2018 Spring Seminar List

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== Spring 2018 LeCosPA Cosmology and Particle Astrophysics Seminars ==

Location : Room 812, Astro-Math Building, NTU

Time : 11:00 am - 12:00 am, Monday

Organizers : Dr. Nugier, Fabien & Dr. TC Liu

Date Name Title Affiliation File
Jan./11 (Thur.)
Prof. Daniel Baumann
Relics from the Early Universe
New light particles arise in many attempts to address shortcomings of the Standard Model of particle physics, but their weak coupling to ordinary matter makes them hard to detect in terrestrial experiments. In the hot environment of the early universe, however, even extremely weakly coupled particles can be produced prolifically and their gravitational effects become detectable in cosmological observations. In this talk, I will show that future observations of the cosmic microwave background and of the large-scale structure of the universe have the sensitivity to detect new particles that were created just fractions of a second after the Big Bang. I will explain why these measurements are robust and how they are important as probes of fundamental physics.
University of Amsterdam
Dr. Kuan-Chou Hou
Dust evolution in galaxy and cosmology simulations
Dust enrichment is one of the most important aspects in galaxy evolution.

The evolution of dust is tightly coupled with the nonlinear evolution of the ISM including star formation and stellar feedback, which drive the chemical enrichment in a galaxy. Numerical hydrodynamical simulation provides a powerful approach to studies of such nonlinear processes.

In this work, we present a single-galaxy and cosmological simulation using smoothed particle hydrodynamics (SPH) with dust evolution. We consider dust production in stellar ejecta, destruction in supernova shocks, dust growth by accretion and coagulation, and dust disruption by shattering for the processes driving the dust evolution. We also treat the evolution of grain sizes distribution by representing the entire grain radius range by small (< 0.03 μm) and large (> 0.03 μm) grains.

In the single galaxy simulation, we present the evolution of dust-to-gas mass ratio and grain size distribution. By further separating dust species into carbonaceous and silicate dust, we can obtain the extinction curves. For the first time, the simulation allows us to examine the dependence of extinction curves on the position, gas density, and metallicity in the galaxy. In the cosmological simulation, we examine the dust mass function and to analyze the dust abundance and dust properties in galaxies statistically. Besides, we also examine the redshift evolution of dust content in galaxies. In particular, we show how the relation between dust abundance and galaxy properties (such as stellar mass and star formation activity) evolves as a function of redshift. The above predictions could be tested by ALMA up to high redshifts.

Seminar Cancelled
Chinese New Year - No Seminar
Dr. I-Non Chiu
Studying Scaling Relations of Galaxy Clusters
Galaxy clusters contain rich information of cosmology and astrophysics. In the past, cluster science was limited by a lack of adequately deep observations in multi-wavelength and was subject to heterogeneous samples with small sizes at low redshift. The situation has been changed due to the recent success of the large mm wavelength surveys—such as the South Pole Telescope (SPT)—that employ the Sunyaev-Zel’dovich Effect (SZE) to identify and study galaxy clusters in their abundance out to the early and distant Universe. Together with the breakthroughs in the area of wide-and-deep optical and NIR surveys, such as the Dark Energy Survey and the Hyper Suprime-Cam survey, we are able to uniformly study these SZE selected samples. In this talk, I will talk about the recent results from the SPT collaboration with emphasis on various observable to mass scaling relations. I will present the unprecedented study of the baryon content of an approximately mass-limited sample of 91 galaxy clusters out to redshift 1.3. I will demonstrate the crucial need for the accurate mass calibration in order to pave a way for cluster science in the future.
File:2018-2-26 Chiu.pdf
Prof. Troshichev
Russian geophysical studies in Antarctica
The geophysical observations (1-min magnetic and riometer measurements) are carried out at four Antartctic stations: Vostok, Mirny, Progress, Novolazarevskaya. Vertical sounding of the ionosphere is fulfilled each 15-minutes at station Mirny. At the near-pole station Vostok, it is also carried 1-min measurements of the ozone content and electric field in the ground atmosphere layer and 1-sec magnetic measurements, the latter being transmitted on-line in the Polar Geophysical Centre (St.Petersburg). Measurements of the solar UV irradiation oscillations in zenith of free atmosphere are carried at the station Novolazarevskaya.

