San Carlos de Bariloche, Argentina

Bariloche Atomic Center
San Carlos de Bariloche, Argentina

The Bariloche Atomic Centre is one of the research and development centres of the Argentine National Atomic Energy Commission. As it name implies, it is located in the city of San Carlos de Bariloche. Bariloche Atomic Centre is responsible for research in physics and nuclear engineering. It also hosts the Balseiro Institute, a collaboration between National University of Cuyo and the National Atomic Energy Commission. The Bariloche Atomic Centre opened in 1955 with its first director, José Antonio Balseiro. Wikipedia.

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Samengo I.,Bariloche Atomic Center | Gollisch T.,University of Gottingen
Journal of Computational Neuroscience | Year: 2013

The space of sensory stimuli is complex and high-dimensional. Yet, single neurons in sensory systems are typically affected by only a small subset of the vast space of all possible stimuli. A proper understanding of the input-output transformation represented by a given cell therefore requires the identification of the subset of stimuli that are relevant in shaping the neuronal response. As an extension to the commonly-used spike-triggered average, the analysis of the spike-triggered covariance matrix provides a systematic methodology to detect relevant stimuli. As originally designed, the consistency of this method is guaranteed only if stimuli are drawn from a Gaussian distribution. Here we present a geometric proof of consistency, which provides insight into the foundations of the method, in particular, into the crucial role played by the geometry of stimulus space and symmetries in the stimulus-response relation. This approach leads to a natural extension of the applicability of the spiketriggered covariance technique to arbitrary spherical or elliptic stimulus distributions. The extension only requires a subtle modification of the original prescription. Furthermore, we present a new resampling method for assessing statistical significance of identified relevant stimuli, applicable to spherical and elliptic stimulus distributions. Finally, we exemplify the modified method and compare it to other prescriptions given in the literature. © Springer Science+Business Media, LLC 2012.

Aligia A.A.,Bariloche Atomic Center
Journal of Physics Condensed Matter | Year: 2012

Using nonequilibrium renormalized perturbation theory, we calculate the retarded and lesser self-energies, the spectral density () near the Fermi energy, and the conductance G through a quantum dot as a function of a small bias voltage V, in the general case of electronhole asymmetry and intermediate valence. The linear terms in and V are given exactly in terms of thermodynamic quantities. When the energies necessary to add the first electron (E d) and the second one (E d+U) to the quantum dot are not symmetrically placed around the Fermi level, G has a term linear in V if, in addition, either the voltage drop or the coupling to the leads is not symmetric. The effects of temperature are discussed. The results simplify for a symmetric voltage drop, a situation usual in experiment. © 2012 IOP Publishing Ltd.

Fiorini F.,Bariloche Atomic Center
Physical Review Letters | Year: 2013

Born-Infeld determinantal gravity formulated in Weitzenböck spacetime is discussed in the context of Friedmann-Robertson-Walker (FRW) cosmologies. It is shown how the standard model big bang singularity is absent in certain spatially flat FRW spacetimes, where the high energy regime is characterized by a de Sitter inflationary stage of geometrical character, i.e., without the presence of the inflaton field. This taming of the initial singularity is also achieved for some spatially curved FRW manifolds where the singularity is replaced by a de Sitter stage or a big bounce of the scale factor depending on certain combinations of free parameters appearing in the action. Unlike other Born-Infeld-like theories in vogue, the one here presented is also capable of deforming vacuum general relativistic solutions. © 2013 American Physical Society.

Jagla E.A.,Bariloche Atomic Center
Physical Review Letters | Year: 2013

The Drössel-Schwabl model of forest fires can be interpreted in a coarse-grained sense as a model for the stress distribution in a single planar fault. Fires in the model are then translated to earthquakes. I show that when a second class of trees that propagate fire only after some finite time is introduced in the model, secondary fires (analogous to aftershocks) are generated, and the statistics of events becomes quantitatively compatible with the Gutenberg-Richter law for earthquakes, with a realistic value of the b exponent. The change in exponent is analytically demonstrated in a simplified percolation scenario. Experimental consequences of the proposed mechanism are indicated. © 2013 American Physical Society.

Jagla E.A.,Bariloche Atomic Center
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The Olami-Feder-Christensen model describes a limiting case of an elastic surface that slides on top of a substrate and is one of the simplest models that display some features observed in actual seismicity patterns. However, temporal and spatial correlations of real earthquakes are not correctly described by this model in its original form. I propose and study a modified version of the model, which includes a mechanism of structural relaxation. With this modification, realistic features of seismicity emerge, which are not obtained with the original version, mainly: aftershocks that cluster spatially around the slip surface of the main shock and follow the Omori law, and averaged frictional properties similar to those observed in rock friction, in particular the velocity-weakening effect. In addition, a Gutenberg-Richter law for the decaying of number of earthquakes with magnitude is obtained, with a decaying exponent within the range of experimentally observed values. Contrary to the original version of the model, a realistic value of the exponent appears without the necessity to fine tune any parameter. © 2010 The American Physical Society.

