9 research outputs found
Yang-Mills instantons in Kaehler spaces with one holomorphic isometry
We consider self-dual Yang-Mills instantons in 4-dimensional Kaehler spaces
with one holomorphic isometry and show that they satisfy a generalization of
the Bogomol'nyi equation for magnetic monopoles on certain 3-dimensional
metrics. We then search for solutions of this equation in 3-dimensional metrics
foliated by 2-dimensional spheres, hyperboloids or planes in the case in which
the gauge group coincides with the isometry group of the metric (SO(3), SO(1,2)
and ISO(2), respectively). Using a generalized hedgehog ansatz the Bogomol'nyi
quations reduce to a simple differential equation in the radial variable which
admits a universal solution and, in some cases, a particular one, from which
one finally recovers instanton solutions in the original Kaehler space. We work
out completely a few explicit examples for some Kaehler spaces of interest.Comment: Latex2e file, 16 pages, no figure
One Thousand and One Bubbles
We propose a novel strategy that permits the construction of completely
general five-dimensional microstate geometries on a Gibbons-Hawking space. Our
scheme is based on two steps. First, we rewrite the bubble equations as a
system of linear equations that can be easily solved. Second, we conjecture
that the presence or absence of closed timelike curves in the solution can be
detected through the evaluation of an algebraic relation. The construction we
propose is systematic and covers the whole space of parameters, so it can be
applied to find all five-dimensional BPS microstate geometries on a
Gibbons-Hawking base. As a first result of this approach, we find that the
spectrum of scaling solutions becomes much larger when non-Abelian fields are
present. We use our method to describe several smooth horizonless multicenter
solutions with the asymptotic charges of three-charge (Abelian and non-Abelian)
black holes. In particular, we describe solutions with the centers lying on
lines and circles that can be specified with exact precision. We show the power
of our method by explicitly constructing a 50-center solution. Moreover, we use
it to find the first smooth five-dimensional microstate geometries with
arbitrarily small angular momentum.Comment: 33 pages. v2: typos correcte
Holographic studies of Einsteinian cubic gravity
Einsteinian cubic gravity provides a holographic toy model of a
nonsupersymmetric CFT in three dimensions, analogous to the one defined by
Quasi-topological gravity in four. The theory admits explicit non-hairy AdS
black holes and allows for numerous exact calculations, fully nonperturbative
in the new coupling. We identify several entries of the AdS/CFT dictionary for
this theory, and study its thermodynamic phase space, finding interesting new
phenomena. We also analyze the dependence of R\'enyi entropies for disk regions
on universal quantities characterizing the CFT. In addition, we show that
is given by a non-analytic function of the ECG coupling, and that the
existence of positive-energy black holes strictly forbids violations of the KSS
bound. Along the way, we introduce a new method for evaluating Euclidean
on-shell actions for general higher-order gravities possessing second-order
linearized equations on AdS. Our generalized action involves the very
same Gibbons-Hawking boundary term and counterterms valid for Einstein gravity,
which now appear weighted by the universal charge controlling the
entanglement entropy across a spherical region in the CFT dual to the
corresponding higher-order theory.Comment: 59 pages, 7 figures, 1 table; v4: typos fixe
Regular Stringy Black Holes?
