# Posters

The booklet of the conference can be downloaded here.

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To tackle the small scale crisis of the cold dark matter model [1], a decaying dark matter model has been proposed, $DDM\rightarrow DM + l$, where $DDM$ is the unstable mother dark matter particle, $DM$ is the stable daughter dark matter particle, and $l$ stands for a light or massless particle. Suppressions on sub-galactic structure formation have been observed in $N$-body investigations on this scenario [2]. Here we apply the Extended Press-Schechter method to calculate the halo mass function subject to particle decay effect and compare it with that measured from $N$-body simulations. This work will help us to better understand the suppression mechanism induced by dark matter decay.

[1] D. H. Weinberg, J. S. Bullock, F. Governato, R. K. de Naray and A. H. G. Peter,
*Cold dark matter: controversies on small scales*, arXiv:1306.0913 [astro-ph.CO]

[2] D. Cheng, M.-C. Chu and J. Tang, *Cosmological structure formation in Decaying Dark Matter models*, J. Cosmology Astropart. Phys. 07 (2015) 009, arXiv:1503.05682 [astro-ph.CO]

It is common to use Friends-of-friends (FoF) method to find the groups in the galaxy sample. This method has the disadvantage of connecting nearby structures, thus making groups larger. In this work we combine the FoF method with multimodality analysis to refine the membership of the FoF groups. As a result, we found the FoF groups richer than 10 members, contained in half of cases more than one refined group, indicating the importance of more precise modelling. Comparison with [1] catalogue showed this method to give similar results, despite the different methodology.

[1] B. Tully,
*Galaxy Groups: A 2MASS Catalog*,
A&A. 149 (2015) 171.

The relativistic evolution of neutron stars, either in a head on collision or in binary orbit is of current interest as such systems are expected to emit detectable gravitational radiation. In this work, numerical simulations of colliding neutron stars, having either a realistic or a $\Gamma=2$ polytropic equation of state (EOS) confirm the rise in central density for the softer EOS. For the binary calculation, our results show that the neutron stars can collapse to black holes before colliding when the EOS is realistic, the central density as the stars approach, when a stiff equation of state is used. Illustrate templates for the gravitational radiation emitted from the binary are calculated and we show that the frequency of the emitted gravitational waves changes more slowly for a realistic EOS. This may result in a stronger signal in the 50-100 Hz band.

This presentation is based on our previous works about investigating supercluster shape, specifically the straightness of superclusters, in various cosmologies.[1][2][3] We measure the specific size $\tilde{S}$ of the supercluster which represents the degree of supercluster straightness and compare $\tilde{S}$ in different cosmologies, on the ground that the shape of filamentary structure of the supercluster will change either if $1)$ the nature of dark energy differs from the Cosmological constant $\Lambda$ or $2)$ the governing law of gravitation deviates from the general theory of relativity at large scale. We identify superclusters by applying FoF algorithm on halo catalogs of N-body simulations for different cosmologies, for example coupled dark energy (cDE) and $f(R)$ gravity models. It is found that both the cDE and $f(R)$ gravity have the effect of significantly bending the superclusters resulting in smaller values of $\tilde{S}$ compared to that of $\Lambda$CDM, whereas the massive neutrinos contribute to straightnening the superclusters. Interestingly, the deviation of the supercluster straightness in cDE ($f(R)$ gravity) from $\Lambda$CDM increases (decreases) with redshift. A physical interpretation of our findings is discussed.

[1] Junsup Shim, Jounghun Lee,
*Dark Sector Coupling Bends the Superclusters*,
Astrophys.J. 777 (2013) 74, [arXiv:1306:1642].

[2] Junsup Shim, Jounghun Lee, Baojiu Li,
*Massive Gravity wrapped in the Cosmic Web*,
Astrophys.J. 784 (2014) 84, [arXiv:1311:7187].

[3] Junsup Shim, Jounghun Lee, Marco Baldi,
*Breaking the Cosmic Degeneracy between Modified Gravity and Massive Neutrinos with the Cosmic Web*,
[arXiv:1404:3639].