Highlighted Papers

This page presents Highlights of published articles selected on the basis of the quality of their scientific achievements and potential wider impact. The PDF of these highlighted papers can be downloaded freely for two months from the publication of the Highlight.

August 2011
EPJ Plus - The twin paradox in a cosmological context

The twin paradox has been a source of debate since it was discovered by Einstein. It can be analytically verified assuming the existence of global nonrotating inertial frames.
The natural nonrotating frame and its identification with "fixed stars" is an aspect of Mach's Principle, which holds that the totality of matter in the universe determines the inertial frames.
Ø. Grøn and Braeck first note that the experiment by Hafele and Keating (1972), who flew atomic clocks eastward and westward around the Earth in commercial aircraft, also shows agreement with the expected result, assuming an inertial frame which is nonrotating with respect to "fixed stars". The authors then show that in the case of two observers in an otherwise empty universe (i.e., without "fixed stars") moving at different speeds on a circular path yield different twin paradox results, depending on whether one or the other – or neither – observer is assumed to be at rest.
The authors ultimately take a fresh look at the work of Brill and Cohen, who studied the geometry inside a massive rotating shell, and conclude that in the black hole limit, such a mass distribution will drag the frames around at its own rotation rate.
Taken together, and given the entire universe closely satisfying the black hole condition, this paper lends further support to the Mach Principle.
["The twin paradox in a cosmological context" by Ø. Grøn and S. Braeck, Eur. Phys. J. Plus (2011) 126 : 79, DOI: 10.1140/epjp/i2011-11079-7]

August 2011
EPJ Plus: Discovering Technicolor

At present there are no known elementary scalar fields. A possible candidate is the as yet undiscovered Higgs particle; however it could well be that this elusive particle is instead composite. This possibility is exhaustively examined in this article, which is both tutorial and extensive review, classifying the diverse technicolor models as extensions of the Standard Model of particle physics. These model extensions are then compared with electroweak precision data, the spectrum of states common to most such models are identified, and their decays and associated experimental signals for the LHC illustrated, including the implementation in event generators important for searches at the LHC. This timely review provides the most complete and up-to-date benchmarks for the potential discovery of technicolor models.
Figure: Cartoon of the Minimal Walking Technicolor Model extension of the SM.
["Discovering Technicolor" by J.R. Andersen et al., Eur. Phys. J. Plus (2011) 126 : 81, DOI: 10.1140/epjp/i2011-11081-1]

August 2011
EPJ Plus: "Eigenvalue problem in two dimensions for an irregular boundary: Neumann condition"

The Helmholtz equation arises in a number of physical contexts as one reduces the wave equation by considering single frequency propagation. One such application appears in studying wave behavior in waveguides. While waveguides in technology are carefully engineered to have, for instance, constant and simple cross-sectional geometries, natural waveguides relax such engineering constraints. (Natural waveguides range across systems from atmospheric and oceanic ducts, to biological systems such as seal and polar bear hair fibers.) In particular the cross section of natural waveguides tends to have a complex boundary shape that is far from the ideal circular or rectangular form of engineered waveguides.
Panda, Chakraborty and Khastgir have provided a new approach to the irregular boundary 2-d Helmholtz equation with Neumann boundary conditions (specified normal derivatives of the field at the boundary). This boundary condition has significant physical importance: it is the natural one for electromagnetic propagation in the TM mode in waveguides.
To date the most successful efforts to solve the irregular boundary Helmholtz equation have been computational, but even this general method has its drawbacks. Panda et al. provide an analytic perturbative approach which solves the irregular boundary problem via a perturbative series. The authors explicitly work out several nontrivial examples. The benefits of this approach include, most importantly, an analytical understanding of the behavior of the solution as the amplitude of the boundary distortion is increased. Another important feature of Panda et al.’s expression is its analytic precision in the terms computed and its analytic error estimates for the terms truncated from the series. Together these give the analytic methods a much larger dynamic range than available computationally.
["Eigenvalue problem in two dimensions for an irregular boundary: Neumann condition" by S. Panda, S. Chakraborty, and S. P. Khastgir, Eur. Phys. J. Plus (2011), DOI: 10.1140/epjp/i2011-11062-4]

June 2011
EPJ Plus: "Ultraviolet Complete Electroweak Model Without a Higgs Particle"

