97 research outputs found
Integrals of periodic motion for classical equations of relativistic string with masses at ends
Boundary equations for the relativistic string with masses at ends are
formulated in terms of geometrical invariants of world trajectories of masses
at the string ends. In the three-dimensional Minkowski space , there are
two invariants of that sort, the curvature and torsion . For these
equations of motion with periodic , constants
of motion are obtained.Comment: 8 pages, REVTEX, no figures and table
Boundary terms in Nambu-Goto string action
We investigate classical strings defined by the Nambu-Goto action with the
boundary term added. We demonstrate that the latter term has a significant
bearing on the string dynamics. It is confirmed that new action terms that
depend on higher order derivatives of string coordinates cannot be considered
as continuous perturbations from the starting string functional. In the case
the boundary term reduces to the Gauss-Bonnet term, a stability analysis is
performed on the rotating rigid string solution. We determined the most generic
solution that the fluctuations grow to. Longitudinal string excitations are
found. The Regge trajectories are nonlinear.Comment: 9 LaTeX pages and 3 PostScript figures (uuencoded), preprint
TPJU-15/9
Non-existence of a dilaton gravity action for the exact string black hole
We prove that no local diffeomorphism invariant two-dimensional theory of the
metric and the dilaton without higher derivatives can describe the exact string
black hole solution found a decade ago by Dijkgraaf, Verlinde and Verlinde. One
of the key points in this proof is the concept of dilaton-shift invariance. We
present and solve (classically) all dilaton-shift invariant theories of
two-dimensional dilaton gravity. Two such models, resembling the exact string
black hole and generalizing the CGHS model, are discussed explicitly.Comment: 24 pages, 3 eps-figures, revised version (more references, clarified
some of the discussion
Comparing user and community co-production approaches in local 'welfare' and 'law and order' services : does the governance mode matter?
This paper analyses the relationship between modes of governance at local level and the adoption of user and community co-production approaches in public safety and social care services, based on a German case study. The findings draw on a series of intensive focus groups with managers and staff of public services in four different regions in Germany, exploring existing levels of co-production and its potential in social care and public safety services, with particular focus on older and young people. The paper provides the first clear research evidence on how approaches to co-production are specific to the modes of governance within which they take place. The paper concludes with policy conclusions, both in the two programme areas concerned and in local public services more generally
Conformal Hamiltonian Dynamics of General Relativity
The General Relativity formulated with the aid of the spin connection
coefficients is considered in the finite space geometry of similarity with the
Dirac scalar dilaton. We show that the redshift evolution of the General
Relativity describes the vacuum creation of the matter in the empty Universe at
the electroweak epoch and the dilaton vacuum energy plays a role of the dark
energy.Comment: 9 pages, 1 figure, submitted to PL
Sinh-Gordon, Cosh-Gordon and Liouville Equations for Strings and Multi-Strings in Constant Curvature Spacetimes
We find that the fundamental quadratic form of classical string propagation
in dimensional constant curvature spacetimes solves the Sinh-Gordon
equation, the Cosh-Gordon equation or the Liouville equation. We show that in
both de Sitter and anti de Sitter spacetimes (as well as in the black
hole anti de Sitter spacetime), {\it all} three equations must be included to
cover the generic string dynamics. The generic properties of the string
dynamics are directly extracted from the properties of these three equations
and their associated potentials (irrespective of any solution). These results
complete and generalize earlier discussions on this topic (until now, only the
Sinh-Gordon sector in de Sitter spacetime was known). We also construct new
classes of multi-string solutions, in terms of elliptic functions, to all three
equations in both de Sitter and anti de Sitter spacetimes. Our results can be
straightforwardly generalized to constant curvature spacetimes of arbitrary
dimension, by replacing the Sinh-Gordon equation, the Cosh-Gordon equation and
the Liouville equation by higher dimensional generalizations.Comment: Latex, 19 pages + 1 figure (not included
Regularizing Property of the Maximal Acceleration Principle in Quantum Field Theory
It is shown that the introduction of an upper limit to the proper
acceleration of a particle can smooth the problem of ultraviolet divergencies
in local quantum field theory. For this aim, the classical model of a
relativistic particle with maximal proper acceleration is quantized canonically
by making use of the generalized Hamiltonian formalism developed by Dirac. The
equations for the wave function are treated as the dynamical equations for the
corresponding quantum field. Using the Green's function connected to these wave
equations as propagators in the Feynman integrals leads to an essential
improvement of their convergence properties.Comment: 9 pages, REVTeX, no figures, no table
Hamiltonian Cosmological Perturbation Theory
The Hamiltonian approach to cosmological perturbations in general relativity
in finite space-time is developed, where a cosmological scale factor is
identified with spatial averaging the metric determinant logarithm.
This identification preserves the number of variables and leads to a
cosmological perturbation theory with the scalar potential perturbations in
contrast to the kinetic perturbations in the Lifshitz version which are
responsible for the ``primordial power spectrum'' of CMB in the inflationary
model. The Hamiltonian approach enables to explain this ``spectrum'' in terms
of scale-invariant variables and to consider other topical problem of modern
cosmology in the context of quantum cosmological creation of both universes and
particles from the stable Bogoliubov vacuum.Comment: 10 pages, text was changed according to the version accepted for
publication in Physics Letters
The Complete Solution of 2D Superfield Supergravity from graded Poisson-Sigma Models and the Super Pointparticle
Recently an alternative description of 2d supergravities in terms of graded
Poisson-Sigma models (gPSM) has been given. As pointed out previously by the
present authors a certain subset of gPSMs can be interpreted as "genuine"
supergravity, fulfilling the well-known limits of supergravity, albeit deformed
by the dilaton field. In our present paper we show that precisely that class of
gPSMs corresponds one-to-one to the known dilaton supergravity superfield
theories presented a long time ago by Park and Strominger. Therefore, the
unique advantages of the gPSM approach can be exploited for the latter: We are
able to provide the first complete classical solution for any such theory. On
the other hand, the straightforward superfield formulation of the point
particle in a supergravity background can be translated back into the gPSM
frame, where "supergeodesics" can be discussed in terms of a minimal set of
supergravity field degrees of freedom. Further possible applications like the
(almost) trivial quantization are mentioned.Comment: 48 pages, 1 figure. v3: after final version, typos correcte
Non-perturbative quenched propagator beyond the infrared approximation
A new approach to the quenched propagator in QED beyond the IR limit is
proposed. The method is based on evolution equations in the proper time.Comment: 13 pages, 1 figure; Misprint on reference correcte
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