Joint Seminars on Cosmology and Gravitation

Date : 1st (Thu) November, 2012
Place : 345, 4th Building (M02 in the map), Tsukuba Campus, KEK14:0015:30 Tomotake Matsumura (KEK) Title: Cosmology using cosmic microwave background polarization Abstract: While the measurements of cosmic microwave background (CMB) radiation played an important role to establish the current understanding of our Universe, it yet contains the rich science to extract from the undetected CMB Bmode polarization signal. In this talk, we review the past CMB experiments and their contributions, and introduce the upcoming experiments, such as POLARBEAR and LiteBIRD, and discuss what science to expect from them. 16:0017:30 Akihiro Ishibashi (Kinki Univ) title: TBA 19:00 Dinner around Tsukuba Center 
Date : 9th (Mon) July, 2012
Place : IPMU Seminar room A (1st floor), Kashiwa Campus, University of Tokyo13:3015:00 Marco Peloso (University of Minnesota) Title: Echoes of particle production during inflation Abstract: The observed cosmological perturbations are in excellent agreement with those predicted by inflation. A strong experimental effort is undergoing to extract further information on inflation through nongaussianity (NG) of the scalar perturbations and through gravity waves (GW). The vacuum modes of the inflaton and of the metric are the most natural candidates for providing observable NG and GW; however, neither effect is guaranteed to be at a detectable level. In this talk we explore an alternative possibility for obtaining observable NG and GW; namely, those induced by particle production during inflation. In some of the models that we consider, the particle production originates from the coupling of the inflaton to another field (the inflaton is necessary coupled to other fields for reheating, and we will discuss examples where these couplings lead to observable signatures already during inflation). More specifically, we show that (1) Observable approximate equilateral NG is obtained in models of natural inflation for the most theoretically motivated values of the axion decay constant (2) Observable approximate local NG is obtained from a dilatonlike coupling between the inflaton and a gauge field, typical of some models of magnetogenesis (3) Observable, and, possibly, parity violating GW are obtained from the production of relativistic particles in a sector gravitationally coupled to the inflaton, without spoiling the approximate scale invariance and gaussianity of the scalar perturbations 15:0015:30 Break 15:3017:00 Chiaki Hikage (Nagoya University) Title:Reconstruction of BAO Ring 18:00 dinner 
Date: 18 (Mon) June, 2012
Place: Room 233, the Science building 1, Hongo campus, Univ. of Tokyo
15:0016:00 Naoki Seto (Kyoto University) Title: Relativistic Resonant Relations between Massive Black Hole Binary and Extreme Mass Ratio Inspiral Abstract: One component of a massive black hole binary (MBHB) might capture a small third body, and then a hierarchical, inclined triple system would be formed. With the postNewtonian approximation including radiation reaction, we numerically analyzed the evolution of the triple. We found that an essentially new resonant relation could arise in the triple system. Here relativistic effects are crucial. Relativistic resonances, including the new one, stably work even for an outer MBHB of comparable masses, and significantly change the orbit of the inner small body. We also made a simplified 1DHamiltonian model that can successfully reproduce various observed trends at the resonant encounters, e.g. the capture rate as a function of inner eccentricity. 16:0016:30 Break 16:3017:30 Masato Minamitsuji (Kyoto University) Title: Cosmology in the cascading gravity model Abstract: The DGP braneworld model was known as a compelling model for explaining the recent cosmic acceleration. However, this model has almost been excluded in terms of both theory and observations. In this talk, we derive cosmological solutions in the particular generalization of the DGP model to the sixdimensional spacetime, where a FLRW codimension2 brane is localized on a codimension1 brane and each brane action contains the induced scalar curvature term. We then argue the properties and stability of these solutions. 
