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 $AdS_5$ 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 $n\times n$ matrices whose commutator differ from the identity by a matrix of rank $r$ are used to construct bispectral differential operators with $r\times r$ 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 $r=1$, 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 $(L, \Lambda)$ of bispectral matrix differential operators is different than those previously studied in that $L$ acts from the left, but $\Lambda$ from the right on a common $r\times r$ 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