Anomaly-induced effective action and Chern-Simons modification of general relativity

Recently it was shown that the quantum vacuum effects of massless chiral fermion field in curved space-time leads to the parity-violating Pontryagin density term, which appears in the trace anomaly with imaginary coefficient. In the present work the anomaly-induced effective action with the parity-violating term is derived. The result is similar to the Chern-Simons modified general relativity, which was extensively studied in the last decade, but with the kinetic terms for the scalar different from those considered previously in the literature. The parity-breaking term makes no effect on the zero-order cosmology, but it is expected to be relevant in the black hole solutions and in the cosmological perturbations, especially gravitational waves.Comment: 15 pages, LaTeX, no Figures. Two references added, correction in the Acknowledgements. Fits the manuscript accepted in Physics Letters

Diversity improves performance in excitable networks

As few real systems comprise indistinguishable units, diversity is a hallmark of nature. Diversity among interacting units shapes properties of collective behavior such as synchronization and information transmission. However, the benefits of diversity on information processing at the edge of a phase transition, ordinarily assumed to emerge from identical elements, remain largely unexplored. Analyzing a general model of excitable systems with heterogeneous excitability, we find that diversity can greatly enhance optimal performance (by two orders of magnitude) when distinguishing incoming inputs. Heterogeneous systems possess a subset of specialized elements whose capability greatly exceeds that of the nonspecialized elements. Nonetheless, the behavior of the whole network can outperform all subgroups. We also find that diversity can yield multiple percolation, with performance optimized at tricriticality. Our results are robust in specific and more realistic neuronal systems comprising a combination of excitatory and inhibitory units, and indicate that diversity-induced amplification can be harnessed by neuronal systems for evaluating stimulus intensities.Comment: 17 pages, 7 figure

RELIEVING SYSTEM DATA BALANCE SWINGING PLATFORM

The balance capacity is defined by many authors as a key factor of the performance. The methods of the research and the evaluation of the balance - employ different tests concerning the single person with the use or addition of little tools both in static and dynamic situation. The evaluation of the balance has. always given big problems. With the realization of this "field" tool and relevant system of data acquisition our goo1 was to make the evaluation objective and possible the test reproduction. The tool consists in a platform in which has been placed a detection system interfaced with a computer, monitor and a printer. It is possible to make detections referred to 'an axis (semi-cylinder) or two axises ( semi-sphere) . In relation to the different positions scheduled by the records the tool detects the balance capacity of the subject staying on it; the value of the balance shown by the person performing during the test is visualized on the monitor through a graphic showing the proceeding of the platform of the disjungtion from the horizontal position. The value is also indicated with a number obtained from the average of the squared values of the disjungtion referred to the unity of time

Fourth derivative gravity in the auxiliary fields representation and application to the black hole stability

We consider an auxiliary fields formulation for the general fourth-order gravity on an arbitrary curved background. The case of a Ricci-flat background is elaborated in full details and it is shown that there is an equivalence with the standard metric formulation. At the same time, using auxiliary fields helps to make perturbations to look simpler and the results more clear. As an application we reconsider the linear perturbations for the classical Schwarzschild solution. We also briefly discuss the relation to the effect of massive unphysical ghosts in the theory.Comment: 11 pages, no figure

Interference of an Array of Independent Bose-Einstein Condensates

Interference of an array of independent Bose-Einstein condensates, whose experiment has been performed recently, is theoretically studied in detail. Even if the number of the atoms in each gas is kept finite and the phases of the gases are not well defined, interference fringes are observed on each snapshot. The statistics of the snapshot interference patterns, i.e., the average fringe amplitudes and their fluctuations (covariance), are computed analytically, and concise formulas for their asymptotic values for long time of flight are derived. Processes contributing to these quantities are clarified and the relationship with the description on the basis of the symmetry-breaking scenario is revealed.Comment: 13 pages, 3 figure