Date: 21 (Mon) May, 2012, 14:00
Place: The MultiPurpose Hall, Tachikawa Memorial Hall, Rikkyo University14:0015:30 Yuichi Sendouda (Hirosaki U) Title: Lorentzviolating gravity and ghost gravity  Weyl gravity as an example 15:3016:00 break 16:0017:30 Maresuke Shiraishi (Nagoya U) Title: Violations of invariance in the CMB bispectrum Abstract: The primordial nonGaussianities are key features to judge the validity of the inflationary models; hence they has been constrained from the CMB bispectra. In these studies, the symmetries under the rotational and parity transformation have been assumed despite a fact that there also exist theories involving the violation of these symmetries at the nonGaussian level. In our recent works, we have newly computed the CMB bispectra induced by these symmetrybreaking nonGaussianities and found some characteristic signals. In this seminar, I would like to present a set of results. 18:00 dinner 
Date: 31 (Mon) January, 2011, 14:0017:30
Place: ICRR, University of Tokyo, Room 601 (Kashiwa Campus)14:0015:30 Takahiko Matsubara (Nagoya) "Perturbation theory and biasing in the largescale structure of the universe" 15:3016:00 break 16:0017:30 Teruaki Suyama (RESCEU) "Nongaussian CMB temperature anisotropy induced by cosmic strings 
Date : 7(Tue) December, 2010, 14:0017:15
Place: Tokyo Institute of Technology, Ookayama Campus, Main Bldg. 1F, H15614:0015:30 Katsuaki Asano (TIT) Title: Highenergy Astrophysics in the FERMI era 15:3015:45 break 15:4517:15 Masamune Oguri (NAOJ) Title: Recent development in cosmology with galaxy clusters 
Date : 19(Tue) October, 2010, 14:3018:00
Place: The MultiPurpose Hall, Tachikawa Memorial Hall, Rikkyo University14:3016:00 Yousuke Itoh (Tohoku University) Title: PostNewtonian equations of motion for relativistic compact binaries Abstract: The gravitational wave (GW) detectors such as LCGT and advanced LIGO may detect several or even tens of GW signals. Among GW sources inspiraling relativistic compact binaries are the most promising sources to those detectors. This is because such systems are known to exist in nature, recent event rate studies suggest at least several GW signals can be expected, and we can use the most optimistic method “matched filtering” thanks to postNewtonian (PN) calculation of waveform templates. This talk shall review one of the fundamental ingredients of PN waveform templates, that is, PN equations of motion for relativistic compact binaries, how those are constructed, to what accuracy those are calculated, and open (theoretical) issues in the PN computations. 16:0016:30 break 16:3018:00 Jerome Novak (Observatoire de Paris) Title: A fullyconstrained formulation of Einstein equations: setup and numerical implementation Abstract: In generalrelativistic numerical simulations of astrophysical systems, it is necessary to fix the choices of variables and gauge.
These issues have attracted many efforts in the last decade, in order to get stable and accurate numerical schemes. Most of these efforts (and success) has been linked with the 3+1 formalism, within which the socalled "free evolution schemes" have been devised. In this seminar, I shall give an overview on the recent results by our group in Meudon, about the alternative "constrained evolution schemes", as well as on the numerical algorithms that have been developed in order to solve the resulting system of partial differential equations. 
Date : 9 (Fri) July, 2010, 14:0017:30
Place : Faculty of Science Bldg.1, 233 (Hongo Campus)14:0015:30 Jonathan Ganc (UT Austin)
Title: A new method for calculating the primordial bispectrum in the squeezed limit.
