Quantum Interactions Between Non-Perturbative Vacuum Fields

We develop an approach to investigate the non-perturbative dynamics of quantum field theories, in which specific vacuum field fluctuations are treated as the low-energy dynamical degrees of freedom, while all other vacuum field configurations are explicitly integrated out from the path integral. We show how to compute the effective interaction between the vacuum field degrees of freedom both perturbatively (using stochastic perturbation theory) and fully non-perturbatively (using lattice field theory simulations). The present approach holds to all orders in the couplings and does not rely on the semi-classical approximation.Comment: 15 pages, 4 figure

Strong CP Violation in External Magnetic Fields

We study the response of the QCD vacuum to an external magnetic field, in the presence of strong CP violation. Using chiral perturbation theory and large N_c expansion, we show that the external field would polarize quantum fluctuations and induce an electric dipole moment of the vacuum, along the direction of the magnetic field. We estimate the magnitude of this effect in different physical scenarios. In particular, we find that the polarization induced by the magnetic field of a magnetar could accelerate electric charges up to energies of the order \theta 10^3 TeV. We also suggest a connection with the possible existence of "hot-spots" on the surface of neutron stars.Comment: 4 pages, 1 figure. Major revision. Phenomenological analysis extende

Ultra-Low Noise Microwave Extraction from Fiber-Based Optical Frequency Comb

In this letter, we report on all-optical fiber approach to the generation of ultra-low noise microwave signals. We make use of two erbium fiber mode-locked lasers phase locked to a common ultra-stable laser source to generate an 11.55 GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz from the carrier.The residual frequency instability of the microwave signals derived from the two optical frequency combs is below 2.3 10^(-16) at 1s and about 4 10^(-19) at 6.5 10^(4)s (in 5 Hz bandwidth, three days continuous operation).Comment: 12 pages, 3 figure

Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study

We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on top of which ferromagnetic SRO islands were grown epitaxially in-situ. When measured on the ferromagnetic islands, the density of states exhibits small gap-like features consistent with the expected short range penetration of the order parameter into the ferromagnet. However, anomalous split-gap structures are measured on the superconductor in the vicinity of ferromagnetic islands. This observation may provide evidence for the recently predicted induced magnetization in the superconductor side of a superconductor/ ferromagnet junction. The length scale of the effect inside the superconductor was found to be an order of magnitude larger than the superconducting coherence length. This is inconsistent with the theoretical prediction of a penetration depth of only a few superconducting coherence lengths. We discuss a possible origin for this discrepancy

Computing the Effective Hamiltonian of Low-Energy Vacuum Gauge Fields

A standard approach to investigate the non-perturbative QCD dynamics is through vacuum models which emphasize the role played by specific gauge field fluctuations, such as instantons, monopoles or vortexes. The effective Hamiltonian describing the dynamics of the low-energy degrees of freedom in such approaches is usually postulated phenomenologically, or obtained through uncontrolled approximations. In a recent paper, we have shown how lattice field theory simulations can be used to rigorously compute the effective Hamiltonian of arbitrary vacuum models by stochastically performing the path integral over all the vacuum field fluctuations which are not explicitly taken into account. In this work, we present the first illustrative application of such an approach to a gauge theory and we use it to compute the instanton size distribution in SU(2) gluon-dynamics in a fully model independent and parameter-free way.Comment: 10 pages, 4 figure

An Ultra-Stable Referenced Interrogation System in the Deep Ultraviolet for a Mercury Optical Lattice Clock

We have developed an ultra-stable source in the deep ultraviolet, suitable to fulfill the interrogation requirements of a future fully-operational lattice clock based on neutral mercury. At the core of the system is a Fabry-P\'erot cavity which is highly impervious to temperature and vibrational perturbations. The mirror substrate is made of fused silica in order to exploit the comparatively low thermal noise limits associated with this material. By stabilizing the frequency of a 1062.6 nm Yb-doped fiber laser to the cavity, and including an additional link to LNE-SYRTE's fountain primary frequency standards via an optical frequency comb, we produce a signal which is both stable at the 1E-15 level in fractional terms and referenced to primary frequency standards. The signal is subsequently amplified and frequency-doubled twice to produce several milliwatts of interrogation signal at 265.6 nm in the deep ultraviolet.Comment: 7 pages, 6 figure

Real CO2 emissions benefits and end user’s operating costs of a plug-in Hybrid Electric Vehicle

Although plug-in Hybrid Electric Vehicles (pHEVs) can be considered a powerful technology to promote the change from conventional mobility to e-mobility, their real benefits, in terms of CO2 emissions, depend to a great extent on the average efficiency of their Internal Combustion Engine and on the energy source mix which is used to supply the electrical demand of pHEV. Furthermore the operating cost of the vehicle should also be taken into account in the design process, since it represents the main driver in the customer’s choice. This article has the purpose of assessing, through numerical simulations, the effects of different technology mixes used to produce electrical energy for the battery recharging, of different Internal Combustion Engines on the pHEV performance, and highlighting the main differences with respect to the regulatory test procedure

Scanning tunneling spectroscopy characterization of the pseudogap and the x = 1/8 anomaly in La2-xSrxCuO4 thin films

Using scanning tunneling spectroscopy we examined the local density of states of thin c-axis La2-xSrxCuO4 films, over wide doping and temperature ranges. We found that the pseudogap exists only at doping levels lower than optimal. For x = 0.12, close to the 'anomalous' x = 1/8 doping level, a zero bias conductance peak was the dominant spectral feature, instead of the excepted V- shaped (c-axis tunneling) gap structure. We have established that this surprising effect cannot be explained by tunneling into (110) facets. Possible origins for this unique behavior are discussed.Comment: 15 pages, 6 figure