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| 1 |
Yungui Gong : On the degeneracies between w0 and wa
The two parameters w0 and wa in CPL parameterization are generally degenerated, we derived two analytical expressions for the degenercies and foud the analytical expressions are consistent with those derived from observations. With the analytical degeneracy relations, cosmological parameters can be more tightly constrained.
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| 2 |
Wontae Kim : Hawing-Page phase transition and AdS soliton
We study the Hawking-Page phase transition between the BTZ black hole and the thermal soliton of $M=-1$. There exists a mass gap so that there does not seem to exist a continuous thermodynamic phase transition. We consistently construct the off-shell free energies of the black hole and the soliton by taking into account the conical space. And then, the continuous off-shell free energy to describe tunneling effect can be realized through non-equilibrium solitons.
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| 3 |
Hongsheng Zhang : MOND cosmology
I shall introduce a recent progress in MOND cosmology. I derive the MOND cosmology which is uniquely corresponding to the original MOND at galaxy scales via entropic gravity method. It inherits the key merit of MOND, that is, it reduces the baryonic matter and non-baryonic dark matter into baryonic matter only. I will show the critical parameter in MOND, i.e., the transition acceleration $a_c$ is essentially a parameter at cosmological scale. Thus the long-standing coincidence problem $a_c\sim cH_{0}$ is solved. More interestingly, a term like age-graphic dark energy emerges naturally. In the frame of this MOND cosmology, only baryonic matter is needed to describe both dark matter and dark energy in standard cosmology.
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| 4 |
Shuang-Nan Zhang : Re-accelerating expansion of the universe revealed by Type Ia supernovae and Planck data
The Hubble constant H0 is the single most important cosmological parameter. A higher value of H0 has been obtained from measurements in the local universe, than that obtained at higher redshift, implying that we are living in a faster expanding bubble. This has made many to debate if the accelerating expansion or dark energy is needed to explain the apparent over-dimming of distant Type Ia supernovae (SNe Ia). Recently the Planck team has reported a lower H0 and a higher matter density. In this talk I will show that the lower H0 is inconsistent with SNe Ia data, and the local bubble density is too low if it is a void embedded in the background of the Lambda-CDM expansion. These can be understood if the bubble is also a global property of the present day universe; observationally it becomes "local" because any observer can only observe the present day universe within a small volume. Therefore the data support a scenario that the universe expands at initially a low, then slightly higher, and finally even higher rate at present. This is evidence for re-accelerating expansion of the universe, driven by increasing dark energy density with cosmic time. It is consistent with an evolving dark energy scenario with the dark energy equation-of-state parameter smaller than -1 at low redshift and decreasing with cosmic time. Alternatively it can be described by the LTB metric, called LTB(t) model here, in which the cosmological redshift is interpreted as time rather than radial coordinate, so that the universe remains homogeneous and complies to the Copernican Principle.
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| 5 |
Alireza Hojjati : Robust Strong Lensing Time Delay Estimation
Strong gravitational lensing of time variable sources such as quasars and supernovae creates observable time delays between the multiple images. Time delays can provide a powerful cosmographic probe through the "time delay distance" involving the ratio of lens, source, and lens-source distances. However, lightcurves of lensed images have measurement gaps, noise, systematics such as microlensing from substructure along an image line of sight, and no a priori functional model, making robust time delay estimation challenging. Using Gaussian process techniques, we demonstrate success in accurate blind reconstruction of time delays and reduction in uncertainties for real data.
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| 6 |
Seoktae Koh : Cosmological Perturbations of a Quartet Scalar Fields
We consider the linear perturbations for the single scalar field inflation model interacting with an additional triad of scalar fields. The background solutions of the three additional scalar fields dependent on spatial coordinates with a constant gradientand the ensuing evolution preserves the homogeneity of the cosmological principle. We find that cosmological observable quantities such as the power spectrum, spectral indices of scalar and tensor perturbations, and the running of the spectral indices have small corrections depending on the lower bound of comoving wavevector which is introudced to have well-defined initial quantum states.
