David Tsang's research while affiliated with University of Maryland, College Park and other places

... Searching for the extremum of this functional numerically using the parameters μ = 0.5, κ = 1, ξ = 0.00071 (cf. ref. [37]) with initial conditions x i = 1ẋ i = 0 on discretized paths with N t = 32 steps and regularized SBP21 operator leads to the results for x 1 (red circles) and x 2 (blue crosses) shown in Fig. 12. ...

... [17][18][19] by implementing the classical limit of the "in-in" approach [20,21] (see also the formalism developed for nonconservative classical systems in Refs. [22,23]). At 3.5PN order, the radiation-reaction force was first calculated in Refs. ...

... [108,249,106]). Visualisations of such oscillations can be found in Fig 2 of Tsang and Butsky [228]. The study of c modes is part of the wider field of discoseismology, which encapsulates a number of different modes of oscillation (e.g. ...

... As a result, mechanisms for exciting eccentricity are needed. Planet-disc interactions are capable of exciting eccentricities, but are limited to modest values 0.2 (Goldreich & Sari 2003;Tsang, Turner & Cumming 2014;Duffell & Chiang 2015;Ragusa et al. 2018). Recently, Petrovich, Wu & Ali-Dib (2019) studied a mechanism for transferring eccentricity from an outer planet to a WJ during the dispersal of a massive protoplanetary disc ...

... An important result of this analysis is the derivation of a "master equation" describing the global behavior of nonaxisymmetric perturbations driven by an external gravitational potential in a two-dimensional (2D) disk. Such an equation was first presented by Goldreich & Tremaine (1979), for the case of adiabatic perturbations in disks with uniform entropy, and was later generalized to disks with general entropy profiles (Baruteau & Masset 2008;Tsang 2014). We present an even more general version of the equation for adiabatic perturbations in disks with thermal relaxation, which reduces to the locally isothermal and adiabatic regimes in the appropriate limits (short and long cooling timescales, respectively). ...

... General relativity challenges this view. The Einstein equations, describing the relationship between spacetime geometry and mass-energy [1], have counterintuitive solutions containing closed time-like curves (CTCs) [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. An event on such a curve would be both in the future and in the past of itself, preventing an ordinary formulation of dynamics according to an "initial condition" problem. ...

... Within the context of standard general relativity, there has now been over 33 years of serious theoretical work on the possibility of "traversable wormholes" [1][2][3][4][5], 29 years of recent work on "time machines" [6][7][8][9][10][11][12], and over 27 years of work on the theoretical possibility of "warp drives" [13][14][15][16][17][18]. These analyses, and their subsequent refinements, are based on "reverse engineering" the space-time metric to encapsulate some potentially interesting physics, and then using the Einstein equations to deduce what the stress-energy tensor must be to support these space-times [1,5,19,20]. ...

... Ho we ver, this would not explain the QPO being much stronger in the Comptonized spectrum than in the disc spectrum, and the line profile variations produced by c modes are quite subtle compared with what we observe (see e.g. fig. 5 in Tsang & Butsky 2013 ), due to the c -mode oscillation only occurring in a narrow range of disc radii. The spiral waves of the AEI model are also consistent with the asymmetric illumination profile we measure here (Varniere, Rodriguez & Tagger 2002 ). ...

... Other electromagnetic counterparts to neutron star mergers have been proposed, with no confirmed observations so far. This include bursts of radiation before merger (Tsang 2013), continuous emission from magnetosphere interactions (Palenzuela et al. 2013), coherent emission from magnetosphere interactions (Most and Philippov 2022), and months to decades-long synchrotron radio emission from the mildly relativistic ejecta as it interacts with the interstellar medium (Hotokezaka et al. 2016). Neutrinos have no impact on the first three, however, and only a minor impact on the third (as neutrino-matter interactions may slightly change the mass/velocity of the outflows). ...

... Strong temporal variability in the detected radio flux, pulse-profile shape, and polarization fraction are often observed (Levin et al. 2012;Camilo et al. 2018;Dai et al. 2019;Lower et al. 2021b). Moreover, rotational variations in the form of rapid increases in spin-down and sudden spin-up (glitches) or, less commonly, spin-down events (antiglitches) are also detected following outbursts (Archibald et al. 2013;Scholz et al. 2017;Hu et al. 2020;Younes et al. 2020;Caleb et al. 2022). These observational properties are likely a result of magnetic stresses from the decaying internal magnetic fields precipitating sudden crustal motion or fracturing, leading to an impulsive release of energy in the form of electromagnetic radiation and occasionally an alteration of the external magnetic field topology (Duncan & Thompson 1992;Harding et al. 1999;Thompson et al. 2002;Younes et al. 2022b) With a spin period of ∼2.1 s, 1E 1547.0−5408 ...