Optical Polarimetry for Fundamental Physics

Sensitive magneto-optical polarimetry was proposed by E. Iacopini and E. Zavattini in 1979 to detect vacuum electrodynamic non-linearity, in particular Vacuum Magnetic Birefringence (VMB). This process is predicted in QED via the fluctuation of electron–positron virtual pairs but can also be due to hypothetical Axion-Like Particles (ALPs) and/or MilliCharged Particles (MCP). Today ALPs are considered a strong candidate for Dark Matter. Starting in 1992 the PVLAS collaboration, financed by INFN, Italy, attempted to measure VMB conceptually following the original 1979 scheme based on an optical cavity permeated by a time-dependent magnetic field and heterodyne detection. Two setups followed differing basically in the magnet: the first using a rotating superconducting 5.5 T dipole magnet at the Laboratori Nazionali di Legnaro, Legnaro, Italy and the second using two rotating permanent 2.5 T dipole magnets at the INFN section of Ferrara. At present PVLAS is the experiment which has set the best limit in VMB reaching a noise floor within a factor 7 of the predicted QED signal: Δn(QED)=2.5×10−23 @ 2.5 T. It was also shown that the noise floor was due to the optical cavity and a larger magnet is the only solution to increase the signal to noise ratio. The PVLAS experiment ended at the end of 2018. A new effort, VMB@CERN, which plans to use a spare LHC dipole magnet at CERN with a new modified optical scheme, is now being proposed. In this review, a detailed description of the PVLAS effort and the comprehension of its limits leading to a new proposal will be given.

Absence of Jamming Avoidance and Flight Path Similarity in Paired Bent-Winged Bats, Miniopterus Fuliginosus

Echolocating bats perceive their surroundings by listening to the echoes of self-generated ultrasound pulses. When multiple conspecifics fly in close proximity to each other, sounds emitted from nearby individuals could mutually interfere with echo reception. Many studies suggest that bats employ frequency shifts to avoid spectral overlap of pulses with other bats. Technical constraints in recording technology have made it challenging to capture subtle changes in the pulse characteristics of bat calls. Therefore, how bats change their behavior to extract their own echoes in the context of acoustic interference remains unclear. Also, to our best knowledge, no studies have investigated whether individual flight paths change when other bats are present, although movements likely reduce acoustic masking. Here, we recorded the echolocation pulses of bats flying alone or in pairs using telemetry microphones. Flight trajectories were also reconstructed using stereo camera recordings. We found no clear tendency to broaden individual differences in the acoustic characteristics of pulses emitted by pairs of bats compared to bats flying alone. However, some bats showed changes in pulse characteristics when in pairs, which suggests that bats can recognize their own calls based on the initial differences in call characteristics between individuals. In addition, we found that the paired bats spend more time flying in the same directions than in the opposite directions. Besides, we found that the flight paths of bats were more similar in “paired flight trials” than in virtual pairs of paired flight trials. Our results suggest that the bats tend to follow the other bat in paired flight. For the following bat, acoustic interference may be reduced, while the opportunity to eavesdrop on other bats’ calls may be increased.

Reinterpretation of Electric Field with Quantum Fluctuations: The Mechanism of Electrostatic Force of Attraction and Repulsion Between Two Point Charges

Vacuum polarization rearranges virtual pairs. This causes the virtual pairs to rigidify in vacuum, reducing the quantum fluctuation energy. The quantum fluctuation energy is a fundamental force of vacuum, as evidenced by the Casimir effect. The change in quantum fluctuation energy was simulated in the superposition of the electric fields. The results show that the increase and decrease of the quantum fluctuation energy between the two point charges is related to the repulsive force and attraction in Coulomb's law.

Mesoscopic capacitor and zero-point energy: Poisson's distribution for virtual charges, pressure, and decoherence control

Mesoscopic capacitor theory, which includes intrinsic inductive effects from quantum tunneling, is applied to conducting spherical shells. The zero-point pressure and the number of virtual charged pairs are determined assuming a Poisson distribution. They are completely defined by a dimensionless mesoscopic parameter (χc) measuring the average number of virtual pairs per solid angle and carrying mesoscopic information. Fluctuations remain finite and well defined. Connections with usual quantum-field-theory limit enables us to evaluate χc ~ 1.007110. Equivalently, for a mesoscopic parallel-plate capacitor, the shot noise distribution becomes operative with χc ~ 0.94705 as well being related to the density of virtual pairs. Temperature decoherence and capacitor control are discussed by considering typical values of quantum dot devices and Coulomb blockade theory.

Kinematic Analyses of 5-DOF 3-RCRR Parallel Mechanism

This paper presents the kinematic analyses of a 5-DOF 3-RCRR parallel mechanism. The end-effector of this mechanism can rotate round rotation center and one reference point on it can translate in a plane parallels to the base platform. Since the traditional Kutzbach-Gru¨bler formula is not valid for this mechanism, the modified Kutzbach-Gru¨bler formula and screw theory are used in the mobility analysis. The Duffy’s spherical analytic theory is used in forward/reverse position analyses. In forward/reverse velocity/acceleration analyses, virtual mechanism principle is used to build a virtual parallel mechanism (3-PvRCRR), which is equivalent to the initial mechanism (3-RCRR) on kinematics if all rates of virtual pairs (Pv) are set to be zero. At the end, some kinematics curves are presented with a numerical example.

Conspecifics influence call design in the Brazilian free-tailed bat, Tadarida brasiliensis

The Brazilian free-tailed bat, Tadarida brasiliensis (Saint-Hilaire, 1824), uses calls that represent a broad continuum of design variation which is dependent upon habitat and situation, and exhibits characteristic changes in call design as bats close in on airborne targets. Here we demonstrate the influence of conspecifics on call design. We found that the peak frequency used in calls varies more as the number of bats flying in the same space increases (measured from single bats and pairs of bats). We investigated this phenomenon through comparing call-parameter differences found between two bats recorded flying together (actual pairs) with call-parameter differences between two bats each recorded flying alone at different locations that were randomly assigned to one another (virtual pairs). We found that actual pairs of bats used calls which differed in peak frequency more so than did virtual pairs. This result is particularly striking given that these frequency differences were greater between bats in the same space than between bats in two different habitats. We argue that these differences indicate that this species is practicing jamming avoidance, air traffic control, or both.

Quantum electrodynamics in intense laser fields

A very intense laser field polarizes the virtual electron-positron pairs that populate the vacuum. This provides for a coupling between different modes of the electromagnetic field, giving rise to effects such as scattering of light by light, a refractive index of the vacuum, vacuum birefringence, etc. Given enough energy in a sufficiently small spacetime region, the virtual pairs can become real, which leads to pair production in the intense field under the action of a third agent. These, as well as related effects, are summarized with respect to their orders of magnitude and conditions under which they might become accessible to experiment. Some other processes that are normally mentioned in this context, such as Thomson (Compton) scattering at high intensities, are considered, too, even though they are unrelated to the vacuum structure of quantum electrodynamics.

A TOPOLOGICAL HAWKING EFFECT

Consideration of particle creation on a topologically nontrivial instanton leads to the possibility of a “topological Hawking effect”, whereby virtual pairs are converted to real particles because of a “change in topology”. This effect, calculable in a coherent state representation, is illustrated here for a manifold with two boundaries and one handle. It is also argued that this effect could provide a natural explanation of the Hot Big Bang scenario whereby the Universe “tunnels into being”.