV is consistent with the current observations. This magnitude is far less than the most stringent limit on the photon mass available so far, which is of the order of m≤10^{−27}eV. |

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 | Halo interactions in the Horizon Run 4 simulation | |

Seokcheon Lee | Redshift space distortion as a standard ruler | |

Xiao-Dong Li | Cosmological Constraint from the Redshift Dependence of Alcock-Paczynski Test | The apparent anisotropy in the distribution of observed galaxies mainly arise from two main reasons, the redshift-space distortion (RSD) effects due to the galaxy peculiar velocities, and the geometric distortion when incorrect cosmological models are assumed for transforming redshift to comoving distance, known as the AP effect. We focus on the redshift dependence of the anisotropic clustering of galaxies to constrain cosmological parameters. Anisotropies produced by the RSD effect are, although very large, maintain a nearly uniform magnitude over a large range of redshift, while the degree of anisotropies introduced by AP varies with redshift by much larger magnitude. We split the BOSS DR12 galaxies into six redshift bins, measure the 2-point correlation function in each redshift bin, and assess the redshift evolution of anisotropies. We obtain tight constraints on Ωm on w. We discuss the caveats and possibilities for improving upon our methodology. We expect our method will play an important role in deriving cosmological constraint from current and future large scale structure surveys. |

Kei-ichi Maeda | The Use of Disformal Transformation | |

Takahiko Matsubara | The integrated perturbation theory | |

Shinji Mukohyama | Status of ghost condensation | |

Teppei Okumura | New constraint on gravity theory at z~1.4 from the Subaru FMOS/FastSound galaxy redshift survey | I will present a cosmological result obtained from a spectroscopic sample of ~2800 emission line galaxies from the FastSound survey. The survey, which uses the Subaru Telescope and covers the redshift ranges of 1.19 |

Sohyun Park | TBA | |

Leandros Perivolaropoulos | Aspects of Dark Energy Eschatology: Big Crunch, Big Rip and Parametrizations | After a brief review of the possible ends of the universe in the presence of dark energy I address the following questions: 1. How generic is the Big Crunch singularity in the presence of potentials with negative range in scalar tensor quintessence? (arXiv:1511.08732). 2. How and when does a strongly bound system dissociate before the Big Rip? What new effects emerge beyond the Newtonian approximation? (arXiv:1603.02569). 3. How can we avoid misleading conclusions when using cosmological data to fit w(z) and predict its future evolution using parametrizations? Is the CPL parameterization adequate to describe a possible non-trivial evolution of w(z)? (arXiv:1603.02164) |

Federico Piazza | Three themes on Dark Energy#&## | |

David Polarski | The promises of Dark Energy | The present accelerated expansion remains an outstanding isuue of cosmology. We will review some of the theoretical models beyond the concordance model, as well as general approaches that have been suggested. These theoretical efforts are crucial in view of present and future observational progress. |

Cristiano Sabiu | Anisotropic Baryon Oscillations and Cosmic Distances | In the era of large spectroscopic surveys like DESI, I introduce a consistent model independent methodology for constraining the geometrical distances measures using the anisotropic clustering of galaxies. These meausrements can help in the future to constrain or break the standard model of LCDM. |

Arman Shafieloo | Search for evidences beyond the concordance model of cosmology | |

Junsup Shim | Varying supercluster shape in different cosmology | |

Hyunmi Song | SDSS-IV and eBOSS science | TBD |

Yong-Seon Song | TBA | |

Alexei A. Starobinsky | Global reconstruction of inflationary models from the power spectrum of density perturbations | Quantitative information about details of inflation obtained from recent CMB observational data on the primordial spectrum of scalar (density) perturbations suggests going further and reconstructing inflationary models phenomenologically using some additional assumptions, mainly aesthetic ones, about the form of the spectrum in the region of smaller scales and smooth behaviour at low space-time curvature. I remind an old result on the reconstruction of the inflaton potential in General Relativity, obtained without expanding the power spectrum in a power series at some scale, and generalize it to the case of f(R) gravity. Predictions for the tensor-to-ratio following from the simplest and most elegant assumptions are summarized. |

Takahiro Tanaka | Revival of classical black hole evaporation? | |

Takahiro Terada | General Pole Inflation | A new paradigm for inflationary model building appeared recently, in which inflationary observables are determined by the structure of a pole in the inflaton kinetic term rather than the shape of the inflaton potential. We comprehensively study this framework with an arbitrary order of the pole taking into account possible additional poles in the kinetic term or in the potential. Depending on the setup, the canonical potential becomes the form of hilltop or plateau models, variants of natural inflation, or monomial or polynomial chaotic inflation. We demonstrate attractor behavior of these models and compute corrections from the additional poles to the inflationary observables. |

Shinji Tsujikawa | Cosmology in generalized Proca theories | We consider a massive vector field with derivative interactions that propagates only the 3 desired polarizations (besides two tensor polarizations from gravity) with second-order equations of motion in curved space-time. The cosmological implications of such generalized Proca theories are investigated for both the background and the linear perturbation by taking into account the Lagrangian up to quintic order. In the presence of a matter fluid with a temporal component of the vector field, we derive the background equations of motion and show the existence of de Sitter solutions relevant to the late-time cosmic acceleration. We also obtain conditions for the absence of ghosts and Laplacian instabilities of tensor, vector, and scalar perturbations in the small-scale limit. Our results are applied to concrete examples of the general functions in the theory, which encompass vector Galileons as a specific case. In such examples, we show that the de Sitter fixed point is always a stable attractor and study viable parameter spaces in which the no-ghost and stability conditions are satisfied during the cosmic expansion history. |

Yi Zheng | Study on the mapping of dark matter clustering from real space to redshift space | The mapping of dark matter clustering from real space to redshift space introduces the anisotropic property to the measured density power spectrum in redshift space, known as the Redshift Space Distortion effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to indefinite cross correlations between the density and velocity fields, and the Finger--of--God effect due to the randomness of the peculiar velocity field. Whilst the full higher order polynomials remain unknown, the other systematics can be controlled consistently within the same order truncation in the expansion of the mapping formula, as shown in this paper. The systematic due to the unknown non--linear density and velocity fields is removed by separately measuring all terms in the expansion directly using simulations. The uncertainty caused by the velocity randomness is controlled by splitting the FoG term into two pieces, 1) the non--local FoG term being independent of the separation vector between two different points, and 2) the local FoG term appearing as an indefinite polynomials which is expanded in the same order as all other perturbative polynomials. Using 100 realizations of simulations, we find that the best fitted non--local FoG function is Gaussian, with only one scale--independent free parameter, and that our new mapping formulation accurately reproduces the observed 2-dimensional density power spectrum in redshift space at the smallest scales by far, up to $k\sim 0.3\hompc$, considering the resolution of future experiments. |