2019 Fall Seminar List

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Editing 2019 Fall Seminar List

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

Location : Room 7S1, LeCosPA center, NTU
if participants more than 20, we will change the lecture room from 7S1 to Room 7W3

Time : 11:00 am - 12:00 am, Monday

Organizers : Che-Yu Chen

Date Name Title Affiliation File
Prof. Mariam Bouhmadi-López
Cosmological constraints of phantom dark energy models
On this talk, we will address three genuine phantom dark energy models where each of them induces the particular future events known as Big Rip, Little Rip and Little Sibling of the Big Rip. The background models are fully determined by a given dark energy equation of state. We first observationally constrain the corresponding model parameters that characterise each paradigm using the available data of supernova type Ia, Cosmic Microwave Background and Baryonic Acoustic Oscillations by using a Markov Chain Monte Carlo method. The obtained fits are used to solve numerically the first order cosmological perturbations. We compute the evolution of the density contrast of (dark) matter and DE, from the radiation dominated era till a totally DE dominated universe. Then, the obtained results are compared with respect to ΛCDM. We obtain the predicted current matter power spectrum and the evolution of fσ8 given by the models studied in this work. Finally, the models are tested by computing the reduced χ2 for the `Gold2017' fσ8 dataset. We will as well address some theoretical issues inherent to the phantom dark energy scenario on its largest scope.
University of Basque Country, Spain

ASIAA-LeCosPA seminar Oct./18 14:20-15:20
Kazunori Kohri
Axion-Like Particles and Recent Observations of the Cosmic Infrared Background Radiation and the GeV-TeV Gamma-rays
The CIBER collaboration released their first observational data of the

Cosmic IR background (CIB) radiation, which has significant excesses at around the wavelength ∼ 1 μm compared to theoretically-inferred values. The amount of the CIB radiation has a significant influence on the opaqueness of the Universe for TeV gamma-rays emitted from distant sources such as AGNs. With the value of CIB radiation reported by the CIBER experiment, through the reaction of such TeV gamma-rays with the CIB photons, the TeV gamma-rays should be significantly absorbed during propagation, which would lead to energy spectra in disagreement with current observations of TeV gamma ray sources. In this talk, I discuss a possible resolution of this tension between the TeV gamma-ray observations and the CIB data in terms of axion [or Axion-Like Particles (ALPs)] that can increase the transparency of the Universe by the anomaly-induced photon-axion mixing. We find a region in the parameter space of the axion mass, m_a ∼ 7.E−10 eV -− 5.E−8 eV, and the axion-photon coupling constant, 1.2E−11 GeV^−1 < g_aγγ < 8.8E−10 GeV^−1 that solves this problem.

KEK/Sokendai/Kavli IPMU File:KazKohri20191018.pdf
Prof. Yu-Tin Huang
Kerr black holes/ Taub-NUT geometry from on-shell S-matrix of higher spin particles/dyons
The no-hair theorem states that black holes are completely characterized by its mass, charge and spin. The same set of quantum numbers also characterize elementary particles. In this talk, we give the precise statement of this correspondence in terms of on-shell observables. In particular, we demonstrate that the classical potential, as well as the scattering angle of rotating blackholes is given by that of minimally coupled higher spin particles. Similarly the solution for Taub-Nut space time is mapped to dyons. This map also teaches us interesting properties of these classical solutions. In particular, the Kerr and Taub-Nut solution is simply a complex shift of Schwarzschild black holes.
Phy. Dept. , NTU File:Yu Tin Huang.pdf



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