As a result of analysis of the Antarctic geophysical data the scientific founding were made, as follows: It was shown that inter-annual changes of the total ozone content in Antarctica can be predicted taking into account the solar irradiation intensity and cycle of the quasi-biennial oscillations (QBO) in the height profiles of zonal winds in the equatorial stratosphere. In 2014, the prediction was made for 2014-2018. Verification of the prediction during 2014-2017 has demonstrated correctness of the forecast method (excluding the short interval in 2015 when the Earth’s atmosphere was suddenly subjected to global changes). The index of the polar cap magnetic activity (PC) has been elaborated based on 1-min magnetic data from Vostok station. The International Association of Geomagnetism and Aeronomy (IAGA) in 2013 recommended “use of the PC index by the international scientific community in its near-real time and definitive forms as a proxy for energy that enters into the magnetosphere during solar wind-magnetosphere coupling”. In this quality the PC index is used at present to monitor the space weather and magnetosphere state and to nowcast the magnetospheric disturbances. Measurements of the solar UV irradiation, carried in zenith of free atmosphere at Novolazarevskaya station (70.46.S, 11.49 E) during summer season in 2008-2015, revealed the short-time (from 3 to 100 min) fluctuations of the solar UV irradiation intensity with maximum in range 297-330 nm, which corresponds to p-mode of solar oscillations, occurring in the interior of Sun. Occurrence of the UV irradiation intensity fluctuations correlates with behavior of such Earth’s atmosphere parameters as altitude of magnetopause and content of “ice water”. The synchronous measurements of the UV fluctuations carried out in Arctica and Antarctica in September of 2013 have demonstrated coherency of UV fluctuations with periods 5-7 min, 25 min, and 35-55 min, the appropriate coefficients of correlation being equal to R ~0.9, ~0.7 and ~0.65.

