Arkady Vilenkin

Learn More
We critically review several recent approaches to solving the two cosmological constant problems. The ‘‘old’’ problem is the discrepancy between the observed value of rL and the large values suggested by particle physics models. The second problem is the ‘‘time coincidence’’ between the epoch of galaxy formation tG and the epoch of L domination tL . It is(More)
In the context of models where the dark energy density rD is a random variable, anthropic selection effects may explain both the ‘‘old’’ cosmological constant problem and the ‘‘time coincidence.’’ We argue that this type of solution to both cosmological constant problems entails a number of definite predictions, which can be checked against upcoming(More)
Cusps of superconducting strings can serve as GRB engines. A powerful beamed pulse of electromagnetic radiation from a cusp produces a jet of accelerated particles, whose propagation is terminated by the shock responsible for GRB. A single free parameter, the string scale of symmetry breaking η ∼ 1014 GeV , together with reasonable assumptions about the(More)
Using the weak-noise theory, we evaluate the probability distribution P(H,t) of large deviations of height H of the evolving surface height h(x,t) in the Kardar-Parisi-Zhang equation in one dimension when starting from a flat interface. We also determine the optimal history of the interface, conditioned on reaching the height H at time t. We argue that the(More)
Let a lattice gas of constant density, described by the symmetric simple exclusion process, be brought in contact with a "target": a spherical absorber of radius R. Employing the macroscopic fluctuation theory (MFT), we evaluate the probability P(T) that no gas particle hits the target until a long but finite time T. We also find the most likely gas density(More)
We investigate the dynamics of relaxation, by surface tension, of a family of curved interfaces between an inviscid and viscous fluids in a Hele-Shaw cell. At t = 0 the interface is assumed to be of the form |y| = Axm, where A > 0, m ≥ 0, and x > 0. The case of 0 < m < 1 corresponds to a smooth shape, m > 1 corresponds to a cusp, whereas m = 1 corresponds(More)
We investigate quasi-two-dimensional relaxation, by surface tension, of a long straight stripe of inviscid fluid trapped inside a viscous fluid in a Hele-Shaw cell. Combining analytical and numerical solutions, we describe the emergence of a self-similar dumbbell shape and find nontrivial dynamic exponents that characterize scaling behavior of the dumbbell(More)