Browsing by Author "Zhang, Hong-Yi"
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Item Beyond Schrödinger-Poisson: nonrelativistic effective field theory for scalar dark matter(Springer Nature, 2021) Salehian, Borna; Zhang, Hong-Yi; Amin, Mustafa A.; Kaiser, David I.; Namjoo, Mohammad HosseinMassive scalar fields provide excellent dark matter candidates, whose dynamics are often explored analytically and numerically using nonrelativistic Schrödinger-Poisson (SP) equations in a cosmological context. In this paper, starting from the nonlinear and fully relativistic Klein-Gordon-Einstein (KGE) equations in an expanding universe, we provide a systematic framework for deriving the SP equations, as well as relativistic corrections to them, by integrating out ‘fast modes’ and including nonlinear metric and matter contributions. We provide explicit equations for the leading-order relativistic corrections, which provide insight into deviations from the SP equations as the system approaches the relativistic regime. Upon including the leading-order corrections, our equations are applicable beyond the domain of validity of the SP system, and are simpler to use than the full KGE case in some contexts. As a concrete application, we calculate the mass-radius relationship of solitons in scalar dark matter and accurately capture the deviations of this relationship from the SP system towards the KGE one.Item Perlecan-Containing Pericellular Matrix Regulates Solute Transport and Mechanosensing Within the Osteocyte Lacunar-Canalicular System(Wiley, 2014) Wang, Bin; Lai, Xiaohan; Price, Christopher; Thompson, William R.; Li, Wen; Quabili, Tonima R.; Tseng, Wei-Ju; Liu, Xiaowei Sherry; Zhang, Hong-Yi; Pan, Jun; Kirn-Safran, Catherine B.; Farach-Carson, Mary C.; Wang, LiyunThe pericellular matrix (PCM), a thin coating surrounding nearly all mammalian cells, plays a critical role in many cell-surface phenomena. In osteocytes, the PCM is believed to control both “outside-in” (mechanosensing) and “inside-out” (signaling molecule transport) processes. However, the osteocytic PCM is challenging to study in situ because it is thin (∼100 nm) and enclosed in mineralized matrix. To this end, we recently developed a novel tracer velocimetry approach that combined fluorescence recovery after photobleaching (FRAP) imaging with hydrodynamic modeling to quantify the osteocytic PCM in young murine bone. In this study, we applied the technique to older mice expressing or deficient for perlecan/HSPG2, a large heparan-sulfate proteoglycan normally secreted in osteocytic PCM. The objectives were (1) to characterize transport within an altered PCM; (2) to test the sensitivity of our approach in detecting the PCM alterations; and (3) to dissect the roles of the PCM in osteocyte mechanosensing. We found that: (1) solute transport increases in the perlecan-deficient (hypomorphic [Hypo]) mice compared with control mice; (2) PCM fiber density decreases with aging and perlecan deficiency; (3) osteocytes in the Hypo bones are predicted to experience higher shear stress (+34%), but decreased fluid drag force (−35%) under 3-N peak tibial loading; and (4) when subjected to tibial loading in a preliminary in vivo experiment, the Hypo mice did not respond to the anabolic stimuli as the CTL mice did. These findings support the hypothesis that the PCM fibers act as osteocyte's sensing antennae, regulating load-induced cellular stimulations and thus bone's sensitivity and in vivo bone adaptation. If this hypothesis is further confirmed, osteocytic PCM could be new targets to develop osteoporosis treatments by modulating bone's intrinsic sensitivity to mechanical loading and be used to design patient-specific exercise regimens to promote bone formation.Item Probing ultralight dark fields in cosmological and astrophysical systems(2023-11-30) Zhang, Hong-Yi; Amin, MustafaDark matter constitutes $26\%$ of the total energy in our universe, but its nature remains elusive. Among the assortment of viable dark matter candidates, particles and fields with masses lighter than $40 \mathrm{eV}$, called ultralight dark matter, stand out as particularly promising thanks to their feasible production mechanisms, consistency with current observations, and diverse and testable predictions. In light of ongoing and forthcoming experimental and observational efforts, it is important to advance the understanding of ultralight dark matter from theoretical and phenomenological perspectives: How does it interact with itself, ordinary matter, and gravity? What are some promising ways to detect it? In this thesis, we aim to explore the dynamics and interaction of ultralight dark matter and other astrophysically accessible hypothetical fields in a relatively model-independent way. Without making specific assumptions about their ultraviolet physics, we first demonstrate a systematic approach for constructing a classical effective field theory for both scalar and vector dark fields and discuss conditions for its validity. Then, we explore the interaction of ultralight dark fields, both gravitational and otherwise, within various contexts such as nontopological solitons, neutron stars, and gravitational waves.