498 research outputs found
Sealed containers in Z
Physical means of securing information, such as sealed envelopes and scratch cards, can be used to achieve cryptographic objectives. Reasoning about this has so far been informal.
We give a model of distinguishable sealed envelopes in Z, exploring design decisions and further analysis and development of such models
Bound States of D-Branes and the Non-Abelian Born-Infeld Action
We attempt to settle the issue as to what is the correct non-abelian
generalisation of the Born-Infeld action, via a consideration of the two-loop
--function for the non-abelian background gauge field in open string
theory. An analysis of the bosonic theory alone shows the recent proposal of
Tseytlin's to be somewhat lacking. For the superstring, however, this proposal
would seem to be correct, and not just within the approximation used in
\cite{tseytlin}. Since it is this latter case that is relevant to the
description of D-branes we, in effect, obtain an independent verification of
Tseytlin's result. Some issues involved in the concept of non-abelian
T--duality are discussed; and it is shown how the interaction between separated
and parallel branes, in the form of massive string states, emerges.Comment: 24 pages, 4 eps figures, LaTeX. Further comments concerning earlier
work added, minor typos corrected. Version to be published in Nucl. Phys.
On the existence of a static black hole on a brane
We study a static black hole localized on a brane in the Randall-Sundrum (RS)
II braneworld scenario. To solve this problem numerically, we develop a code
having the almost 4th-order accuracy. This code derives the highly accurate
result for the case where the brane tension is zero, i.e., the spherically
symmetric case. However, a nonsystematic error is detected in the cases where
the brane tension is nonzero. This error is irremovable by any systematic
methods such as increasing the resolution, setting the outer boundary at more
distant location, or improving the convergence of the numerical relaxation. We
discuss the possible origins for the nonsystematic error, and conclude that our
result is naturally interpreted as the evidence for the nonexistence of
solutions to this setup, although an "approximate" solution exists for
sufficiently small brane tension. We discuss the possibility that the black
holes produced on a brane may be unstable and lead to two interesting
consequences: the event horizon pinch and the brane pinch.Comment: 26 pages, 9 figures, submitted to JHE
Entropy of Anisotropic Universe and Fractional Branes
We obtain the entropy of a homogeneous anisotropic universe applicable, by
assumption, to the fractional branes in the universe in the model of Chowdhury
and Mathur. The entropy for the 3 or 4 charge fractional branes thus obtained
is not of the expected form E^{{3/2}} or E^2. One way the expected form is
realised is if p \to \rho for the transverse directions and if the compact
directions remain constant in size. These conditions are likely to be enforced
by brane decay and annihilation, and by the S, T, U dualities. T duality is
also likely to exclude high entropic cases, found in the examples, which arise
due to the compact space contracting to zero size. Then the 4 charge fractional
branes may indeed provide a detailed realisation of the maximum entropic
principle we proposed recently to determine the number (3 + 1) of large
spacetime dimensions.Comment: Version 2: 21 pages. More discussion and references added. To appear
in General Relativity and Gravitatio
High Spin Glueballs from the Lattice
We discuss the principles underlying higher spin glueball calculations on the
lattice. For that purpose, we develop numerical techniques to rotate Wilson
loops by arbitrary angles in lattice gauge theories close to the continuum. As
a first application, we compute the glueball spectrum of the SU(2) gauge theory
in 2+1 dimensions for both parities and for spins ranging from 0 up to 4
inclusive. We measure glueball angular wave functions directly, decomposing
them in Fourier modes and extrapolating the Fourier coefficients to the
continuum. This allows a reliable labelling of the continuum states and gives
insight into the way rotation symmetry is recovered. As one of our results, we
demonstrate that the D=2+1 SU(2) glueball conventionally labelled as J^P = 0^-
is in fact 4^- and that the lightest ``J=1'' state has, in fact, spin 3.Comment: Minor changes in the text; the spin 4 glueball mass is taken further
out in Euclidean time at higher beta values. 41 pages, 20 figure
Generalized Conformal Quantum Mechanics of D0-brane
We study the generalized conformal quantum mechanics of the probe D0-brane in
the near horizon background of the bound state of source D0-branes. We
elaborate on the relationship of such model to the M theory in the light cone
frame.Comment: 14 pages, RevTeX, revised version with added references to appear in
Phys. Rev.
g=1 for Dirichlet 0-branes
Dirichlet 0-branes, considered as extreme Type IIA black holes with spin
carried by fermionic hair, are shown to have the anomalous gyromagnetic ratio
g=1, consistent with their interpretation as Kaluza-Klein modes.Comment: 13 pages, Late
Massive IIA flux compactifications and U-dualities
We attempt to find a rigorous formulation for the massive type IIA
orientifold compactifications of string theory introduced in hep-th/0505160. An
approximate double T-duality converts this background into IIA string theory on
a twisted torus, but various arguments indicate that the back reaction of the
orientifold on this geometry is large. In particular, an AdS calculation of the
entropy suggests a scaling appropriate for N M2-branes, in a certain limit of
the compactification, though not the one studied in hep-th/0505160. The
M-theory lift of this specific regime is not 4 dimensional. We suggest that the
generic limit of the background corresponds to a situation analogous to
F-theory, where the string coupling is small in some regions of a compact
geometry, and large in others, so that neither a long wavelength 11D SUGRA
expansion, nor a world sheet expansion exists for these compactifications. We
end with a speculation on the nature of the generic compactification.Comment: JHEP3 LaTeX - 34 pages - 3 figures; v2: Added references; v3: mistake
in entropy scaling corrected, major changes in conclusions; v4: changed
claims about original DeWolfe et al. setup, JHEP versio
Open Heterotic Strings
We classify potential cosmic strings according to the topological charge
measurable outside the string core. We conjecture that in string theory it is
this charge that governs the stability of long strings. This would imply that
the SO(32) heterotic string can have endpoints, but not the E_8 x E_8 heterotic
string. We give various arguments in support of this conclusion.Comment: 15 pages. v.2: typos, references correcte
Supersymmetry without Supersymmetry
We present four-dimensional M-theory vacua with N>0 supersymmetry which, from
the perspective of perturbative Type IIA string theory, have N=0. Such vacua
can appear when the compactifying 7-manifold is a U(1) fibration. The missing
superpartners are Dirichlet 0-branes. Someone unable to detect Ramond-Ramond
charge would thus conclude that these worlds have no unbroken supersymmetry. In
particular, the gravitinos (and also some of the gauge bosons) are 0-branes not
seen in perturbation theory but which curiously remain massless however weak
the string coupling.Comment: Latex, 16 pages. Minor revisions and reference adde
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