| 4 (Mon) | 5 (Tue) | 6 (Wed) | 7 (Thu) | 8 (Fri) |
|---|---|---|---|---|
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15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar K. Koyama [pdf] |
15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar E. Linder [pdf] |
15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar G. Zhao [pdf] |
Workshop Day1 Room: K206 |
Workshop Day2 Room: YH110 (Panasonic Auditorium) Banquet Room: K102 |
| 11 (Mon) | 12 (Tue) | 13 (Wed) | 14 (Thu) | 15 (Fri) |
|---|---|---|---|---|
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10:30 - 11:00 Coffee Break 11:00 - 12:00 Seminar N. Kaiser [pdf] 15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar M. Takada [pdf] |
15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar D. Bacon [pdf] |
15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar D. Bacon [pdf] |
10:30 - 11:00 Coffee Break 11:00 - 12:00 Seminar D. Bacon [pdf] 15:00 - 15:30 Coffee Break 15:30 - 16:30 Seminar Y-S. Song [pdf] |
The measurements of the growth rate of structure formation provide valuable information about the nature of the cosmic acceleration. In my talk, I will discuss the recent developments of perturbation theory based approaches to model the redshift space power spectrum and correlation function and their application to general dark energy and modified gravity models. I also touch upon the effective field theory approach of larger scale structure.
Modifying gravity in theory is relatively easy, but learning about gravity from observational data is hard. Constraints tend to apply to one particular theory of gravity, with one particular functional form, with one particular set of parameters. With classes such as Horndeski gravity or an effective field theory approach, there are four or more free functions of time in addition to the cosmic expansion history, and no clear guide to their parametrization. We instead focus on observational aspects of cosmic structure growth and ask whether there are unbiased signatures of modified gravity that can be constrained by future surveys.
The origin of the cosmic acceleration has been one of the key problems to solve in modern sciences. According to what we know so far, it might be due to the effect of dark energy, or to our misunderstanding of gravity. In this talk, I will explore the possibilities and practicalities of tackling this challenging cosmic acceleration problem using large scale structure surveys including BOSS, eBOSS and DESI. I will also address the issue of tension among different kinds of recent astronomical observations, and offer a solution to release the tension using the dynamical dark energy.
In the conventional framework for cosmological dynamics it is assumed that there is a "scale factor" a(t) that obeys the Friedmann equation for a perfectly homogeneous universe, while particles move with `peculiar' motions that are driven by the gravity associated with the spatial fluctuations of the density. This gives the conventional equations of particle motion that are commonly solved in numerical N-body simulations. It has sometimes been questioned whether this is legitimate and whether in fact the emergence of non-linear structure has some `backreaction' on the global expansion rate. If so this could have significant implications for cosmology. It has been suggested recently that this is indeed the case, and this allows the successes of `concordance cosmology' without the need for dark energy. Here I argue that, in the Newtonian limit, which should be a good approximation in the low-z universe where the need for dark energy is already apparent, one should not think about there being a background equation of motion for a(t) and a separate set of equations for the motions of particles relative to this background. Rather there are just equations of motion for the particles in re-scaled coordinates x = r / a(t). These are valid for arbitrary scaling, but if a(t) is assumed to obey the Friedmann equation they reduce to the conventional system. The Friedmann equation is, from this perspective, an `auxiliary relation' that simplifies the equations of motion for the particles. This view also makes clear that the conventional equations are exact and explains why, in the Newtonian context, there is no backreaction effect. I will also discuss how relativistic effects may modify this conclusion.
We use the Subaru Hyper Suprime-Cam (HSC) to conduct a high-cadence (2 min sampling) 7~hour long observation of the Andromeda galaxy (M31) to search for the microlensing magnification of stars in M31 due to intervening primordial black holes (PBHs) in the halo regions of the Milky Way (MW) and M31. The combination of an aperture of 8.2m, a field-of-view of 1.5 degree diameter, and excellent image quality (~ 0.6'') yields an ideal dataset for the microlensing search. If PBHs in the mass range M_PBH=[10^{-13},10^{-6}]Msun make up a dominant contribution to dark matter (DM), the microlensing optical depth for a single star in M31 is tau~10^{4}-10^{-7}, owing to the enormous volume and large mass content between M31 and the Earth. The HSC observation allows us to monitor more than tens of millions of stars in M31 and in this scenario we should find many microlensing events. To test this hypothesis, we extensively use an image subtraction method to efficiently identify candidate variable objects, and then monitor the light curve of each candidate with the high cadence data. Although we successfully identify a number of real variable stars such as eclipse/contact binaries and stellar flares, we find only one possible candidate of PBH microlensing whose genuine nature is yet to be confirmed. We then use this result to derive the most stringent upper bounds on the abundance of PBHs in the mass range. When combined with other observational constraints, our constraint rules out almost all the mass scales for the PBH DM scenario where all PBHs share a single mass scale.
I will discuss the latest results from the Dark Energy Survey, including discussion of galaxy clustering, cosmic shear, galaxy-galaxy lensing, and cross-correlations with the CMB. I will describe the resulting cosmological constraints and their implications.
We are entering an exciting phase in the study of cosmology, with major telescopes such as SKA, LSST and Euclid coming to the fore in the next few years. I will discuss the cosmological benefits that can be gained by combining the data from these telescopes: precise measurements of dark energy and gravity parameters, removal of systematic effects, and joint exploration of cosmological probes.
Gravitational lensing, both strong and weak, has become a powerful tool in understanding the dark Universe. I will describe some of the latest results in this field, including insights into dark matter and dark energy physics, constraints on theories of gravity, and use of the probe at microwave and radio wavelengths.
SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) is a proposed all-sky spectroscopic survey satellite designed to address all three science goals in NASA's Astrophysics Division: probe the origin and destiny of our Universe; explore whether planets around other stars could harbor life; and explore the origin and evolution of galaxies. SPHEREx will scan a series of Linear Variable Filters systematically across the entire sky. The SPHEREx data set will contain R=40 spectra fir 0.7<λ<4 micro m and R=150 spectra for 4.1<λ<4.8 micro m for every 6.2 arc second pixel over the entire-sky. In this talk, we detail the extra-galactic and cosmological studies SPHEREx will enable and present detailed systematic effect evaluations. We also outline the Ice and Galaxy Evolution Investigations.
