Papers by Kostas Philippides
The International Journal of Assessment and Evaluation, 2015
AIP Conference Proceedings, 1995
We outline the pinch technique for constructing gauge invariant Green's functions in gauge theori... more We outline the pinch technique for constructing gauge invariant Green's functions in gauge theories and derive the Ward identities that must be satisfied by the gauge invariant three boson vertices of the standard model. They are generalizations of their tree level Ward identities and are shown to be crucial for the delicate gauge cancellations of the S-matrix. 1
Rethinking Language Diversity and Education, Jan 15, 2015
European educational systems, aligned with the decisions taken by the Council of Europe, are maki... more European educational systems, aligned with the decisions taken by the Council of Europe, are making great efforts to improve students’ command of foreign languages, as there are many students who leave compulsory education with a limited ability to communicate in a foreign language despite the fact that foreign language learning is considered to be one of the key competences in Europe. As for Greece, a lot of reforms have taken place in an effort to incorporate multilingualism, skill development, critical thinking and multi-literacies connected to multimodality of texts in modern environments of communication into the foreign languages Curriculum. At the cutting edge of education in Greece, the Model Experimental Schools (attracting excellent students from different sociocultural backgrounds) promote and support experimental practices of curricula, teaching methods and material, and innovative and creative actions, one of which is CLIL (Content and Language Integrated Learning). This is because CLIL is believed to improve students’ linguistic competence, develop students’ skills and learning strategies, and enhance motivation and critical thinking. In this context, CLIL, integrating English and Physics, is being implemented in the 1st grade of the 2nd Model Experimental Upper High School of Thessaloniki this year. Formative and summative assessment is to examine the effectiveness of the approach in an educational environment, where the teaching language is Greek and English has little social presence, as well as investigate any influences on the degree of comprehension of the Physics content relative to a control group taught the same material in their native Greek language. A questionnaire at the end of the project is going to explore students’ attitude towards CLIL Key words: Content and Language Integrated Learning (CLIL), language competence, teaching language, content, culture, communication, assessment.
Using the S--matrix pinch technique we obtain to one loop order, gauge independent $\gamma W^-W^+... more Using the S--matrix pinch technique we obtain to one loop order, gauge independent $\gamma W^-W^+$ and $Z W^-W^+$ vertices in the context of the standard model, with all incoming momenta off--shell. We show that the vertices so constructed satisfy simple QED--like Ward identities. These gauge invariant vertices give rise to expressions for the magnetic dipole and electric quadrupole form factors
Physics Letters B, 1996
The pinch technique (PT) is applied to neutral current amplitudes, focusing on the mixing problem... more The pinch technique (PT) is applied to neutral current amplitudes, focusing on the mixing problem. Extending recent arguments due to Papavassiliou and Pilaftsis, it is shown that the use of the PT self-energies does not shift the complex-valued position of the pole through order O(g 4). This leads (to the same accuracy) to a simple interpretation of M Z , the mass measured at LEP, in terms of the PT self-energies. It is pointed out that the PT approach provides a convenient and rather elegant formalism to discuss important neutral current amplitudes, such as those relevant to four-fermion processes and LEP2.
Physical Review D, 2011
We find that, in the local V-A theory, the radiative corrections to pion β-decay involving the we... more We find that, in the local V-A theory, the radiative corrections to pion β-decay involving the weak vector current, when evaluated in the current algebra (CA) formulation in which quarks are the fundamental underlying fields, show a small difference with the more elementary calculations based directly on the pion fields. We show that this difference arises from a specific short-distance effect that depends on the algebra satisfied by the weak and electromagnetic currents. On the other hand, we present a simple theoretical argument that concludes that this difference does not occur when the CA formulation is compared with the chiral perturbation theory (χPT) approach. Comparisons with previous studies, and with a more recent calculation based on χPT, are included. We also briefly review the important differences between the results in the local V-A theory and the Standard Model.
