Photon mass and quantum effects of the Aharonov-Bohm type

The magnetic field due to the photon rest mass $m_{ph}$ modifies the standard results of the Aharonov-Bohm effect for electrons, and of other recent quantum effects. For the effect involving a coherent superposition of beams of particles with opposite electromagnetic properties, by means of a table-top experiment, the limit $m_{ph}x10^{-51}g$ is achievable, improving by 6 orders of magnitude that derived by Boulware and Deser for the Aharonov-Bohm effect.Comment: 5 page

Relativistic Aharonov-Casher Phase in Spin One

The Aharonov-Casher (AC) phase is calculated in relativistic wave equations of spin one. The AC phase has previously been calculated from the Dirac-Pauli equation using a gauge-like technique \cite{MK1,MK2}. In the spin-one case, we use Kemmer theory (a Dirac-like particle theory) to calculate the phase in a similar manner. However the vector formalism, the Proca theory, is more widely known and used. In the presence of an electromagnetic field, the two theories are `equivalent' and may be transformed into one another. We adapt these transformations to show that the Kemmer theory results apply to the Proca theory. Then we calculate the Aharonov-Casher phase for spin-one particles directly in the Proca formalism.Comment: 12 page

Effect of temperature and light intensity on the representation of motion information in the fly's visual system

To comprehend how the brain performs efficient computation, it is important to understand the way sensory information is represented in the nervous system. Under natural conditions, sensory signals have to be processed with sufficient accuracy under functional and resources constraints. Here I use motion vision in the fly Calliphora vicina to study the influence of two behaviorally relevant environmental properties - temperature and light intensity - on the representation of motion information in the responses of the neuron H1. The goal was to quantify how these environmental properties affect the response variability, information content, coding efficiency and temporal scale. I show that the firing precision is determined largely by the light intensity rather than by temperature. Moreover, a better firing precision barely improves the information rate, which closely follows the mean firing rate. Altogether, my results suggest that the robustness of the motion information processing against temperature variations depends on the quality of the input signal. Furthermore, flies seem to use the input signal-to-noise ratio to improve the information rate and reduce the time-scale of the response simultaneously, by increasing the mean firing rate, rather than the firing precision

The Sagnac effect and the role of simultaneity in relativity theory

We thoroughly examine the role of absolute and relative simultaneity in the interpretation of the Sagnac effect, using an approach that allows for determining the local speed along the light path. If the local speed of light is assumed to be c over the whole closed contour, there is no agreement with the observed result. There is agreement if the local speed is c along an open section of the contour only. Thus a rigorous and coherent interpretation of the Sagnac effect favours absolute over relative simultaneity. The implications for the Lorentz transformations and synchronization by means of the Global Positioning System are considered.publishedVersio

Modular Acquisition and Stimulation System for Timestamp-Driven Neuroscience Experiments

Dedicated systems are fundamental for neuroscience experimental protocols that require timing determinism and synchronous stimuli generation. We developed a data acquisition and stimuli generator system for neuroscience research, optimized for recording timestamps from up to 6 spiking neurons and entirely specified in a high-level Hardware Description Language (HDL). Despite the logic complexity penalty of synthesizing from such a language, it was possible to implement our design in a low-cost small reconfigurable device. Under a modular framework, we explored two different memory arbitration schemes for our system, evaluating both their logic element usage and resilience to input activity bursts. One of them was designed with a decoupled and latency insensitive approach, allowing for easier code reuse, while the other adopted a centralized scheme, constructed specifically for our application. The usage of a high-level HDL allowed straightforward and stepwise code modifications to transform one architecture into the other. The achieved modularity is very useful for rapidly prototyping novel electronic instrumentation systems tailored to scientific research.Comment: Preprint submitted to ARC 2015. Extended: 16 pages, 10 figures. The final publication is available at link.springer.co

Light propagation and local speed in the linear Sagnac effect

We investigate rigorously the behaviour of light propagation in the closed contour of the linear Sagnac effect. Assuming that the local light speed is c in a section of the contour, our approach ma..

Nuevos efectos cuánticos del tipo Aharonov-Bohm y la masa del fotón

Proca equations foresee the possibility of a nonzero photon mass. In this context of electrodynamics of finite range, the approaches used to determine the mass of the photon, or its upper limits, are traditionally based on classical methods. In this paper, we present a brief overview of the latest experimental methods that are based on a quantum approach. It is shown that quantum approaches can compete and even surpass traditional methods.Las ecuaciones de Proca prevén la posibilidad de una masa no nula del fotón. En este contexto de la electrodinámica de rango finito, los enfoques utilizados para determinar la masa del fotón, o sus límites superiores, están basados tradicionalmente en métodos clásicos. En este trabajo, se presenta una breve reseña de métodos experimentales más recientes que se basan en un enfoque cuántico. Se muestra que los enfoques cuánticos pueden competir y hasta superar los métodos clásicos

Bound states in the dynamics of a dipole in the presence of a conical defect

In this work we investigate the quantum dynamics of an electric dipole in a $(2+1)$-dimensional conical spacetime. For specific conditions, the Schr\"odinger equation is solved and bound states are found with the energy spectrum and eigenfunctions determined. We find that the bound states spectrum extends from minus infinity to zero with a point of accumulation at zero. This unphysical result is fixed when a finite radius for the defect is introduced.Comment: 4 page