Da Rold L.,Bariloche Atomic Center
Journal of High Energy Physics | Year: 2011

The Standard Model with a light Higgs provides a very accurate description of the electroweak precision observables. The largest deviation between the Standard Model predictions and the experimental measurements, the forward-backward asymmetry of the bottom quark Ab FB, can be interpreted as an indication of new physics at the TeV scale. The strong agreement between theory and experiment in the branching fraction of the Z into b-quarks puts strong constraints for new physics aiming to solve the A b FB puzzle. We study a class of natural composite Higgs models that can solve the Ab FB anomaly reproducing the observed Rb as well as the top and bottom masses. We find that the subgroup of - the custodial symmetry able to protect ZbLb̄L from large corrections generated by the top sector play an important role if we want to maintain naturalness in the composite sector. We make a thorough study of the composite operators mixing with the b-quark, determine their embedding under the global composite symmetry and the parameter space that lead - to the correct Zbb̄ couplings while keeping the top and bottom masses to their physical values. We study the predictions for the spectrum of light fermionic resonances and the corrections to Zt-t̄ in this scenario. © SISSA 2011.

Huerta M.,Bariloche Atomic Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

We calculate numerically the logarithmic contribution to the entanglement entropy of a cylindrical region in three spatial dimensions for both, free scalar and Dirac fields. The coefficient is universal and proportional to the type c conformal anomaly in agreement with recent analytical predictions. We also calculate the mass corrections to the entanglement entropy for scalar and Dirac fields in a disk. These apparently unrelated problems make contact through the dimensional reduction procedure valid for free fields whereby the entanglement entropy for the cylinder can be calculated as an integral over masses of the disk entanglement entropies. Coming from the same numerical evaluation in the lattice, each coefficient is cross checked by the other, testing in this way the two results simultaneously. © 2012 Elsevier B.V.

Casini H.,Bariloche Atomic Center | Huerta M.,Bariloche Atomic Center
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We show, using strong subadditivity and Lorentz covariance, that in three-dimensional space-time the entanglement entropy of a circle is a concave function. This implies the decrease of the coefficient of the area term and the increase of the constant term in the entropy between the ultraviolet and infrared fixed points. This is in accordance with recent holographic c theorems and with conjectures about the renormalization group flow of the partition function of a three sphere (F theorem). The irreversibility of the renormalization group flow in three dimensions would follow from the argument provided there is an intrinsic definition for the constant term in the entropy at fixed points. We discuss the difficulties in generalizing this result for spheres in higher dimensions. © 2012 American Physical Society.

Jagla E.A.,Bariloche Atomic Center
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We study analytically and by numerical simulations the statistics of the aftershocks generated after large avalanches in models of interface depinning that include viscoelastic relaxation effects. We find in all the analyzed cases that the decay law of aftershocks with time can be understood by considering the typical roughness of the interface and its evolution due to relaxation. In models where there is a single viscoelastic relaxation time there is an exponential decay of the number of aftershocks with time. In models in which viscoelastic relaxation is wave-vector dependent we typically find a power-law dependence of the decay rate that is compatible with the Omori law. The factors that determine the value of the decay exponent are analyzed. © 2014 American Physical Society.

Caceres M.O.,Bariloche Atomic Center
Journal of Statistical Physics | Year: 2014

The stochastic dynamics toward the final attractor in exponential distributed time-delay non-linear models is presented, then the passage time statistic is studied analytically in the small noise approximation. The problem is worked out by going to the associated two-dimensional system. The mean first passage time 〈te〉 from the unstable state for this non-Markovian type of system has been worked out using two different approaches: firstly, by a rigorous adiabatic Markovian approximation (in the small mean delay-time ε = λ-1; secondly, by introducing the stochastic path perturbation approach to get a non-adiabatic theory for any λ. This first passage time distribution can be written in terms of the important parameters of the models. We have compared both approaches and we have found excellent agreement between them in the adiabatic limit. In addition, using our non-adiabatic approach we predict a crossover and a novel behavior for the relaxation scaling-time as a function of the delay parameter which for λ ≪ goes as 〈te〉 ~ 1/√λ. © 2014 Springer Science+Business Media New York.

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