Physical Review D, 1995
In the context of the Standard Model we extend the S{matrix pinch technique for non{conserved cur... more In the context of the Standard Model we extend the S{matrix pinch technique for non{conserved currents to the case of three boson vertices. We outline in detail how e ective gauge invariant three boson vertices can be constructed, with all three incoming momenta o {shell. Explicit closed expressions for the vertices W W + , ZW W + , and W W + are reported. The three boson vertices so constructed satisfy naive QED{like Ward identities which relate them to the gauge invariant gauge boson self{energies previously constructed by the same method. The derivation of the aforementioned Ward identities relies on the sole requirement of complete gauge invariance of the S{matrix element considered; in particular, no knowledge of the explicit closed form of the three boson vertices involved is necessary. The validity of one of these Ward identities is demonstrated explicitly, through a detailed diagrammatic one-loop analysis, in the context of three di erent gauges.
Physical Review D, 1993
We use the S-matrix pinch technique to derive to one-loop order gauge-independent yR' 8' and ZW+ ... more We use the S-matrix pinch technique to derive to one-loop order gauge-independent yR' 8' and ZW+ W vertices in the context of the standard model, with all three incoming momenta off shell. We show that the y W W vertex so constructed is related to the gauge-independent W self-energy, derived by Degrassi and Sirlin, by a very simple QED-like Ward identity. The same results are obtained by the pinch technique applied directly to the process e + e~W W. Explicit calculations give rise to expressions for static properties of the 8'gauge bosons such as the magnetic dipole and electric quadrupole moments, which satisfy the crucial properties of infrared finiteness as well as gauge independence.
Physical Review D, 1995
We propose a decomposition of the S-matrix into individually gauge invariant sub-amplitudes, whic... more We propose a decomposition of the S-matrix into individually gauge invariant sub-amplitudes, which are kinematically akin to propagators, vertices, boxes, etc. This decompsition is obtained by considering limits of the S-matrix when some or all of the external particles have masses larger than any other physical scale. We show at the one-loop level that the e ective gluon self-energy so de ned is physically equivalent to the corresponding gauge independent self-energy obtained in the framework of the pinch technique. The generalization of this procedure to arbitrary gluonic n-point functions is brie y discussed.
Physical Review D, 1996
The S-matrix is known to be independent of the gauge fixing parameter to all orders in perturbati... more The S-matrix is known to be independent of the gauge fixing parameter to all orders in perturbation theory. In this paper by employing the pinch technique we prove at one loop a stronger version of this independence. In particular we show that one can use a gauge fixing parameter for the gauge bosons inside quantum loops which is different from that used for the bosons outside loops, and the S-matrix is independent from both. Possible phenomenological applications of this result are briefly discussed.
Physical Review D, 1999
The dependence of the differential cross-section for on-shell W-pair production on the anomalous ... more The dependence of the differential cross-section for on-shell W-pair production on the anomalous trilinear gauge couplings invariant under C and P is examined. It is shown that the contributions of the anomalous magnetic moments of the W boson due to the photon and the Z can be individually projected out by means of two appropriately constructed polynomials. The remaining four anomalous couplings are shown to satisfy a set of model-independent sum rules. Specific models which predict special relations among the anomalous couplings are then studied; in particular, the composite model of Brodsky and Hiller, and the linear and non-linear effective Lagrangian approaches. The relations predicted by these models, when combined with the aforementioned sum rules, give rise to definite predictions, particular to each model. These predictions can be used, at least in principle, in order to exclude or constrain such models.
Physical Review D, 1999
We present a new, model independent method for extracting bounds for the anomalous ␥WW couplings ... more We present a new, model independent method for extracting bounds for the anomalous ␥WW couplings from hadron collider experiments. At the partonic level we introduce a set of three observables which are constructed from the unpolarized differential cross section for the process dū →W Ϫ ␥ by appropriate convolution with a set of simple polynomials depending only on the center-of-mass angle. One of these observables allows for the direct determination of the anomalous coupling usually denoted by ⌬, without any simplifying assumptions, and without relying on the presence of a radiation zero. The other two observables impose two sum rules on the remaining three anomalous couplings. The inclusion of the structure functions is discussed in detail for both pp and pp colliders. We show that, whilst for pp experiments this can be accomplished straightforwardly, in the pp case one has to resort to somewhat more elaborate techniques, such as the binning of events according to their longitudinal momenta. ͓S0556-2821͑99͒01523-4͔
Physical Review D, 2000
We present a model-independent method for determining anomalous gauge boson couplings from ongoin... more We present a model-independent method for determining anomalous gauge boson couplings from ongoing and future e + e − → W + W − experiments. First we generalize an already existing method, which relies on the study of four observables constructed through appropriate projections of the unpolarized differential cross-section. In particular, we retain both linear and quadratic terms in the unknown couplings, and compute contributions to these observables originating from anomalous couplings which do not separately conserve the discrete C, P , and T symmetries. Second, we combine the above set of observables with three additional ones, which can be experimentally obtained from the total cross-sections for polarized final state W bosons. The resulting set of seven observables may provide useful information for constraining, and in some cases for fully determining, various of the possible anomalous gauge boson couplings.
