634 research outputs found
Distribution of Flux Vacua around Singular Points in Calabi-Yau Moduli Space
We study the distribution of type IIB flux vacua in the moduli space near
various singular loci, e.g. conifolds, ADE singularities on P1, Argyres-Douglas
point etc, using the Ashok- Douglas density det(R + omega). We find that the
vacuum density is integrable around each of them, irrespective of the type of
the singularities. We study in detail an explicit example of an Argyres-Douglas
point embedded in a compact Calabi-Yau manifold.Comment: 27 pages, 1 figure; v2: minor change, references added ; v3:
references added, published versio
Intersecting M-branes
We present the magnetic duals of G\"uven's electric-type solutions of D=11
supergravity preserving or of the D=11 supersymmetry. We interpret
the electric solutions as orthogonal intersecting membranes and the
magnetic solutions as orthogonal intersecting 5-branes, with ; these
cases obey the general rule that -branes can self-intersect on
-branes. On reduction to these solutions become electric or
magnetic dilaton black holes with dilaton coupling constant (for )
or (for ). We also discuss the reduction to D=10.Comment: Derivation of an intersection rule added. Some additional refs.
Version accepted for publication in PLB. Phyzzx macr
On the Taxonomy of Flux Vacua
We investigate several predictions about the properties of IIB flux vacua on
Calabi-Yau orientifolds, by constructing and characterizing a very large set of
vacua in a specific example, an orientifold of the Calabi-Yau hypersurface in
. We find support for the prediction of Ashok and Douglas
that the density of vacua on moduli space is governed by where and are curvature and K\"ahler forms on the moduli
space. The conifold point on moduli space therefore serves as an
attractor, with a significant fraction of the flux vacua contained in a small
neighborhood surrounding . We also study the functional dependence of
the number of flux vacua on the D3 charge in the fluxes, finding simple power
law growth.Comment: 22 pages, harvmac; v2 typos corrected, refs added; v3 minor error
correcte
DNA damage: A main determinant of vascular aging
Vascular aging plays a central role in health problems and mortality in older people. Apart from the impact of several classical cardiovascular risk factors on the vasculature, chronological aging remains the single most important determinant of cardiovascular problems. The causative mechanisms by which chronological aging mediates its impact, independently from classical risk factors, remain to be elucidated. In recent years evidence has accumulated that unrepaired DNA damage may play an important role. Observations in animal models and in humans indica
The energy and stability of D-term strings
Cosmic strings derived from string theory, supergravity or any theory of
choice should be stable if we hope to observe them. In this paper we consider
D-term strings in D=4, N=1 supergravity with a constant Fayet-Iliopoulos term.
We show that the positive deficit angle supersymmetric D-term string is
non-perturbatively stable by using standard Witten-Nester techniques to prove a
positive energy theorem. Particular attention is paid to the negative deficit
angle D-term string, which is known to violate the dominant energy condition.
Within the class of string solutions we consider, this violation implies that
the negative deficit angle D-term string must have a naked pathology and
therefore the positive energy theorem we prove does not apply to it. As an
interesting aside, we show that the Witten-Nester charge calculates the total
gravitational energy of the D-term string without the need for a cut-off, which
may not have been expected.Comment: 18 pages. v2: minor changes and references adde
Mersenne Primes, Polygonal Anomalies and String Theory Classification
It is pointed out that the Mersenne primes and associated
perfect numbers play a significant role in string
theory; this observation may suggest a classification of consistent string
theories.Comment: 10 pages LaTe
Supermembranes and Super Matrix Models
We review recent developments in the theory of supermembranes and their
relation to matrix models.Comment: Invited lecture presented at the Corfu Workshop, September 20 - 26,
1998, of the TMR Project "Quantum Aspects of Gauge Theories, Supersymmetry
and Unification" (ERBFMRXCT96-0045), to appear in the proceedings. Latex 41
p
Realistic D-Brane Models on Warped Throats: Fluxes, Hierarchies and Moduli Stabilization
We describe the construction of string theory models with semirealistic
spectrum in a sector of (anti) D3-branes located at an orbifold singularity at
the bottom of a highly warped throat geometry, which is a generalisation of the
Klebanov-Strassler deformed conifold. These models realise the Randall-Sundrum
proposal to naturally generate the Planck/electroweak hierarchy in a concrete
string theory embedding, and yielding interesting chiral open string spectra.
We describe examples with Standard Model gauge group (or left-right symmetric
extensions) and three families of SM fermions, with correct quantum numbers
including hypercharge. The dilaton and complex structure moduli of the geometry
are stabilised by the 3-form fluxes required to build the throat. We describe
diverse issues concerning the stabilisation of geometric Kahler moduli, like
blow-up modes of the orbifold singularities, via D term potentials and gauge
theory non-perturbative effects, like gaugino condensation. This local
geometry, once embedded in a full compactification, could give rise to models
with all moduli stabilised, and with the potential to lead to de Sitter vacua.
Issues of gauge unification, proton stability, supersymmetry breaking and
Yukawa couplings are also discussed.Comment: 46 pages, 13 figures (figures 3 and 13 corrected
Bioinspired Breathable Architecture for Water Harvesting
Thuja plicata is a coniferous tree which displays remarkable water channelling properties. In this article, an easily fabricated mesh inspired by the hierarchical macro surface structure of Thuja plicata branchlets is described which emulates this efficient water collection behaviour. The key parameters are shown to be the pore size, pore angle, mesh rotation, tilt angle (branch droop) and layering (branch overlap). Envisaged societal applications include water harvesting and low cost breathable architecture for developing countries
D-branes from M-branes
The 2-brane and 4-brane solutions of ten dimensional IIA supergravity have a
dual interpretation as Dirichlet-branes, or `D-branes', of type IIA superstring
theory and as `M-branes' of an -compactified eleven dimensional
supermembrane theory, or M-theory. This eleven-dimensional connection is used
to determine the ten-dimensional Lorentz covariant worldvolume action for the
Dirichlet super 2-brane, and its coupling to background spacetime fields. It is
further used to show that the 2-brane can carry the Ramond-Ramond charge of the
Dirichlet 0-brane as a topological charge, and an interpretation of the 2-brane
as a 0-brane condensate is suggested. Similar results are found for the
Dirichlet 4-brane via its interpretation as a double-dimensional reduction of
the eleven-dimensional fivebrane. It is suggested that the latter be
interpreted as a D-brane of an open eleven-dimensional supermembrane.Comment: Version to appear in Physics Letters B. Incorporates minor revisions
to previous revised version. 16 p
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