Thanks to the great accuracy in predicting experimental data, the standard model of particle physics is widely considered to be a building block of our current knowledge of the structure of matter. In spite of this success, we are still lacking an essential piece of evidence, namely the detection of the Higgs boson, a hypothetical massive elementary particle whose existence makes it possible to explain how most of the known elementary particles become massive. In this paper, an alternative electroweak model is presented that assumes running coupling constants described by energy-dependent entire functions. Contrary to the conventional formulation the action contains no physical scalar fields and no Higgs particle, even if the foreseen masses for particles are compatible with known experimental values. In addition the vertex couplings possess an energy scale for predicting scattering amplitudes that can be tested in current particle accelerators. As a result the paper provides an essential alternative to the current established knowledge in the field and addresses an issue that might soon be resolved, as the Large Hadron Collider could provide the experimental evidence of the existence or non-existence of the Higgs boson.
["Ultraviolet Complete Electroweak Model Without a Higgs Particle" by J.W. Moffat, Eur. Phys. J. Plus (2011), DOI: 10.1140/epjp/i2011-11053-5]

June 2011
EPJ Plus: "Biquaternionic Proca-type generalization of gravity"

S. Demir and M. Tanish, from Anadolu University of Eskisehir (Turkey), propose yet another piece of the puzzle of treating field theories in a unified, mathematically elegant way. Since the mid-seventies there have been several attempts to work with unified field theories by using the algebras of quaternions and octonions. These algebras are the more restrictive two of the four algebras allowed by the Hurwitz theorem (the other two are the algebra of the real numbers and the algebra of the complex numbers). Starting with real numbers each subsequent algebra becomes more restrictive: the quaternions are associative but non-commutative; the octonions are not only non-commutative but also non-associative, the hardest algebra to work into a field theory. Characteristic of these algebras is that they each double the "algebraic dimensions", starting with one-dimensional real algebra, the next being the two-dimensional complex algebra, then the four-dimensional quaternionic algebra, and finally the eight-dimensional octonionic algebra, with interesting consequences for the field theories worked out through these algebras. Through the use of biquaternionic formalism (still within the algebra of quaternions) Demir and Tanish combine gravitomagnetic monopole terms with a Proca-type generalization of gravity in one compact form. This formalism also provides similar results for unified Maxwell’s equations with non-vanishing photon mass and Dirac monopoles. Demir and Tanish have also devised a compact gravitational wave equation with Proca-type generalization of Heaviside monopoles, and developed the most generalized form of homogeneous Klein-Gordon equation for the graviton. Finally, the authors demonstrate that all field equations of the gravity can be transcribed as one biquaternionic equation. Consequently, the biquaternionic formalism used in this paper presents a compact, simpler, and more elegant tool for deriving alternative formulations related to gravitoelectromagnetism.
["Biquaternionic Proca-type generalization of gravity" by S. Demir and M. Tanıslı, Eur. Phys. J. Plus (2011), DOI: 10.1140/epjp/i2011-11051-7]

May 2011
EPJ Plus: "The present role of small particle accelerators for the study of Cultural Heritage"

This paper is a first critical discussion of the contemporary role that small particle accelerators play in the field of applications related to Cultural Heritage for non-destructive materials analysis and dating, such as ion beam analysis (IBA) and accelerator mass spectroscopy (AMS). This analysis is put in perspective by comparing accelerator-based methods to other techniques, pointing out the corresponding pros and cons. It is stressed that IBA can address questions that cannot be answered by conventional techniques like X-ray fluorescence (the latter having however the advantage of portability). It is shown in particular that IBA can still yield unrivalled results thanks to novel uses of its potential, such as providing elemental maps and resolving layer structures. This was strikingly demonstrated in a recent PIXE (Particle Induced X-ray Emission) analysis at LABEC of Mantegna’s famous painting Madonna con Bambino (see figure), which used the scanning external proton microbeam set-up to produce a high-resolution elemental mapping. The use of different, even precious, pigments to paint tiny details is thus pointed out, which can be of great interest to art historians and restorers. In addition, by utilizing the different absorption rates of different X-ray energies, even the paint layer structure can sometimes be reconstructed: for example, in the case shown in the upper part of the figure, it is shown that the Virgin’s veil was made with a gold paint over a background of ultramarine blue, lightened with lead-white. No other technique can provide such information in a totally non-destructive way and with no pick-up of samples.
["The present role of small particle accelerators for the study of Cultural Heritage" by P. A. Mandò, M. E. Fedi, N. Grassi, Eur. Phys. J. Plus (2011), DOI: 10.1140/epjp/i2011-11041-9]