Bulletin of the American Physical Society
2021 Joint Spring Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 66, Number 2
Thursday–Sunday, April 8–11, 2021; Virtual
Session C05: APS: Astrophysics and Space Science-I |
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Saturday, April 10, 2021 10:00AM - 10:12AM |
C05.00001: The relic abundance of dark matter -- a nontrivial physics and mathematics problem Trevor Croteau, Caden LaFontaine, Brandon Torres, Spencer Ellis, Sabrina Hernandez, Drue Lubanski, Bailey Tallman, Diego Cristancho Guerrero, Roland Allen A vast number of dark matter candidates have been proposed, but almost none of them have provided a well-defined and natural explanation of the observed abundance of dark matter. We will discuss the following aspects of this problem: (1) The ``WIMP miracle'': A weakly interacting massive particle can have very roughly the observed abundance if its mass is $\sim$ 100 GeV and the interactions responsible for annihilation in the early universe are not too strong (or too weak). (2) A nonlinear Boltzmann equation can be derived that yields the relic abundance in the present universe, but this equation is quite nontrivial to solve. One approach will be described. (3) The cross-section for annihilation has been found to be too large for the most natural dark matter candidate of supersymmetry, a relatively light neutralino, making the relic density too small by about an order of magnitude. (4) We propose a candidate, resulting from an extended Higgs sector, that will yield the observed abundance with a particle mass of about 75 GeV, as described in two other talks at this conference. [Preview Abstract] |
Saturday, April 10, 2021 10:12AM - 10:24AM |
C05.00002: The evolution of toroidal magnetic clouds on their way from Sun to the Earth's orbit Talon Weaver, Evgeny Romashets, Cristian Bahrim We report studies about properties of magnetic clouds. These clouds are created from solar flares, propagate in interplanetary space and upon arrival to the Earth's orbit could interact with the magnetopause initiating geomagnetic storms. Our model considers three forces acting on the cloud during its propagation: the drag force from ambient solar wind plasma, diamagnetic force due to draping of interplanetary magnetic field, and the gravitational pull from the Sun (Romashets and Vandas, JGR, 2001). The solar source magnetic field maps provided by the Wilcox Solar Observatory are used to determine magnetic field magnitude at the point of ejection. The velocity of the ambient solar wind is interpolated in such a way that it agrees with plasma measurements at 1 AU. Density of solar wind plasma is determined from the continuity equation (i.e. the number of particles in equals to the number of particles out through any sphere of radius less than 1 AU); and it agrees with in-situ plasma measurement. The magnetic cloud expands because total pressure in interplanetary space decreases along the cloud's trajectory. Our model describes the relationship between the ratio of the major to the minor radii of the toroidal cloud and the helio-distance (Sun-Earth), and it will reveal the influence of parameters, such as the drag coefficient on the evolution of the magnetic cloud. Results for selected fast and slow magnetic clouds observed during 1998 to 2001 will be reported. [Preview Abstract] |
Saturday, April 10, 2021 10:24AM - 10:36AM |
C05.00003: How unbiased statistical methods lead to biased scientific discoveries: A case study in the analysis of Gamma-Ray Bursts Christopher Bryant, Joshua Osborne, Amir Shahmoradi Statistical methods are frequently built upon assumptions that limit their applicability to certain problems and conditions. Failure to recognize these limitations can lead to conclusions that may be inaccurate or biased. An example of such methods is the non-parametric Efron-Petrosian test statistic used in the studies of truncated data. We argue and show how the inappropriate use of this statistical method can lead to biased conclusions when the assumptions under which the method is valid do not hold. We do so by reinvestigating the evidence recently provided by multiple independent reports on the evolution of the luminosity/energetics distribution of cosmological Long-duration Gamma-Ray Bursts (LGRBs) with redshift. We show that the effects of detection threshold have been likely significantly underestimated in the majority of previous studies. This underestimation of detection threshold leads to severely incomplete LGRB samples that exhibit strong apparent luminosity-redshift or energetics-redshift correlations. We further confirm our findings by performing extensive Monte Carlo simulations of the cosmic rates and the luminosity/energy distributions of LGRBs and their detection process. [Preview Abstract] |
Saturday, April 10, 2021 10:36AM - 10:48AM |
C05.00004: Post-merger gravitational wave searches using the Cross-Correlation Algorithm Tanazza Khanam, Alessandra Corsi, Rob Coyne, Eric Sowell After the multi-messenger detection of the binary neutron star merger GW170817, associated with gamma-ray burst (GRB) 170817a, one big open question left is the nature of the compact remnant which acts as a central engine for the GRB. In the context of cosmological GRBs, it has been suggested that X-ray afterglows showing light-curve plateaus at timescales of order 10$^{\mathrm{2\thinspace }}$-10$^{\mathrm{4\thinspace }}$s since the GRB/merger could harbor a long-lived central engine, such as a long-lived highly magnetized NS (magnetar). Newly born magnetars have also been proposed as potential gravitational wave (GW) sources. Motivated by these considerations, we present first results from a new GW data analysis method (the Cross Correlation Algorithm-CoCoA) targeting long-lived GWs from magnetars formed in binary NS mergers associated with GRBs. We show how our search method improves substantially on previously published results for post-merger GW searches in GW170817, but requires a more restrictive hypothesis on the GW signal properties. We conclude by discussing the prospects for these types of searches in future runs of the LIGO detectors. [Preview Abstract] |
Saturday, April 10, 2021 10:48AM - 11:00AM |
C05.00005: New Justification and Proof for the Accelerated Movement of the Universe Gh. Saleh, M. J. Faraji Based on Saleh Theory, the Universe has a rotational motion around itself and an expansion from the inside out. So its total velocity is equal to the rotational velocity plus the linear one. The linear is the effect of the remaining energy of the primary energy of the Big Bang with a constant speed. The rotational motion is of a kind that its angular velocity is constant and created by the effect of a primary energy. So the Universe radius is the only variable parameter. The Universe radius is a vector from the center of the Universe (the beginning of the Big Bang) to the desired point and has a varying length and rotational angle. As a result, the speed of the Universe depends solely on the Universe radius and it increases as a result of a linear velocity. The acceleration of the Universe is the summation of angular acceleration and the linear one. Since the linear and angular acceleration are zero, there is no force that would lead to a change. Therefore, there is no force that would be applied from the outside and the linear and angular accelerations are zero; the variant speed is based on the variant radius. In this article we have proved that how the expansion could be explained based on these motions. [Preview Abstract] |
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