1,145 research outputs found
On de-Sitter geometry in crater statistics
The cumulative size-frequency distributions of impact craters on planetary
bodies in the solar system appear to approximate a universal inverse square
power-law for small crater radii. In this article, we show how this
distribution can be understood easily in terms of geometrical statistics, using
a de-Sitter geometry of the configuration space of circles on the Euclidean
plane and on the unit sphere. The effect of crater overlap is also considered.Comment: 6 pages, 2 figures, accepted by MNRAS. Version 2: title modified,
appendix added, some small change
Six-Dimensional Yang Black Holes in Dilaton Gravity
We study the six-dimensional dilaton gravity Yang black holes of
hep-th/0607193, which carry (1,-1) charge in SU(2)xSU(2) gauge group. We find
what values of the asymptotic parameters (mass and scalar charge) lead to a
regular horizon, and show that there are no regular solutions with an extremal
horizon.Comment: 10 pages, 8 EPS graph
Nature tourism and Irish film
This article provides a historical overview and reading of seminal Irish film from the perspective of nature tourism. Within Irish cultural studies, tourism is frequently equated with an overly romantic image of the island, which has been used to sell the country abroad. However, using notions like the tourist gaze and taking on board influential debates around space/place, one can posit a more progressive environmental vision of nature and landscape in our readings of film
Equilibrium Two-Dimensional Dilatonic Spacetimes
We study two-dimensional dilaton gravity coupled to massless scalar fields
for static solutions. In addition to the well known black hole, we find another
class of solutions that may be understood as that of the black hole in
equilibrium with a radiation bath. We claim that there is a solution that is
qualitatively unchanged after including Hawking radiation and back-reaction and
is furthermore geodesically complete. We compute the thermodynamics of these
spacetimes and their mass. We end with a brief discussion of the linear
response about these solutions, its significance to stability and noise and a
speculation regarding the endpoint of Hawking evaporation in four dimensions.
(plain TeX; one figure, available upon request.)Comment: 22 pages, M.I.T. preprint CTP#217
A Dilatonic Deformation of AdS_5 and its Field Theory Dual
We find a nonsupersymmetric dilatonic deformation of geometry as an
exact nonsingular solution of the type IIB supergravity. The dual gauge theory
has a different Yang-Mills coupling in each of the two halves of the boundary
spacetime divided by a codimension one defect. We discuss the geometry of our
solution in detail, emphasizing the structure of the boundary, and also study
the string configurations corresponding to Wilson loops. We also show that that
the background is stable under small scalar perturbations.Comment: 19 pages, 8 figures, v2 minor changes, added references, version to
appear in JHE
Testing Effective String Models of Black Holes with Fixed Scalars
We solve the problem of mixing between the fixed scalar and metric
fluctuations. First, we derive the decoupled fixed scalar equation for the
four-dimensional black hole with two different charges. We proceed to the
five-dimensional black hole with different electric (1-brane) and magnetic
(5-brane) charges, and derive two decoupled equations satisfied by appropriate
mixtures of the original fixed scalar fields. The resulting greybody factors
are proportional to those that follow from coupling to dimension (2,2)
operators on the effective string. In general, however, the string action also
contains couplings to chiral operators of dimension (1,3) and (3,1), which
cause disagreements with the semiclassical absorption cross-sections.
Implications of this for the effective string models are discussed.Comment: 13 pages, harvmac; minor typos correcte
On the uniqueness and global dynamics of AdS spacetimes
We study global aspects of complete, non-singular asymptotically locally AdS
spacetimes solving the vacuum Einstein equations whose conformal infinity is an
arbitrary globally stationary spacetime. It is proved that any such solution
which is asymptotically stationary to the past and future is itself globally
stationary.
This gives certain rigidity or uniqueness results for exact AdS and related
spacetimes.Comment: 18pp, significant revision of v
Spin Calogero Particles and Bispectral Solutions of the Matrix KP Hierarchy
Pairs of matrices whose commutator differ from the identity by a
matrix of rank are used to construct bispectral differential operators with
matrix coefficients satisfying the Lax equations of the Matrix KP
hierarchy. Moreover, the bispectral involution on these operators has dynamical
significance for the spin Calogero particles system whose phase space such
pairs represent. In the case , this reproduces well-known results of
Wilson and others from the 1990's relating (spinless) Calogero-Moser systems to
the bispectrality of (scalar) differential operators. This new class of pairs
of bispectral matrix differential operators is different than
those previously studied in that acts from the left, but from the
right on a common eigenmatrix.Comment: 16 page
Heterotic/type I duality, D-instantons and an N=2 AdS/CFT correspondence
D-instanton effects are studied for the IIB orientifold T^2/I\Omega(-1)^{F_L}
of Sen using type I/heterotic duality. An exact one loop threshold calculation
of t_8 \tr F^4 and t_8(\tr F^2)^2 terms for the heterotic string on T^2 with
Wilson lines breaking SO(32) to SO(8)^4 is related to D-instanton induced terms
in the worldvolume of D7 branes in the orientifold. Introducing D3 branes and
using the AdS/CFT correspondence in this case, these terms are used to
calculate Yang-Mills instanton contributions to four point functions of the
large N_c limit of N=2 USp(2N_c) SYM with four fundamental and one
antisymmetric tensor hypermultiplets.Comment: 25 pages, harvmac(b), one figure, v2: minor changes, version to
appear in PR
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