Abstract: In 2003, Creminelli and Zaldarriaga proposed a consistency relation for the primordial curvature perturbation of all singlefield inflation models; it related the bispectrum in the squeezed limit to the spectral tilt. Notably, their result is produced via classical arguments whereas most bispectrum calculations use quantum field theory (via the inin formalism, for example). We have applied similar arguments to calculate the squeezedlimit primordial bispectrum using the inin formalism and have arrived at a generic formula that doesn't rely on a slowroll approximation. We were not able to verify the consistency relation in all generality, though it should be able to be demonstrated by our technique if it does, in fact, hold in general; we did explicitly verify it for slowroll inflation (a known result) and for powerlaw inflation. Our technique could also be useful for calculating the singlefield trispectrum in the squeezed limit and could be adapted for certain types of multifield inflation models.15:3016:00 Break 16:0017:30 Norihiro Tanahashi (YITP, Kyoto)
Title: Extradimension detection by gravitational wave observations
Abstract: Inspired by the gauge/gravity correspondence, it was conjectured for the RSII braneworld model, which is composed of fivedimensional AdS bulk spacetime and a fourdimensional brane in it, that the fivedimensional classical gravity in the bulk spacetime is equivalent to some fourdimensional quantum field theory coupled to gravity on the brane. In this scenario, the Hawking radiation from a fourdimensional black hole is largely enhanced due to existence of the new quantum fields, and the enhancement factor is related to the extradimension scale. We would like to discuss observational consequences of this scenario, especially focusing on gravitational wave observations. Black hole binaries are typical targets for the gravitational wave detectors, and those binaries will lose their energy and angular momentum due to the enhanced Hawking radiation. This effect will be detectable if the enhancement factor, i.e., the extradimension scale, is sufficiently large. Observations of this effect may give a new constraints on the extradimension scale. In the presentation, we will introduce constraints on the extradimension scale by observations of LISA which was given by McWilliams (arXiv:0912.4744) recently, and discuss further constraints from BH/BH or NS/BH binary observations by DECIGO.

Date : 9 (Wed) June, 2010, 14:0018:00
Place : IPMU Seminar room B, Kashiwa Campus of the University of Tokyo14:0015:00 Sanjay Jhingan (Jamia Millia Islamia)
Title: Gravitational Collapse: Black Holes and Visible Singularities
Abstract: TBA15:0015:30 Break 15:3016:30 Christopher S. Gauthier (Michigan Center for Theoretical Physics)
Title: Kessence Interactions with Neutrinos: Flavor Oscillations without Mass
Abstract:In this talk we discuss a novel means of coupling neutrinos to a Lorentz violating background kessence field. Kessence is a model of dark energy, which uses a noncanonical scalar field to drive the late time accelerated expansion of the universe. We propose that neutrinos couple to the kessence induced metric G_{\mu\nu}, rather than the spacetime metric g_{\mu\nu} The immediate effect that this has will be to modify the energymomentum relation of the neutrino. This implies that the neutrino velocity will in general be different from the speed of light, even if the neutrino is massless. Later we will see that kessence can also induce neutrino oscillations even without a neutrino mass term. It will be shown that if kessence couples nondiagonally to the neutrino flavor eigenstates, then this leads to an oscillation length that goes like \lambda\sim E^{1}, where E is the neutrino energy. This should be contrasted with the case of purely mass induced neutrino oscillations, which result in a \lambda\sim E type behavior. Thus, kessence induced neutrino oscillations have a very different observational signature than neutrino oscillations created by mass. However, observations favor a leading order \lambda\sim E behavior. While kessence induced neutrino oscillations are not favored experimentally, our result places tight constraints on the possible interaction that a kessence background can have with neutrinos. All nontrivial physical effects discussed here require the sound speed of kessence fluctuations to be different from the speed of light, and hence are primarily a consequence of Lorentz violation.16:3017:00 Break 17:0018:00 Giovanni Marozzi (Institut d'Astrophysique de Paris)
Title: Covariant and gauge invariant formulation of the cosmological backreaction
Abstract: I will show, using a gauge invariant prescription to average scalar quantities, a generalcovariant formulation of the socalled cosmological "backreaction". These effective covariant equations allow us to describe in explicitly gauge invariant form the way classical or quantum inhomogeneities affect the average evolution of our Universe. 
