4,574 research outputs found
Topological Aspects of Gauge Fixing Yang-Mills Theory on S4
For an space-time manifold global aspects of gauge-fixing are
investigated using the relation to Topological Quantum Field Theory on the
gauge group. The partition function of this TQFT is shown to compute the
regularized Euler character of a suitably defined space of gauge
transformations. Topological properties of the space of solutions to a
covariant gauge conditon on the orbit of a particular instanton are found using
the isometry group of the base manifold. We obtain that the Euler
character of this space differs from that of an orbit in the topologically
trivial sector. This result implies that an orbit with Pontryagin number
\k=\pm1 in covariant gauges on contributes to physical correlation
functions with a different multiplicity factor due to the Gribov copies, than
an orbit in the trivial \k=0 sector. Similar topological arguments show that
there is no contribution from the topologically trivial sector to physical
correlation functions in gauges defined by a nondegenerate background
connection. We discuss possible physical implications of the global gauge
dependence of Yang-Mills theory.Comment: 13 pages, uuencoded and compressed LaTeX file, no figure
M-theory on a Time-dependent Plane-wave
We propose a matrix model on a homogeneous plane-wave background with 20
supersymmetries. This background is anti-Mach type and is equivalent to the
time-dependent background. We study supersymmetries in this theory and
calculate the superalgebra. The vacuum energy of the abelian part is also
calculated. In addition we find classical solutions such as graviton solution,
fuzzy sphere and hyperboloid.Comment: 19pages, no figures, LaTeX, JHEP3.cl
Uniqueness of M-theory PP-Wave Background with Extra Supersymmetries
We examine Killing spinor equations of the general eleven-dimensional pp-wave
backgrounds, which contain a scalar H(x^m,x^-) in the metric and a three-form
\xi(x^m,x^-) in the flux. Considering non-harmonic extra Killing spinors, we
show that if the backgrounds admit at least one extra Killing spinor in
addition to the standard 16 Killing spinors, they can be reduced to the form
with H=A_{mn}(x^-)x^mx^n and \xi(x^-) modulo coordinate transformations. We
further examine the cases in which the extra Killing spinor is characterized by
a set of Cartan matrices. The super-isometry algebras of the resulting
backgrounds are also derived.Comment: 25 pages, LaTeX2e, comments added, version to appear in PR
Topological 2-form Gravity in Four Dimensions
A kind of topological field theory is proposed as a candidate to describe the
global structure of the 2-form Einstein gravity with or without a cosmological
constant. Indeed in the former case, we show that a quantum state in the
candidate gives an exact solution of the Wheeler-DeWitt equation. The BRST
quantization based on the Batalin-Fradkin-Vilkovisky (BFV) formalism is carried
out for this topological version of the 2-form Einstein gravity.Comment: 15 page
Kaigorodov spaces and their Penrose limits
Kaigorodov spaces arise, after spherical compactification, as near horizon
limits of M2, M5, and D3-branes with a particular pp-wave propagating in a
world volume direction. We show that the uncompactified near horizon
configurations K\times S are solutions of D=11 or D=10 IIB supergravity which
correspond to perturbed versions of their AdS \times S analogues. We derive the
Penrose-Gueven limits of the Kaigorodov space and the total spaces and analyse
their symmetries. An Inonu-Wigner contraction of the Lie algebra is shown to
occur, although there is a symmetry enhancement. We compare the results to the
maximally supersymmetric CW spaces found as limits of AdS\times S spacetimes:
the initial gravitational perturbation on the brane and its near horizon
geometry remains after taking non-trivial Penrose limits, but seems to
decouple. One particuliar limit yields a time-dependent homogeneous plane-wave
background whose string theory is solvable, while in the other cases we find
inhomogeneous backgrounds.Comment: latex2e, 24 page
More on Penrose limits and non-local theories
We obtain the Penrose limit of six dimensional Non-Commutative Open String
(NCOS) theory and show that in the neighborhood of a particular null
geodesic it leads to an exactly solvable string theory (unlike their
counterparts in four or in other dimensions). We describe the phase structure
of this theory and discuss the Penrose limit in different phases including Open
D-string (OD1) theory. We compute the string spectrum and discuss their
relations with the states of various theories at different phases. We also
consider the case of general null geodesic for which the Penrose limit leads to
string theory in the time dependent pp-wave background and comment on the
renormalization group flow in the dual theory.Comment: latex, 22 pages, minor corrections, references added, published
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Power-law singularities in string theory and M-theory
We extend the definition of the Szekeres-Iyer power-law singularities to
supergravity, string and M-theory backgrounds, and find that are characterized
by Kasner type exponents. The near singularity geometries of brane and some
intersecting brane backgrounds are investigated and the exponents are computed.
The Penrose limits of some of these power-law singularities have profiles
for . We find the range of the
exponents for which and the frequency squares are bounded by 1/4. We
propose some qualitative tests for deciding whether a null or timelike
spacetime singularity can be resolved within string theory and M-theory based
on the near singularity geometry and its Penrose limits.Comment: 32 page
Graviton-Scalar Interaction in the PP-Wave Background
We compute the graviton two scalar off-shell interaction vertex at tree level
in Type IIB superstring theory on the pp-wave background using the light-cone
string field theory formalism. We then show that the tree level vertex vanishes
when all particles are on-shell and conservation of p_{+} and p_{-} are
imposed. We reinforce our claim by calculating the same vertex starting from
the corresponding SUGRA action expanded around the pp-wave background in the
light-cone gauge.Comment: 26 pages, harvmac One reference added. A few comments changed in the
introduction. The "cyclic perms." term removed from some equations as
unnecessary and equations (2.38) and (3.19) are corrected accordingl
Singularities and closed time-like curves in type IIB 1/2 BPS geometries
We study in detail the moduli space of solutions discovered in LLM relaxing
the constraint that guarantees the absence of singularities. The solutions fall
into three classes, non-singular, null-singular and time machines with a
time-like naked singularity. We study the general features of these metrics and
prove that there are actually just two generic classes of space-times - those
with null singularities are in the same class as the non-singular metrics.
AdS/CFT seems to provide a dual description only for the first of these two
types of space-time in terms of a unitary CFT indicating the possible existence
of a chronology protection mechanism for this class of geometries.Comment: 34 pages, 7 figures, LaTeX. References adde
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