380 research outputs found
A remark on the asymptotic form of BPS multi-dyon solutions and their conserved charges
We evaluate the gauge invariant, dynamically conserved charges, recently
obtained from the integral form of the Yang-Mills equations, for the BPS
multi-dyon solutions of a Yang-Mills-Higgs theory associated to any compact
semi-simple gauge group G. Those charges are shown to correspond to the
eigenvalues of the next-to-leading term of the asymptotic form of the Higgs
field at spatial infinity, and so coinciding with the usual topological charges
of those solutions. Such results show that many of the topological charges
considered in the literature are in fact dynamical charges, which conservation
follows from the global properties of classical Yang-Mills theories encoded
into their integral dynamical equations. The conservation of those charges can
not be obtained from the differential form of Yang-Mills equations.Comment: Version to be published in JHEP, Journal of High Energy Physics (19
pages, no figures, some examples added
Regularity and stability of electrostatic solutions in Kaluza-Klein theory
We investigate the family of electrostatic spherically symmetric solutions of
the five-dimensional Kaluza-Klein theory. Besides black holes and wormholes, a
new class of geodesically complete solutions is identified. A monopole
perturbation is carried out, enabling us to prove analytically the stability of
a large class of solutions, including all black holes and neutral solutions.Comment: 2 pages, "mprocl.sty" with LATEX 2.09, contribution to the 9th Marcel
Grossmann meeting (MG9), Rome, July 200
Electrostatic solutions in Kaluza-Klein theory: geometry and stability
We investigate the family of electrostatic spherically symmetric solutions of
the five-dimensional Kaluza-Klein theory. Both charged and neutral cases are
considered. The analysis of the solutions, through their geometrical
properties, reveals the existence of black holes, wormholes and naked
singularities. A new class of regular solutions is identified. A monopole
perturbation study of all these solutions is carried out, enabling us to prove
analytically the stability of large classes of solutions. In particular, the
black hole solutions are stable, while for the regular solutions the stability
analysis leads to an eigenvalue problem.Comment: Latex file, 21 page
The radical left's turn towards civil society in Greece: One strategy, two paths
The Communist Party of Greece (KKE) and the Coalition of the Radical Left (SYRIZA) made remarkable ‘turns towards civil society’ over the last decade. It is argued that this was primarily a response aimed at strengthening their social legitimacy, which had reached its lowest point in the early 1990s. Differences in the way the two parties attempted to stabilise and engage their membership and re-establish links to trade unions and new social movements can be attributed to their distinct ideological and organisational legacies. Despite those differences, their respective linkage strategies were both successful until the game-changing 2012 Greek national elections, which brought about the remarkable rise of SYRIZA and the electoral demise of the KKE
Falsifying Tree Level String Motivated Bouncing Cosmologies
The string effective action at tree level contains, in its bosonic sector,
the Einstein-Hilbert term, the dilaton, and the axion, besides scalar and gauge
fields coming from the Ramond-Ramond sector. The reduction to four dimensions
brings to scene moduli fields. We generalize this effective action by
introducing two arbitrary parameters, and , connected with the
dilaton and axion couplings. In this way, more general frameworks can be
analyzed. Regular solutions with a bounce can be obtained for a range of
(negative) values of the parameter which, however, exclude the pure
string configuration (). We study the evolution of scalar
perturbations in such cosmological scenarios. The predicted primordial power
spectrum decreases with the wavenumber with spectral index , in
contradiction with the results of the . Hence, all such effective string
motivated cosmological bouncing models seem to be ruled out, at least at the
tree level approximation.Comment: Latex file, 19 pages, 3 figures in eps forma
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