Date : 21 (Fri.) May, 2010, 14:0017:30
Place : Waseda university, North tower of Building 55, 2FConference room14:0015:30 Frans Klinkhamer (Karlsruhe Institute of Technology)
Title: Two universes from qtheory
Abstract: The qtheory approach to the main Cosmological Constant Problem gives a general explanation of how the gravitating vacuum energy density can be selfadjusted to zero in an equilibrium state. Perturbations away from the equilibrium state may result in a small positive value of the effective vacuum energy density. Two possible types of perturbations are considered with energy scales set by QCD and electroweak physics. This leads to two possible universes. The first corresponds to a QCDscale modifiedgravity model, which may give a satisfactory description of the present Universe, both qualitatively and quantitatively. The second corresponds to an effective LambdaCDM model universe with a calculated value for the effective cosmological constant Lambda which is of the correct order of magnitude, provided there is new TeVscale physics.15:3016:00 Break 16:0017:30 Yoshihisa Kitazawa (KEK)
Title: Boltzmann equation in de Sitter space
Abstract: In a time dependent background like de Sitter space, FeynmanDyson perturbation theory breaks down due to infrared divergences. We investigate an interacting scalar field theory in SchwingerKeldysh formalism. We derive a Boltzmann equation from a SchwingerDyson equation inside the cosmological horizon. Our solution shows that the particle production is compensated by the reduction of the onshell states due to unitarity. Although the degrees of freedom inside the horizon leads to a small and diminishing screening effect of the cosmological constant, there is a growing screening effect from those outside the horizon. 
Date: 23 (Fri.) April, 2010, 14:0017:30
Place: ICRR, University of Tokyo, Room 601 (Kashiwa Campus)14:0015:00 Masahide Yamaguchi (Tokyo Inst. of Tech.)
Title: "Dark energy and inflation"
Abstract: We are going to discuss the relation between dark energy and inflation.15:0015:30 break 15:3016:30 Shinji Tsujikawa (Tokyo Univ. of Sci.)
Title: "Dark energy and modifications of gravity"
Abstract: The current accelerated expansion of the Universe may originate from some modification to Einstein gravity. In these theories the laws of gravity are modified so that the cosmic acceleration is realized without recourse to a dark energy component, a fact which makes these models attractive. We discuss the cosmological viability of modified gravity dark energy models as well as the consistency with local gravity constraints. Our analysis includes a wide variety of dark energy models such as f(R) gravity and scalartensor theories. We also study observational signatures of such modified gravity models and show that these models are in general strongly constrained from observations such as galaxy clustering, cosmic microwave background, and weak lensing. 
Date: 9 (Tue.), February, 2010, 14:0017:30
Place: 4th Bldg Seminar Hall (1st floor) KEK Tsukuba Campus14:0015:30 Yudai Suwa (U Tokyo/KEK)
Title: "Memory effect of gravitational waves"
Abstract:The gravitational waves have ``memory effect'', which leads a constantoffset of gravitational signals. In this talk, the formation of memoryby anisotropic energy emission (especially for neutrinos fromastrophysical object) will be discussed.15:3016:00 break 16:0017:30 ChiangMei Chen (NCU Taiwan/KEK)
Title: "The RN/CFT correspondence"
Abstract:We discuss the holographic dual CFT (conformal field theory) of RN(ReissnerNordstrom) black holes. Firstly we compute the rightmovingcentral charge of CFT from the dimensional reduced 2D effectiveaction. We further verify the duality by matching the absorption crosssection of a scalar field propagating in a near extremal RN black holeand the two point function of dual CFT operator. 
