1,046 research outputs found
Genuine Dyons in Born-Infeld Electrodynamics
Study of magnetic monopoles in the original version of Born-Infeld (BI)
electrodynamics is performed. It then is realized that interesting new physics
emerge and they include exotic behavior of radial electric monopole field such
as its regularity as and its changing behavior with the absence or
presence of the radial magnetic monopole field. This last point has been
interpreted as the manifestation of the existence of point-like dyons in
abelian BI theory. Two pieces of clear evidences in favor of this dyon
interpretation are provided. It is also demonstrated that despite these unique
features having no analogues in standard Maxwell theory, the cherished Dirac
quantisation condition remains unchanged. Lastly, comments are given concerning
that dyons found here in the original version of BI electrodynamics should be
distinguished from the ones with the same name or BIons being studied in the
recent literature on D-brane physics.Comment: 19 pages, Revtex, references added, no other change
Yang-Mills Instantons Sitting on a Ricci-flat Worldspace of Double D4-brane
Thus far, there seem to be no complete criteria that can settle the issue as
to what the correct generalization of the Dirac-Born-Infeld (DBI) action,
describing the low-energy dynamics of the D-branes, to the non-abelian case
would be. According to recent suggestions, one might pass the issue of
worldvolume solitons from abelian to non-abelian setting by considering the
stack of multiple, coincident D-branes and use it as a guideline to construct
or censor the relevant non-abelian version of the DBI action. In this spirit,
here we are interested in the explicit construction of SU(2) Yang-Mills (YM)
instanton solutions in the background geometry of two coincident probe D4-brane
worldspaces particularly when the metric of target spacetime in which the probe
branes are embedded is given by the Ricci-flat, magnetic extremal 4-brane
solution in type IIA supergravity theory with its worldspace metric being given
by that of Taub-NUT and Eguchi-Hanson solutions, the two best-known
gravitational instantons. And then we demonstrate that with this YM instanton-
gravitational instanton configuration on the probe D4-brane worldvolume, the
energy of the probe branes attains its minimum value and hence enjoys stable
state provided one employs the Tseytlin's non-abelian DBI action for the
description of multiple probe D-branes. In this way, we support the arguments
in the literature in favor of Tseytlin's proposal for the non-abelian DBI
action.Comment: 39 pages, Revtex, some more comments adde
An Exact String Theory Model of Closed Time-Like Curves and Cosmological Singularities
We study an exact model of string theory propagating in a space-time
containing regions with closed time-like curves (CTCs) separated from a finite
cosmological region bounded by a Big Bang and a Big Crunch. The model is an
non-trivial embedding of the Taub-NUT geometry into heterotic string theory
with a full conformal field theory (CFT) definition, discovered over a decade
ago as a heterotic coset model. Having a CFT definition makes this an excellent
laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and
the Milne/Misner-type chronology horizon which separates them. In an effort to
uncover the role of stringy corrections to such geometries, we calculate the
complete set of alpha' corrections to the geometry. We observe that the key
features of Taub-NUT persist in the exact theory, together with the emergence
of a region of space with Euclidean signature bounded by time-like curvature
singularities. Although such remarks are premature, their persistence in the
exact geometry is suggestive that string theory theory is able to make physical
sense of the Milne/Misner singularities and the CTCs, despite their
pathological character in General Relativity. This may also support the
possibility that CTCs may be viable in some physical situations, and may be a
natural ingredient in pre-Big-Bang cosmological scenarios.Comment: 37 pages, 4 figures. V2: discussion of computation of metric refined,
references adde
Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light
Hypothetical influences of variability of light velocity due to the
parameters of the source of radiation, for the results of spectral measurements
of stars to search for exoplanets are considered. Accounting accelerations of
stars relative to the barycenter of the star - a planet (the planets) was
carried out. The dependence of the velocity of light from the barycentric
radial velocity and barycentric radial acceleration component of the star
should lead to a substantial increase (up to degree of magnitude) semi-major
axes of orbits detected candidate to extrasolar planets. Consequently, the
correct comparison of the results of spectral method with results of other
well-known modern methods of detecting extrasolar planets can regard the
results obtained in this paper as a reliable test for testing the invariance of
the velocity of light.Comment: 11 pages, 5 figure
String theory and the Classical Stability of Plane Waves
The presence of fields with negative mass-squared typically leads to some
form of instability in standard field theories. The observation that, at least
in the light-cone gauge, strings propagating in plane wave spacetimes can have
worldsheet scalars with such tachyon-like masses suggests that the supergravity
background may itself be unstable. To address this issue, we perform a
perturbative analysis around the type IIB vacuum plane wave, the solution which
most obviously generates worldsheet scalars with negative mass-squared. We
argue that this background is perturbatively stable.Comment: 23 pages, no figures; v2: very minor changes, references added,
version accepted by PR
Non-BPS Dyons and Branes in the Dirac-Born-Infeld Theory
Non-BPS dyon solutions to D3-brane actions are constructed when one or more
scalar fields describing transverse fluctuations of the brane, are considered.
