210 research outputs found
Nueva especie de Nebria Latreille, 1802 de los Montes de León, noroeste de España (Coleoptera, Carabidae: Nebriinae)
Nebria leonensis sp. n. from the Sierras de la Cabrera Baja and del Teleno (southern Montes de León) is described. This species, related to N. lafresnayei Serville, 1821, is characterised by its slender body, long and light brown extremities, the form of its pronotum, and evenly rounded elytra, which are conspicuously flattened on the discus. The differentiating characters and the habitat are described. A determination key to the species and subspecies of the group to which the new species belongs is presented.Se describe Nebria leonensis sp. n. de las sierras de la Cabrera Baja y del Teleno (sur de los Montes de León). Esta especie, relacionada con Nebria lafresnayei Serville, 1821, se caracteriza especialmente por su cuerpo delgado, largas extremidades de color marrón claro, forma del pronoto, y élitros uniformemente redondeados y claramente deprimidos en el disco. Además de describir los caracteres que la definen y el hábitat, se presentan unas breves notas sobre la historia faunística de los montes de León, y una clave de determinación de las especies y subespecies del grupo al que pertenece la nueva especie
Tres nuevos Typhlocharis Dieck, 1869 (Coleoptera, Caraboidea, Trechidae) de Navarra (España)
Three new species of the genus Typhlocharis Dieck, from Navarra (North Spain) are described: T. monasticus sp. n., T. peregrinus sp. n. and T. navaricus sp. n. These species make up a group well differentiated from the rest of the genus Typhlocharis by the peculiar morphology of the female genitalia and the sexual dimorphism.Se describen 3 nuevas especies del género Typhlocharis Dieck, procedentes de Navarra (norte de España): T. monasticus sp. n., T. peregrinus sp. n. y T. navaricus sp. n. Forman un grupo de especies bien diferenciado del resto de Typhlocharis por la peculiar morfología de la genitalia femenina y el dimorfismo sexual
On Slow-roll Moduli Inflation in Massive IIA Supergravity with Metric Fluxes
We derive several no-go theorems in the context of massive type IIA string
theory compactified to four dimensions in a way that, in the absence of fluxes,
preserves N=1 supersymmetry. Our derivation is based on the dilaton, Kaehler
and complex structure moduli dependence of the potential of the
four-dimensional effective field theory, that is generated by the presence of
D6-branes, O6-planes, RR-fluxes, NSNS 3-form flux, and geometric fluxes. To
demonstrate the usefulness of our theorems, we apply them to the most commonly
studied class of toroidal orientifolds. We show that for all but two of the
models in this class the slow-roll parameter \epsilon is bounded from below by
numbers of order unity as long as the fluxes satisfy the Bianchi identities,
ruling out slow-roll inflation and even the existence of de Sitter extrema in
these models. For the two cases that avoid the no-go theorems, we provide some
details of our numerical studies, demonstrating that small \epsilon can indeed
be achieved. We stress that there seems to be an \eta-problem, however,
suggesting that none of the models in this class are viable from a cosmological
point of view at least at large volume, small string coupling, and leading
order in the \alpha'-expansion.Comment: 34 pages, v3: summary table added, comments added, accepted for
publication in PR
D-Terms from Generalized NS-NS Fluxes in Type II
Orientifolds of type II string theory admit a certain set of generalized
NS-NS fluxes, including not only the three-form field strength H, but also
metric and non-geometric fluxes, which are related to H by T-duality. We
describe in general how these fluxes appear as parameters of an effective N=1
supergravity theory in four dimensions, and in particular how certain
generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term
contributions to the effective scalar potential. We illustrate these phenomena
in type IIB with the example of a certain orientifold of T^6/Z_4.Comment: 31+1 pages, uses utarticle.cls; v2: references adde
(Anti-)Brane backreaction beyond perturbation theory
We improve on the understanding of the backreaction of anti-D6-branes in a
flux background that is mutually BPS with D6-branes. This setup is analogous to
the study of the backreaction of anti-D3-branes inserted in the KS throat, but
does not require us to smear the anti-branes or do a perturbative analysis
around the BPS background. We solve the full equations of motion near the
anti-D6-branes and show that only two boundary conditions are consistent with
the equations of motion. Upon invoking a topological argument we eliminate the
boundary condition with regular H flux since it cannot lead to a solution that
approaches the right kind of flux away from the anti-D6-brane. This leaves us
with a boundary condition which has singular, but integrable, H flux energy
