Search results for "annihilation"
showing 10 items of 1016 documents
Positron Annihilation Characteristics in Superstrong Magnetic Fields
2010
The recent interest in positrons distribution in the space revealed the anomalous presence of high energetic positrons. There are different possible origins of such positrons, including the decay of heavy particles in the dark matter, also pulsars or neutron stars. In our study we calculated the annihilation properties of the electron – positron bound system in superstrong magnetic fields expected for neutron stars. For this aim we use solutions of the (relativistic) Bethe-Salpeter equation derived by L.B. Leinson and A. Perez [1]. The results indicate strong dependency of the annihilation properties (rate and intensity) on the value of the magnetic field.
Superregular Breathers in Optics and Hydrodynamics: Omnipresent Modulation Instability beyond Simple Periodicity
2015
Since the 1960s, the Benjamin-Feir (or modulation) instability (MI) has been considered as the self-modulation of the continuous “envelope waves” with respect to small periodic perturbations that precedes the emergence of highly localized wave structures. Nowadays, the universal nature of MI is established through numerous observations in physics. However, even now, 50 years later, more practical but complex forms of this old physical phenomenon at the frontier of nonlinear wave theory have still not been revealed (i.e., when perturbations beyond simple harmonic are involved). Here, we report the evidence of the broadest class of creation and annihilation dynamics of MI, also called superre…
Atomic physics of positronium with intense slow positron beams
2002
Abstract The theory of quantum electrodynamics has presented a complete calculation of the energy levels of positronium (Ps, e + e − ) up to the order R ∞ α 4 . The annihilation rates for para -Ps (1 1 S 0 ) and ortho -Ps (1 1 S 1 ) are completely known up to the order R ∞ α 5 and R ∞ α 6 , respectively. The present experimental uncertainty for spectroscopic results is 5–100 times larger than the theoretical uncertainty. For the annihilation rates the experimental situation is even worse. The theoretical predictions have presently reached a level of precision which is a challenge to experimentalists! The experimental uncertainty for the fine- and hyperfine transitions in the Ps atom is dete…
On Anomaly-Free Dark Matter Models
2019
We investigate the predictions of anomaly-free dark matter models for direct and indirect detection experiments. We focus on gauge theories where the existence of a fermionic dark matter candidate is predicted by anomaly cancellation, its mass is defined by the new symmetry breaking scale, and its stability is guaranteed by a remnant symmetry after the breaking of the gauge symmetry. We find an upper bound on the symmetry breaking scale by applying the relic density and perturbative constraints. The anomaly-free property of the theories allows us to perform a full study of the gamma lines from dark matter annihilation. We investigate the correlation between predictions for final-state radia…
Isotropic extragalactic flux from dark matter annihilations: lessons from interacting dark matter scenarios
2016
The extragalactic gamma-ray and neutrino emission may have a contribution from dark matter (DM) annihilations. In the case of discrepancies between observations and standard predictions, one could infer the DM pair annihilation cross section into cosmic rays by studying the shape of the energy spectrum. So far all analyses of the extragalactic DM signal have assumed the standard cosmological model (LambdaCDM) as the underlying theory. However, there are alternative DM scenarios where the number of low-mass objects is significantly suppressed. Therefore the characteristics of the gamma-ray and neutrino emission in these models may differ from LambdaCDM as a result. Here we show that the extr…
Assessment of the CTOCD-DZ methodin a hierarchy of coupled cluster methods
2010
Gauge origin independent calculations of nuclear magnetic shielding tensors are carried out inside the formalism of the continuous transformation of the origin of the current density leading to formal annihilation of its diamagnetic contribution (CTOCD-DZ). We employ the unrelaxed linear response approach with a hierarchy of different coupled cluster methods in order to assess the importance of the level of approximation in the coupled cluster expansion. The basis set dependence of the computed nuclear magnetic shielding constants is also analyzed in the series of correlation consistent basis sets, with the aim of designing optimized basis sets of relatively small size.
Annihilation Characteristics of Confined 2D Positronium
2012
The 2D Positronium (2D Ps) atom confined in the 2D cave has been considered and its properties were compared with the 3D Positronium located in the infinity square well potential. Basing on the solution of Schrödinger equation for the 2D hydrogen atom the wave function of the 2D Ps was given. It allows us to calculate, for instance the angular correlation of the annihilation radiation (ACAR) of such a system. It was shown that the ACAR is much broad than ACAR for the 3D Ps and that for the Ps in the bubble model.
Influence of Electron-Electron Correlations and Lattice Effects on Positron-Electron Enhancement Factors
2010
We present an approach taking into account the effect of electron-electron (e-e) correlations on electron-positron (e-p) momentum density distributions. The approach bases on the modification of the Bethe-Goldstone (B-G) equation for the positron in the electron gas due to self-energy effects. The example calculations have been performed for selected parameters corresponding to simple metals. The calculated dependencies exhibit the increase of the e-p enhancement factors below Fermi momentum, like Kahana enhancements, and a decrease above the Fermi sphere, leading to a many-body “tail” in the e-p momentum density distributions. Moreover, the influence of lattice effects on enhancement facto…
Observation ofB0Meson Decay toa1±(1260)π∓
2006
We present a measurement of the branching fraction of the decay B-0 -> a(1)(+/-)(1260)pi(-/+) with a(1)(+/-)(1260)->pi(-/+)pi(+/-)pi(+/-). The data sample corresponds to 218x10(6) B (B) over bar pairs produced in e(+)e(-) annihilation through the Upsilon(4S) resonance. We measure the branching fraction B(B-0 -> a(1)(+/-)(1260)pi(-/+))B(a(1)(+/-)(1260)->pi(-/+)pi(+/-)pi(+/-))=(16.6 +/- 1.9 +/- 1.5)x10(-6), where the first error quoted is statistical and the second is systematic.
Algebraic Treatment of a Three-Oscillator System: Applications to Some Molecular Models
1997
Abstract A new algebraic treatment of a three-oscillator system, called 3d formalism, is proposed. First, arbitrary tensor operators, expressed in terms of elementary creation and annihilation boson operators, are built within the standard algebraic chain u (3) ⊃ so (3) ⊃ so (2). Their matrix elements are next derived in a standard basis. Some applications, which require few adaptions or extensions, are proposed. They allow one to recover, for instance, Hecht's and tetrahedral Hamiltonians associated with threefold degenerate modes of spherical molecules and the vibron model Hamiltonian introduced for diatomic molecules.