Date: 26 (Tue.), January, 2010
Place: Room 4151, Ground floor, Rikkyo University (Ikebukuro), Building No 4, Annex14:3016:00 Bernard Carr (Queen Mary University of London/RESCEU)
Title: NEW COSMOLOGICAL CONSTRAINTS ON PRIMORDIAL BLACK HOLES
Abstract:Constraints on the formation of primordial black holes  especiallythe ones which are small enough to evaporate  provide a unique probeof the early universe and high energy physics. In this talk I willreview some of the constraints discussed in my recent paper with Kohri,Sendouda and Yokoyama. For evaporating black holes, the dominant onesare associated with big bang nucleosynthesis and the extragalacticphoton background, but there are also other limits associated with thecosmic microwave background, cosmic rays and various types of relicparticles. For larger nonevaporating black holes, important constraintscome from their gravitational and astrophysical effects.16:0016:30 break 16:3018:00 Umpei Miyamoto (Rikkyo University)
Title: Phases of higherdimensional black holes from fluid/solid mechanics
Abstract:Recently, importance of blackhole studies in higherdimensional GRand string/M theory is increasing both from theoretical andexperimental points of view. In this talk, I will talk about how wecan learn about the stability, phase diagrams, and dynamics ofhigherdimensional black holes from similar fluid/solid phenomena.Then, I will show the background physics behind the similaritiesbetween the black holes and fluid lumps from the view point of arecent progress in the gauge/gravity correspondence. 
24 (Tue), November, 2009, 14:00  16:30
Place: IPMU General Research Building Room 630, Kashiwa Campus of the University of Tokyo.14:00  15:00 Alexei A. Starobinsky (Landau Institute / RESCEU)
Title: To the local beginning of inflation and beyond
Abstract: Though such observable quantities as the spectrum and statistics of primordial scalar and tensor perturbations are independent on initial conditions at the local beginning of sufficiently long inflation, there exist many other quantities and effects which do depend on them. Observing these effects or their consequences will give some knowledge on the initial conditions. Examples are probabilities (branching ratios) of decay into different vacua and rms fluctuations of light scalar fields after inflation. Analytic expressions for these quantities derived using the original (probability conserving) stochastic approach are presented and their dependence on the initial conditions is discussed. Generically there seems to be no rule fixing these conditions uniquely. In particular, 'eternal' inflation is not eternal enough for this purpose, as well as for reaching equilibrium values for all observables.
15:00  15:30 coffee break 15:30  16:30 Masato Minamitsuji (Sogang University)
Title: Scalar field in the anisotropic Universe
Abstract: We discuss the quantization and behavior of a scalar field in the BianchiI and BianchiIX cosmological models.
16:30  17:30 Antonio Enea Romano
Title: Apparent cosmological acceleration, dark energy and inhomogeneities.
Abstract: It well known that inhomogeneous spherically symmetric cosmological models (LTB) can explain the luminosity distance data without invoking dark energy.
In this context we first clarify the relation between apparent cosmological acceleration $a_{\Lambda CDM}$ and spatially averaged acceleration $a_D$ , and show that in general a positive $a_D$ does not correspond to models which are able to fit observational data, giving some examples.
We then present some new analytical results in the low redshift regime for the luminosity distance $D_L(z)$ and the redshift spherical shell energy density $mn(z)$, and introduce a general approach to the solution of the inversion problem of mapping a LTB model to observations.

16 (Fri), October, 14:00  17:30
Place : South tower of Building 55, Room number 410
14:00  15:30 Dr. Hiroyuki Abe (Waseda univ.)
Title : Phenomenological (cosmological) aspects of nonperturbative
moduli stabilization
Abstract : We show some phenomenological and cosmological aspects of higherdimensional supergravity/string models, where some of moduli fields arising from the compactification of extra dimensions are stabilized by nonperturbative effects such as gaugino condensations (the KKLTtype stabilization).
Within such a framework, we find a parameter region avoiding the so called little hierarchy problem in the minimal supersymmetric standard model, and derive typical superparticle spectra which may allow the lightest superparticle to be a dark matter candidate.
15:30  16:00 Break 16:00  17:30 Dr. Antonino Flachi (YITP)
Title : Brane world black holes and quantum back reaction
Abstract : We analyze the effects of the back reaction due to a conformal field theory (CFT) on a black hole spacetime with negative cosmological constant.
