arXiv subjects

A. Abd El-Hady

Publications and source records attributed to A. Abd El-Hady.

14 recordsLinked to original sources

arXiv2011

Random matrix theory for mixed regular-chaotic dynamics in the super-extensive regime

We apply Tsallis's q-indexed nonextensive entropy to formulate a random matrix theory (RMT), which may be suitable for systems with mixed regular-chaotic dynamics. We consider the super-extensive regime of q < 1. We obtain analytical expressions for the level-spacing distributions, which are strictly valid for 2 \times 2 random-matrix ensembles, as usually done in the standard RMT. We compare the results with spacing distributions, numerically calculated for random matrix ensembles describing a harmonic oscillator perturbed by Gaussian orthogonal and unitary ensembles.

math-ph↗

arXiv2006

Level statistics for two-dimensional oscillators

We consider the level statistics of two-dimensional harmonic oscillators with incommensurable frequencies, which are known to have picket-fence type spectra. We propose a parametric representation for the level-spacing distribution and level-number variance, and study the variation of the parameters with the frequency ratio and the size of the spectra. By introducing an anharmonic perturbation, we observe a gradual transition to the Poisson statistics. We describe the level spectra in transition from harmonic to Poissonian statistics as a superposition of two independent sequences, one for each of the two extreme statistics. We show that this transition provides a suitable description for the evolution of the spectrum of a disordered chain with increasing long range correlations between the lattice sites.

cond-mat.stat-mech↗

arXiv2006

Superradiance and subradiance in the electromagnetic radiative decay of X(3872)

It is pointed out that if the molecular interpretation of the recently observed resonance X(3872) is valid, then nature may have prepared a good laboratory for us to examine the phenomenon of superradiance and subradiance of Dicke. The superradiance and supradiance factors are evaluated and the effects on the electromagnetic radiative decay of X(3872) are discussed. Our results using coordinate space representation is similar to the momentum space results of Voloshin.

hep-ph↗

arXiv2006

Radiative decays of Bc mesons in a Bethe-Salpeter model

We evaluate the complete spectrum of the Bc mesons, below the open flavor BD threshold, in a Bethe-Salpeter model. We make predictions for the radiative decay widths of the Bc excited states. We compare our results with those of other models.

hep-ph↗

arXiv2001

Influence of symmetry breaking on the fluctuation properties of spectra

We study the effect of gradual symmetry breaking in a non-integrable system on the level fluctuation statistics. We consider the case when the symmetry is represented by a quantum number that takes one of two possible values, so that the unperturbed system has a spectrum composed of two independent sequences. When symmetry-breaking perturbation is represented by a random matrix with an adjustable strength, the shape of the spectrum monotonously evolves towards the Wigner distribution as the strength parameter increases. This contradicts the observed behaviour of the acoustic resonance spectra in quartz blocks during the breaking of a point-group symmetry that has two eigenvalues, where the system changes in the beginning towards the Poisson statistics then turns back to the GOE statistics. This behaviour is explained by assuming that the symmetry breaking perturbation removes the degeneracy of a limited number of levels, thus creating a third chaotic sequence. As symmetry breaking increases, the new sequence grows at the expense of the initial pair until it overwhelms the whole spectrum when the symmetry completely disappears. The calculated spacing distribution and spectral rigidity are able to describe the evolution of the observed acoustic resonance spectra.

nlin.CD↗

arXiv2000

Hyperon Nonleptonic Decays in Chiral Perturbation Theory Reexamined

We recalculate the leading nonanalytic contributions to the amplitudes for hyperon nonleptonic decays in chiral perturbation theory. Our results partially disagree with those calculated before, and include new terms previously omitted in the P-wave amplitudes. Although these modifications are numerically significant, they do not change the well-known fact that good agreement with experiment cannot be simultaneously achieved using one-loop S- and P-wave amplitudes.

