688 research outputs found
Dynamics of Extreme Black Holes and Massive String States
In a recent paper, Duff and Rahmfeld argued that certain massive
states of the four-dimensional heterotic string correspond to extreme black
hole solutions. We provide further, dynamical, evidence for this identification
by comparing the scattering of these elementary string states with that of the
corresponding extreme black holes, in the limit of low velocities.Comment: 18 pages, harvma
On the Bartnik extension problem for the static vacuum Einstein equations
We develop a framework for understanding the existence of asymptotically flat
solutions to the static vacuum Einstein equations with prescribed boundary data
consisting of the induced metric and mean curvature on a 2-sphere. A partial
existence result is obtained, giving a partial resolution of a conjecture of
Bartnik on such static vacuum extensions. The existence and uniqueness of such
extensions is closely related to Bartnik's definition of quasi-local mass.Comment: 33 pages, 1 figure. Minor revision of v2. Final version, to appear in
Class. Quantum Gravit
More on Four-Dimensional Extremal Black Holes
We consider an embedding of the extremal four-dimensional
Reissner-Nordstr\"om black hole into type string theory. The equivalent
type configuration, in the D-brane weak-coupling picture, is a bound
state of D1- and D5-branes threaded by fundamental type strings. The
bound state involves also a NSNS solitonic 5-brane, mimicking the role of the
Kaluza-Klein magnetic monopole. The statistical entropy derived by counting the
degeneracy of the BPS-saturated excitations of this bound state agrees
perfectly with the (semiclassical) Bekenstein-Hawking formula.Comment: 19 pages, using Latex, no figure
Monopoles and Instantons in String Theory
In recent work, several classes of solitonic solutions of string theory with
higher-membrane structure have been obtained. These solutions can be classified
according to the symmetry possessed by the solitons in the subspace of the
spacetime transverse to the membrane. Solitons with four-dimensional spherical
symmetry represent instanton solutions in string theory, while those with
three-dimensional spherical symmetry represent magnetic monopole-type
solutions. For both of these classes, we discuss bosonic as well as heterotic
solutions.Comment: 16 page
Some Remarks on Effective Range Formula in Potential Scattering
In this paper, we present different proofs of very recent results on the
necessary as well as sufficient conditions on the decrease of the potential at
infinity for the validity of effective range formulas in 3-D in low energy
potential scattering (Andr\'e Martin, private communication, to appear. See
Theorem 1 below). Our proofs are based on compact formulas for the
phase-shifts. The sufficiency conditions are well-known since long. But the
necessity of the same conditions for potentials keeping a constant sign at
large distances are new. All these conditions are established here for
dimension 3 and for all angular momenta
Curcumin induces apoptosis of upper aerodigestive tract cancer cells by targeting multiple pathways
Curcumin, a natural compound isolated from the Indian spice Haldi or curry powder , has been used for centuries as a traditional remedy for many ailments. Recently, the potential use of curcumin in cancer prevention and therapy urges studies to uncover the molecular mechanisms associated with its anti-tumor effects. In the current manuscript, we investigated the mechanism of curcumin-induced apoptosis in upper aerodigestive tract cancer cell lines and showed that curcumin-induced apoptosis is mediated by the modulation of multiple pathways such as induction of p73, and inhibition of p-AKT and Bcl-2. Treatment of cells with curcumin induced both p53 and the related protein p73 in head and neck and lung cancer cell lines. Inactivation of p73 by dominant negative p73 significantly protected cells from curcumin-induced apoptosis, whereas ablation of p53 by shRNA had no effect. Curcumin treatment also strongly inhibited p-AKT and Bcl-2 and overexpression of constitutively active AKT or Bcl-2 significantly inhibited curcumin-induced apoptosis. Taken together, our findings suggest that curcumin-induced apoptosis is mediated via activating tumor suppressor p73 and inhibiting p-AKT and Bcl-2
Total Widths And Slopes From Complex Regge Trajectories
Maximally complex Regge trajectories are introduced for which both Re
and Im grow as ( small and
positive). Our expression reduces to the standard real linear form as the
imaginary part (proportional to ) goes to zero. A scaling formula for
the total widths emerges: constant for large M, in very
good agreement with data for mesons and baryons. The unitarity corrections also
enhance the space-like slopes from their time-like values, thereby resolving an
old problem with the trajectory in charge exchange. Finally, the
unitarily enhanced intercept, , \nolinebreak is in
good accord with the Donnachie-Landshoff total cross section analysis.Comment: 9 pages, 3 Figure
Nucleation of -Branes and Fundamental Strings
We construct a solution to the low-energy string equations of motion in five
dimensions that describes a circular loop of fundamental string exponentially
expanding in a background electric -field. Euclideanising this gives an
instanton for the creation of a loop of fundamental string in a background
-field, and we calculate the rate of nucleation. Solutions describing
magnetically charged strings and -branes, where the gauge field comes from
Kaluza-Klein reduction on a circle, are also constructed. It is known that a
magnetic flux tube in four (reduced) spacetime dimensions is unstable to the
pair creation of Kaluza-Klein monopoles. We show that in dimensions,
magnetic ``fluxbranes" are unstable to the nucleation of a magnetically
charged spherical -brane. In ten dimensions the instanton describes the
nucleation of a Ramond-Ramond magnetically charged six-brane in type IIA string
theory. We also find static solutions describing spherical charged -branes
or fundamental strings held in unstable equilibrium in appropriate background
fields. Instabilities of intersecting magnetic fluxbranes are also discussed.Comment: 28 pages, harvmac (b), reference added, typos correcte
A compactness theorem for scalar-flat metrics on manifolds with boundary
Let (M,g) be a compact Riemannian manifold with boundary. This paper is
concerned with the set of scalar-flat metrics which are in the conformal class
of g and have the boundary as a constant mean curvature hypersurface. We prove
that this set is compact for dimensions greater than or equal to 7 under the
generic condition that the trace-free 2nd fundamental form of the boundary is
nonzero everywhere.Comment: 49 pages. Final version, to appear in Calc. Var. Partial Differential
Equation
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