We study the geometry numerically obtained by taking into account the energy momentum tensor of CFT. We find a sequence of configurations without a horizon in thermal equilibrium ({\it CFT stars}), followed by a sequence of configurations with a horizon.
We discuss the thermodynamic property of the system and how back reaction effects alter the spacetime structure.
We also provide an interpretation of the above sequence of solutions in terms of the AdS/CFT correspondence. The dual fivedimensional description is given by the KarchRandall model, in which a sequence of fivedimensional floating black holes followed by a sequence of brane localized black holes correspond to the above solutions.

28 (Tue), July, 2009,13:30  17:00
Place: ICRR, University of Tokyo, Room 601 (Kashiwa Campus)
13:30  15:00 Takeo Moroi (Tohoku)
Title: Decay of scalar condensate in QFT15:30  17:00 Masayasu Kamimura (RIKEN/Kyushu)
Title: Bigbang nucleosysnthesis reactions catalyzed by SUSY particle stau

10 (Wed), June, 2009, 14:00  17:30
Place: KEK, 4th Building Room 244 (2nd Floor)
14:00  15:30 Nobuchika Okada (KEK)
Title: Higgs portal to dark matter in the Nightmare Scenario
Abstract: Even if new physics beyond the standard model exists at some high energy, it is generally possible that the LHC experiment could find only the Higgs boson but nothing else. This is particle physicists' Nightmare Scenario. On the other hand, the existence of the dark matter has been established from various observations and according to the Weakly Interacting Massive Particle (WIMP) dark matter hypothesis, a stable and chargeneutral WIMP with mass of O(1 GeV)(1 TeV) is a promising candidate for thermal relic dark matter. We discuss the way how to incorporate such a WIMP dark matter in the nightmare scenario and investigate a possibility that the dark matter can overcome the nightmare through its coupling with the Higgs boson.16:00  17:30 Hideki Maeda (Centro de Estudios Cientificos)
Title: Dynamical black holes with symmetry in EinsteinGaussBonnet gravity

22 (Fri), May, 2009
Place: Multipurpose hall, 3rd floor, Tachikawa Hall,Rikkyo University
14:30  16:00 Motoyuki Saijo (Rikkyo University)
Title: Collapse of a rotating supermassive star to a supermassive black hole
abstract: We all believe that there exists a supermassive black hole in the centre of galaxy, but the actual formation process is still a mystery. Here we stand on the path to form a supermassive black hole from a supermassive star. In order to focus on this dynamical process, three dimensional general relativistic hydrodynamics is desirable. After a brief introduction about the supermassive objects and expected gravitational waves to be detected, I will review the ideas in numerical relativity which we use in our computation. Then, I will demonstrate our computational results about the dynamic behaviour of the black hole formation process. Here, I will especially focus on the post black hole formation stage, that there exists a quasiperiodic waves after the ringdown in gravitational waveform. The typical frequency of the quasiperiodic waves approximately correspond to gravitational waves from a particle at ISCO orbiting around a Kerr black hole. The radiation may be detected in the future spacebased detector LISA, which may tells us the environment of the supermassive object.16:00  16:30 Break 16:30  18:00 Dr. Leor Barack (University of Southampton, UK)
Title: Gravitational selfforce (with application to extrememassratio binary inspirals)
abstract: The radiative inspiral of compact stellarmass objects into massive black holes in galactic nuclei is a key source for LISA  the proposed spacebased gravitational wave observatory. Each of these inspiralling objects is an extremely effective probe of the strongfield geometry of the central black hole, and its gravitational wave signal encodes a wealth of detailed information about this geometry. Decoding this information will require accurate theoretical templates of the gravitational waveforms, which, in turn, requires an accurate model of the orbital evolution. The inspiral dynamics can be described in a perturbative fashion in terms of an effective gravitational selfforce. Knowledge of the local self force acting on the inspiralling body is an important prerequisite in the program to model astrophysical inspirals. I will begin this talk by reviewing the general theory of the gravitational selfforce in curved spacetime, and proceed to describe how this theory is being applied today in actual calculations of the self force for inspiral orbits. As a particular application, I will present a recent calculation of the shift in the location and frequency of the ISCO (innermost stable circular orbit) of a Schwarzschild black hole due to the conservative piece of the gravitational self force.

