Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session Z13: Alternative Cosmologies and Modified GravityRecordings Available
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Chair: Michal Pirog, West Virginia University Room: Empire |
Tuesday, April 12, 2022 3:45PM - 3:57PM |
Z13.00001: Late-time Universe, H0-tension, and unparticles Maryam Aghaei Abchouyeh, Maurice Van Putten ΛCDM is increasingly facing challenges in late-time cosmology, notably in the Hubble parameter H(z) at redshift zero, known as H0-tension. There are various efforts to alleviate this tension mostly by models with extra parameters. We elaborate on unparticle cosmology as a modification for late-time ΛCDM mainly for its potential to alleviate H0-tension. Unparticle cosmology proposes a scale invariant contribution by a dimensionless parameter δ. The ambiguities in the model demand for different avenues to inspect it and here we try some of them. The dynamical behavior of unparticle cosmology with and without Λ, shows that for most values of δ∈[ -6,1] (corresponding to dU∈[-2,3/2]), the late-time universe will be Λ and matter dominated respectively, with negligible contribution of unparticles. It predicts H(z) in the future to be zero or constant, the latter pointing to a stable de Sitter phase for our universe. Our data analysis shows δ=-2.06±0.46 as the best fit to data ruling out the conventional value of dU=3/2. However, there is a pronounced gap between the models and what is demanded by observational data, in qQ-diagram for all δ. We conclude that unparticle cosmology can not relax late-time ΛCDM challenges, but it provides a pointer to holographic limit of dark energy δ=-2. |
Tuesday, April 12, 2022 3:57PM - 4:09PM |
Z13.00002: The New Cosmology C G Hood The New Cosmology |
Tuesday, April 12, 2022 4:09PM - 4:21PM |
Z13.00003: An Alternate Explanation for Dark Matter and Dark Energy based on Spacetime Surface Tension Howard A Perko A mechanical model has been introduced at prior conferences for describing spacetime with surface tension. In this presentation, the model is applied to cosmology. It is shown that the stress-energy tensor with surface tension can be mathematically rearranged to provide components resembling dark matter and dark energy. The model is used to predict stellar velocity and compared with rotation curves for 15 galaxies. Model predictions are shown to match initial slope, shape, and distant flatness of measured rotation curves. In order to provide this match, mass to light ratios must be assumed that are much lower than previously thought and galaxy luminosity has to be approximately proportionate to the square of galactic mass. When this proportion is reinserted into the model, the Tully-Fisher relation is derived. Dark matter and dark energy are postulated to be the cosmological effects of surface tension of spacetime. |
Tuesday, April 12, 2022 4:21PM - 4:33PM |
Z13.00004: Generalized Logotropic Models and their Cosmological Constraints Hachemi Benaoum We propose a new class of cosmological unified dark sector models called "{\em Generalized Logotropic Models}". The logotropic model is just a special case of our generalized model. |
Tuesday, April 12, 2022 4:33PM - 4:45PM |
Z13.00005: Misinterpreting Modified Gravity as Dark Energy: a Quantitative Study Yuewei Wen Standard cosmological data analyses typically constrain simple phenomenological dark-energy parameters, for example the present-day value of the equation of state parameter, w0 , and its variation with scale factor, wa. However, results from such analyses cannot easily indicate the presence of modified gravity. Even if general relativity does not hold, experimental data could still be fit sufficiently well by a phenomenological w0waCDM, unmodified-gravity model. Hence, it would be useful to know if there are generic signatures of modified gravity in standard analyses. We present, for the first time to our knowledge, a quantitative mapping showing how modified gravity models look when (mis)interpreted within the standard unmodified-gravity analysis. Scanning through a broad space of modified-gravity models, and assuming a near-future survey consisting of CMB, BAO, and SNIa observations, we report values of the best-fit set of cosmological parameters including (w0, wa) that would be inferred if modified gravity were at work. We find that modified gravity models that can masquerade as standard gravity lead to very specific biases in standard-parameter spaces. We also comment on implications for measurements of the amplitude of mass fluctuations described by the parameter S8. |
Tuesday, April 12, 2022 4:45PM - 4:57PM |
Z13.00006: On the Effect of Hubble Expansion on Wide Binary and Spiral Galaxy Rotation Flattening During and After Cosmic Deceleration-to-Acceleration Crossover Thomas E Chamberlain The discovery of cosmic acceleration advances space-time theory and serves to resolve the tension between dark matter and modified gravity. An initial advance from the discovery is the inward-infinite light-speed stipulation within the Hubble expansion that reveals increasing lookback-time dilation which, upon rotation into epochal space-time, gives agreement with observed cosmic acceleration in the local universe. The present work helps resolve the DM vs modified gravity tension by more deeply deriving, to leading order, a relativistic inverse-radius (subfield) gravitation in a spiral galaxy—by joining the lookback and Schwarzschild time-dilations within the Lorentz transformation—thereby determining the asymptotic/flattened rotation speed for comparison with the Tully-Fisher relation. In the first of two derivations, subfield gravity is derived within the deceleration-to-acceleration crossover, wherein the crucial H(r)=r0H0/r relation is justified and employed. The same equation is derived in the current universe, starting with the lookback-time equation and again evoking the Lorentz transformation to neglect order (rH/c)2 terms. Far field orbital-speeds for spiral galaxies agree with the Tully-Fisher relation, and accord with observations of wide-binary rotation speeds. |
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