2017 Spring Seminar List

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Spring 2017 LeCosPA Cosmology and Particle Astrophysics Seminars

Location : Room 812, Astro-Math Building, NTU
Time : 11:00-12:00, Monday
Time for ASIAA/LeCosPA Joint Seminar : 14:20-15:20 on specific Thursdays
Organizers : Dr. Jakub Ripa & Dr. Dong-han Yeom

Date Name Title Affiliation File
02/20
Semester starts
02/27
National holiday
03/06
Prof. Yasha Neiman
Both AdS and CFT from twistor space
We consider one of the simplest holographic models: higher-spin gravity in 4 dimensions vs. a free vector model in 3 dimensions. We present a picture in which both the bulk and boundary local descriptions descend from a unified description in twistor space. Higher-spin gravity is closely tied to the Penrose transform, which relates bulk massless fields to twistor functions. We develop a new geometric perspective on the Penrose transform, whereby it becomes a peculiar representation of a CPT reflection. We then identify a boundary version of the transform, relating twistor functions to bilocal operators and sources in the CFT. This allows us to write the partition function in manifestly higher-spin-covariant language, line by line in the Feynman diagrams. The famous ambiguity in the bulk Penrose transform becomes related to the gauge redundancy in the boundary sources.
Okinawa Institute of Science and Technology
File:Neiman.pdf
03/13
Prof. Michel Koenig
20 years of laboratory astrophysics at LULI
Laboratory astrophysics has been a growing domain since the last 20 years thanks to the development of both high energy and high intensity lasers. This domain is part of a larger field called High Energy Density Physics that emerged with the ICF programs. In this seminar, I will present an overview of the research in laboratory astrophysics, establish the scaling laws that governs the dynamic processes in the Universe and the laboratory. Then I will describe some of the work we performed on planetary physics that is part of the identical domain of laboratory astrophysics. Finally, I will focus in more details on radiation hydrodynamics, in particular radiative shocks that can be studied using high energy lasers. Here, recent research performed at LULI laboratory connected to radiation hydrodynamics astrophysical situations is related to radiative shocks occurring in supernovae explosions, in magneto-spherical accretion in young stellar objects, in cataclysmic variables (mCVs) as well as in accreting neutron stars. During the last ten years European scientists have been international leaders in this area, exploiting competitive EU facilities (LULI2000, VULCAN, LIL, ORION, GEKKO XII & in the near future LMJ+PETAL). In this new field, 2D-3D radiation hydrodynamics simulations are necessary both to design experiments and to perform relevant analysis of experimental data. In this talk, I will show both experimental results obtained on the major EU facilities and the GekkoXII laser (Japan) and the associated hydrodynamic simulations. These are performed with the HEDP version of the FLASH code, developed at the University of Chicago with inputs coming from the laser-plasma community.
Ecole Polytechnique
File:Koenig.pdf
03/20
Dr. Henry Tsz-King Wong
Latest results in neutrino physics and the TEXONO program
We will provide an update on the latest results and status in neutrino physics, as well as the TEXONO research programs on neutrino and dark matter.
Academia Sinica Institute of Physics
File:Wong.pdf
03/27
Prof. Keisuke Izumi
"Penrose inequality" for photon surface
Penrose inequality shows the maximum area of black hole horizon. Equality holds iff spacetime metric is Schwarzschild solution. We do a similar discussion for “photon surface”, not for horizon. We introduce a concept showing the strong gravity region "loosely trapped surface". We proof that the area $A_0$ of loosely trapped surface satisfies the inequality $A_0 \le 4\pi (3Gm)^2$, where $m$ is ADM mass of the spacetime. The equality holds iff the spacetime metric is Schwarzschild solution, and then the loosely trapped surface is the photon sphere of Schwarzschild solution.
Nagoya University
File:Izumi.pdf
04/03
National holiday
04/10
Prof. William G. Unruh
"Infomation paradox" and firewalls
Much has been made over the past 30 years of the so called information paradox and recently of firewalls. The arguments seem to be based on a complete misunderstanding of both quantum theory and General Relativity. I will review a recent paper with R. Wald where we try to analyse the various arguments pointing out the strengths and weaknesses of them.
