Symmetries in nonlinear Bethe-Heitler process

Nonlinear Bethe-Heitler process in a bichromatic laser field is investigated using strong-field QED formalism. Symmetry properties of angular distributions of created $e^-e^+$ pairs are analyzed. These properties are showed to be governed by a behavior of the vector potential characterizing the laser field, rather than by the respective electric field component.Comment: 4 pages, 4 figure

Double quiver gauge theory and nearly Kahler flux compactifications

We consider G-equivariant dimensional reduction of Yang-Mills theory with torsion on manifolds of the form MxG/H where M is a smooth manifold, and G/H is a compact six-dimensional homogeneous space provided with a never integrable almost complex structure and a family of SU(3)-structures which includes a nearly Kahler structure. We establish an equivalence between G-equivariant pseudo-holomorphic vector bundles on MxG/H and new quiver bundles on M associated to the double of a quiver Q, determined by the SU(3)-structure, with relations ensuring the absence of oriented cycles in Q. When M=R^2, we describe an equivalence between G-invariant solutions of Spin(7)-instanton equations on MxG/H and solutions of new quiver vortex equations on M. It is shown that generic invariant Spin(7)-instanton configurations correspond to quivers Q that contain non-trivial oriented cycles.Comment: 42 pages; v2: minor corrections; Final version to be published in JHE

Fermion Pair Production From an Electric Field Varying in Two Dimensions

The Hamiltonian describing fermion pair production from an arbitrarily time-varying electric field in two dimensions is studied using a group-theoretic approach. We show that this Hamiltonian can be encompassed by two, commuting SU(2) algebras, and that the two-dimensional problem can therefore be reduced to two one-dimensional problems. We compare the group structure for the two-dimensional problem with that previously derived for the one-dimensional problem, and verify that the Schwinger result is obtained under the appropriate conditions.Comment: Latex, 14 pages of text. Full postscript version available via the worldwide web at http://nucth.physics.wisc.edu/ or by anonymous ftp from ftp://nucth.physics.wisc.edu:/pub/preprints

Multiple colliding electromagnetic pulses: a way to lower the threshold of e+e−e^+e^- pair production from vacuum

The scheme of simultaneous multiple pulse focusing on one spot naturally arises from the structural features of projected new laser systems, such as ELI and HiPER. It is shown that the multiple pulse configuration is beneficial for observing $e^+e^-$ pair production from vacuum under the action of sufficiently strong electromagnetic fields. The field of the focused pulses is described using a realistic three-dimensional model based on an exact solution of the Maxwell equations. The $e^+e^-$ pair production threshold in terms of electromagnetic field energy can be substantially lowered if, instead of one or even two colliding pulses, multiple pulses focused on one spot are used. The multiple pulse interaction geometry gives rise to subwavelength field features in the focal region. These features result in the production of extremely short $e^+e^-$ bunches.Comment: 10 pages, 4 figure

Quiver Gauge Theory of Nonabelian Vortices and Noncommutative Instantons in Higher Dimensions

We construct explicit BPS and non-BPS solutions of the Yang-Mills equations on the noncommutative space R^{2n}_\theta x S^2 which have manifest spherical symmetry. Using SU(2)-equivariant dimensional reduction techniques, we show that the solutions imply an equivalence between instantons on R^{2n}_\theta x S^2 and nonabelian vortices on R^{2n}_\theta, which can be interpreted as a blowing-up of a chain of D0-branes on R^{2n}_\theta into a chain of spherical D2-branes on R^{2n} x S^2. The low-energy dynamics of these configurations is described by a quiver gauge theory which can be formulated in terms of new geometrical objects generalizing superconnections. This formalism enables the explicit assignment of D0-brane charges in equivariant K-theory to the instanton solutions.Comment: 45 pages, 4 figures; v2: minor correction

SU(3)-Equivariant Quiver Gauge Theories and Nonabelian Vortices

We consider SU(3)-equivariant dimensional reduction of Yang-Mills theory on Kaehler manifolds of the form M x SU(3)/H, with H = SU(2) x U(1) or H = U(1) x U(1). The induced rank two quiver gauge theories on M are worked out in detail for representations of H which descend from a generic irreducible SU(3)-representation. The reduction of the Donaldson-Uhlenbeck-Yau equations on these spaces induces nonabelian quiver vortex equations on M, which we write down explicitly. When M is a noncommutative deformation of the space C^d, we construct explicit BPS and non-BPS solutions of finite energy for all cases. We compute their topological charges in three different ways and propose a novel interpretation of the configurations as states of D-branes. Our methods and results generalize from SU(3) to any compact Lie group.Comment: 1+56 pages, 9 figures; v2: clarifying comments added, final version to appear in JHE

Quiver Gauge Theory and Noncommutative Vortices

We construct explicit BPS and non-BPS solutions of the Yang-Mills equations on noncommutative spaces R^{2n}_theta x G/H which are manifestly G-symmetric. Given a G-representation, by twisting with a particular bundle over G/H, we obtain a G-equivariant U(k) bundle with a G-equivariant connection over R^{2n}_theta x G/H. The U(k) Donaldson-Uhlenbeck-Yau equations on these spaces reduce to vortex-type equations in a particular quiver gauge theory on R^{2n}_theta. Seiberg-Witten monopole equations are particular examples. The noncommutative BPS configurations are formulated with partial isometries, which are obtained from an equivariant Atiyah-Bott-Shapiro construction. They can be interpreted as D0-branes inside a space-filling brane-antibrane system.Comment: talk by O.L. at the 21st Nishinomiya-Yukawa Memorial Symposium, Kyoto, 15 Nov. 200

Migration of latent fingermarks on non-porous surfaces:observation technique and nanoscale variations

Latent fingermark morphology was examined over a period of approximately two months. Variation in topography was observed with atomic force microscopy and the expansion of the fingermark occurred in the form of the development of an intermediate area surrounding the main fingermark ridge. On an example area of a fingermark on silicon, the intermediate region exists as a uniform 4nm thick deposit; on day 1 after deposition this region extends approximately 2µm from the edge of the main ridge deposit and expands to a maximum of ~ 4µm by day 23. Simultaneously the region breaks up, the integrity is compromised by day 16, and by day 61 the area resembles a series of interconnected islands, with coverage of approximately 60%. Observation of a similar immediate area and growth with time on surfaces such as Formica was possible by monitoring the mechanical characteristics of the fingermark and surfaces though phase contrast in tapping mode AFM. The presence of this area may affect fingermark development, for example affecting the gold distribution in vacuum metal deposition. Further study of time dependence and variation with donor may enable assessment of this area to be used to evaluate the age of fingermarks

Vortex mass in a superfluid at low frequencies

An inertial mass of a vortex can be calculated by driving it round in a circle with a steadily revolving pinning potential. We show that in the low frequency limit this gives precisely the same formula that was used by Baym and Chandler, but find that the result is not unique and depends on the force field used to cause the acceleration. We apply this method to the Gross-Pitaevskii model, and derive a simple formula for the vortex mass. We study both the long range and short range properties of the solution. We agree with earlier results that the non-zero compressibility leads to a divergent mass. From the short-range behavior of the solution we find that the mass is sensitive to the form of the pinning potential, and diverges logarithmically when the radius of this potential tends to zero.Comment: 4 page