22 (Wed), April, 2009
Place: RESCEU, University of Tokyo
14:30  15:30 Takehiko Asaka (Niigata)
Title: Neutrino masses and baryon asymmetry of the universe16:30  17:30 Damien A. Easson (IPMU)
Title: Searching for the microphysics of Inflation

27 (Fri), February, 2009, 13:30  17:00
Place: IPMU Prefab. B, Kashiwa Campus of the University of Tokyo.
13:30  15:00 Niayesh Afshordi (Perimeter Institute)
Title: The end of the cosmological constant problem!
abstract: Cosmological constant problem is arguably the deepest gap in our understanding of modern physics. I first introduce a modification of Einstein gravity, gravitational aether, which decouples the quantum field theory vacuum from gravity, solving the cosmological constant problem. I will then show how the formation of stellarmass black holes could trigger the onset of cosmic acceleration (and dark energy) in the context of this model. The model can be tested through its effect on big bang nucleosynthesis, cosmological structure formation, and possible correlations between black hole formation and cosmic acceleration at late times.15:00  15:30 coffee break 15:30  17:00 Ghazal Geshnizjani (Perimeter Institute)
Title: Observational Evidence for CosmologicalScale Extra Dimensions
abstract: I present a case that current observations may already indicate new gravitational physics on cosmological scales. The excess of power seen in the Lymanalpha forest and smallscale CMB experiments, the anomalously large bulk flows seen both in peculiar velocity surveys and in kinetic SZ, and the higher ISW crosscorrelation all indicate that structure may be more evolved than expected from LCDM. I argue that these observations find a natural explanation in models with infinitevolume (or, at least, cosmologicalsize) extra dimensions, where the graviton is a resonance with a tiny width. The longitudinal mode of the graviton mediates an extra scalar force which speeds up structure formation at late times, thereby accounting for the above anomalies. The required graviton Compton wavelength is relatively small compared to the present Hubble radius, of order 300600 Mpc. Moreover, with certain assumptions about the behavior of the longitudinal mode on superHubble scales, our modified gravity framework can also alleviate the tension with the low quadrupole and the peculiar vanishing of the CMB correlation function on large angular scales, seen both in COBE and WMAP. This relies on a novel mechanism that cancels a latetime ISW contribution against the primordial SachsWolfe amplitude.
 28 (Wed), January, 2009, 14:00  17:30
Place: Waseda University
14:30  15:30 Alexei Starobinsky (Landau Institute / RESCEU)
Title: f(R) models of inflation and dark energy in the Universe
Abstract : Since 1980, a variant of the f(R) fourthorder theory of gravity (with small oneloop nonlocal corrections) was known to provide an internally selfconsistent scenario of the early Universe with an initial quaside Sitter (inflationary) stage followed by the graceful exit to the radiationdominated FRW stage via reheating in the regime of a narrow parametric resonance, in which all matter in the Universe arises as a result of gravitational particle creation. Its predictions regarding spectra of primordial density perturbations and gravitational waves remain in agreement with the most recent observational data. A few years ago it was proposed to use this class of models for description of dark energy in the present Universe. However, this problem appeared to be more complicated, mainly due to the presence of nonrelativistic matter and radiation, so many attempts in this direction failed. Still recently some f(R) models of dark energy have been found which can satisfy laboratory, Solar system and cosmological tests. They represent an interesting alternative to the standard cosmological model with a cosmological constant. Further problems and most critical tests for such models are outlined.16:00  17:30 Brian Powell ( IPMU )
Title : What we know (and may ever know) about inflation
Abstract : I will discuss the current status of inflation in light of recent CMB and LSS measurements, focusing on a novel numerical technique of potential reconstruction based on the flow formalism. This approach reveals that little information is known about the earliest moments of observable inflation, indicating that nonslowroll behavior is possible. The associated power spectra exhibit strong suppression of power on large scales. In addition to exotic inflationary dynamics, such spectra might also be produced by modifying the initial vacuum state of fluctuations, as might arise from a preinflationary expansion phase. Lastly, I will discuss the future prospects of potential reconstruction as might be expected with the upcoming Planck mission. I will focus on potential reconstruction within the larger class of noncanonical inflation models, a class including DBI and kinflation, and conclude that a measurement of nonGaussianities will be essential for a successful reconstruction program.
