1,017 research outputs found
On Black-Brane Instability In an Arbitrary Dimension
The black-hole black-string system is known to exhibit critical dimensions
and therefore it is interesting to vary the spacetime dimension , treating
it as a parameter of the system. We derive the large asymptotics of the
critical, i.e. marginally stable, string following an earlier numerical
analysis. For a background with an arbitrary compactification manifold we give
an expression for the critical mass of a corresponding black brane. This
expression is completely explicit for , the dimensional torus of
an arbitrary shape. An indication is given that by employing a higher
dimensional torus, rather than a single compact dimension, the total critical
dimension above which the nature of the black-brane black-hole phase transition
changes from sudden to smooth could be as low as .Comment: 1+14 pages, 2 eps figures. Replaced with the published versio
Classical Effective Field Theory for Weak Ultra Relativistic Scattering
Inspired by the problem of Planckian scattering we describe a classical
effective field theory for weak ultra relativistic scattering in which field
propagation is instantaneous and transverse and the particles' equations of
motion localize to the instant of passing. An analogy with the non-relativistic
(post-Newtonian) approximation is stressed. The small parameter is identified
and power counting rules are established. The theory is applied to reproduce
the leading scattering angle for either a scalar interaction field or
electro-magnetic or gravitational; to compute some subleading corrections,
including the interaction duration; and to allow for non-zero masses. For the
gravitational case we present an appropriate decomposition of the gravitational
field onto the transverse plane together with its whole non-linear action. On
the way we touch upon the relation with the eikonal approximation, some
evidence for censorship of quantum gravity, and an algebraic ring structure on
2d Minkowski spacetime.Comment: 29 pages, 2 figures. v4: Duration of interaction is determined in Sec
4 and detailed in App C. Version accepted for publication in JHE
Topology change in General Relativity and the black-hole black-string transition
In the presence of compact dimensions massive solutions of General Relativity
may take one of several forms including the black-hole and the black-string,
the simplest relevant background being R^{3+1} * S^1. It is shown how Morse
theory places constraints on the qualitative features of the phase diagram, and
a minimalistic diagram is suggested which describes a first order transition
whose only stable phases are the uniform string and the black-hole. The diagram
calls for a topology changing ``merger'' transition in which the black-hole
evolves continuously into an unstable black-string phase. As evidence a local
model for the transition is presented in which the cone over S^2 * S^2 plays a
central role. Horizon cusps do not appear as precursors to black hole merger. A
generalization to higher dimensions finds that whereas the cone has a tachyon
function for d=5, its stability depends interestingly on the dimension - it is
unstable for d10.Comment: 28 pages, 13 figures, v2: minor changes, v3: published version. See
"Note added" at end of introductio
Holographic repulsion and confinement in gauge theory
We show that for asymptotically anti-deSitter backgrounds with negative
energy, such as the AdS soliton and regulated negative mass AdS-Schwarzshild
metrics, the Wilson loop expectation value in the AdS/CFT conjecture exhibits a
Coulomb to confinement transition. We also show that the quark-antiquark () potential can be interpreted as affine time along null geodesics on
the minimal string world sheet,and that its intrinsic curvature provides a
signature of transition to confinement phase. The result demonstrates a UV/IR
relation in that the boundary separation of the pair exhibits an
inverse relationship with the radial descent of the world sheet into the bulk.
Our results suggest a generic (holographic) relationship between confinement in
gauge theory and repulsive gravity, which in turn is connected with singularity
avoidance in quantum gravity.Comment: 8 pages, 4 figure
Hall effect and geometric phases in Josephson junction arrays
Since effectively the local contact vortex velocity dependent part of the Magnus force in a Josephson junction array is zero in the classical limit, we predict zero classical Hall effect. In the quantum limit because of the geometric phases due to the finite superfluid density at superconductor grains, rich and complex Hall effect is found in this quantum regime due to the Thouless-Kohmoto-Nightingale-den-Nijs effect
From Black Strings to Black Holes
Using recently developed numerical methods, we examine neutral compactified
non-uniform black strings which connect to the Gregory-Laflamme critical point.
By studying the geometry of the horizon we give evidence that this branch of
solutions may connect to the black hole solutions, as conjectured by Kol. We
find the geometry of the topology changing solution is likely to be nakedly
singular at the point where the horizon radius is zero. We show that these
solutions can all be expressed in the coordinate system discussed by Harmark
and Obers.Comment: 6 pages, 5 figures, RevTe
Synthesis, in vitro antioxidant and antimicrobial activities of some novel 3-substitued-4-(3-methoxy-4-isobutyryloxybenzylideneamino)-4,5-dihydro- 1H-1,2,4-triazol-5-one derivatives
271-282In this study, 3-alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones have been reacted with 3-methoxy-4-isobutyryloxybenzaldehyde 2 to afford the corresponding nine new 3-alkyl(aryl)-4-(3-methoxy-4-isobutyryloxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 3. Then, the acetylation reactions of compounds 3 have been investigated and 4 type compounds have been obtained. The compounds 3 have also been treated with morpholine/1-methylpiperazine in the presence of formaldehyde according to the Mannich reaction to synthesize 1-(morpholine-4-yl-methyl)-3-alkyl(aryl)-4-(3-methoxy-4-isobutyryloxy-benzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 5, and 1-(1-methylpiperazin-4-yl-methyl)-3-alkyl(aryl)-4-(3-methoxy-4-isobutyryloxybenzylideneamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 6, respectively. The structures of twenty four new compounds have been characterized by IR, 1H and 13C NMR and MS spectroscopic methods. In addition, the newly synthesized compounds have been screened for their antimicrobial activities. Furthermore, these twenty four new compounds have been analyzed for their in vitro potential antioxidant activities by three different methods
Diffusion limited aggregation as a Markovian process: site-sticking conditions
Cylindrical lattice diffusion limited aggregation (DLA), with a narrow width
N, is solved for site-sticking conditions using a Markovian matrix method
(which was previously developed for the bond-sticking case). This matrix
contains the probabilities that the front moves from one configuration to
another at each growth step, calculated exactly by solving the Laplace equation
and using the proper normalization. The method is applied for a series of
approximations, which include only a finite number of rows near the front. The
fractal dimensionality of the aggregate is extrapolated to a value near 1.68.Comment: 27 Revtex pages, 16 figure
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