Laser-beam scintillations for weak and moderate turbulence

The scintillation index is obtained for the practically important range of weak and moderate atmospheric turbulence. To study this challenging range, the Boltzman-Langevin kinetic equation, describing light propagation, is derived from first principles of quantum optics based on the technique of the photon distribution function (PDF) [G. P. Berman et al., Phys. Rev. A 74, 013805 (2006)]. The paraxial approximation for laser beams reduces the collision integral for the PDF to a two-dimensional operator in the momentum space. Analytical solutions for the average value of PDF as well as for its fluctuating constituent are obtained using an iterative procedure. The calculated scintillation index is considerably greater than that obtained within the Rytov approximation even at moderate turbulence strength. The relevant explanation is proposed.Comment: 11 pages, 4 figure

Possibility to study eta-mesic nuclei and photoproduction of slow eta-mesons at the GRAAL facility

A new experiment is proposed with the aim to study eta-mesic nuclei and low-energy interactions of eta with nuclei. Two decay modes of eta produced by a photon beam inside a nucleus will be observed, namely a collisional decay \eta N \to \pi N inside the nucleus and the radiative decay \eta \to \gamma \gamma outside. In addition, a collisional decay of stopped S_{11}(1535) resonance inside the nucleus, S_{11}(1535) N \to N N, will be studied. The experiment can be performed using the tagged photon beam at ESRF with the end-point energy 1000 MeV and the GRAAL detector which includes a high-resolution BGO calorimeter and a large acceptance lead-scintillator time-of-flight wall. Some results of simulation and estimates of yields are given.Comment: 20 pages, 19 figure

The de Rham cohomology of the algebra of polynomial functions on a simplicial complex

We consider the algebra $A^0 (X)$ of polynomial functions on a simplicial complex $X$. The algebra $A^0 (X)$ is the $0$th component of Sullivan's dg-algebra $A^\bullet (X)$ of polynomial forms on $X$. Our main interest lies in computing the de Rham cohomology of the algebra $A^0(X)$, that is, the cohomology of the universal dg-algebra $\Omega ^\bullet _{A^0(X)}$. There is a canonical morphism of dg-algebras $P:\Omega ^\bullet _{A^0(X)} \to A^\bullet (X)$. We prove that $P$ is a quasi-isomorphism. Therefore, the de Rham cohomology of the algebra $A^0 (X)$ is canonically isomorphic to the cohomology of the simplicial complex $X$ with coefficients in $k$. Moreover, for $k=\mathbb{Q}$ the dg-algebra $\Omega ^\bullet _{A^0 (X)}$ is a model of the simplicial complex $X$ in the sense of rational homotopy theory.Comment: 8 page

Fourth-order moment of the light field in atmosphere for moderate and strong turbulence

Collisionless Boltzmann equation is used to describe the intensity correlations in partially saturated and fully saturated regimes in terms of photon distribution function in the phase space. Explicit expression for fourth moment of the light fields is obtained for the case of moderate and strong turbulence. Such expression consists of two terms accounting for two regions in the phase space that independently contribute to the correlation function. It is shown that present solution agrees with previous results for fully saturated regime. Additionally it embodies the effect of partially saturated radiation where the correlations of photon trajectories are important and the magnitude of the scintillation index is well above the unity. Fourth moment is used to study the fluctuations of transmittance which consider the effect of finite detector aperture.Comment: 10 pages, 5 figure