1,675 research outputs found
The effect of metapopulation processes on the spatial scale of adaptation across an environmental gradient
We show that the butterfly Aricia agestis (Lycaenidae) is adapted to its
thermal environment in via integer changes in the numbers of generations per year
(voltinism): it has two generations per year in warm habitats and one generation per
year in cool habitats in north Wales (UK). Voltinism is an “adaptive peak” since
individuals having an intermediate number of generations per year would fail to
survive the winter, and indeed no populations showed both voltinism types in nature.
In spite of this general pattern, 11% of populations apparently possess the “wrong”
voltinism for their local environment, and population densities were lower in thermally
intermediate habitat patches. Population dynamic data and patterns of genetic
differentiation suggest that adaptation occurs at the metapopulation level, with local
populations possessing the voltinism type appropriate for the commonest habitat type
within each population network. When populations and groups of populations go
extinct, they tend to be replaced by colonists from the commonest thermal environment
nearby, even if this is the locally incorrect adaptation. Our results illustrate how
stochastic population turnover can impose a limit on local adaptation over distances
many times larger than predicted on the basis of normal dispersal movements
String Necklaces and Primordial Black Holes from Type IIB Strings
We consider a model of static cosmic string loops in type IIB string theory,
where the strings wrap cycles within the internal space. The strings are not
topologically stabilised, however the presence of a lifting potential traps the
windings giving rise to kinky cycloops. We find that PBH formation occurs at
early times in a small window, whilst at late times we observe the formation of
dark matter relics in the scaling regime. This is in stark contrast to previous
predictions based on field theoretic models. We also consider the PBH
contribution to the mass density of the universe, and use the experimental data
to impose bounds on the string theory parameters.Comment: 45 pages, 9 figures, LaTeX; published versio
Effective Actions near Singularities
We study the heterotic string compactified on K3 x T^2 near the line T=U,
where the effective action becomes singular due to an SU(2) gauge symmetry
enhancement. By `integrating in' the light W^\pm vector multiplets we derive a
quantum corrected effective action which is manifestly SU(2) invariant and
non-singular. This effective action is found to be consistent with a residual
SL(2,Z) quantum symmetry on the line T=U. In an appropriate decompactification
limit, we recover the known SU(2) invariant action in five dimensions.Comment: 33 pages, LaTeX. v2: cosmetic correction on titlepage. v3: references
and note adde
Non-Abelian (p,q) Strings in the Warped Deformed Conifold
We calculate the tension of -strings in the warped deformed conifold
using the non-Abelian DBI action. In the large flux limit, we find exact
agreement with the recent expression obtained by Firouzjahi, Leblond and
Henry-Tye up to and including order terms if is also taken to be
large. Furthermore using the finite prescription for the symmetrised trace
operation we anticipate the most general expression for the tension valid for
any . We find that even in this instance, corrections to the tension
scale as which is not consistent with simple Casimir scaling.Comment: 18 pages, Latex, 1 figure; Added a discussion of the case when the
warp factor parameter and typos correcte
Dielectric (p,q) Strings in a Throat
We calculate the (p,q) string spectrum in a warped deformed conifold using
the dielectric brane method. The spectrum is shown to have the same functional
form as in the dual picture of a wrapped D3-brane with electric and magnetic
fluxes on its world volume. The agreement is exact in the limit where q is
large. We also calculate the dielectric spectrum in the S-dual picture. The
spectrum in the S-dual picture has the same form as in the original picture but
it is not exactly S-dual invariant due to an interchange of Casimirs of the
non-Abelian gauge symmetries. We argue that in order to restore S-duality
invariance the non-Abelian brane action should be refined, probably by a better
prescription for the non-Abelian trace operation
Pressure-Temperature Phase Diagram of Antiferromagnetism and Superconductivity in CeRhIn5 and CeIn3 : In-NQR Study under Pressure
We report the novel pressure() - temperature() phase diagram of
antiferromagnetism and superconductivity in CeRhIn and CeIn revealed by
the In nuclear-spin-lattice-relaxation () measurement. In the
itinerant magnet CeRhIn, we found that the N\'eel temperature is
reduced at 1.23 GPa with an emergent pseudogap behavior. In CeIn,
the localized magnetic character is robust against the application of pressure
up to 1.9 GPa, beyond which the system evolves into an itinerant
regime in which the resistive superconducting phase emerges. We discuss the
relationship between the phase diagram and the magnetic fluctuations.Comment: 4 pages, 3 figures, to be published in Phys.Rev.B. Rapid
D-Brane Propagation in Two-Dimensional Black Hole Geometries
We study propagation of D0-brane in two-dimensional Lorentzian black hole
backgrounds by the method of boundary conformal field theory of SL(2,R)/U(1)
supercoset at level k. Typically, such backgrounds arise as near-horizon
geometries of k coincident non-extremal NS5-branes, where 1/k measures
curvature of the backgrounds in string unit and hence size of string worldsheet
effects. At classical level, string worldsheet effects are suppressed and
D0-brane propagation in the Lorentzian black hole geometry is simply given by
the Wick rotation of D1-brane contour in the Euclidean black hole geometry.