 10 (Wed), December, 2008, 14:10  18:30
Place: KEK, Tsukuba campus, YonGoKan Bldg
14:10  15:40 David Wiltshire (U. Canterbury)
Title: Cosmological equivalence principle and dark energy without dark energy
Abstract: The problem of the synchronization of clocks and normalization of gravitational energy in general relativity does not have a unique or obvious solution in the absence of exact symmetries of the background. I return to first principles and extend the strong equivalence principle in application to averaged dynamical fields in cosmology, to include the role of the evolving average background density in the calibration of inertial frames. This leads to a "radically conservative" solution to the problem of dark energy in cosmology, using only general relativity and matter obeying the strong energy condition. The proposal yields a model universe which appears to be quantitatively viable, in terms of its fit to supernovae luminosity distances, the angular scale of the sound horizon in the cosmic microwave background anisotropy spectrum, and the baryon acoustic oscillation scale. I will briefly overview the observational status of the proposal, as well as discussing the foundational issues.15:40  15:50 discussion 15:50  16:10 Coffee break 16:10  17:40 Toshifumi Futamase (Tohoku U)
Title: Recent developements of weak lensing17:40  17:50 discussion 18:30  dinner
 14 (Tue), October, 2008, 14:00  17:30
Place: RESCEU, University of Tokyo
14:30  15:30 Shuichiro Yokoyama (Nagoya U)
Title: New delta N formula for multicomponent inflation16:30  17:30 Masahiro Morikawa (Ochanomizu U)
Title: Cosmic dark turbulence and scaling of gravitating system
 30 (Tue), September, 2008, 14:30  18:00
Place: Rikkyo University (Ikebukuro), Building No 4, Room 4232
14:30  16:00 Takashi Tamaki (Waseda U / Rikkyo U)
Title: Diversity of gravitating Qball16:30  18:00 Atsushi Taruya (U of Tokyo)
Title: Nonlinear gravitational evolution of largescale structure and precision cosmology 
23 (Wed), July, 2008, 14:00  17:00
Place: IPMU Prefab. B, Kashiwa Campus of the University of Tokyo.
14:00  15:00 Latham Boyle (CITA)
Title: Binary black hole merger: symmetry and the spin expansion
Abstract: Two spinning black holes emit gravitational waves as they orbit, and eventually merge to form a single black hole. How do the properties of the final black hole depend on those of the initial black holes? We regard binary black hole (BBH) merger as a map from a simple initial state (two black holes, with dimensionless spins a and b) to a simple final state (a Kerr black hole with mass m, dimensionless spin s, and recoil kick velocity k). By expanding this map around a = b = 0 and applying symmetry constraints, we obtain a simple formalism that is remarkably successful at explaining existing BBH simulations, and makes detailed new predictions about the merger process. We discuss some astrophysical/cosmological applications of this formalism.15:30  17:00 Contributed talks
 Kazunori Nakayama (ICRR, U of Tokyo)
"Impacts of gravitational wave background detection on SUSY"  Keisuke Izumi (Kyoto U)
"How to construct the seed metric of many blackrings"  Kinya Oda (Osaka U)
"Black hole thermodynamics for quarkgluon hydrodynamics"
 Kazunori Nakayama (ICRR, U of Tokyo)
Contact: joint_cosmo@ipmu.jp