We study cosmological effects of homogeneous tachyon field as dark energy. We concentrate on two different scalar field potentials, the inverse square potential and the exponential potential. These models have a unique feature that the matter density parameter and the density parameter for tachyons remain comparable for a large range in redshift. It is shown that there exists a range of paramet...

This paper presents work done in collaboration with E. Farhi, J. Goldstone, and A. Lue which is described in full in Ref. [1]. We consider a variant of the standard electroweak theory in which the Higgs sector has been modified so that there is a classically stable weak scale soliton. We explore fermion number violating processes which involve soliton decay. A soliton can decay by tunnelling un...

Recent experiments with trapped cooled atoms have produced evidences for Bose-Einstein condensation. Among the atoms used are 7 Li ones, with attractive low energy interaction. Stability of their condensate is studied, with a conclusion that for a number of atoms below the critical value there exist a metastable minimum, separated from collapse by a potential barrier. The lifetime due to tunnel...

This thesis presents efficient algorithms for drawing planar graphs. Graph drawing addresses the problem of constructing geometric representation of information and finds applications in almost every branch of science and technology. In this thesis we study rectangular drawings, orthogonal drawings, convex drawings and our newly defined box-rectangular drawings. Rectangular drawings and box-rec...

We show that the transmission through single and double -function potential barriers of strength P =VWb / vF in bilayer graphene is periodic in P with period . For a certain range of P values we find states that are bound to the potential barrier and that run along the potential barrier. Similar periodic behavior is found for the conductance. The spectrum of a periodic succession of -function b...

New developments in HPD design are presented, triggered by applications in high energy physics and astrophysics. The presented HPD designs are based on three innovations. (i) In order to achieve the highest possible surface coverage in a RICH detector, we introduced a photoelectron focussing method which is efficient to the periphery of the photocathode. (ii) To prevent positive ion feedback in...

We examine the effect of subdividing the potential barrier along the reaction coordinate on Kramers’ escape rate for a model potential. Using the known supersymmetric potential approach, we show the existence of an optimal number of subdivisions that maximises the rate.

We show that quantum Zeno dynamics can be mimicked by the isolated evolution of an unobserved system in an effective potential. Monitoring frequently whether a particle remains in a region of space leads to the same wave-packet dynamics as placing the region on top of a potential barrier and letting the particle evolve on its own, without external couplings. We focus on very frequent but not co...

We generally investigate the scalar field model with the lagrangian L = F (X) − V (φ), which we call it General Non-Canonical Scalar Field Model. We find that it is a special square potential(with a negative minimum) that drives the linear field solution(φ = φ 0 t) while in K-essence model(with the lagrangian L = −V (φ)F (X)) the potential should be taken as an inverse square form. Hence their ...

A spatially-discrete sine-Gordon system with some novel features is described. There is a topological or Bogomol'nyi lower bound on the energy of a kink, and an explicit static kink which saturates this bound. There is no Peierls potential barrier, and consequently the motion of a kink is simpler, especially at low speeds. At higher speeds, it radiates and slows down.