Taking account of string worldsheet effects, boundary state of the Lorentzian
D0-brane is formally constructible via Wick rotation from that of the Euclidean
D1-brane. However, the construction is subject to ambiguities in boundary
conditions. We propose exact boundary states describing the D0-brane, and
clarify physical interpretations of various boundary states constructed from
different boundary conditions. As it falls into the black hole, the D0-brane
radiates off to the horizon and to the infinity. From the boundary states
constructed, we compute physical observables of such radiative process. We find
that part of the radiation to infinity is in effective thermal distribution at
the Hawking temperature. We also find that part of the radiation to horizon is
in the Hagedorn distribution, dominated by massive, highly non-relativistic
closed string states, much like the tachyon matter. Remarkably, such
distribution emerges only after string worldsheet effects are taken exactly
into account. From these results, we observe that nature of the radiation
distribution changes dramatically across the conifold geometry k=1 (k=3 for the
bosonic case), exposing the `string - black hole transition' therein.Comment: 51 pages, 5 figures, v2: referece added, note added replying the
comment made in hep-th/060206
Open String Attractors
We present a simple example of a supersymmetric attractor mechanism in the
purely open string context of D-branes embedded in curved space-time. Our
example involves a class of D3-branes embedded in the 2-charge D1-D5 background
of type IIB whose worldvolume contains a 2-sphere. Turning on worldvolume
fluxes, these branes carry induced (p,q) string charges. Supersymmetric
configurations display a flow of the open string moduli towards an attractor
solution independent of their asymptotics. The equations governing this
mechanism closely resemble the attractor flow equations for supersymmetric
black holes in closed string theory. The BPS equations take the form of a
gradient flow and describe worldvolume solitons interpolating between an AdS_2
geometry where the two-sphere has collapsed, and an attractor solution with
AdS_2 x S^2 geometry. In these limiting solutions, the preserved supersymmetry
is enhanced from 4 to 8 supercharges. We also discuss the interpretation of our
solutions as intersecting brane configurations placed in the D1-D5 background,
as well as the S-duality transformation to the F1-NS5 background.Comment: 37 pages, 6 figures. v2: small corrections, figure and references
adde
Negative Energy in String Theory and Cosmic Censorship Violation
We find asymptotically anti de Sitter solutions in N=8 supergravity which
have negative total energy. This is possible since the boundary conditions
required for the positive energy theorem are stronger than those required for
finite mass (and allowed by string theory). But stability of the anti de Sitter
vacuum is still ensured by the positivity of a modified energy, which includes
an extra surface term. Some of the negative energy solutions describe classical
evolution of nonsingular initial data to naked singularities. Since there is an
open set of such solutions, cosmic censorship is violated generically in
supergravity. Using the dual field theory description, we argue that these
naked singularities will be resolved in the full string theory.Comment: 23 pages, 2 figures, v2: argument for forming naked singularities
clarified, references adde
Determination of pi-N scattering lengths from pionic hydrogen and pionic deuterium data
The pi-N s-wave scattering lengths have been inferred from a joint analysis
of the pionic hydrogen and the pionic deuterium x-ray data using a
non-relativistic approach in which the pi-N interaction is simulated by a
short-ranged potential. The pi-d scattering length has been calculated exactly
by solving the Faddeev equations and also by using a static approximation. It
has been shown that the same very accurate static formula for pi-d scattering
length can be derived (i) from a set of boundary conditions; (ii) by a
reduction of Faddeev equations; and (iii) through a summation of Feynman
diagrams. By imposing the requirement that the pi-d scattering length,
resulting from Faddeev-type calculation, be in agreement with pionic deuterium
data, we obtain bounds on the pi-N scattering lengths. The dominant source of
uncertainty on the deduced values of the pi-N scattering lengths are the
experimental errors in the pionic hydrogen data.Comment: RevTeX, 20 pages,4 PostScript figure
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