University of British Columbia
04/17
Prof. Chow-Choong Ngeow
Classical pulsating stars from synoptic surveys and their applications in astrophysics: selected examples
Classical pulsating stars such as Cepheids and RR Lyrae are valuable astrophysical tools, because they can be used to test theories on stellar structure, pulsation and evolution. On the other hand, they are standard candles that can be used to serve as distance tracers, and ultimately provide a crucial component in measuring the Hubble constant. In this talk I will give the studies of Cepheids and RR Lyrae based on few synoptic sky survey projects, including the Optical Gravitational Lensing Experiment (OGLE), the Sloan Digital Sky Survey (SDSS), the Palomar Transients Factory (PTF) and the Large Magellanic Cloud Near-Infrared Synoptic Survey (LMCNISS). For examples, I will demonstrate how I use the PTF data to search for the so-called ultra-long period Cepheids in M31 galaxy, and how is our LMCNISS data helped in improving the measurement of Hubble constant.
National Central University
File:Ngeow.pdf
04/24
Prof. Chorng-Yuan Hwang
Dark matter in galaxies and galaxy clusters
I would discuss some properties of dark matter in galaxies and clusters of galaxies in this talk. Evidence of dark matter in galaxies were usually found in the outer regions of spiral galaxies. I will show evidence for dark matter in the central regions of some star forming galaxies using ALMA observations. The accelerations in these regions are so large that it would be impossible for the dark matter to be explained by the conventional modified Newtonian dynamics (MOND). On the other hand, little dark matter has been found in elliptical galaxies. I will also present evidence from optical observations of SDSS to show that the dark matter in elliptical galaxies is as abundant as that in spiral galaxies, in contradiction to previous observations. Finally, by assuming the dark matter to be composed of neutralinos, we used the detection upper limit on diffuse radio emission in a sample of galaxy clusters to put constraint on the properties of the neutralino. We investigated the constraints on minimal Supergravity (mSUGRA) and minimal supersymmetric standard model (MSSM) parameter space by scanning the parameters using the DARKSUSY package. Even by using the very shallow results from radio sky survey, we are able to exclude 40 combinations of mSUGRA parameters and 573 combinations of MSSM parameters.
National Central University
05/01
Dr. Yoshinori Matsuo
Static black holes with back reaction from vacuum energy
We study spherically symmetric static solutions to the semi-classical Einstein equation sourced by the vacuum energy of quantum fields in the curved space-time of the same solution. We found solutions that are small deformations of the Schwarzschild metric for distant observers, but without horizon. Instead of being a robust feature of objects with high densities, the horizon is sensitive to the energy-momentum tensor in the near-horizon region.
National Taiwan University
File:Matsuo.pdf
05/08
Dr. Teppei Okumura
Precision cosmology with galaxy redshift surveys
Revealing the acceleration of the cosmic expansion is one of the most important issues in cosmology. The mysterious dark energy could be driving the acceleration, or gravity law predicted from Einstein’s theory of general relativity could be breaking down at cosmological scales. To investigate the origin of the acceleration, observations of large-scale structure of the Universe traced by galaxy surveys are considered as the best probe through a measurement of baryon acoustic oscillations (BAO) and redshift-space distortions (RSD). In this talk, I will first demonstrate that the accuracy of the current theoretical models for extracting the dark energy or gravity properties is not high enough for the future precision surveys such as the DESI and Subaru PFS surveys. Particularly, incorrect modeling of redshift-space distortions of satellite galaxies easily leads to a wrong constraint on gravity theories. I will present two complementary approaches which overcome this problem. One is to predict the galaxy power spectrum by combining cosmological perturbation theory and halo model. Another is to reconstruct the power spectrum of dark matter halos from the observed galaxy distribution.
Academia Sinica Institute of Astronomy and Astrophysics
File:Okumura.pdf
05/15
Prof. Jiunn-Wei Chen
Bell inequality in the sky and in holography
National Taiwan University
File:Chen.pdf
05/22
Dr. Hui-Tzu Tu
SN 1987A and Weinberg's Higgs portal dark radiation and dark matter
The observed duration of neutrino burst events from Supernova 1987A in several detectors confirmed the standard picture of neutrino cooling of post-collapse supernova. This strongly constrains the possibility of weakly-interacting light particles being produced in the supernova core and leading to efficient energy loss. We apply this constraint on Weinberg’s Higgs portal model, in which Goldstone bosons play the role of dark radiation, while dark matter candidate is a Majorana fermion. We estimate the rate for Goldstone boson production and propagation by taking into account the uncertainties in nuclear physics, and find that the supernova constraint is indeed competitive to those from terrestrial laboratories.
