# Posters

The booklet of the conference can be downloaded here.

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Various models of dark energy have been proposed to explain cosmic acceleration. Quintessence is one of dark energy models in the form of a scalar field. With its Lagrangian that takes a form of kinetic component and its potential, it is possible for this scalar field to drive late-time cosmic acceleration.

In this work, cosmic dynamics with the presence of a quintessence has been derived. I will start by reviewing about phase plane analysis of a model with exponential potential [1]. After that, cosmic dynamics for the case of non-exponential potential is derived. In the case of non-exponential potential, there will be a tracker solution that attract other trajectories to a common evolutionary path [2].

In addition, I will discuss about reconstruction of quintessence from observations, starting from reconstruction of the field potential, to the evolution of its equation of state. I will also review about statefinder parameters [3] that can be used to distinguish any dark energy models from cosmological constant. Finally, $(w_\phi,w'_\phi)$ plane as a classification of quintessence models is discussed.

[1] E. J. Copeland, A. R. Liddle and D. Wands,
*Exponential potentials and cosmological scaling solutions*,
Phys. Rev. D 57 (1998) 4686 [gr-qc/9711068].

[2] L. Amendola and S. Tsujikawa, Dark Energy: Theory and Observations, Cambridge University Press, Cambridge U.K. (2010), pg. 145.

[3] V. Sahni, T. D. Saini, A. A. Starobinsky and U. Alam,
*Statefinder – a new geometrical diagnostic of dark energy*,
JETP Lett. 77 (2003) 201 [astro-ph/0201498].

This author had put forward a theory about 10 years ago, explaining the CMB in terms of curvature. If one were to use the Earth as an analogue to the surface of the Universe, and height as an analogue to the “Time” dimension, then one can see that as a tower is observed further and further from the observer, it not only diminishes with size due to perspective geometry, but also shrinks in height due to the fact that it is tilted backward away from the observer. This author then went on to explain that the CMB, was the limit to that shrinking and tilting and forms an area, which is analogous to the line that is formed in the limit to the Earth’s horizon. In the General Theory of Relativity, this view would be called the Gravito-Electric field of the Universe. The Gravito-Electric field can’t be the complete model however, there has to also be a Gravito-Magnetic field. The Gravito-Magnetic field, also known as “frame-dragging” or the “Lense-Thirring Effect” must also play a role, as it is unlikely the Universe does not also have some angular momentum. One must take care with the Gravito-Magnetic field as it is frame dependent. The frame is clear when it is one observer, observing the entire Universe. The Gravito-Magnetic field shows up as the non-uniform dimpling of the CMB. Another theory had been put forward by a Professor at MIT, who at the same conference as this author, resurrected the Cosmic Inflation theory which was championed by Alan Guth and earlier Andrei Linde, which explained the non-uniformity of the CMB as due to gas expanding in the early Universe. The results of the Wilkinson Microwave Anisotropy probe and the Gravity Probe B are used by this author to support the theory that he put forward and contest the competing Cosmic Inflation Theory, which has received some criticism.

The orbital angular momentum (OAM) of photons can be produced by a scattering of the Kerr black hole~[1,2]. However, reasons why the OAM of photons is generated by the Kerr black hole seems not to be clarified completely. In this poster, we investigate a mechanism of generating OAM of photons in a gravitational lensing system using the wave optics and explain why the Kerr black hole can produce the OAM of photons.

[1] M. Anselmino, M. Harwit,
*Photon orbital angular momentum in astrophysics*,
Astrophys. J. 597, 1266 (2003) [astrop-ph/0307430].

[2] H. Yang and M. Casals
*Wavefront twisting by rotating black holes: orbital angular
momentum generation and phase coherence detection*
Phys. Rev. D 90, 023014 (2014) [arXiv:1404.0722].

Consider the vacuum near the black hole as thermal bath, and using the thermal equilibrium and Euclidean time (imaginary time). We obtain the Hawking temperature of black hole and after that we will research the evaporation of the different types of black holes.

[1]
S.W.Hawking
*Particle creation by the black hole*,
Commun. math. Phys.43, 199-220 (1975).

[2]
S.W.Haking,
*Black Hole explosions*,
Nature 248, 30 , (1974).

[3]
A.Zee
*Quantum field theory in a nutshell 2nd edition*
Princeton University Press, 2006

[4]
Maulik K.Parlik, Frank Wilczeck
*hawking radiation as tunneling*
Physical Review Letters Vol 85, Num 43, 5042-5045

The detection of the very high energy $\gamma$-ray sources at red-shifts from z = 0.018 to z = 2.979 with SHALON telescopes gives an opportunity to constrain the Extragalactic Background Light (EBL) density, as the TeV $\gamma$-rays can be absorbed due to interaction of low-energy photons of EBL. So, based on the modification of $\gamma$-ray spectra of the proximate and distant metagalactic sources with influence of EBL one can reconstruct the cosmological history of EBL. Spectral energy distributions of EBL constrained from observations of NGC1275 (z=0.0179), Mkn421 (z=0.031), Mkn501 (z=0.034), Mkn180 (z=0.046), 3c382 (z=0.0578), 4c+31.63 (z=0.295), OJ 287 (z=0.306), 3c454.3 (z=0.859), 4c+55.17 (z=0.896), 1739+522 (z=1.375), B2 0242+43 (z=2.243) and B2 0743+25(z=2.979) together with data from measurements and models are presented. Also, the results of the extragalactic source observation are presented with integral spectra, images and spectral energy distributions for each of sources at energies above 800 GeV.

The detection of TeV $\gamma$-ray sources at high red-shifts is the evidence of less average spectral density of Extragalactic Background Light and thus the less star formation rate at early evolution stage, than it is previously believed. Also, the possible explanation of the detected very high energy gamma-emission from the distant AGNi is the re-scattering of primary TeV-photons on the Dark Matter particles, so called WISP - weakly interacting slim particles. The axion-like particles has been considered to be a candidate for such weakly interacting slim particles.

The recent discoveries of strongly lensed type Ia supernovae yielded the first direct measurements of image magnifications in gravitational lensing (e.g., [1]). As magnification is thus becoming an important observable, it is also desirable to gain a better theoretical understanding of this concept beyond its usual formulation in the quasi-Newtonian approximation. This poster describes how the standard definition of gravitational lensing magnification may be generalized to Lorentzian spacetimes, and shows how this definition can be interpreted geometrically in terms of the van Vleck determinant and the exponential map (based on [2]).

[1] R. Quimby, M. C. Werner, M. Oguri, et al., *Extraordinary magnification of the ordinary type Ia supernova PS1-10afx*, Astrophys. J. 768 (2013) L20 (5pp)

[2] A. B. Aazami and M. C. Werner, *Magnification in gravitational lensing via the exponential map*, forthcoming (2015)