Supersymmetric Euler-Heisenberg effective action: Two-loop results

The two-loop Euler-Heisenberg-type effective action for N = 1 supersymmetric QED is computed within the background field approach. The background vector multiplet is chosen to obey the constraints D_\a W_\b = D_{(\a} W_{\b)} = const, but is otherwise completely arbitrary. Technically, this calculation proves to be much more laborious as compared with that carried out in hep-th/0308136 for N = 2 supersymmetric QED, due to a lesser amount of supersymmetry. Similarly to Ritus' analysis for spinor and scalar QED, the two-loop renormalisation is carried out using proper-time cut-off regularisation. A closed-form expression is obtained for the holomorphic sector of the two-loop effective action, which is singled out by imposing a relaxed super self-duality condition.Comment: 27 pages, 2 eps figures, LaTeX; V2: typos corrected, comments and reference adde

Strongly focused light beams interacting with single atoms in free space

We construct 3-D solutions of Maxwell's equations that describe Gaussian light beams focused by a strong lens. We investigate the interaction of such beams with single atoms in free space and the interplay between angular and quantum properties of the scattered radiation. We compare the exact results with those obtained with paraxial light beams and from a standard input-output formalism. We put our results in the context of quantum information processing with single atoms.Comment: 9 pages, 9 figure

Parametrization of Born-Infeld Type Phantom Dark Energy Model

Applying the parametrization of dark energy density, we can construct directly independent-model potentials. In Born-Infeld type phantom dark energy model, we consider four special parametrization equation of state parameter. The evolutive behavior of dark energy density with respect to red-shift $z$, potentials with respect to $\phi$ and $z$ are shown mathematically. Moreover, we investigate the effect of parameter $\eta$ upon the evolution of the constructed potential with respect to $z$. These results show that the evolutive behavior of constructed Born-Infeld type dark energy model is quite different from those of the other models.Comment: 5 pages, 4 figures, Accepted for publication in Astrophysics & Space Scienc

The kk-essence scalar field in the context of Supernova Ia Observations

A $k$-essence scalar field model having (non canonical) Lagrangian of the form $L=-V(\phi)F(X)$ where $X=1/2g^{\mu\nu}\nabla_{\mu}\phi\nabla_{\nu}\phi$ with constant $V(\phi)$ is shown to be consistent with luminosity distance-redshift data observed for type Ia Supernova. For constant $V(\phi)$, $F(X)$ satisfies a scaling relation which is used to set up a differential equation involving the Hubble parameter $H$, the scale factor $a$ and the $k$-essence field $\phi$. $H$ and $a$ are extracted from SNe Ia data and using the differential equation the time dependence of the field $\phi$ is found to be: $\phi(t) \sim \lambda_0 + \lambda_1 t + \lambda_2 t^2$. The constants $\lambda_i$ have been determined. The time dependence is similar to that of the quintessence scalar field (having canonical kinetic energy) responsible for homogeneous inflation. Furthermore, the scaling relation and the obtained time dependence of the field $\phi$ is used to determine the $X$-dependence of the function $F(X)$.Comment: 8 pages, 5 figures, Late

Generalized Global Defect Solutions

We investigate the presence of defect structures in generalized models described by real scalar field in $(1,1)$ space-time dimensions. We work with two distinct generalizations, one in the form of a product of functions of the field and its derivative, and the other as a sum. We search for static solutions and study the corresponding linear stability on general grounds. We illustrate the results with several examples, where we find stable defect structures of modified profile. In particular, we show how the new defect solutions may give rise to evolutions not present in the standard scenario in higher spatial dimensions.Comment: RevTex, 10 pages, 2 figures; version to appear in EPJ

Resolving Curvature Singularities in Holomorphic Gravity

We formulate holomorphic theory of gravity and study how the holomorphy symmetry alters the two most important singular solutions of general relativity: black holes and cosmology. We show that typical observers (freely) falling into a holomorphic black hole do not encounter a curvature singularity. Likewise, typical observers do not experience Big Bang singularity. Unlike Hermitian gravity \cite{MantzHermitianGravity}, Holomorphic gravity does not respect the reciprocity symmetry and thus it is mainly a toy model for a gravity theory formulated on complex space-times. Yet it is a model that deserves a closer investigation since in many aspects it resembles Hermitian gravity and yet calculations are simpler. We have indications that holomorphic gravity reduces to the laws of general relativity correctly at large distance scales.Comment: 14 pages, 7 figure

Born-Infeld Type Phantom Model in the ω−ω′\omega-\omega' Plane

In this paper, we investigate the dynamics of Born-Infeld(B-I) phantom model in the $\omega-\omega'$ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to $N$(the logarithm of the scale factor $a$). We find the scalar field equation of motion in $\omega-\omega'$ plane, and show mathematically the property of attractor solutions which correspond to $\omega_\phi\sim-1$, $\Omega_\phi=1$, which avoid the "Big rip" problem and meets the current observations well.Comment: 6 pages, 3 figures, some references adde

Predictions and Observations in Theories with Varying Couplings

We consider a toy universe containing conventional matter and an additional real scalar field, and discuss how the requirements of gauge and diffeomorphism invariance essentially single out a particular set of theories which might describe such a world at low energies. In these theories, fermion masses and g-factors, as well as the electromagnetic coupling turn to be scalar field dependent; fermion charges and the gravitational coupling might be assumed to be constant. We then proceed to study the impact of a time variation of the scalar field on measurements of atomic spectra at high redshifts. Light propagation is not affected by a sufficiently slow change of the fine structure constant, but changes of the latter as well as variations of fermion masses and g-factors do affect the observed atomic spectra. Finally, we prove the independence of these predictions on the chosen conformal frame, in a further attempt to address differing views about the subject expressed in the literature.Comment: 19 pages, no figures; uses RevTeX

Information theoretic security by the laws of classical physics

It has been shown recently that the use of two pairs of resistors with enhanced Johnson-noise and a Kirchhoff-loop-i.e., a Kirchhoff-Law-Johnson-Noise (KLJN) protocol-for secure key distribution leads to information theoretic security levels superior to those of a quantum key distribution, including a natural immunity against a man-in-the-middle attack. This issue is becoming particularly timely because of the recent full cracks of practical quantum communicators, as shown in numerous peer-reviewed publications. This presentation first briefly surveys the KLJN system and then discusses related, essential questions such as: what are perfect and imperfect security characteristics of key distribution, and how can these two types of securities be unconditional (or information theoretical)? Finally the presentation contains a live demonstration.Comment: Featured in MIT Technology Review http://www.technologyreview.com/view/428202/quantum-cryptography-outperformed-by-classical/ ; Plenary talk at the 5th IEEE Workshop on Soft Computing Applications, August 22-24, 2012, (SOFA 2012). Typos correcte