Search results for "Particle physics"
showing 10 items of 6826 documents
Underlying A_4 Symmetry for the Neutrino Mass Matrix and the Quark Mixing Matrix
2002
The discrete non-Abelian symmetry $A_4$, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter $U_{e3}$ is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and $\tau \to \mu \gamma$ should be in the experimentally accessible range.
Radiative Pion Photoproduction from the Proton and π + Meson Polarizabilities
1995
We study the possibility of investigating radiative pion photoproduction from the proton at the microtron MAMI-B with the aim to obtain an experimental information about the π + meson polarizabilities. It is shown that an exposition time of about 30 days will allow to determine the π + meson polarizability with quite high accuracy.
Universal extra dimensions andZ→bb¯
2003
We study, at the one loop level, the dominant contributions from a single universal extra dimension to the process $\stackrel{\ensuremath{\rightarrow}}{Z}b\overline{b}.$ By resorting to the gaugeless limit of the theory we explain why the result is expected to display a strong dependence on the mass of the top quark, not identified in the early literature. A detailed calculation corroborates this expectation, giving rise to a lower bound for the compactification scale which is comparable to that obtained from the $\ensuremath{\rho}$ parameter. An estimate of the subleading corrections is furnished, together with a qualitative discussion on the difference between the present results and thos…
Hidden Oscillations in Electromechanical Systems
2016
In this paper an electromechanical system with two different types of motor is considered. It is shown that during the spin-up, the system with DC motor may experience unwanted vibration—the Sommerfeld effect. This is a well-known effect when the motor of electromechanical system gets stuck near the resonance zone instead of reaching its nominal power. The absence of this effect is demonstrated in the system with synchronous motor. Nowadays, there are many works devoted to the study of this effect in various systems. Here we discuss the Sommerfeld effect from the point of view of localization of the so-called hidden oscillations.
Plasmonic Focusing Reduces Ensemble Linewidth
2012
In this chapter I present an effect the coating of gold nanorods with a silver shell is evocating: a reduction of the ensemble plasmon linewidth by changing the plasmon-shape relation, which connects the particle shape with its plasmon resonance wavelength. This change, we term “plasmonic focusing” (Sect. 10.2), leads to less variation of resonance wavelengths for the same particle size distribution. Section 10.3 explains the effect of increasing single particle linewidth during the coating process, which is therefore not the reason for the observed ensemble linewidth decrease. This is rather a result from a change in the plasmon-shape relation explained in Sect. 10.4. Using a simple model,…
Theρ(ω)/B*(B) system and bound states in the unitary local Hidden Gauge approach
2016
In this work, we study systems composed of a ρ/ω and B* meson pair. We find three bound states in isospin, spin-parity channels (1/2, 0+ ), (1/2, 1+ ) and (1/2, 2+ ). The state with J = 2 can be a good candidate for the B * 2 (5747). We also study the ρB system, and a bound state with mass 5728 MeV and width around 20 MeV is obtained, which can be identified with the B 1 (5721) resonance. In the case of I = 3/2, one obtains repulsion and thus, no exotic (molecular) mesons in this sector are generated in the approach.
Initial state anisotropies in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model
2012
In hydrodynamicalmodeling of heavy-ion collisions the initial state spatial anisotropies translate into momentum anisotropies of the final state particle distributions. Thus, understanding the origin of the initial anisotropies and quantifying their uncertainties is important for the extraction of specific QCD matter properties, such as viscosity, from the experimental data. In this work we study the wounded nucleon approach in the Monte Carlo Glauber model framework, focusing especially on the uncertainties which arise from the modeling of the nucleon-nucleon interactions between the colliding nucleon pairs and nucleon-nucleon correlations inside the colliding nuclei. We compare the black …
Approximate NNLO predictions for the stop-pair production cross section at the LHC
2013
If the minimal supersymmetric standard model at scales of around 1 TeV is realized in nature, the total top-squark pair production cross section should be measurable at the CERN Large Hadron Collider. In this work we present precise predictions for this observable, which are based upon approximate NNLO formulas obtained using soft-collinear effective theory methods.
Compton scattering off nucleons near threshold
2008
The energy dependence of the magnetic polarizability β has been evaluated by use of the delta resonance in the s- and u-channel of the Compton scattering amplitude. It was the idea to extract the influence of higher order terms (higher than ω2, ω = |k| being the photon energy) in the analysis of the polarizability. The static paramagnetic polarizability βPara(0) has been substituted by an energy dependent βδPara(k) and the result is compared with experimental data.
Possible detection of a radio event correlated with a γ-ray burst
1977
COSMIC bursts of electromagnetic radiation, both isolated and in connection with other impulsive astrophysical phenomena, have been sought for many years1, with only one suggestive positive result2, until, in 1973, the discovery of γ-ray bursts3 of cosmic origin prompted a new series of observations4. In 1975 we started a systematic search for electromagnetic bursts at v.h.f. and u.h.f. The system, based at Medicina (Bologna, Italy), is semi-automatic and assures highly efficient data collection. Simultaneous observations at different frequencies facilitate the evaluation of disturbances of local origin and, hopefully, their isolation. Regular observations started in July 1976, and we repor…