Arctic and Antarctic Research Institute, St.Petersburg
Prof. Chopin Soo
Cosmic time and gravitation
In an ever-expanding spatially closed universe, the fractional change of the volume is the preeminent intrinsic time interval to describe evolution in General Relativity (GR). With this additional physical input, the constraints are no longer first class, but can in fact be turned into a set of second class constraints when the physical degrees of freedom (d.o.f.) are identified with transverse-traceless excitations. A true physical Hamiltonian for intrinsic time evolution emerges, together with a reduced phase space with two d.o.f. apposite to functional integral methods. Freed from the first class Dirac algebra, deformation of the Hamiltonian constraint is permitted, it is revealed that four-covariance is not really needed to capture the physical content of Einstein's theory, and natural extension of the Hamiltonian while maintaining spatial diffeomorphism invariance leads to a theory with Cotton-York term as the ultra-violet completion of Einstein's GR. The framework provides a rigorous canonical foundation for the consistency of Horava gravity theories which are obtained by changing GR through its physical reduced Hamiltonian.
National Cheng Kung University (NCKU)
Dr. Kin-Wang Ng
Inflation, primordial black holes, and gravitational waves
We discuss the production of primordial black holes and associated gravitational waves in inflation models. These primordial black holes may constitute the dark matter and the associated gravitational waves may be detectable by pulsar timing arrays and gravity-wave interferometry experiments.
File:2018-3-12 Ng.pdf
NTU Study Day -- No Seminar
Dr. Yuan Fang
Laboratory Astrophysics with High Power Lasers
File:2018-4-9 Fang.pdf
Dr. Toshiya Namikawa
Cosmology with cosmic microwave background polarization
One of the promising cosmological probes in the next decades is the CMB polarization. While CMB temperature anisotropies have been already measured very precisely, CMB polarization, in particular a twisting pattern in the polarization map (B mode) is not well measured. The detection of B mode at more than degree angular scale opens new window into the inflationary universe and high energy physics beyond the standard model. Precise polarization data also enables us to measure gravitational lensing of CMB which is a key probe to understand the properties of neutrinos, dark matter and dark energy. I have been working in the area of intersection between theoretical and observational cosmology, particularly focusing on the weak gravitational lensing and CMB. In this talk, after a brief introduction of CMB cosmology, I will first present my analysis works in the BICEP2/Keck Array collaborations. I will also talk about synergy between CMB experiments and galaxy surveys such as the galaxy-lensing cross correlation with Subaru-Hyper Suprime Cam and CMB experiments, and delensing B mode with mass tracers.
File:2018-4-16 Namikawa.pdf
Prof. Kwei-Chou Yang
Co-Decaying Dark Matter, Galactic Center Gamma-Ray Excess from the Cascade Annihilations, and Muon g−2
Prof. Lin Feng-Li
Eigenstate Thermalization Hypothesis in 2D CFT and its implication to AdS/CFT.
In this talk, I will discuss ETH in 2D CFT in the large central charge limit based on my works done in the past 2 years with my collaborators. We calculate the entanglement entropy, Renyi entropies and various dissimilarity distance measures to compare the eigenstates and thermal states in the short-interval expansion. Our results reveal the subtlety of thermalization in 2D CFT and its implication to quantum gravity nature of the dual AdS gravity.
Dr. Simon Archambault
ARA Status and Development
The Askaryan Radio Array (ARA) is a neutrino detector currently under construction at the South Pole, next to the IceCube experiment. Its aim is to detect neutrinos resulting from the interaction of ultra-high-energy cosmic rays and the Cosmic Microwave Background (the GZK process). The experiment uses radio antennas to detect the Askaryan emission from the neutrinos interacting in the Antarctica ice sheet. Once fully operational, ARA’s sensitivity should be nearly 10 times better than IceCube, after 3 years of observations. A successful analysis requires a good understanding of the antenna and detector properties, especially their behavior when in ice. This talk will present work done at Chiba University to further this understanding, including calibration measurements done both in air and in ice, compared to simulations using the finite-difference time-domain algorithm.
Chiba University
File:2018-5-7 Archambault.pdf
May/9 (Wed.)
Prof. Eric Hsiao
Special Seminar [Wednesday!]: What in heaven's name are Type Ia supernovae?
After three decades of successful use as cosmological distance indicators and efforts to observe and model these objects in detail, we still have very incomplete knowledge of the origins of Type Ia supernovae (SNe Ia). They play a crucial role in galaxy evolution and chemical enrichment. Furthermore, observations of distant SNe Ia led to the discovery of dark energy, and they remain the most direct method for studying the cosmic acceleration. Understanding their progenitor system(s) and explosion mechanism(s) is the key to improve precision for the next generation of dark energy experiments, such as those planned aboard the Wide Field Infrared Survey Telescope (WFIRST). In this talk, I will describe what we know so far from observational and modeling efforts, and our plans going forward.
Florida State University
File:2018-5-9 Hsiao.pdf

Dr. B.K. Shin
The air fluorescence yield measurement with 11~15 GeV beam at SLAC
We will present the sFLASH experiment; instruments, measurement and preliminary result. The sFLASH is a measurement of the air fluorescence yield (AFY) at End Station A of the Stanford Linear Accelerator Center (SLAC). The AFY is defined the number of emission photons per energy deposit in the air and is an important parameter to determine the energy of cosmic-ray by detection of the fluorescence detector.

