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: higherspin 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. Higherspin 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 higherspincovariant 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 magnetospherical 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, 2D3D 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 laserplasma community.


Ecole Polytechnique

File:Koenig.pdf

03/20

Dr. Henry TszKing 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. ChowChoong 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 NearInfrared Synoptic Survey (LMCNISS). For examples, I will demonstrate how I use the PTF data to search for the socalled ultralong 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. ChorngYuan 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 semiclassical Einstein equation sourced by the vacuum energy of quantum fields in the curved spacetime 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 energymomentum tensor in the nearhorizon 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 largescale structure of the Universe traced by galaxy surveys are considered as the best probe through a measurement of baryon acoustic oscillations (BAO) and redshiftspace 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 redshiftspace 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. JiunnWei Chen

Bell inequality in the sky and in holography



National Taiwan University

File:Chen.pdf

05/22

Dr. HuiTzu 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 postcollapse supernova. This strongly constrains the possibility of weaklyinteracting 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 WheelerDeWitt 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 WheelerDeWitt 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 efoldings of the inflation. The probability distribution of boundary conditions prefers the tunneling boundary condition to the noboundary 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. DaShin 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 spacetime. 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 BECBCS Crossover from the Exact OneLoop 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 nonthermal WIMP

In this talk, I will present the effect of the elastic scattering on the nonthermal WIMP, which is produced by direct decay of heavy particles at the end of reheating. The nonthermal WIMP becomes important when the reheating temperature is well below the freezeout 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 crosssection 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 pwave annihilating dark matter crucially relies on the elastic scattering rate because the annihilation crosssection 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

Nearinfrared and submillimeter spectroscopy of highredshift quasar candidates

Highredshift quasars are important probes of the early Universe. However, they are extremely rare and difficult to find. Most of the known highredshift 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 nearIR surveys as their Lyman alpha emission is redshifted to nearIR. 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, allsky midIR WISE, and some other smaller area nearinfrared surveys. As a result of this work, we created a unique sample of highredshift 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, nearinfrared spectroscopy of highredshift 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(65) and CO(76) emission lines originating in the interstellar medium of quasar host galaxies. In this talk we will present our sample of highredshift quasar candidates and first results of their spectroscopic followup in nearinfrared and submillimeter.


National Central University

File:EK.pdf

07/03

Dr. YueLin Sming Tsai

The Fuzzy Dark Matter cosmological simulation for Lymanalpha forest

With recent Lymanalpha forest data from BOSS and XQ100 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 Nbody simulations. For the FDM with mass 10 −22 eV the solitonic core size is around kpc and the QP can have a nonnegligible impact on structure formation. By including the QP into cosmological simulations, we find that the BOSS and XQ100 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 Nbody and hydrodynamic simulations.


National Center for Theoretical Sciences

File:Tsai.pdf

07/10

Dr. LungYih 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 bestfit 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: spin2 dark matter

The ghostfree massive spin2 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 spin2 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 oneloop 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 RunII, the HLLHC and the ILC.


National Taiwan University

File:Kikuchi.pdf

07/31


Semester ends