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| 7 |
Jiro Soda : Non-Gaussianity from Form Fields
In string theory, there are various form fields. In this talk, I will show those form fields can induce Non-Gaussianity in primordial fluctuations. I will also discuss compatibility of our results with the Planck data.
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| 8 |
Hyung Won Lee : Evolution of non-minimally coupled galieon model
We calculated the cosmological evolution for density parameters and equations of states for non-minimally coupled galileon model.
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| 9 |
Shi Pi : Equilateral non-Gaussianity in Quasi-single Field Inflation
We investigate the quasi-single field inflation in the case when the effective mass of the isocurvature perturbation is large. We use in-in formulism to calculate its non-Gaussianity originated from the three-heavy isocurvature perturbation interaction, and compare the result with that got by the effective field theory. We proved the equivalence of these two different method and confirm that the non-Gaussianity generated by three-heavy-field may dominate even in the large mass limit.
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| 10 |
Mark G Jackson : Inflationary Effects from High Energy Physics
Although the observed CMB is at very low energy, it encodes ultra high-energy physics in spatial variations of the photon temperature and polarization fluctuations. This effect is believed to be dominated by the initial quantum state of the Universe. I will describe the first theoretical tools by which to construct such a state from fundamental physics. One can then use this technique to reliably calculate corrections to the power spectrum, non-Gaussianity, etc from high-energy physics. We may soon be able to compare these predictions against experiment, allowing one to rule out classes of inflationary models.
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| 11 |
Dong-Hoon Kim : Gravitational waves from cosmic bubble collisions: computation of time-domain waveforms
Cosmic bubbles are nucleated through the Coleman-de Luccia tunneling process and each bubble will undergo an unbounded number of collisions with other bubbles. We focus in particular on the collisions of two equal-sized bubbles and model it using a real scalar field potential, where the field initially in the "false vacuum" state tunnels quantum mechanically to the "true vacuum" state, repeating the transition back and forth and eventually settling down in the true vacuum. With the help of this scalar field model we numerically compute the gravitational radiation produced by the two colliding bubbles in a straightforward manner: in the linearized gravity approximation, a 'time-domain' gravitational waveform is directly obtained by integrating the stress-energy tensor over the volume of the wave source, where the stress-energy tensor is expressed in terms of the scalar field and therefore contains all necessary information of the bubble collisions. Further, we calculate the power spectrum of the gravitational radiation and investigate how the gross features of the bubble collisions, such as the vacuum energies and collision time scale, are associated with the gravitational radiation; in particular, with a characteristic frequency of the radiation and with the amount of the radiation energy released.
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| 12 |
Hyeong-Chan Kim : A new synthesis of matter and gravity: A nongravitating matter
We present a new manifestation of the nonlinearity of the gravity-matter interactions. We show explicitly that there exists a nongravitating dynamical scalar-field solution in Eddington-inspired Born-Infeld gravity. This kind of solution has not been found in previous literatures based on general relativity, or other modified-gravity theories. The nongravitating solution obtained in this work is unstable to perturbations.
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| 13 |
Inyong Cho : EiBI Inflation
We investigate a nonsingular initial state of the Universe which leads to inflation naturally. The model is described by a scalar field with a quadratic potential in Eddington-inspired Born-Infeld gravity. The curvature of this initial state is given by the mass scale of the scalar field which is much smaller than the Planck scale. Therefore, in this model, quantum gravity is not necessary in understanding this pre-inflationary stage, no matter how large the energy density becomes. The initial state in this model evolves eventually to a long inflationary period which is similar to the usual chaotic inflation.
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| 14 |
Masahide Yamaguchi : Effective field theory approach to quasi-single field inflation andeffects of heavy fields
We discuss the possibility that dark matter axions form a Bose-Einstein condensate (BEC) due to the gravitational self-interactions. The formation of BEC occurs in the condensed regime, where the transition rate between different momentum states is large compared to the energy exchanged in the transition. The time evolution of the quantum state occupation number of axions in the condensed regime is derived based on the in-in formalism. We recover the expression for the thermalization rate due to self-interaction of the axion field, which was obtained in the other literature. It is also found that the leading order contributions for interactions between axions and other species vanish, which implies that the axion BEC does not give any significant modifications on standard cosmological parameters.
