Bulletin of the American Physical Society
Joint Fall 2017 Meeting of the Texas Section of the APS, Texas Section of the AAPT, and Zone 13 of the Society of Physics Students
Volume 62, Number 16
Friday–Saturday, October 20–21, 2017; The University of Texas at Dallas, Richardson, Texas
Session B1: Astro I |
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Chair: Louis Stigari, Texas A&M University Room: DGAC 1.102A |
Friday, October 20, 2017 2:45PM - 2:57PM |
B1.00001: Seeking insights on gravity theory and cosmic acceleration from consistency tests between cosmological data sets. Mustapha Ishak, Weikang Lin Testing general relativity at cosmological scales and probing the cause of cosmic acceleration are among the important objectives targeted by incoming and future astronomical surveys and experiments. I present our recent results on consistency tests that can provide insights about the underlying gravity theory and cosmic acceleration using cosmological data sets. We use new statistical measures that can detect discordances when present. We also use an algorithmic procedure that is able to identify in some cases whether an inconsistency is due to problems related to systematic effects in the data or to the underlying model. Some recent published tensions between data sets are also examined using our formalism, e.g. the Hubble constant, Planck and Large-Scale-Structure. [Preview Abstract] |
Friday, October 20, 2017 2:57PM - 3:09PM |
B1.00002: Testing gravity theories using primordial gravitational waves and CMB experiments Weikang Lin, Mustapha Ishak Primordial gravitational waves constitute a promising probe of the very early universe and the law of gravity. We study the changes to tensor-mode perturbations that can arise in various modified gravity (MG) theories, and physically parametrize of these MG effects and how they affect the spectrum of the Cosmic Microwave Background (CMB) B-mode polarization. We show that current data exclude some region in the MG parameter space. Considering foreground subtraction, we then perform a forecast of the constraints on the MG parameters by future experiments COrE, Stage-IV and PIXIE. Assuming the tensor-to-scalar ratio $r=0.01$, we find the minimum detectable MG effects. In particular, the minimum detectable graviton mass is about $7.8\sim9.7\times10^{-33}$ eV, of the same magnitude order as the graviton mass in massive gravity theories that produce late-time cosmic acceleration. Finally, we find that the standard inflation consistent relation $(n_T=-r/8$) does not hold in MG. In some cases, the future experiments will be able to distinguish the standard and the MG consistent relations. In sum, primordial gravitational waves provide a complementary avenue to test gravity theories. [Preview Abstract] |
Friday, October 20, 2017 3:09PM - 3:21PM |
B1.00003: Effects of Self-Calibration of Intrinsic Alignment on Cosmological Parameter Constraints from Future Cosmic Shear Surveys Ji Yao, Mustapha Ishak-Boushaki, Weikang Lin, Michael Troxel Intrinsic alignments (IA) of galaxies have been recognized as one of the most serious contaminants to weak lensing. The IA self-calibration (SC) method was shown in previous studies to be able to reduce the GI contamination by up to a factor of 10 for the 2-point and 3-point correlations. The SC method does not require the assumption of an IA model in its working and can extract the GI signal from the same photo-z survey offering the possibility to test and understand structure formation scenarios and their relationship to IA models. We study the effects of the IA SC mitigation method on the precision and accuracy of cosmological parameter constraints from future cosmic shear surveys LSST, WFIRST and Euclid. We perform analytical and numerical calculations to estimate the loss of precision and the residual bias in the best fit cosmological parameters We take into account uncertainties from photometric redshifts and the galaxy bias. We find that the confidence contours are slightly inflated from applying the SC method itself while a significant increase is due to the inclusion of the photo-z uncertainties. The bias of cosmological parameters is reduced from several-$\sigma $, when IA is not corrected for, to below 1-$\sigma $ after SC is applied. [Preview Abstract] |
Friday, October 20, 2017 3:21PM - 3:33PM |
B1.00004: Modified gravity in N-body simulations Eske Pedersen In recent years there have been suggested many extensions to Einstein's general relativity, in an attempt to explain the acceleration of the universe without invoking Dark energy. We normally refer to this group of theories as modified gravity. However how do we test modified gravity theories on the non-linear scale? For the last ten years or so we have been building N-body simulations that mainly simulate one or two of these theories, to test the theories on the non-linear scale. What I will discuss is an attempt on instead of creating simulations just for one theory, creating an effective framework that can be adapted to either specific theories or an effective parameterization. The framework we are introducing is inspired by a recently proposed Parameterized Post-Friedmann Framework for Modified Gravity. The talk will be an introduction to this implementation in Gadget-2 and how I did this, and in the end we will discuss how to move on and possible frameworks to implement instead. Gadget-2 is one of the most trusted N-body simulation codes of the recent decades, and was used to create the millennium simulation. [Preview Abstract] |
Friday, October 20, 2017 3:33PM - 3:45PM |
B1.00005: Impact of 7Be(alpha, gamma) reaction on Big Bang Nucleosynthesis Michael Hartos, Carlos Bertulani, Suqing Hou, S Shubhchintak We will discuss the impact of the $^7$Be($\alpha,\gamma$) reaction on the primordial abundance of elements during the Big Bang epoch. Specific applications to the so-called BBN $^7$Li problem will be addressed. [Preview Abstract] |
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