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Afterpulsing is a factor limiting the distance over which discrete-variable quantum key distribution systems are secure, and a common feature in single-photon detectors. The relevance of this phenomenon stems from its stochastic, self-interacting nature and the fact that its rate rises with the number of avalanche events, which increases the quantum bit error rate. Here we introduce an effective analytic model, including dead-time and afterpulsing corrections, where afterpulsing correction depends on dead-time value. This model is useful to evaluate the performance of prepare and measure quantum key distribution protocols (standard and decoy versions) that use gated single photon detectors. The model provides an expression to numerically optimize the secret key rate over the full distance range for secure communication, enabling in this way the calculation of quantum bit error rate and secure key rate. In the conventional procedure, the dead-time value is fixed regardless of distance, limiting the distance range of the channel due to remaining afterpulsing effects, which are more relevant at higher operating frequencies. Here we demonstrate that optimizing the dead-time values increases the distance range of the channel to share secret keys., Comment: 13 pages, 9 figures

Wide binary stars are within the low-acceleration regime in which galactic rotation curves deviate from Newtonian or general relativistic predictions. It has recently been observed that their rotation rates are similarly anomalous in a way that dark matter cannot explain, since it must be smooth on these small scales to fit galaxy rotation curves. Here, it is shown that Newtonian/GR models cannot predict these wide binaries since dark matter cannot be applied. It is also shown that MoND cannot predict these systems. However, a model which assumes that inertia is due to Unruh radiation made inhomogeneous in space by relativistic horizons (QI, quantised inertia) can predict these wide binaries, and it has the advantage of not needing an adjustable parameter., Comment: 9 pages, 1 figure. Accepted by Astrophysics and Space Science on 26/7/2019

We report on the use of Z-scan technique with a beam composed with two modes, to probe the nonlinear optical properties of phosphate glasses doped with Er$^{3+}$-Yr$^{3+}$ and silver nanoparticles. Understanding the linear and nonlinear properties of these materials is crucial to evaluate if they are candidates to be used as gain media in lasers or optical amplifiers. Experiments are carried out by implementing the open-aperture Z-scan technique with bimodal laser pumping ($LG_{00}$ and $LG_{20}$) at 908.6 nm. The analysis is performed using a simplifiedmodel that incorporates nonlinear absorption and saturation intensity of the samples. The advantage of using a beam with a bimodal structure is that it allows us to evaluate the energy transfer between the modes, which is relevant since the optical active media act as an intermediary. This process is incorporated through an effective phenomenological parameter in the model that we use in our analysis., Comment: 9 pages, 8 figures

We consider crystal chirp effects on SPDC when pumping at 800 nm. The typical distribution produced in frequency-momentum space is a pop tab-like structure which turns out to be suitable for the implementation of versatile light sources. Our analyzes consider the effect of internal and external parameters in the process; in the former we include the crystal chirp and length, while in the latter temperature, as well as pump chirp and beam properties. We report evidence of the appropriateness of SPDC from chirped crystals to manipulate the frequency and transverse momentum properties of the light produced. We briefly comment on potential usefulness of the types of light produced, in particular for quantum information applications., Comment: 7 pages, 6 figures, theory

We study the chronocyclic character, i.e. the joint temporal and spectral properties, of the single-photon constituents of photon pairs generated by spontaneous parametric down conversion. In particular we study how single photon properties, including purity and single-photon chirp, depend on photon pair properties, including the type of signal-idler spectral and correlations and the level of pump chirp., Comment: 13 pages, 6 figures

In this work, it has been investigated whether photonic density of states maps can be applied to the design of photonic crystal-based devices. For this reason, comparison between photonic density of states maps and transmittance maps was carried out. Results of comparison show full correspondence between these characteristics. Photonic density of states maps appear to be preferable for the design of photonic crystal devices, than photonic band gap maps presented earlier and than transmittance maps shown in the paper., Comment: 5 pages, 6 figures

In the paper, we propose the new technology for mass production of the photonic crystal devices and all-optical integrated circuits. We carry out the brief analysis of positive and negative sides paying attention to recent advances in silicon fibers fabrication which is crucial moment in the proposed technology., Comment: 3 pages, 4 figures

We propose a new method for mass production of the photonic crystal devices on the basis of widely-known and well-developed technology such as microstructured optical fibers. In this paper, we investigate the optical properties of side-excited microstructured optical fiber and discuss the conditions for utilization such a structure as a planar photonic crystal device, namely, the high-quality resonance filter., Comment: 7 pages, 7 figures

