68,864 research outputs found
Techniques for n-Particle Irreducible Effective Theories
In this paper we show that the skeleton diagrams in the m-Loop nPI effective
action correspond to an infinite resummation of perturbative diagrams which is
void of double counting at the m-Loop level. We also show that the variational
equations of motion produced by the n-Loop nPI effective theory are equivalent
to the Schwinger-Dyson equations, up to the order at which they are consistent
with the underlying symmetries of the original theory. We use a diagrammatic
technique to obtain the 5-Loop 5PI effective action for a scalar theory with
cubic and quartic interactions, and verify that the result satisfies these two
statements.Comment: 43 pages, 48 figures, add a paragraph in conclusions, Figs. 25,45,46
changed, typos corrected, final version to appear in PR
More Toda-like (0,2) mirrors
In this paper, we extend our previous work to construct (0,2) Toda-like
mirrors to A/2-twisted theories on more general spaces, as part of a program of
understanding (0,2) mirror symmetry. Specifically, we propose (0,2) mirrors to
GLSMs on toric del Pezzo surfaces and Hirzebruch surfaces with deformations of
the tangent bundle. We check the results by comparing correlation functions,
global symmetries, as well as geometric blowdowns with the corresponding (0,2)
Toda-like mirrors. We also briefly discuss Grassmannian manifolds.Comment: 49 pages, LaTeX; v2: references adde
Power spectra from an inflaton coupled to the Gauss-Bonnet term
We consider power-law inflation with a Gauss-Bonnet correction inspired by
string theory. We analyze the stability of cosmological perturbations and
obtain the allowed parameter space. We find that for GB-dominated inflation
ultra-violet instabilities of either scalar or tensor perturbations show up on
small scales. The Gauss-Bonnet correction with a positive (or negative)
coupling may lead to a reduction (or enhancement) of the tensor-to-scalar ratio
in the potential-dominated case. We place tight constraints on the model
parameters by making use of the WMAP 5-year data.Comment: 5 pages, 4 figures, RevTeX, references added, published versio
Content Based Image Retrieval by Convolutional Neural Networks
Hamreras S., Benítez-Rochel R., Boucheham B., Molina-Cabello M.A., López-Rubio E. (2019) Content Based Image Retrieval by Convolutional Neural Networks. In: Ferrández Vicente J., Álvarez-Sánchez J., de la Paz López F., Toledo Moreo J., Adeli H. (eds) From Bioinspired Systems and Biomedical Applications to Machine Learning. IWINAC 2019. Lecture Notes in Computer Science, vol 11487. Springer.In this paper, we present a Convolutional Neural Network (CNN) for feature extraction in Content based Image Retrieval (CBIR). The proposed CNN aims at reducing the semantic gap between low level and high-level features. Thus, improving retrieval results. Our CNN is the result of a transfer learning technique using Alexnet pretrained network. It learns how to extract representative features from a learning database and then uses this knowledge in query feature extraction. Experimentations performed on Wang (Corel 1K) database show a significant improvement in terms of precision over the state of the art classic approaches.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
On the Cauchy problem for the magnetic Zakharov system
In this paper, we study the Cauchy problem of the magnetic type Zakharov
system which describes the pondermotive force and magnetic field generation
effects resulting from the non-linear interaction between plasma-wave and
particles. By using the energy method to derive a priori bounds and an
approximation argument for the construction of solutions, we obtain local
existence and uniqueness results for the magnetic Zakharov system in the case
of
Secondary Rayleigh-Taylor type Instabilities in the Reconnection Exhaust Jet as a Mechanism for Supra-Arcade Downflows
Supra-arcade downflows (hereafter referred to as SADs) are low-emission,
elongated, finger-like features usually observed in active-region coronae above
post-eruption flare arcades. Observations exhibit downward moving SADs
intertwined with bright upward moving spikes. Whereas SADs are dark voids,
spikes are brighter, denser structures. Although SADs have been observed for
decades, the mechanism of formation of SADs remains an open issue. In our
three-dimensional resistive magnetohydrodynamic simulations, we demonstrate
that secondary Rayleigh-Taylor type instabilities develop in the downstream
region of a reconnecting current sheet. The instability results in the
formation of low-density coherent structures that resemble SADs, and
high-density structures that appear to be spike-like. Comparison between the
simulation results and observations suggests that secondary Rayleigh-Taylor
type instabilities in the exhaust of reconnecting current sheets provide a
plausible mechanism for observed SADs and spikes
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