Academia Sinica Institute of Physics
05/29
National holiday
06/05
Prof. Yasusada Nambu
Probability of boundary conditions in quantum cosmology
One of the main interest in quantum cosmology is to determine boundary conditions for the wave function of the universe which can predict observational data of our universe. For this purpose, we solve the Wheeler-DeWitt equation for a closed universe with a scalar field numerically and evaluate probabilities for boundary conditions of the wave function of the universe. To impose boundary conditions of the wave function, we use exact solutions of the Wheeler-DeWitt equation with a constant scalar field potential. We specify the exact solutions by introducing two real parameters to discriminate boundary conditions, and obtain the probability for these parameters under the requirement of sufficient e-foldings of the inflation. The probability distribution of boundary conditions prefers the tunneling boundary condition to the no-boundary boundary condition. Furthermore, for large values of a model parameter related to the inflaton mass and the cosmological constant, the probability of boundary conditions selects a unique boundary condition different from the tunneling type.
Nagoya University
File:Nambu.pdf
06/12
Prof. Da-Shin Lee
Analog model of quantum phenomena in curved spacetime using cold atomic condensates
We explore possible analogies between quantum phenomena in curved spacetime and cold laboratory condensates whose speed of sound can be tuned by means of an external field. In the first instance, the creation of causal horizons when a system undergoes rapid changes can lead to the creation of defects e.g. cosmic strings and monopoles. We see to what extent this can be mimicked in condensates by the spontaneous creation of vortices in a field ramp. Secondly, by examining the phonon geodesics in the acoustic metric we can look for spontaneous phonon creation that mimics spontaneous particle creation in curved space-time. Also, the fluctuating nature of the phonon background suggests analogies with quantum gravity.

References: [1] D.-S. Lee, C. Y. Lin, and R. J. Rivers: “Derivation of Hydrodynamics for the Gapless Mode in the BEC-BCS Crossover from the Exact One-Loop Effective Action”, Phys. Rev. Lett. 98, 020603 (2007). [2] C.-Y. Lin, D.-S. Lee, and R. J. Rivers, “The role of Causality in Tunable Fermi Gas Condensates,” J. Phys. Cond. Matter 25, 04211 (2013). [3] J.-T. Hsiang, C.-Y. Lin, D.-S. Lee, and R. J. Rivers, “Quantum Stochastic Behavior in Cold Fermi Gases: Phonon Propagation,” Phys. Rev. A 91, 051603(R) (2015).

National Dong Hwa University
File:Lee.pdf
06/19
Prof. Chang Sub Shin
A map of the non-thermal WIMP
In this talk, I will present the effect of the elastic scattering on the non-thermal WIMP, which is produced by direct decay of heavy particles at the end of reheating. The non-thermal WIMP becomes important when the reheating temperature is well below the freeze-out temperature. Usually, two limiting cases have been considered so far. One is that the produced high energetic dark matter particles are quickly thermalized due to the elastic scattering with background radiations. The corresponding relic abundance is determined by the thermally averaged annihilation cross-section at the reheating temperature. The other one is that the initial abundance is too small for the dark matter to annihilate so that the final relic is determined by the initial amount itself. The regions between these two limits are more interesting, and it is showed that the relic density depends not only on the annihilation rate, but also on the elastic scattering rate. Especially, the relic abundance of the p-wave annihilating dark matter crucially relies on the elastic scattering rate because the annihilation cross-section is sensitive to the dark matter velocity. I will categorize the parameter space into several regions where each region has distinctive mechanism for determining the relic abundance of the dark matter at the present Universe, and present the consequence on the (in)direct detection.