Most interesting point of the sFLASH is used ~10^20 eV artificial air showers which is the similar process of cosmic-ray interact with air. The shower in sFLASH was generated by interaction an alumina target which depth of 0~10 inches with the beam of 11 GeV~15 GeV x 10^9 electrons. The number of photons was measured by Photomultiplier tubes (PMTs) which the same model of Telescope Array, the experiment of UHECR, and energy deposition was estimated using simulation package Geant4 and FLUKA with beam condition of energy and charge of the pulse measured by Integrating Charge Transformer (ICT, the product of Bergoz). With that instruments and method, we succeeded to take data of AFY at 2016 September.

Dr. Teppei Okumura
Probing physical boundaries of dark matter halos from cosmic density and velocity fields
In the current paradigm of cosmic structure formation, galaxies, which are observed as a tracer of the large-scale structure of the universe, are considered to be formed within dark-matter halos. Dark matter halos thus play a fundamental role in both structure formation and cosmological studies. Recently, the phase-space structure in halo outskirts has been extensively studied based on N-body simulations, leading to the discovery of a steepening in the outer density profile of dark-matter halos. This feature is interpreted as a sharp density enhancement associated with the orbital apocenter of the recently accreted matter in the growing halo potential. The location of this steepening is referred to as the splashback radius and depends on cosmology as well as on halo mass and redshift. The splashback radius provides a physical boundary of halos, and is related to the transition scale between the 1-halo and 2-halo regimes in the galaxy power spectrum or correlation function to a certain extent.

In this talk I will present an analysis of the splashback features of dark-matter halos based on cosmic density and velocity fields. Besides the density correlation function binned by the halo orientation angle which was used in the literature, we introduce, for the first time, the corresponding velocity statistic, alignment momentum correlation function. Using large-volume, high-resolution N-body simulations, we measure the alignment statistics of density and velocity. On halo scales, ~1 Mpc/h, we detect the splashback feature, which is found more prominent than in the density correlation. We also find that the splashback radius determined from the density correlation becomes ∼ 3.5% smaller that from the momentum correlation, with their correlation coefficient being 0.605. Moreover, the orientation-dependent splashback feature due to halo asphericity is measured when the density profile is determined by dark-matter particles, which can be used as a test of collisional CDM.

Dr. Hiroyuki Ishida
Impact of initial condition in the nuMSM
In this talk, we present a model called nuMSM in which three right-handed neutrinos whose masses are below the electroweak scale are introduced into the SM. In this model, since usual leptogenesis doesn't work due to smallness of Majorana mass scale, oscillation phenomena can be a seed of lepton asymmetry as different type of leptogenesis. We investigate the impact of initial value of lepton asymmetry generated by Weinberg operators on final lepton asymmetry. We find that there is possibility to give significant impact on baryogenesis scenario. We also discuss its impact to help the production of the DM in the model
Prof. Otto Kong
Particle Dynamics on the Quantum Spacetime
It is about a dream idea since my days as a student, to understand the noncommutative/quantum structure of the spacetime. After some years of quite serious effort, I have gone through a big circle, getting back to the very starting point where a solid picture of a quantum model of the physical space(time) and particle dynamics on it got clarified, together with a quite concrete and promising mathematical framework to take the subject to the 'fundamental' level. I see it as an extremely beautiful integration of modern mathematics and theoretical physics. If Einstein relativity says that space and time should be seen as a whole --- the spacetime, we have a quantum relativity perspective saying spacetime and particle energy-momentum (the momentum space) should be seen as a whole. The phase space is the right model for our spacetime, which can be described by some finite dimensional real number geometry only as classical approximations.
Dr. Martin Spinrath
Direct Detection Prospects for the Cosmic Neutrino Background and Other Cosmic Relics
The Cosmic Neutrino Background is a solid prediction of the Standard Model of Cosmology

and Particle Physics. There is plenty of indirect evidence for its existence but so far it escaped direct detection. I will explain the difficulties in such an endeavor and present some recent ideas and proposals for it. Interestingly, some of the proposals could act simultaneously as a dark matter experiment.

Dragon Boat Festival - No Seminar