1,144 research outputs found
Primordial magnetic field and spectral distortion of cosmic background radiation
The role played by a primordial magnetic field during the pre-recombination
epoch is analysed through the cyclotron radiation (due to the free electrons)
it might produce in the primordial plasma. We discuss the constraint implied by
the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy
The polarization of F1 strings into D2 branes: "Aut Caesar aut nihil"
We give matrix and supergravity descriptions of type IIA F-strings polarizing
into cylindrical D2 branes. When a RR four-form field strength F_4 is turned on
in a supersymmetric fashion (with 4 supercharges), a complete analysis of the
solutions reveals the existence of a moduli space of F1 -> D2 polarizations
(Caesar) for some fractional strengths of the perturbation, and of no
polarization whatsoever (nihil) for all other strengths of the perturbation.
This is a very intriguing phenomenon, whose physical implications we can only
speculate about. In the matrix description of the polarization we use the
Non-Abelian Born-Infeld action in an extreme regime, where the commutators of
the fields are much larger than 1. The validity of the results we obtain,
provides a direct confirmation of this action, although is does not confirm or
disprove the symmetrized trace prescription.Comment: 14 page
Non-Abelian Giant Gravitons
We argue that the giant graviton configurations known from the literature
have a complementary, microscopical description in terms of multiple
gravitational waves undergoing a dielectric (or magnetic moment) effect. We
present a non-Abelian effective action for these gravitational waves with
dielectric couplings and show that stable dielectric solutions exist. These
solutions agree in the large limit with the giant graviton configurations
in the literature.Comment: 8 pages. Contribution to the proceedings of the RTN workshop in
Leuven, Belgium, September 200
Supertube domain-walls and elimination of closed time-like curves in string theory
We show that some novel physics of supertubes removes closed time-like curves
from many supersymmetric spaces which naively suffer from this problem. The
main claim is that supertubes naturally form domain-walls, so while analytical
continuation of the metric would lead to closed time-like curves, across the
domain-wall the metric is non-differentiable, and the closed time-like curves
are eliminated. In the examples we study the metric inside the domain-wall is
always of the G\"odel type, while outside the shell it looks like a localized
rotating object, often a rotating black hole. Thus this mechanism prevents the
appearance of closed time-like curves behind the horizons of certain rotating
black holes.Comment: 22 pages, JHEP3 class. V2: Some corrections and clariffications,
references added. V3: more corrections to formulas, results unchanged. V4:
minor typos, as published in PR
Quantizing three-spin string solution in AdS_5 x S^5
As was recently found in hep-th/0304255, there exists a simple
non-supersymmetric classical solution describing a closed string rotating in
S^5 and located at the center of AdS_5. It is parametrized by the angular
momentum J of the center of mass and two equal SO(6) angular momenta J' in the
two other orthogonal rotation planes. The dual N=4 SYM operators should be
scalar operators in SU(4) representations [0,J-J',2J'] or [J'-J,0,J'+J]. This
solution is stable if J' > 3/2 J and for large J + 2 J' its classical energy
admits an expansion in positive powers of g_eff = \lambda/(J + 2 J')^2: E= J +
2 J' + g_eff J' + ... . This suggests a possibility of a direct comparison with
perturbative SYM results for the corresponding anomalous dimensions in the
sector with g_eff << 1, by analogy with the BMN case. We conjecture that all
quantum sigma model string corrections are then subleading at large J', so that
the classical formula for the energy is effectively exact to all orders in
\lambda. It could then be interpolated to weak coupling, representing a
prediction for the anomalous dimensions on the SYM side. We test this
conjecture by computing the 1-loop superstring sigma model correction to the
classical energy.Comment: 25 pages, harvmac. v5: minor misprints in eqs
(2.6),(2.16),(2.20),(2.21) correcte
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
Kappa-symmetry for coincident D-branes
A kappa-symmetric action for coincident D-branes is presented. It is valid in
the approximation that the additional fermionic variables, used to incorporate
the non-abelian degrees of freedom, are treated classically. The action is
written as a Bernstein-Leites integral on the supermanifold obtained from the
bosonic worldvolume by adjoining the extra fermions. The integrand is a very
simple extension of the usual Green-Schwarz action for a single brane; all
symmetries, except for kappa, are manifest, and the proof of kappa-symmetry is
very similar to the abelian case.Comment: 18 pages. References 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
On Charged Black Holes in Anti-de Sitter Space
We study the region inside the event horizon of charged black holes in five
dimensional asymptotically anti-de Sitter space, using as a probe two-sided
correlators which are dominated by spacelike geodesics penetrating the horizon.
The spacetimes we investigate include the Reissner-Nordstrom black hole and
perturbations thereof. The perturbed spacetimes can be found exactly, enabling
us to perform a local scan of the region between the inner and outer horizons.
Surprisingly, the two-sided correlators we calculate seem to be geometrically
protected from the instability of the inner horizon.Comment: 1+37 pages, 20 ps and eps figures, LaTeX. References added and
changes made to section
Non-Abelian BIonic Brane Intersections
We study "fuzzy funnel" solutions to the non-Abelian equations of motion of
the D-string. Our funnel describes n^6/360 coincident D-strings ending on n^3/6
D7-branes, in terms of a fuzzy six-sphere which expands along the string. We
also provide a dual description of this configuration in terms of the world
volume theory of the D7-branes. Our work makes use of an interesting non-linear
higher dimensional generalization of the instanton equations.Comment: 17 pages uses harvmac; v2: small typos corrected, refs adde
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