International Journal of Modern Physics A

Fully differential studies of single ionization of neutral atoms by charged particle impact have proven to be extremely powerful to advance our understanding of the few-body dynamics in atomic processes. Until a few years ago, such data were only available for electron impact and were mostly limited to electrons ejected into the scattering plane. When fully differential data were finally obtained for ion impact covering the entire three-dimensional space, very surprising features were observed. It then became clear that our understanding of ionization processes in atomic collisions is not nearly as complete as previously assumed. Here, we review the development of experimental and theoretical studies of three-dimensional fully differential single ionization cross-sections since then.

We discuss quantum fluctuations of a class of rotating strings in AdS₅ × S⁵. In particular, we develop a systematic method to compute the one-loop sigma-model effective actions in closed forms as expansions for large spins. As examples, we explicitly evaluate the leading terms for the constant radii strings in the SO(6) sector with two equal spins, the SU(2) sector, and the SL(2) sector. We also obtain the leading quantum corrections to the space–time energy for these sectors.

The CP conserved nonleptonic K → πππ decays are discussed within the chiral quark model, including chiral perturbation theory corrections. For the chiral loop correction, they are presented in a way to be more manageable and easier for use. Furthermore a new identity for the imaginary part of the chiral loop corrections is derived. All amplitudes are parametrized in terms of quark and gluon condensate and the constituent quark mass. The same values for these parameters that can be obtained by a fit of the ΔI = 1/2 rule in K → 2π give a reasonably good fit in the K → 3π case. We compare with the work of other groups.

We investigate a local cosmic string with a phenomenological energy–momentum tensor as prescribed by Vilenkin, in the presence of C-field. The solutions of full nonlinear Einstein's equations for exterior and interior regions of such a string are presented.

A chiral superfield strength in conformal supergravity at linearized level is obtained by acting two superspace derivatives on chiral superfield strength which can be described in terms of twistor superfields. By decomposing SU(4)_R representation of twistor superfields into the SU(2)_R representation with an invariant U(1)_R charge, the surviving twistor superfields contain the physical states of conformal supergravity. These twistor superfields are functions of homogeneous coordinates of weighted complex projective space WCP^3|4 where the two weighted fermionic coordinates have weight -1 and 3.

Our aim is to study the electron–positron vacuum pressures in the presence of a strong magnetic field B. To that end, we obtain a general energy–momentum tensor, depending on external parameters, which in the zero temperature and zero density limit leads to vacuum expressions which are approximation-independent. Anisotropic pressures arise, and in the tree approximation of the magnetic field case, the pressure along B is positive, whereas perpendicular to B it is negative. Due to the common axial symmetry, the formal analogy with the Casimir effect is discussed, which in addition to the usual negative pressure perpendicular to the plates, there is a positive pressure along the plates. The formal correspondence between the Casimir and blackbody energy–momentum tensors is also discussed. The fermion hot vacuum behavior in a magnetic field is also briefly discussed.

We study a possibly integrable model of Abelian gauge fields on a two-dimensional surface M, with volume form μ. It has the same phase-space as ideal hydrodynamics, a coadjoint orbit of the volume-preserving diffeomorphism group of M. Gauge field Poisson brackets differ from the Heisenberg algebra, but are reminiscent of Yang–Mills theory on a null surface. Enstrophy invariants are Casimirs of the Poisson algebra of gauge invariant observables. Some symplectic leaves of the Poisson manifold are identified. The Hamiltonian is a magnetic energy, similar to that of electrodynamics, and depends on a metric whose volume element is not a multiple of μ. The magnetic field evolves by a quadratically nonlinear "Euler" equation, which may also be regarded as describing geodesic flow on SDiff(M, μ). Static solutions are obtained. For uniform μ, an infinite sequence of local conserved charges beginning with the Hamiltonian are found. The charges are shown to be in involution, suggesting integrability. Besides being a theory of a novel kind of ideal flow, this is a toy-model for Yang–Mills theory and matrix field theories, whose gauge-invariant phase-space is conjectured to be a coadjoint orbit of the diffeomorphism group of a noncommutative space.

In this work we apply Thompson's method (of the dimensions and scales) to study some features of the Quantum Electrodynamics and Chromodynamics. This heuristic method can be considered as a simple and alternative way to the Renormalization Group approach and when applied to QED-Lagrangian is able to obtain in a first approximation both the running coupling constant behavior of α(μ) and the mass m(μ). The calculations are evaluated only at d_c = 4, where d_c is the upper critical dimension of the problem, so that we obtain the logarithmic behavior both for the coupling α and the excess of mass Δm on the energy scale μ. Although our results are well known in the vast literature of field theories, the advantage of Thompson's method, beyond its simplicity is that it is able to extract directly from QED-Lagrangian the physical (finite) behavior of α(μ) and m(μ), bypassing hard problems of divergences which normally appear in the conventional renormalization schemes applied to field theories like QED. Quantum Chromodynamics (QCD) is also treated by the present method in order to obtain the quark condensate value. Besides this, the method is also able to evaluate the vacuum pressure at the boundary of the nucleon. This is done by assumming a step function behavior for the running coupling constant of the QCD, which fits nicely to some quantities related to the strong interaction evaluated through the MIT-bag model.

We investigate how the data from various future neutrino oscillation experiments will constrain the physics parameters for a three active neutrino mixing model. The investigations properly account for the degeneracies and ambiguities associated with the phenomenology as well as estimates of experimental measurement errors. Combinations of various reactor measurements with the expected J-PARC (T2K) and NuMI offaxis (Nova) data, both with and without the increased flux associated with proton driver upgrades, are considered. The studies show how combinations of reactor and offaxis data can resolve degeneracies (e.g. the θ₂₃ degeneracy) and give more precise information on the oscillation parameters. A primary purpose of this investigation is to establish the parameter space regions where CP violation can be discovered and where the mass hierarchy can be determined. We find that, even with augmented flux from proton drivers, such measurements demand that sin² 2θ₁₃ be fairly large and in the range where it is measurable by reactor experiments.

The energy distribution in the Locally Rotationally Symmetric (LRS) Bianchi type II space–time is obtained by considering the Møller energy–momentum definition in both Einstein's theory of general relativity and teleparallel theory of relativity. The energy distribution which includes both the matter and gravitational field is found to be zero in both of these different gravitation theories. This result agrees with previous works of Cooperstock and Israelit, Rosen, Johri et al., Banerjee and Sen, Vargas, and Aydogdu and Salti. Our result — the total energy of the universe is zero — supports the view points of Albrow and Tryon.