We study the first-order corrections to the singular 4-dimensional
massless stringy black holes studied in the nineties in the context of the
Heterotic Superstring. We show that the corrections not only induce a
non-vanishing mass and give rise to an event horizon, but also eliminate the
singularity giving rise to a regular spacetime whose global structure includes
further asymptotically flat regions in which the spacetime's mass is positive
or negative. We study the timelike and null geodesics and their effective
potential, showing that the spacetime is geodesically complete. We discuss the
validity of this solution, arguing that the very interesting and peculiar
properties of the solution are associated to the negative energy contributions
coming from the terms quadratic in the curvature. As a matter of fact, the
10-dimensional configuration is singular. We extract some general lessons on
attempts to eliminate black-hole singularities by introducing terms of higher
order in the curvature.Comment: 5 pages, 2 figure
Open Strings in IIB Orientifold Reductions
We consider type IIB compactifications on a general 4D group manifold with
different types of possible spacetime filling O-planes and the corresponding
D-branes parallel to them. Once fluxes allowed by the associated orientifold
projection are included, a 6D gauged supergravity is
obtained. In this paper we show how the consistent coupling to dynamical open
strings living on the spacetime filling D-branes may be captured by the
inclusion of extra vector multiplets and extra embedding tensor deformations on
the gauged supergravity side. As a result, the quadratic constraints on the
embedding tensor consistently reproduce the source corrected 10D Bianchi
identities. Furthermore, the field strength modifications induced by the open
string sector could potentially be understood as U-dual versions of the
Green-Schwarz terms. Finally, the entire scalar potential of the theory exactly
matches the one obtained from reduction of the bulk action plus the source
contributions.Comment: 45 pages, 1 figur
Beyond the near-horizon limit: Stringy corrections to Heterotic Black Holes
We study the first-order in corrections to 4-charge black holes
(with the Reissner-Nordstr\"om black hole as a particular example) beyond the
near-horizon limit in the Heterotic Superstring effective action framework. The
higher-curvature terms behave as delocalized sources in the equations of motion
and in the Bianchi identity of the 3-form. For some charges, this introduces a
shift between their values measured at the horizon and asymptotically. Some of
these corrections and their associated charge shifts, but not all of them, can
be canceled using appropriate SU instantons for the heterotic gauge
fields. The entropy, computed using Wald's formula, is in agreement with the
result obtained via microstate counting when the delocalized sources are
properly taken into account.Comment: 46 page
How cyclic chain topology can reduce the crystallization rate of Poly(3- hexylthiophene) and promote the formation of liquid crystalline phases in comparison with linear analogue chains
We have studied how cyclic topology affects the crystallization and morphology of π-conjugated poly(3-
hexylthiophene) (P3HT) molecules by comparing linear and cyclic analogues for the first time, with three
different chain lengths. We employ a range of experimental techniques including wide-angle X-ray
scattering (WAXS), polarized light optical microscopy (PLOM), differential scanning calorimetry (DSC) and a
combination of Polarized Light Optical Microscopy (PLOM) and Spectroscopy (S). The crystallization and
melting points, melting/crystallization enthalpies, and overall crystallization kinetics of cyclic P3HTs are
found to be substantially lower than their linear counterparts. The results are explained by the higher
rigidity of cyclic molecules, as predicted by density functional theory (DFT) calculations, in the low
molecular weight range explored here, in comparison with linear P3HT chains. Additionally, we have found
that cyclic P3HT can form liquid crystalline phases above their crystalline melting points and a new crystal
form at lower temperatures. PLOM, WAXS, DSC and PLOM/S results indicate that cyclic P3HTs display
bipolar and concentric nematic textures that disappear at a well-defined nematic-isotropic transition
temperature. Such liquid crystalline textures are completely absent in the linear P3HTs analogues studied
here. We conclude that the cyclic topology induces the formation of liquid crystalline phases as the rigid
P3HT oligomers can self-assemble above their crystalline melting temperatures.J.M. acknowledges support from the Provincial Council of Gipuzkoa under the program Fellow Gipuzkoa
and “Fomento San Sebastián” in the framework program “Retorno del Talento Local” Donostia up! 2016.
We acknowledge the help of Dr. Jaime Martín and Ms. Sara Marina with the combined
Microscopy/Spectroscopy measurements. J.M. and A.J.M. acknowledge funding by Mineco MAT2017-
83014-C2-1-P project. N.D. and O.C. are grateful to the Science Policy Office of the Belgian Federal
Government (PAI 7/5) and to the Belgian FRFC-FNRS (n°2.4508.12). O.C. is Research Associates of the
F.R.S.-FNRS. G.L. is grateful to the Youth Innovation Promotion Association of the Chinese Academy of
Sciences (2015026). D.W. and A.J.M acknowledge the support from the National Natural Science
Foundation of China (51820105005). All authors gratefully acknowledge the support of the EU through the
H2020-MSCA-RISE-2017-778092 BIODEST project. Technical and human support provided by IZO-SGI,
SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) is gratefully acknowledged for assistance and generous
allocation of computational resources