33,992 research outputs found
Lagrangian analysis of `trivial' symmetries in models of gravity
We study the differences between Poincare and canonical hamiltonian
symmetries in models of gravity through the corresponding Noether identities
and show that they are equivalent modulo trivial gauge symmetries.Comment: 4 pages, LaTeX; Based on presentation at the conference "Relativity
and Gravitation: 100 Years after Einstein in Prague," held in Prague, June
201
Interpolating Action for Strings and Membranes - a Study of Symmetries in the Constrained Hamiltonian Approach
A master action for bosonic strings and membranes, interpolating between the
Nambu--Goto and Polyakov formalisms, is discussed. The role of the gauge
symmetries vis-\`{a}-vis reparametrization symmetries of the various actions is
analyzed by a constrained Hamiltonian approach. This analysis reveals the
difference between strings and higher branes, which is essentially tied to a
degree of freedom count. The cosmological term for membranes follows naturally
in this scheme. The conncetion of our aproach with the Arnowitt--Deser--Misner
representation in general relativity is illuminated.Comment: LaTex, 23 pages; discussion on ADM representation included and new
references adde
Self dual models and mass generation in planar field theory
We analyse in three space-time dimensions, the connection between abelian
self dual vector doublets and their counterparts containing both an explicit
mass and a topological mass. Their correspondence is established in the
lagrangian formalism using an operator approach as well as a path integral
approach. A canonical hamiltonian analysis is presented, which also shows the
equivalence with the lagrangian formalism. The implications of our results for
bosonisation in three dimensions are discussed.Comment: 15 pages,Revtex, No figures; several changes; revised version to
appear in Physical Review
Voros product, noncommutative inspired Reissner-Nordstr{\"o}m black hole and corrected area law
We emphasize the importance of the Voros product in defining a noncommutative
inspired Reissner-Nordstr\"{o}m black hole. The entropy of this black hole is
then computed in the tunneling approach and is shown to obey the area law at
the next to leading order in the noncommutative parameter .
Modifications to entropy/area law is then obtained by going beyond the
semi-classical approximation. The leading correction to the semiclassical
entropy/area law is found to be logarithmic and its coefficient involves the
noncommutative parameter .Comment: 12 pages Late
Charge-dependence of the coupling constant and charge-dependence of the NN interaction
The recent determination of the charged coupling constant,
, by the Uppsala Neutron Research Group implies that there may be
considerable charge-splitting of the pion coupling constant. We investigate the
consequences of this for the charge-independence breaking (CIB) of the
scattering length, . We find that depends
sensitively on the difference between and the neutral
coupling constant, . Moreover, if is only about 3%
larger than , then the established theoretical explanation of
(in terms of pion mass splitting) is completely wiped out.Comment: 9 pages, fbs styles, 1 figure; dedicated to Walter Gl\"ockle on the
occasion of his 60th birthda
Star formation in evolving molecular clouds
Molecular clouds are the principle stellar nurseries of our universe, keeping
them in the focus of both observational and theoretical studies. From
observations, some of the key properties of molecular clouds are well known but
many questions regarding their evolution and star formation activity remain
open. While numerical simulations feature a large number and complexity of
involved physical processes, this plenty of effects may hide the fundamentals
that determine the evolution of molecular clouds and enable the formation of
stars. Purely analytical models, on the other hand, tend to suffer from rough
approximations or a lack of completeness, limiting their predictive power. In
this paper, we present a model that incorporates central concepts of
astrophysics as well as reliable results from recent simulations of molecular
clouds and their evolutionary paths. Based on that, we construct a
self-consistent semi-analytical framework that describes the formation,
evolution and star formation activity of molecular clouds, including a number
of feedback effects to account for the complex processes inside those objects.
The final equation system is solved numerically but at much lower computational
expense than, e.g., hydrodynamical descriptions of comparable systems. The
model presented in this paper agrees well with a broad range of observational
results, showing that molecular cloud evolution can be understood as an
interplay between accretion, global collapse, star formation and stellar
feedback.Comment: 11 pages, 11 figures. Accepted for publication in A&
Hamiltonian vs Lagrangian Embedding of a Massive Spin-one Theory Involving 2-form Field
We consider the Hamiltonian and Lagrangian embedding of a first-order,
massive spin-one, gauge non-invariant theory involving anti-symmetric tensor
field. We apply the BFV-BRST generalised canonical approach to convert the
model to a first class system and construct nil-potent BFV-BRST charge and an
unitarising Hamiltonian. The canonical analysis of the St\"uckelberg
formulation of this model is presented. We bring out the contrasting feature in
the constraint structure, specifically with respect to the reducibility aspect,
of the Hamiltonian and the Lagrangian embedded model. We show that to obtain
manifestly covariant St\"uckelberg Lagrangian from the BFV embedded
Hamiltonian, phase space has to be further enlarged and show how the reducible
gauge structure emerges in the embedded model.Comment: Revtex, 13 pages, no figure, to appear in Int. J. Mod. Phys.
Noncommuting Electric Fields and Algebraic Consistency in Noncommutative Gauge theories
We show that noncommuting electric fields occur naturally in
-expanded noncommutative gauge theories. Using this noncommutativity,
which is field dependent, and a hamiltonian generalisation of the
Seiberg-Witten Map, the algebraic consistency in the lagrangian and hamiltonian
formulations of these theories, is established. A comparison of results in
different descriptions shows that this generalised map acts as canonical
transformation in the physical subspace only. Finally, we apply the hamiltonian
formulation to derive the gauge symmetries of the action.Comment: 16 pages, LaTex, considerably expanded version with a new section on
`Gauge symmetries'; To appear in Phys. Rev.
Second generation planet formation in NN Serpentis?
In this paper, we study the general impact of stellar mass-ejection events in
planetary orbits in post-common envelope binaries with circumbinary planets
like those around NN Serpentis. We discuss a set of simple equations that
determine upper and lower limits for orbital expansion and investigate the
effect of initial eccentricity. We deduce the range of possible semi-major axes
and initial eccentricity values of the planets prior to the common-envelope
event. In addition to spherically-symmetric mass-ejection events, we consider
planetary dynamics under the influence of an expanding disk. In order to have
survived, we suggest that the present planets in NN Ser must have had
semi-major axes AU and high eccentricity values which is
in conflict with current observations. Consequently, we argue that these
planets were not formed together with their hosting stellar system, but rather
originated from the fraction of matter of the envelope that remained bound to
the binary. According to the cooling age of the white dwarf primary of
yr, the planets around NN Ser might be the youngest known so far and open up a
wide range of further study of second generation planet formation.Comment: 4 pages, 2 figure
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