Coulomb's law modification in nonlinear and in noncommutative electrodynamics

We study the lowest-order modifications of the static potential for Born-Infeld electrodynamics and for the $\theta$-expanded version of the noncommutative U(1) gauge theory, within the framework of the gauge-invariant but path-dependent variables formalism. The calculation shows a long-range correction ($1/r^5$-type) to the Coulomb potential in Born-Infeld electrodynamics. However, the Coulomb nature of the potential (to order $e^2$) is preserved in noncommutative electrodynamics.Comment: 14 pages, 1 figur

Remarks on Screening in a Gauge-Invariant Formalism

In this paper we display a direct and physically attractive derivation of the screening contribution to the interaction potential in the Chiral Schwinger model and generalized Maxwell-Chern-Simons gauge theory. It is shown that these results emerge naturally when a correct separation between gauge-invariant and gauge degrees of freedom is made. Explicit expressions for gauge-invariant fields are found.Comment: 13 pages, 1 figure, to appear in PR

Critical analysis of interpersonal trust determinants in virtual teams, working in capability planning in the identification of capability gaps or needs, to provide required future military capability in the UK’s MOD

The United Kingdom’s Ministry of Defence (MOD) balances defence policy aspirations and available resources through the capability planning process. Arguably, the cornerstone of this process is the cross-functional integration of skills and capabilities across defence. This is realised through a construct of Virtual Teams (VTs) called Capability Planning Groups (CPGs). Literature on the topic of interpersonal trust in VTs highlights the development of trust as a key element, if not the most significant, in pursuing desired outcomes. Furthermore, literature on this topic, in a defence context, is scarce. This thesis undertakes a specific research approach, in accordance with its aim: To develop a critical analysis of interpersonal trust determinants in VTs, working in capability planning for the identification of capability gaps or needs, to provide required future military capability. Consequently, three research questions are investigated: What are the pertinent determinants of interpersonal trust in the CPG?; What, if any, are the issues surrounding those determinants within the CPG?; and, What risks are there, beyond the interpersonal relationships, which could influence the trust behaviour of CPG members? A critical review of pertinent literature is followed by the development of a research methodology under a phenomenological paradigm. Building from this, fieldwork was undertaken in two phases. As a result of semi-structured interviews to the members of a number of CPGs, the way in which interpersonal trust is generically perceived was conceptualised, and confirmation of the interpersonal trust determinants considered in an adapted model of interpersonal trust in CPGs was provided. In addition, a cross-case analysis allowed the integration of the data gathered, in order to identify target areas to be covered in the second wave of data collection. Subsequently, in Phase II, information was gathered through a survey questionnaire addressed to the whole population under consideration, in order to increase the robustness of the study, by confirming and providing further insights about key issues identified, as well as underpinning more powerful conclusions. From this, interpersonal trust determinants pertaining to the CPGs, as well as the issues and risks regarding interpersonal trust, were asserted. A major finding was the conceptualisation of these issues and risks, because they are critical in determining if a specific behaviour will be taken. Moreover, as highlighted in the Defence Reform Report (2011), some of these are already identified as very real concerns, and appear as structural or enduring problems at MOD level. These elements are deemed a central focus for future research, because of their significance as contextual variables that have to be addressed in order to stimulate interpersonal trust and, consequently, improve performance in the CPGs. As the use of VTs is considered most likely to increase over time in MOD organisations, the findings from this research will be useful to all personnel involved in capability planning, and other cross-functional activities. In particular, it could inform the design of organisational processes and systems as capability management is taken forward. Finally, the issues and risks associated with such virtual trust are asserted as not believed to be a manifestation of dysfunctional strategic planning because defence organisations can have clarity of purpose, can have clear direction, and yet still send competing messages. Paradoxically, that is the weakness of being strong. The analysis suggests that action has to be taken in order to stimulate interpersonal trust, because it is important to avoid or mitigate negative effects of contextual variables influencing CPGs. To this end, it is crucial to understand the role that interpersonal trust plays in the cross-functional work that is critical for the successful integration of skills and capabilities, and to ensure that people involved in capability planning and other cross-functional activities are assisted in understanding the nature of this challenging and complex context