hep-ph↗

arXiv1999

Chiral Perturbation Theory for |Delta I|=3/2 Hyperon Decays

We study the |Delta I|=3/2 amplitudes of hyperon non-leptonic decays of the form B->B'+pi in the context of chiral perturbation theory. The lowest-order predictions are determined in terms of only one unknown parameter and are consistent within errors with current data. We investigate the theoretical uncertainty of these predictions by calculating the leading non-analytic corrections. We also present an estimate for the size of the S-wave Lambda and Cascade decays which vanish at leading order. We find that the corrections to the lowest-order predictions are within the expectations of naive power counting and, therefore, that this picture can be tested more accurately with improved measurements.

hep-ph↗

arXiv1999

Semileptonic and non-leptonic B_c decays

We make predictions for the exclusive semileptonic and the non-leptonic decay widths of the B_c meson. We evaluate the B_c semileptonic form factors for different decay channels in a relativistic model, and use factorization to obtain the non-leptonic decay widths.

hep-ph↗

arXiv1998

$B_c$ mesons in a Bethe-Salpeter model

We apply our Bethe-Salpeter model for mesons to the $B_c$ family with parameters fixed in our previous investigation. We evaluate the mass of the pseudo-scalar $B_c$ meson as 6.356 GeV/$c^2$ and 6.380 GeV/$c^2$ and the lifetime as 0.47 ps and 0.46 ps respectively in two reductions of the Bethe-Salpeter Equation, in good agreement with the recently reported mass of 6.40 $\pm$ 0.39 (stat.) $\pm$ 0.13 (syst.) GeV/$c^2$ and lifetime of $0.46^{+0.18}_{-0.16}$ (stat.) $\pm$ 0.03 (syst.) ps by the CDF Collaboration. We evaluate the decay constant of the $B_c$ meson and compare different contributions to its decay width.

hep-ph↗

arXiv1997

Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar B} \to D^* l {\barν} $ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l {\barν} $ decays. The form factors are then used to obtain non-leptonic decay partial widths for $ B\to D π(K) $ and $B \to D D (D_s) $ in the factorization approximation.

hep-ph↗

arXiv1997

CP Violation in B Decays from Anomalous tbW Interactions

We calculate the effect of new CP violating interactions parameterized by an anomalous $tbW$ coupling on CP-odd observables in B decays. We find that couplings consistent with current bounds induce observable effects in some CP asymmetries that will be measured in B-factories. The new effects are sufficiently large that they can actually test specific models that give rise to these $tbW$ interactions.

hep-ph↗

arXiv1996

B --> D(D^*) Form Factors in a Bethe-Salpeter model

We calculate the form factors for the semileptonic decays of the $B$ meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. We show that our model is consistent with the constraints of Heavy Quark Effective Theory (HQET) and we extract the matrix elements that represent the $1/m_Q$ corrections to the form factors in HQET. With available data, we obtain $V_{cb} $=$ (31.9 \pm 1.4)\times10^{-3}$.

hep-ph↗

arXiv1994

Relativistic Meson Spectroscopy and In-Medium Effects

We extend our earlier model of $q\bar q$ mesons using relativistic quasipotential (QP) wave equations to include open-flavor states and running quark-gluon coupling effects. Global fits to meson spectra are achieved with rms deviations from experiment of 43-50 MeV. We examine in-medium effects through their influence on the confining interaction and predict the confining strength at which the masses of certain mesons fall below the threshold of their dominant decay channel.

nucl-th↗

arXiv1994

Isgur-Wise Function and $V_{cb}$ from Bethe-Salpeter Equations

We calculate the Isgur-Wise function from the solutions of the Bethe-Salpeter equations. The shape of the Isgur-Wise function thus calculated is a prediction of the Bethe-Salpeter equations and does not depend on undetermined parameters. We develop an analytical approximation to our Isgur-Wise function in the form $ξ( ω) = η[ 1 - \frac{ρ^2}η (ω- 1) + a (ω- 1)^{3/2}]$ where $ρ^2 = 1.279$, $a = .91$, $η= .9942$ and $ω$ is the recoil velocity. The Isgur-Wise function is then used to obtain $V_{cb}$ from the recent experimental data of ${\bar B} \to D^* \ell \barν$ decay. Our best estimate of $V_{cb}$ is $(34.7 \pm 2.5) \times 10^{-3}$, which is comparable to some of the latest estimates in the literature.

hep-ph↗