The picture emerging from such non-BPS configurations is analysed, in
particular the response of the D-brane-string system to small perturbations.Comment: 16 pages, 4 figures, Revtex fil
Dyons in Nonabelian Born-Infeld Theory
We analyze a nonabelian extension of Born--Infeld action for the SU(2) group.
In the class of spherically symmetric solutions we find that, besides the
Gal'tsov--Kerner glueballs, only the analytic dyons have finite energy. The
presented analytic and numerical investigation excludes the existence of pure
magnetic monopoles of 't Hooft--Polyakov type.Comment: 12 pages, 3 figure
Curved branes from string dualities
We describe a simple method for generating new string solutions for which the
brane worldvolume is a curved space. As a starting point we use solutions with
NS-NS charges combined with 2-d CFT's representing different parts of
space-time. We illustrate our method with many examples, some of which are
associated with conformally invariant sigma models. Using U-duality, we also
obtain supergravity solutions with RR charges which can be interpreted as
D-branes with non-trivial worldvolume geometry. In particular, we discuss the
case of a D5-brane wrapped on AdS_3 x S^3, a solution interpolating between
AdS_3 x S^3 x R^5 and AdS_3 x S^3 x S^3 x R, and a D3-brane wrapped over S^3 x
R or AdS_2 x S^2. Another class of solutions we discuss involves NS5-branes
intersecting over a 3-space and NS5-branes intersecting over a line. These
solutions are similar to D7-brane or cosmic string backgrounds.Comment: 21 pages, harvmac; misprint correcte
String Multiplets from an Invariant 2-Brane
We study a three-dimensional gauge theory obtained from the dimensional
reduction of a D4-brane worldvolume theory in the background of space-time
moduli. An SL(3) symmetry in this theory, which acts on fields as well as
coupling constants, is identified. By comparing the energies with the string
tensions, we show that certain 1/2 supersymmetric classical solutions of this
theory can be identified as SL(3,Z) multiplets of type II strings in eight
dimensions. Results are then generalized to the non-linear Born-Infeld action.
We also discuss the possibility of 1/8 BPS states in this theory and their
representations in terms of string networks.Comment: 17 pages, Latex, minor correction
Classical glueballs in non-Abelian Born-Infeld theory
It is shown that the Born-Infeld-type modification of the quadratic
Yang-Mills action suggested by the superstring theory gives rise to classical
particle-like solutions prohibited in the standard Yang-Mills theory. This
becomes possible due to the scale invariance breaking by the Born-Infeld
non-linearity. New classical glueballs are sphaleronic in nature and exhibit a
striking similarity with the Bartnik-McKinnon solutions of the Yang-Mills
theory coupled to gravity.Comment: Revtex, 4 pages, 2 eps figure
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