2019 Spring Seminar List

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Editing 2019 spring Seminar List

== Spring 2019 LeCosPA Cosmology and Particle Astrophysics Seminars ==

Location : Room 7S1, LeCosPA center, NTU

Time : 11:00 am - 12:00 am, Thursday

Organizers : Tsungche liu and Rio Saitou


Date Name Title Affiliation File
Feb/26 (Special seminar at AM812)
Ippei Obata
Axion Dark Matter Search with Optical Cavity Experiment
The outline of this talk is mainly based on our recent paper 10.1103/PhysRevLett.121.161301. In this talk, I will present a novel experimental approach to search for axion dark matter which does not need a conventional strong magnetic field but use an optical cavity. This new method aims to measure the difference of phase velocity between two circular-polarized photons which is caused by the coupling to axion dark matter. The experimental sensitivity is in principle only limited by quantum noise which enables us to probe tiny axion-photon coupling g_{aγ} <~ 10^{−11}GeV^{-1} with axion mass range m_a <~ 10^{-10}eV, which is competitive with other experimental proposals.
ICRR,Tokyo university
Mar/7
Pisin Chen
Tabletop analog black holes to investigate the information loss paradox
abstract :
LeCosPA, NTU
Mar/14
Aniket Agrawal
Tensor Non-Gaussianity from Axion-Gauge-Fields Dynamics
I will talk about an inflation model in which a spectator axion field is coupled to an SU(2) gauge field and produces a large three-point function (bispectrum) of primordial gravitational waves, on the scales relevant to the cosmic microwave background experiments. The amplitude of the bispectrum at the equilateral configuration is characterized by $B_{h}/P_h^2=\mathcal{O}(10)\times \Omega_A^{-1}$, where $\Omega_A$ is a fraction of the energy density in the gauge field and $P_h$ is the power spectrum of gravitational waves produced by the gauge field. These gravitational waves are chiral, and can have a scale-independent power spectrum over a large range of wavenumbers, necessitating the measurement of TB and EB cross correlations along with measurement of non-Gaussianity to claim quantum fluctuations of the metric.
ASIAA File:Tensor ng from inflation.pdf
Mar/21
Shohei Aoyama
Dust grains in Cosmological simulations
The distribution of dark matter is one of the important issues of

cosmology. However, because dark matter cannot be observed directly by electromagnetic observatory, galaxies are used to trace the dark matter distribution. Hence the optical property of galaxies is important for cosmology. In galaxies, dust grains play an important role in the star formation and the modification of intrinsic spectral energy distribution. For former, dust grains are an efficient catalyst of molecular hydrogen formation. For latter, dust grains absorb ultraviolet photons, which originates young and massive stars, and reemit the infrared light. Because the absorption efficiency highly depends on the grain size distribution and spatial distribution of dust grains, we have to predict both of them theoretically. In order to realize the prediction, hydro-dynamical simulations are a powerful tool. In order to complete the simulation within reasonable timescale, we implemented two-size model (Hirashira 2015) into GADGET3-Osaka code. By considering the size distribution, we have been able to treat grain-grain interactions such as coagulation and shattering, which are growth and destruction process of dust grains, respectively. We obtained grain size distribution at every spatial point and radial distribution of dust grain around massive galaxies, which is comparable to that in observation. In addition to the spatial distribution of dust grains, we calculated the radiation transfer by Mie theory, we obtained the luminosity function of infrared luminous galaxies. At z=0, we roughly realized observed luminosity function taken by Herschel satellite.

ASIAA
Mar/28
Yen-Wei Liu
Acausality in Transverse-Traceless Spin-2 Gravitational Waves
The transverse-traceless (TT) portion of the metric perturbations has been widely used to study the physical observables in gravitational wave physics. However, through an explicit calculation of the relevant Green's functions, we show that, in both Minkowski background and spatially-flat cosmologies with constant equation-of-state, the TT gravitational waves receive contributions from the source(s) outside the null cone of the observer, which therefore prevents the TT perturbation from being a standalone observable. In this talk, I will demonstrate this acausal character and discuss how the other gauge-invariant variables must be incorporated to ensure strictly causal gravitational tidal forces, and, being intimately related, the violation of micro-causality for the quantum operators associated with free massless spin-1 and spin-2 states will also be pointed out.
NCU File:LeCosPA 0328 - Yen-Wei Liu.pdf
April/11
Kai-Feng Chen
Explore the universe with big Data at LHC
abstract
Phys, NTU
April/25
Laurent Baulieu
On the Stochastic Quantisation of Quantum Gravity, and its physical predictions for the early cosmology
abstract
CNRS and UNESCO.

LPTHE Sorbonne Université Paris

May/2
Rampei Kimura
Are redshift-space distortions actually a probe of growth of structure?
Although multiple cosmological observations indicate the existence of dark matter and dark energy, cosmological tests of interactions between them have not yet been established. We point out that, in the presence of a coupling between dark matter and dark energy, a peculiar velocity of total matter field is determined not only by a logarithmic time-derivative of its density perturbation but also by density perturbations for both dark matter and baryonic matter, leading to a large modification of the physical interpretation of observed data obtained by measurements of redshift-space distortions. We reformulate a galaxy two-point correlation function in the redshift space based on the modified continuity and Euler equations. We conclude from the resultant formula that redshift space distortions provide us information on the coupling between dark matter and the scalar field by combining weak lensing measurements.

We will also discuss future prospects of constraining specific models using future surveys.

Waseda University
May/11
Yi Yang
title
abstract
NCKU
May/16
name
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abstract
affiliation
may/23
Mustafa Amin
title
abstract
Rice university’
TBD
Daniel R. Terno
title
abstract
Macquarie University Sydney
June/6
name
title
abstract
affiliation
June/13
name
title
abstract
affiliation
June/20
name
title
Abstract
affiliation


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