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| 15 |
Jae-Hyuk Oh : Stochastic quantization and holographic Wilsonian renormalization group
We study relation between stochastic quantization and holographic Wilsonian renormalization group flow. Considering stochastic quantization of the boundary on-shell actions with the Dirichlet boundary condition for certain $AdS$ bulk gravity theories, we find that the radial flows of double trace deformations in the boundary effective actions are completely captured by stochastic time evolution with identification of the $AdS$ radial coordinate `$r$' with the stochastic time '$t$' as $r=t$. More precisely, we investigate Langevin dynamics and find an exact relation between radial flow of the double trace couplings and 2-point correlation functions in stochastic quantization. We also show that the radial evolution of double trace deformations in the boundary effective action and the stochastic time evolution of the Fokker-Planck action are the same. We demonstrate this relation with a couple of examples: (minimally coupled)massless scalar fields in $AdS_2$ and U(1) vector fields in $AdS_4$.
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| 16 |
Dimitri Polyakov : Higher Spin Algebra and Holographic Fluid in AdS_5/CFT_4
We study the graviton's beta-function in AdS string sigma-model, perturbed by vertex operators for Vasiliev's higher spin gauge fields in AdS_5. The result is given by the Ricci tensor with cosmological term and the matter stress-energy tensor contributed by spin 1 and spin 3 excitations. The matter tensor turns out to be the one of conformal second order hydrodynamics, with the spin 3 contribution being crucial to ensure the conformal structure in the second order of the gradient expansion. We conjecture that contributions from the higher spin values correspond to higher orders of holographic gradient expansion in conformal hydrodynamics, which structure is controlled by higher spin algebra in AdS_5.
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| 17 |
Gungwon Kang : Gravitational Radiation Captures of Two Black Holes in Weakly Hyperbolic Orbits
We have numerically studied gravitational radiation capturing processes of two non-spinning equal mass black holes in weakly hyperbolic orbits (e.g., eccentricities of 1.0 ~ 1.4). Understanding this capturing process is important to evaluate the formation rate of black hole binaries near the supermassive black hole in galactic nuclei. The capturing cross sections obtained in full general relativity agree well with the corresponding 2.5 post Newtonian results for small initial energies, but differ up to about 40% for large initial energies. We also confirmed that most of gravitational wave emissions occur when two black holes encounter closely. This explains why the multipole contributions higher than l=2 are negligible (e.g., about 1%) even if the orbit is quite eccentric or non-quasi-circular. The features of energy and angular momentum extractions and gravitational wave forms are also analyzed.
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| 18 |
Jae-Weon Lee : Supermassive black holes and BEC/ scalar field dark matter
It is suggested that supermassive black holes can form from collapse of scalar field dark matter, which could explain the early formation of galaxies. The stability of scalar field dark matter around the black holes is also discussed.
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| 19 |
Mu-In Park : 3D Higher Spin Black Holes and Statistical Entropy
I consider black holes in 3D higher spin gravity and its ststistical black hole entropy from the Chern-Simons construction of 3D gravity.
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| 20 |
Jinsu Kim : Non-gaussianity from non-minimal coupling in hybrid model
Motivated by the recent ‘Higgs-inflation’ scenario based on a single inflaton field, we consider more generic two-field inflation with non-minimal coupling term. The analytic expressions for cosmological observables with the product as well as additively separable potential are derived when the the non-minimal coupling term is dominated by one of the two inflaton fields. As a concrete example we analyze a hybrid model with V = μ2φ2 (1 + cos(χ/σ)) with the non minimal coupling αφR and found the model predicts a small non-Gaussianity in the most of parameter space which is consistent with the recent results from Planck2013 and WMAP9.
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| 21 |
Agus Suroso : Nonminimal derivative coupling of scalar fields in five dimensional cosmology
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