We consider the forward-backward pion charge asymmetry for the e^{+}e^{-}\to\pi^{+}\pi^{-}\gamma process. At tree level we consider bremsstrahlung and double resonance contributions. Although the latter contribution is formally sub-leading, it is enhanced at low dipion invariant mass due to $\rho$ resonant effects. We consider also four alternative models to describe the final state radiation at the loop level: Resonance Chiral Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and Linear Sigma Model. The last three models yield results compatible with experimental data. The Kaon Loop Model requires an energy dependent phase to achieve the agreement., Comment: Revised version, conclusions changed, 11 pages, 8 figs, version to appear in PLB

In the work, the new method for the design of the wavelength division multiplexer on the basis of 2D photonic crystal integrated circuit for the ultra-short pulses channel separation is proposed and investigated. The method is based on the analysis of full photonic bandgap maps that allows defining the ultra-short pulse demultiplexer parameters selection. For the method approbation, there was synthesized the device in which the wideband filters are used for the channel separation. As it was expected, the device effectively separates 50 fs pulse channels with 1.31 and 1.55 microns wavelengths. The obtained spectral characteristics and pulse pattern responses validate the efficiency of the proposed method and the applicability of such devices to the integrated photonic information processing circuits.

We show that therecently observed pion invariant mass distribution of the phi ->pi0 pi0 gamma decay can be satisfactorily described by the chiral U(3) X U(3) Linear Sigma Model., Comment: 5 Pags. 2 Figs. Contribution to DAFNE99, Frascati Italy Nov (99)

Chiral Ward identities lead to consistent accounting for the sigma's width in the linear sigma model's Feynman rules. Reanalysis of pion scattering data at threshold imply a mass for the sigma of 600+ 200 - 100 MeV., Comment: latex; VIII EMPC (Oaxaca, Nov 98) Proceedings

We enforce chiral Ward identities on the vertices of the linear sigma model to take into account the width of the scalar sigma, considered as a true physical resonance. We consider pion scattering at very low energies and, from a fit to the measured phase shifts in the various angular momentum and isospin channels, conclude a mass for the sigma of 600+200-100 MeV. Its width turns out to be of the same size.

We evaluate the omega to rho pi transition and the omega to 3 pi decay using a Quark Level Linear Sigma Model ($QL\sigma M$). We obtain $g^{QL\sigma M}_{\omega\rho\pi}= (10.33 - 14.75) GeV^{-1}$ to be compared with other model dependent estimates averaging to $g_{\omega\rho\pi} = 16 GeV^{-1}$. We show that in the $QL\sigma M$ a contact term is generated for the $\omega \to 3 \pi$ decay. Although the contact contribution by itself is small, the interference effects turn out to be important., Comment: 12 pages, LaTeX, 3 eps figures, uses epsf.sty

We work out predictions of the Linear Sigma Model for the $\gamma \gamma \to\pi^0 \pi^0$ cross section. We consider the sigma width, which is introduced in a consistent way with chiral Ward identities. The results of Chiral Perturbation Theory are recovered in the $m_\sigma \to \infty$ limit. A fit to existing experimental results is consistent with a light and broad $\sigma$ meson., Comment: 7 pages, 3 figures. The sigma width is introduced in a consistent way with chiral symmetry. Results for the cross section are affected by the corresponding changes

The dual Schrodinger equation for x in terms of psi derived by Faraggi and Matone [hep-th/9606063] with techniques inspired by field theory duality can be derived almost trivially from differential calculus., Comment: latex, two pages

We re-consider the quantum mechanics of scale invariant potentials in two dimensions. The breaking of scale invariance by quantum effects is analyzed by the explicit evaluation of the phase shift and the self-adjoint extension method. We argue that the breaking of scale invariance reported in the literature for the $\delta$(r) potential, is an example of explicit and not an anomaly or quantum mechanical symmetry breaking., Comment: 15 pp in latex, no figures

We assume the stability of vacuum under radiative corrections in the context of the standard electroweak theory. We find that this theory behaves as a good effective model already at cut off energy scales as low as 0.7 TeV. This stability criterion allows to predict m_H= 318 +- 13 GeV for the Higgs boson mass., Comment: Latex, 5 pages, 1 Postscript figure included

We analyze the consistency of the Chiral Lagrangian approach to the description of the spin 3/2 interacting theory. We argue that to lowest order in the 1/m expansion, the formalism leads to the appropriated constraints and the theory is free of the so called ``off shell" ambiguities., Comment: 12 pages, Latex