Related papers: Cherenkov radiation as ghost instability
The gravitational waveforms of a chaotic system will exhibit sensitive dependence on initial conditions. The waveforms of nearby orbits decohere on a timescale fixed by the largest Lyapunov exponent of the orbit. The loss of coherence has…
Thermal energy points toward a disordered, completely uniform state acting counter to gravity's tendency to generate order and structure through gravitational collapse. It is, therefore, expected to contribute to the stabilization of a…
Understanding the role of higher derivatives is probably one of the most relevant questions in quantum gravity theory. Already at the semiclassical level, when gravity is a classical background for quantum matter fields, the action of…
We examine linear and quasi-liner stages of Cherenkov-drift instability in the relativistic magnetized electron-positron plasma. The external magnetic field lines are assumed to be slightly curved. In this case the curvature drift of…
We continue to investigate various instabilities of the fixed backgrounds related to the de Sitter space. It is shown that in many cases the in/in perturbation theory contains IR/UV mixing and thus is non-renormalizible. The application of…
An optical response of one-dimensional string made of dipoles with a periodically varying density excited by a spot of light moving along the string at the superluminal (sub-luminal) velocity is theoretically studied. The Cherenkov…
A review of the new of the problem of dark energy using modified gravity approach is considered. An explanation of the difficulties facing modern cosmology is given and different approaches are presented. We show why some models of gravity…
The distinction between modified gravity and quintessence or dynamical dark energy is difficult. Many models of modified gravity are equivalent to models of coupled quintessence by virtue of variable transformations. This makes an…
We remark that Ostrogradsky ghosts in higher-derivative gravity, with a finite number of derivatives, are fictitious as they result from an unjustified truncation performed in a complete theory containing infinitely many curvature…
Modified gravity is one of the most promising candidates for explaining the current accelerating expansion of the Universe, and even its unification with the inflationary epoch. Nevertheless, the wide range of models capable to explain the…
We study Cerenkov radiation from moving straight strings which glisse with respect to each other in such a way that the projected intersection point moves faster than light. To calculate this effect we develop classical perturbation theory…
The effects arising from accelerated and decelerated motion of a point charge inside a medium are studied. The motion is manifestly relativistic and may be produced by a constant uniform electric field. It is shown that in addition to the…
We review how the (absence of) Ostrogradsky instability manifests itself in theories with multiple fields. It has recently been appreciated that when multiple fields are present, the existence of higher derivatives may not automatically…
Charged particles in the geodesic trajectory of an external gravitational field do not emit electromagnetic radiation. This is expected from the application of the equivalence principle. We show here that charged particles propagating in an…
We derive the formula of the complex Doppler shift in a two-dimensional, dispersive metamaterial and we show that a moving, monochromatic radiation source generates multiple frequency modes. The role of the group velocity is stressed and…
We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)strings move with relativistic velocities without intercommutation. String interactions via dilaton, two-form and gravity (gravity being the…
Lorentz invariance is such an important principle of fundamental physics that it should constantly be subjected to experimental scrutiny as well as theoretical questioning. Distant astrophysical sources of energetic photons with rapid time…
Vortices and black holes set the scene for many interesting dynamical processes in physics. Here, we study the dynamical instability of quantised vortices and rotational superradiance around rotating black holes, illustrating in the process…
The equations of in-medium gluodynamics are proposed. Their classical lowest order solution is explicitly shown for a color charge moving with constant speed. For nuclear permittivity larger than 1 it describes emission of Cherenkov gluons…
We study cosmological perturbations in mimetic matter scenario with a general higher derivative function. We calculate the quadratic action and show that both the kinetic term and the gradient term have the wrong sings. We perform the…