Nuclear Physics B, 1995
The vacuum{polarization contributions of O(b n 1 n s) to the relation between the pole{mass M of ... more The vacuum{polarization contributions of O(b n 1 n s) to the relation between the pole{mass M of a quark and the MS parameterm(M) are evaluated by a straightforward method. They are found to approximate very well the exact answer, known through O(2 s), thus providing a simple physical interpretation. Results are also given for the cases when the vacuum{polarization contributions are dened by the pinch technique prescription and specic background eld gauges. Assuming that the terms n 3 are also dominant, we e v aluate M t =m t (M t), compare the results with those of optimization methods, briey discuss M b =m b (M b), and estimate the irreducible errors in the perturbative series. Implications for the electroweak amplitude are emphasized. An update of the QCD corrections to this amplitude, including an estimate of the theoretical error, is given. Recently [1{2], Eq.(1) in the top quark case has been studied using the BLM [14], PMS
Nuclear Physics B, 1996
A simple and testable necessary condition for the gauge independence of the Pinch Technique self-... more A simple and testable necessary condition for the gauge independence of the Pinch Technique self-energies at two loops is discussed. It is then shown that, in the case of the Z and W self-energies, the condition is indeed satisfied by the Papavassiliou-Pilaftsis formulation.
Journal of Physics G: Nuclear and Particle Physics, 2002
ABSTRACT
The European Physical Journal C, 1999
The W −fusion scattering process W + W − → ZZ for off-shell W bosons is studied, focusing on the ... more The W −fusion scattering process W + W − → ZZ for off-shell W bosons is studied, focusing on the issue of its high-energy behaviour which is known to be anomalous. It is shown that the unitarity violating terms can be isolated and extracted in a well-defined and efficient way using the pinchtechnique. This restores the good high energy behaviour of the cross section and, in particular, makes possible the identification of the Higgs resonance in the invariant mass distribution m ZZ of the Z pair. The discarded terms, which are proportional to the off-shellness of the W bosons, cancel against similar terms originating from the remaining diagrams for the full physical process f 1 f 2 → f 1 f 2 ZZ. This cancellation ensures the gauge invariance of our result, which therefore constitutes a meaningful separation between signal and background when they both contribute coherently. Equipped with this result, we are able to define a resonant approximation for the process pp → ZZ + 2 jets + X, which circumvents the problem of good high energy behaviour without having to resort to the lengthy calculation of the complete set of diagrams. In this approximation only the W − and Z−fusion signal graphs are included, i.e. the ones which contain the Higgs resonance. We have verified that the approximate resonant cross section describes very well the full result not only close to the resonance but also beyond it.
Physical Review D, 1996
We show that in the framework of the pinch technique the universal part of the parameter can be m... more We show that in the framework of the pinch technique the universal part of the parameter can be meaningfully de ned, beyond one loop. The universal part so obtained satis es the crucial requirements of gauge-independence, niteness, and process-independence, even when subleading contributions of the top quark are included. The mechanism which enforces the aforementioned properties is explained in detail, and several subtle eld theoretical issues are discussed. Explicit calculations of the sub-leading two-loop corrections of order O(G 2 m 2 t M 2 Z) are carried out in the context of an SU(2) model, with M W = M Z , and various intermediate and nal results are reported.
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Papers by Kostas Philippides