The photino sector and a confining potential in a supersymetric Lorentz-symmetry-violating model

We study the spectrum of the minimal supersymmetric extension of the Carroll-Field-Jackiw model for Electrodynamics with a topological Chern-Simons-like Lorentz-symmetry violating term. We identify a number of independent background fermion condensates, work out the gaugino dispersion relation and propose a photonic effective action to consider aspects of confinement induced by the SUSY background fermion condensates, which also appear to signal Lorentz-symmetry violation in the photino sector of the action. Our calculations of the static potential are carried out within the framework of the gauge-invariant but path-dependent variables formalism which are alternative to the Wilson loop approach. Our results show that the interaction energy contains a linear term leading to the confinement of static probe charges.Comment: 11 pages, photino dispersion relation is extended to included the case the photino acquires mass through spontaneous SUSY breakin

Aspects of CPT-even Lorentz-symmetry violating physics in a supersymmetric scenario

Background fermion condensates in a landscape dominated by global SUSY are reassessed in connection with a scenario where Lorentz symmetry is violated in the bosonic sector (actually, the photon sector) by a $CPT$-even $k_F$-term. An effective photonic action is discussed that originates from the supersymmetric background fermion condensates. Also, the photino mass emerges in terms of a particular condensate contrary to what happens in the $k_{AF}$-violation. Finally, the interparticle potential induced by the effective photonic action is investigated and a confining profile is identified.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1102.3777 by other author

On scale symmetry breaking and confinement in D=3 models

Within the framework of the gauge-invariant, but path-dependent, variables formalism, we study the connection between scale symmetry breaking and confinement in three-dimensional gluodynamics. We explicitly show that the static potential profile contains a linear potential, leading to the confinement of static charges. Also, we establish a new type of equivalence among different three-dimensional effective theories.Comment: 6 pages, references adde

Entropic force, noncommutative gravity and ungravity

After recalling the basic concepts of gravity as an emergent phenomenon, we analyze the recent derivation of Newton's law in terms of entropic force proposed by Verlinde. By reviewing some points of the procedure, we extend it to the case of a generic quantum gravity entropic correction to get compelling deviations to the Newton's law. More specifically, we study: (1) noncommutative geometry deviations and (2) ungraviton corrections. As a special result in the noncommutative case, we find that the noncommutative character of the manifold would be equivalent to the temperature of a thermodynamic system. Therefore, in analogy to the zero temperature configuration, the description of spacetime in terms of a differential manifold could be obtained only asymptotically. Finally, we extend the Verlinde's derivation to a general case, which includes all possible effects, noncommutativity, ungravity, asymptotically safe gravity, electrostatic energy, and extra dimensions, showing that the procedure is solid versus such modifications.Comment: 8 pages, final version published on Physical Review

Aspects of Magnetic Field Configurations in Planar Nonlinear Electrodynamics

In the framework of three-dimensional Born-Infeld Electrodynamics, we pursue an investigation of the consequences of the space-time dimensionality on the existence of magnetostatic fields generated by electric charges at rest in an inertial frame, which are present in its four-dimensional version. Our analysis reveals interesting features of the model. In fact, a magnetostatic field associated with an electric charge at rest does not appear in this case. Interestingly, the addition of the topological term (Chern-Simons) to Born-Infeld Electrodynamics yields the appearance of the magnetostatic field. We also contemplate the fields associated to the would-be-magnetic monopole in three dimensions.Comment: 8 page

Solutions for f(R) gravity coupled with electromagnetic field

In the presence of external, linear / nonlinear electromagnetic fields we integrate f(R) \sim R+2{\alpha}\surd(R+const.) gravity equations. In contrast to their Einsteinian cousins the obtained black holes are non-asymptotically flat with a deficit angle. In proper limits we obtain from our general solution the global monopole solution in f(R) gravity. The scale symmetry breaking term adopted as the nonlinear electromagnetic source adjusts the sign of the mass of the resulting black hole to be physical.Comment: 7 pages no figure, final version for publication in European Physical Journal