262 research outputs found
Evolving wormhole geometries within nonlinear electrodynamics
In this work, we explore the possibility of evolving (2+1) and
(3+1)-dimensional wormhole spacetimes, conformally related to the respective
static geometries, within the context of nonlinear electrodynamics. For the
(3+1)-dimensional spacetime, it is found that the Einstein field equation
imposes a contracting wormhole solution and the obedience of the weak energy
condition. Nevertheless, in the presence of an electric field, the latter
presents a singularity at the throat, however, for a pure magnetic field the
solution is regular. For the (2+1)-dimensional case, it is also found that the
physical fields are singular at the throat. Thus, taking into account the
principle of finiteness, which states that a satisfactory theory should avoid
physical quantities becoming infinite, one may rule out evolving
(3+1)-dimensional wormhole solutions, in the presence of an electric field, and
the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2:
minor corrections, including a referenc
Traversable wormholes coupled to nonlinear electrodynamics
In this work we explore the possible existence of static, spherically
symmetric and stationary, axisymmetric traversable wormholes coupled to
nonlinear electrodynamics. Considering static and spherically symmetric (2+1)
and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event
horizon and the non-violation of the null energy condition at the throat. For
the former spacetime, the principle of finiteness is imposed, in order to
obtain regular physical fields at the throat. Next, we analyze the
(2+1)-dimensional stationary and axisymmetric wormhole, and also verify the
presence of an event horizon, rendering the geometry non-traversable.
Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole
geometry, we find that the field equations impose specific conditions that are
incompatible with the properties of wormholes. Thus, we prove the non-existence
of the general class of traversable wormhole solutions, outlined above, within
the context of nonlinear electrodynamics.Comment: 9 pages, Revtex4. V2: major change in title; considerable additions
in the Introduction and in the rotating solution, no physics changes;
correction of a reference, one reference added; now 10 pages. This version to
appear in Classical and Quantum Gravit
Chiral SU(3) Bethe Salpeter Model: Extension to SU(6) and SU(8) Spin-Flavor Symmetries
Consistent SU(6) and SU(8) spin-flavor extensions of the SU(3) flavor
Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian are constructed, which
incorporate vector meson degrees of freedom. In the charmless sector, the
on-shell approximation to the Bethe-Salpeter (BS) approach successfully
reproduces previous SU(3) WT results for the lowest-lying s--wave negative
parity baryon resonances. It also provides some information on the dynamics of
heavier ones and of the lightest d-wave negative parity resonances, as e.g. the
Lambda(1520). For charmed baryons the scheme is consistent with heavy quark
symmetry, and our preliminary results in the strangeness-less charm C=+1 sector
describe the main features of the three-star J^P=1/2^- Lambda_c(2595) and
J^P=3/2^- Lambda_c(2625) resonances. We also find a second broad J^P=1/2^-
state close to the Lambda_c(2595)Comment: Presented at Chiral07: Chiral Symmetry in Hadron and Nuclear Physics
November 13-16, 2007, Osaka University, Japa
Inflation-Produced Magnetic Fields in Nonlinear Electrodynamics
We study the generation of primeval magnetic fields during inflation era in
nonlinear theories of electrodynamics. Although the intensity of the produced
fields strongly depends on characteristics of inflation and on the form of
electromagnetic Lagrangian, our results do not exclude the possibility that
these fields could be astrophysically interesting.Comment: 6 page
Charmed baryon resonances with heavy-quark symmetry
We study charmed baryon resonances that are generated dynamically from a
coupled-channel unitary approach that implements heavy-quark symmetry. Some
states can already be identified with experimental observations, such as
, , or ,
while others need a compilation of more experimental data as well as an
extension of the model to include higher order contributions. We also compare
our model to previous SU(4) schemes.Comment: 4 pages, to appear in the proceedings of the Workshop on the Physics
of Excited Nucleon (NSTAR2009), Beijing, April 19-22, 200
The Semileptonic to Decays in QCD Sum Rules
We analyze the semileptonic rare decays of meson to and
axial vector mesons. The
decays are significant flavor changing neutral current decays of the meson.
These decays are sensitive to the new physics beyond SM, since these processes
are forbidden at tree level at SM. These decays occurring at the quark level
via transition, also provide new opportunities for
calculating the CKM matrix elements and . In this study, the
transition form factors of the decays
are calculated using three-point QCD sum rules approach. The resulting form
factors are used to estimate the branching fractions of these decays.Comment: 18 pages, 7 figures, version to appear in JP
Rotating Black Branes in the presence of nonlinear electromagnetic field
In this paper, we consider a class of gravity whose action represents itself
as a sum of the usual Einstein-Hilbert action with cosmological constant and an
gauge field for which the action is given by a power of the Maxwell
invariant. We present a class of the rotating black branes with Ricci flat
horizon and show that the presented solutions may be interpreted as black brane
solutions with two event horizons, extreme black hole and naked singularity
provided the parameters of the solutions are chosen suitably. We investigate
the properties of the solutions and find that for the special values of the
nonlinear parameter, the solutions are not asymptotically anti-deSitter. At
last, we obtain the conserved quantities of the rotating black branes and find
that the nonlinear source effects on the electric field, the behavior of
spacetime, type of singularity and other quantities.Comment: 7 pages, 5 figures, to appear in EPJ
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