density.Comment: 12 pages + appendices, 1 figure; v2: minor changes, version published
in JHE
The problematic backreaction of SUSY-breaking branes
In this paper we investigate the localisation of SUSY-breaking branes which,
in the smeared approximation, support specific non-BPS vacua. We show, for a
wide class of boundary conditions, that there is no flux vacuum when the branes
are described by a genuine delta-function. Even more, we find that the smeared
solution is the unique solution with a regular brane profile. Our setup
consists of a non-BPS AdS_7 solution in massive IIA supergravity with smeared
anti-D6-branes and fluxes T-dual to ISD fluxes in IIB supergravity.Comment: 27 pages, Latex2e, 5 figure
Persistent anti-brane singularities
Anti-D-branes inserted in warped throat geometries (supported by fluxes that
carry D-brane charges) develop unphysical singularities. It has been argued
that these singularities could be resolved when one goes beyond the linearized
approximation or includes the effects of brane polarization. In this paper we
consider anti-D6 branes, whose singularities have been shown to exist at the
full non-linear level, and demonstrate that there is no D8 brane polarization
that can resolve the singularity. We comment on the potential implications of
this result for the resolution of anti-D3 brane singularities in the
Klebanov-Strassler geometry.Comment: 16 pages; v2: comments added, version to appear in JHE
The neural basis of video gaming
Video game playing is a frequent recreational activity. Previous studies have reported an involvement of dopamine-related ventral striatum. However, structural brain correlates of video game playing have not been investigated. On magnetic resonance imaging scans of 154 14-year-olds, we computed voxel-based morphometry to explore differences between frequent and infrequent video game players. Moreover, we assessed the Monetary Incentive Delay (MID) task during functional magnetic resonance imaging and the Cambridge Gambling Task (CGT). We found higher left striatal grey matter volume when comparing frequent against infrequent video game players that was negatively correlated with deliberation time in CGT. Within the same region, we found an activity difference in MID task: frequent compared with infrequent video game players showed enhanced activity during feedback of loss compared with no loss. This activity was likewise negatively correlated with deliberation time. The association of video game playing with higher left ventral striatum volume could reflect altered reward processing and represent adaptive neural plasticity
Toroidal Orientifolds in IIA with General NS-NS Fluxes
Type IIA toroidal orientifolds offer a promising toolkit for model builders,
especially when one includes not only the usual fluxes from NS-NS and R-R field
strengths, but also fluxes that are T-dual to the NS-NS three-form flux. These
new ingredients are known as metric fluxes and non-geometric fluxes, and can
help stabilize moduli or can lead to other new features. In this paper we study
two approaches to these constructions, by effective field theory or by toroidal
fibers twisted over a toroidal base. Each approach leads us to important
observations, in particular the presence of D-terms in the four-dimensional
effective potential in some cases, and a more subtle treatment of the
quantization of the general NS-NS fluxes. Though our methods are general, we
illustrate each approach on the example of an orientifold of T^6/Z_4.Comment: 59 pages, references adde
Supersymmetric Vacua in Random Supergravity
We determine the spectrum of scalar masses in a supersymmetric vacuum of a
general N=1 supergravity theory, with the Kahler potential and superpotential
taken to be random functions of N complex scalar fields. We derive a random
matrix model for the Hessian matrix and compute the eigenvalue spectrum.
Tachyons consistent with the Breitenlohner-Freedman bound are generically
present, and although these tachyons cannot destabilize the supersymmetric
vacuum, they do influence the likelihood of the existence of an `uplift' to a
metastable vacuum with positive cosmological constant. We show that the
probability that a supersymmetric AdS vacuum has no tachyons is formally
equivalent to the probability of a large fluctuation of the smallest eigenvalue
of a certain real Wishart matrix. For normally-distributed matrix entries and
any N, this probability is given exactly by P = exp(-2N^2|W|^2/m_{susy}^2),
with W denoting the superpotential and m_{susy} the supersymmetric mass scale;
for more general distributions of the entries, our result is accurate when N >>
1. We conclude that for |W| \gtrsim m_{susy}/N, tachyonic instabilities are
ubiquitous in configurations obtained by uplifting supersymmetric vacua.Comment: 26 pages, 6 figure
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