73 research outputs found
Screening Stringy Horizons
It has been argued recently that string theory effects qualitatively modify
the effective black hole geometry experienced by modes with radial momentum of
order . At tree level, these -effects can be
explicitly worked out in two-dimensional string theory, and have a natural
explanation in the T-dual description as coming from the integration of the
zero-mode of the linear dilaton, what yields a contribution that affects the
scattering phase-shift in a peculiar manner. It has also been argued that the
phase-shift modification has its origin in a region of the moduli space that
does not belong to the exterior black hole geometry, leading to the conclusion
that at high energy the physics of the problem is better described by the dual
model. Here, we elaborate on this argument. We consider the contribution of
worldsheet instantons in the 2D Euclidean black hole sigma-model and study its
influence on the phase-shift at high energy.Comment: 14 page
Timelike duality, -theory and an exotic form of the Englert solution
Through timelike dualities, one can generate exotic versions of -theory
with different spacetime signatures. These are the -theory with signature
, the -theory, with signature and the theories with
reversed signatures , and . In ,
is the number of space directions, the number of time directions, and
refers to the sign of the kinetic term of the form.
The only irreducible pseudo-riemannian manifolds admitting absolute
parallelism are, besides Lie groups, the seven-sphere
and its pseudo-riemannian version . [There is
also the complexification , but it is of
dimension too high for our considerations.] The seven-sphere has been found to play an important role in -dimensional
supergravity, both through the Freund-Rubin solution and the Englert solution
that uses its remarkable parallelizability to turn on non trivial internal
fluxes. The spacetime manifold is in both cases . We show
that enjoys a similar role in -theory and construct the exotic
form of the Englert solution, with non zero internal
fluxes turned on. There is no analogous solution in -theory.Comment: 18 pages, v2: typos fixe
Conformal field theories from deformations of theories with symmetry
We construct a set of non-rational conformal field theories that consist of
deformations of Toda field theory for sl(n). Besides conformal invariance, the
theories still enjoy a remnant infinite-dimensional affine symmetry. The case
n=3 is used to illustrate this phenomenon, together with further deformations
that yield enhanced Kac-Moody symmetry algebras. For generic n we compute
N-point correlation functions on the Riemann sphere and show that these can be
expressed in terms of sl(n) Toda field theory correlation functions.Comment: 27 pages. Typos corrected. Discussion adde
Einstein-Cartan gravitational collapse of a homogeneous Weyssenhoff fluid
We consider the gravitational collapse of a spherically symmetric homogeneous
matter distribution consisting of a Weyssenhoff fluid in the presence of a
negative cosmological constant. Our aim is to investigate the effects of
torsion and spin averaged terms on the final outcome of the collapse. For a
specific interior spacetime setup, namely the homogeneous and isotropic FLRW
metric, we obtain two classes of solutions to the field equations where
depending on the relation between spin source parameters, the collapse
procedure culminates in a spacetime singularity or it is replaced by a
non-singular bounce. We show that, under certain conditions, for a specific
subset of the former solutions, the formation of trapped surfaces is prevented
and thus the resulted singularity could be naked. The curvature singularity
that forms could be gravitationally strong in the sense of Tipler. Our
numerical analysis for the latter solutions shows that the collapsing dynamical
process experiences four phases, so that two of which occur at the pre-bounce
and the other two at post-bounce regimes. We further observe that there can be
found a minimum radius for the apparent horizon curve, such that the main
outcome of which is that there exists an upper bound for the size of the
collapsing body, below which no horizon forms throughout the whole scenario.Comment: 23 pages, 11 figure
Duality and higher Buscher rules in p-form gauge theory and linearized gravity
We perform an in-depth analysis of the transformation rules under duality for
couplings of theories containing multiple scalars, -form gauge fields,
linearized gravitons or mixed symmetry tensors. Following a similar
reasoning to the derivation of the Buscher rules for string background fields
under T-duality, we show that the couplings for all classes of aforementioned
multi-field theories transform according to one of two sets of duality rules.
These sets comprise the ordinary Buscher rules and their higher counterpart;
this is a generic feature of multi-field theories in spacetime dimensions where
the field strength and its dual are of the same degree. Our analysis takes into
account topological theta terms and generalized -fields, whose behavior
under duality is carefully tracked. For a 1-form or a graviton in 4D, this
reduces to the inversion of the complexified coupling or generalized metric
under electric/magnetic duality. Moreover, we write down an action for
linearized gravity in the presence of -term from which we obtain
previously suggested on-shell duality and double duality relations. This also
provides an explanation for the origin of theta in the gravitational duality
relations as a specific additional sector of the linearized gravity action.Comment: 34 page
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