Asia Pacific Center for Theoretical Physics
File:Shin.pdf
06/26
Dr. Ekaterina Koptelova
Near-infrared and submillimeter spectroscopy of high-redshift quasar candidates
High-redshift quasars are important probes of the early Universe. However, they are extremely rare and difficult to find. Most of the known high-redshift quasars were discovered at z~6, while only a few are known at z>6.5. The quasars at z>6.5 can be found only in the large area and deep near-IR surveys as their Lyman alpha emission is redshifted to near-IR. We performed selection of promising z>6.5 quasar candidates by combining the photometric data of the large area surveys, such as PanSTARRS1 (PS1) 3pi, 2MASS, all-sky mid-IR WISE, and some other smaller area near-infrared surveys. As a result of this work, we created a unique sample of high-redshift quasar candidates. The confirmation of their quasar identity requires spectroscopic observations. The common way for quasar identification is detection of their redshifted Lyman alpha line. However, near-infrared spectroscopy of high-redshift quasars is extremely time consuming. As an alternative, we have been performing submillimeter spectroscopy of our candidates with ALMA, by simultaneously scanning for the redshifted CO(6-5) and CO(7-6) emission lines originating in the interstellar medium of quasar host galaxies. In this talk we will present our sample of high-redshift quasar candidates and first results of their spectroscopic follow-up in near-infrared and submillimeter.
National Central University
File:EK.pdf
07/03
Dr. Yue-Lin Sming Tsai
The Fuzzy Dark Matter cosmological simulation for Lyman-alpha forest
With recent Lyman-alpha forest data from BOSS and XQ-100 some authors suggested that the lower mass limit on the fuzzy dark matter (FDM) should be pushed up to 10 −21 eV. However, such limits are mainly based on Lambda CDM simulations with the FDM initial condition, but, however, without including the important effects of quantum pressure (QP) in the N-body simulations. For the FDM with mass 10 −22 eV the solitonic core size is around kpc and the QP can have a non-negligible impact on structure formation. By including the QP into cosmological simulations, we find that the BOSS and XQ-100 data cannot exclude the FDM with mass down to 10 −22 eV, in contrast to recent claims. We shall also comment on the numerical uncertainties involved in N-body and hydrodynamic simulations.
National Center for Theoretical Sciences
File:Tsai.pdf
07/10
Dr. Lung-Yih Chiang
Excessive shift of the CMB acoustic peaks of the Cold Spot area
Measurement of the acoustic peak positions of the cosmic microwave background (CMB) temperature anisotropies has been instrumental in deciding the geometry and content of the universe. Acoustic peak positions vary from patch to patch in different parts of the sky due to statistical fluctuation. In this letter we present the statistics of the peak positions of small patches from ESA Planck data. It is found that the peak positions have significantly high variance compared to the 100 CMB simulations with best-fit LambdaCDM model with lensing and Doppler boosting effects included, both of which can significantly shift the peaks of small patches. Examining individual patches, we find the one containing the mysterious "Cold Spot", an area near the Eridanus constellation where the temperature is lower than Gaussian theory predicts, displays large synchronous shift of peak positions towards smaller multipole numbers (i.e. larger scales) with significance lower than 1.11 x 10^{-4}. The combination of large synchronous shifts in acoustic peaks and lower than usual temperature at the Cold Spot area results in a 4.73 sigma detection (significance p~1.11 x 10^{-6}) against the LambdaCDM model, prompting us to propose one of the possible accounts for both anomalies: some localised unknown force to stretch the space around the Cold Spot area so that the acoustic peak positions are shifted towards large scales and the temperature is dragged down.
Academia Sinica Institute of Astronomy and Astrophysics
07/17
Dr. Federico R. Urban
Heavier and darker: spin-2 dark matter
The ghost-free massive spin-2 field of bigravity turns out to be an amusing Dark Matter candidate. I will review the theoretical foundations of bigravity, and outline the qualities and phenomenology of spin-2 gravitational dark matter.
National Institute of Chemical Physics and Biophysics
File:Urban.pdf
07/24
Dr. Mariko Kikuchi
Fingerprinting Higgs sectors by using precision measurements of the Higgs boson couplings
From the point of view of future precision measurements of the discovered Higgs boson (h), higher order calculations of the couplings of h are very important. We calculate the one-loop corrections to the hVV (V=W, Z), hff (f=b, c , tau) and hhh vertices in the two Higgs doublet models with a softly broken Z2 symmetry, the inert Higgs doublet model and the model with a real singlet scalar field. We discuss how we are able to discriminate extended Higgs sectors by measuring characteristic patterns of deviations in the couplings for h at future coupling precision measurements. Moreover, we examine how we can separate and identify extended Higgs models by detecting the patterns of the coupling deviations using the future precision data for the decays at the LHC Run-II, the HL-LHC and the ILC.
National Taiwan University
File:Kikuchi.pdf
07/31
Semester ends


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