Semiclassical Calculation of Photon-Stimulated Schwinger Pair Creation

We consider the electron-positron pair creation by a photon in an external constant electric field. The presented treatment is based on a purely quasiclassical calculation of the imaginary part of the on-shell photon polarization operator. By using this approach we find the pair production rate for photons with polarization parallel as well as orthogonal to the external electric field in the leading order in the parameter $eE / m ^ 2$, which has been recently found by other methods. For the orthogonal polarization we also find a new contribution to the rate, which is leading in the ratio of the photon energy to the electron mass $\omega/m$. We also reproduce by a purely geometrical calculation the exponential factor in the probability of the stimulated pair creation at arbitrary energy of the photon.Comment: 16 pages, 4 figure

Bottomonium dipion transitions

Dipion transitions of the subthreshold bottomonium levels $\Upsilon (nS)\to \Upsilon (n'S) \pi\pi$ with $n>n', n=2,3,4, n'=1,2$ are studied in the framework of the chiral decay Lagrangian, derived earlier. The channels $B\bar B, B\bar B^*+ c.c, B^* \bar B^*$ are considered in the intermediate state and realistic wave functions of $\Upsilon (n S),B$ and $B^*$ are used in the overlap matrix elements. Imposing the Adler zero requirement on the transition matrix element, one obtains 2d and 1d dipion spectra in reasonable agreement with experiment.Comment: 34 pages, 18 figure

More nonperturbative corrections to the fine and hyperfine splitting in the heavy quarkonium

The leading nonperturbative effects to the fine and hyperfine splitting were calculated some time ago. Recently, they have been used in order to obtain realistic numerical results for the lower levels in bottomonium systems. We point out that a contribution of the same order $O(\Lambda_{QCD}^4/m^3 \alpha_s^2)$ has been overlooked. We calculate it in this paper.Comment: 9 pages, LaTeX, More self-contained and lengthier version without changing physical outputs. To be published in Phys. Rev.

Discussing the possibility of observation of parity violation in heavy ion collisions

It was recently argued that in heavy ion collision the parity could be broken. This Note addresses the question of possibility of the experimental detection of the effect. We discuss how parity violating effects would modify the final particle distributions and how one could construct variables sensitive to the effect, and which measurement would be the (most) conclusive. Discussing different observables we also discuss the question if the ``signals'' can be faked by ``conventional'' effects (such as anisotropic flow, etc.) and make estimates of the signals.Comment: LaTeX, 5 pages; some corrections in chapter III; main results are unchange

Remarks on Decay of Defects with Internal Degrees of Freedom

We consider the decay of metastable walls and strings populated by additional degrees of freedom. The examples involve the decay of an axion wall in an external magnetic field, pionic walls, metastable walls in dense QCD. It is shown that the induced fermions escape from the wall during the decay process providing an example of the chiral magnetic effect. An absolute stabilization of metastable and unstable walls in a large magnetic field is found. A possible higher dimensional generalization of the chiral magnetic effect is mentioned.Comment: 17 page

On domain shapes and processes in supersymmetric theories

A supersymmetric theory with several scalar superfields generically has several domain wall type classical configurations which interpolate between various supersymmetric vacua of the scalar fields. Depending on the couplings, some of these configurations develop instability and decay into multiple domain walls, others can form intersections in space. These phenomena are considered here in a simplest, yet non-trivial, model with two scalar superfields.Comment: 10 pages, LaTeX, 5 figures in LaTe