arXiv subjects

Julius F. Bonart

Publications and source records attributed to Julius F. Bonart.

2 recordsLinked to original sources

arXiv2026

Diffusive in plain sight: An inconspicuous law of market impact

Decomposing market impact as the difference between realized and counterfactual returns, and requiring both to be diffusive, yields a structural identity that restricts admissible impact dynamics at the level of individual participants. This constraint implies the square-root law in the information-neutral regime and a crossover toward linear impact under strong informational coupling, consistent with empirical observations. It further implies that impact must adapt to each participant's order-flow statistics, with consequences for theories of optimal execution and no-arbitrage. In the information-neutral regime, cumulative impact is itself diffusive, providing a diagnostic that many propagator and latent-liquidity models fail to satisfy. Under this regime, market impact retains an undetermined all-pass degree of freedom that prevents its reduction to a pure surprise model. This residual freedom accommodates transient impact dynamics and can generate strictly positive impact costs.

q-fin.TR↗

arXiv2010

Resistive double-diffusive instability in the dead-zones of protostellar disks

We outline a novel linear instability that may arise in the dead-zones of protostellar disks, and possibly the fluid interiors of planets and protoplanets. In essence it is an axisymmetric buoyancy instability, but one that would not be present in a purely hydrodynamical gas. The necessary ingredients for growth include a negative radial entropy gradient (of any magnitude), weak magnetic fields, and efficient resistive diffusion (in comparison with thermal diffusion). The character of the instability is local, axisymmetric, and double-diffusive, and it attacks lengths much shorter than the resistive scale. Like the axisymmetric convective instability, it draws its energy from the negative radial entropy gradient; but by utilising the diffusing magnetic field, it can negate the stabilising influence of rotation. Its nonlinear saturated state, while not transporting appreciable angular momentum, could drive radial and vertical mixing, which may influence the temperature structure of the disk, dust dynamics and, potentially, planet formation.

astro-ph.EP↗