34 research outputs found
Nonabelian D-branes and Noncommutative Geometry
We discuss the nonabelian world-volume action which governs the dynamics of N
coincident Dp-branes. In this theory, the branes' transverse displacements are
described by matrix-valued scalar fields, and so this is a natural physical
framework for the appearance of noncommutative geometry. One example is the
dielectric effect by which Dp-branes may be polarized into a noncommutative
geometry by external fields. Another example is the appearance of
noncommutative geometries in the description of intersecting D-branes of
differing dimensions, such as D-strings ending on a D3- or D5-brane. We also
describe the related physics of giant gravitons.Comment: 21 pages, Latex, ref. adde
A Novel Long Range Spin Chain and Planar N=4 Super Yang-Mills
We probe the long-range spin chain approach to planar N=4 gauge theory at
high loop order. A recently employed hyperbolic spin chain invented by
Inozemtsev is suitable for the SU(2) subsector of the state space up to three
loops, but ceases to exhibit the conjectured thermodynamic scaling properties
at higher orders. We indicate how this may be bypassed while nevertheless
preserving integrability, and suggest the corresponding all-loop asymptotic
Bethe ansatz. We also propose the local part of the all-loop gauge transfer
matrix, leading to conjectures for the asymptotically exact formulae for all
local commuting charges. The ansatz is finally shown to be related to a
standard inhomogeneous spin chain. A comparison of our ansatz to semi-classical
string theory uncovers a detailed, non-perturbative agreement between the
corresponding expressions for the infinite tower of local charge densities.
However, the respective Bethe equations differ slightly, and we end by refining
and elaborating a previously proposed possible explanation for this
disagreement.Comment: 48 pages, 1 figure. v2, further results added: discussion of the
relationship to an inhomogeneous spin chain, normalization in sec 3 unified,
v3: minor mistakes corrected, published versio
Thermal Partition Functions for S-branes
We calculate the thermal partition functions of open strings on the S-brane
backgrounds (the bouncing or rolling tachyon backgrounds) both in the bosonic
and superstring cases. According to hep-th/0302146, we consider the discretized
temperatures compatible with the pure imaginary periodicity of tachyon
profiles. The ``effective Hagedorn divergence'' is shown to appear no matter
how low temperature is chosen (including zero-temperature). This feature is
likely to be consistent with the large rate of open string pair production
discussed in hep-th/0209090 and also emission of closed string massive modes
hep-th/0303139. We also discuss the possibility to remove the divergence by
considering the space-like linear dilaton backgrounds as in hep-th/0306132.Comment: 33 pages, no figure; v2 typos corrected, a reference adde
Meson Spectroscopy in AdS/CFT with Flavour
We compute the meson spectrum of an N=2 super Yang-Mills theory with
fundamental matter from its dual string theory on AdS_5 x S_5 with a D7-brane
probe. For scalar and vector mesons with arbitrary R-charge the spectrum is
computed in closed form by solving the equations for D7-brane fluctuations; for
matter with non-zero mass m_q it is discrete, exhibits a mass gap of order m_q
/ sqrt(g_s N) and furnishes representations of SO(5) even though the manifest
global symmetry of the theory is only SO(4). The spectrum of mesons with large
spin J is obtained from semiclassical, rotating open strings attached to the
D7-brane. It displays Regge-like behaviour for J << sqrt(g_s N), whereas for J
>> sqrt(g_s N) it corresponds to that of two non-relativistic quarks bound by a
Coulomb potential. Meson interactions, baryons and `giant gauge bosons' are
briefly discussed.Comment: LaTeX, 39 pages, 4 figures, uses epsf. v2: typos corrected.
references adde
Fuzzy Sphere Dynamics and Non-Abelian DBI in Curved Backgrounds
We consider the non-Abelian action for the dynamics of -branes in the
background of -branes, which parameterises a fuzzy sphere using the SU(2)
algebra. We find that the curved background leads to collapsing solutions for
the fuzzy sphere except when we have branes in the background, which
is a realisation of the gravitational Myers effect. Furthermore we find the
equations of motion in the Abelian and non-Abelian theories are identical in
the large limit. By picking a specific ansatz we find that we can
incorporate angular momentum into the action, although this imposes restriction
upon the dimensionality of the background solutions. We also consider the case
of non-Abelian non-BPS branes, and examine the resultant dynamics using
world-volume symmetry transformations. We find that the fuzzy sphere always
collapses but the solutions are sensitive to the combination of the two
conserved charges and we can find expanding solutions with turning points. We
go on to consider the coincident 5-brane background, and again construct
the non-Abelian theory for both BPS and non-BPS branes. In the latter case we
must use symmetry arguments to find additional conserved charges on the
world-volumes to solve the equations of motion. We find that in the Non-BPS
case there is a turning solution for specific regions of the tachyon and radion
fields. Finally we investigate the more general dynamics of fuzzy
in the -brane background, and find collapsing solutions
in all cases.Comment: 49 pages, 3 figures, Latex; Version to appear in JHE
Comments on Half S-Branes
Following hep-th/0305177, we write the boundary state of half S-brane in
bosonic string theory as a grand canonical partition function of a unitary
matrix model. From this representation, it follows that the annulus amplitude
can be written as a grand canonical partition function of a unitary two-matrix
model. We also show that the contribution of the exponentially growing
couplings to the timelike oscillators can be resummed in a certain annulus
amplitude.Comment: 27 pages, lanlmac; v2: reference adde
The Self-dual String Soliton in AdS_4\times S^7 spacetime
We construct self-dual string soliton solutions in spacetime, starting from the covariant equations of motion of M5-brane.
We study the properties of the solutions and find that their action are
linearized, indicating the BPS nature of the solutions, and they have the same
electric and magnetic charge. The straight string soliton solution represents
the configuration of the membranes ending on M5-brane with a straight string
intersection, and it behaves like the spiky solution in flat spacetime. The
spherical string soliton solution, which could be related to the straight one
by a conformal transformation, represents the membranes ending on M5-brane with
a spherical intersection.Comment: 15 pages;typos corrected, references added;published versio
Non-commutative Branes from M-theory
The analysis of the worldvolume effective actions of the M-theory
Kaluza-Klein monopole and 9-brane suggests that it should be possible to
describe non-abelian configurations of M2-branes or M5-branes if the M2-branes
are transverse to the eleventh direction and the M5-branes are wrapped on it.
This is determined by the fact that the Kaluza-Klein monopole and the M9-brane
are constrained to move in particular isometric spacetimes. We show that the
same kind of situation is implied by the analysis of the brane descent
relations in M-theory. We compute some of the non-commutative couplings of the
worldvolume effective actions of these non-abelian systems of M2 and M5 branes
and show that they indicate the existence of configurations corresponding to N
branes expanding into a higher dimensional M-brane. The reduction to Type II
brings up new descriptions of coincident D-branes at strong coupling. We show
that these systems have the right non-commutative charges to describe certain
expanded configurations playing a role in the framework of the AdS/CFT
correspondence. Finally, we discuss the realization of non-commutative brane
configurations as topological solitons in non-abelian brane-antibrane systems.Comment: 31 pages, latex file, references adde