Search results for " Quantum Mechanics."
showing 10 items of 197 documents
New neutrino mass sum rule from the inverse seesaw mechanism
2012
A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum rules. One of these implies a lower bound on the effective neutrinoless double beta mass parameter, even for normal hierarchy neutrinos. Here we propose a new model based on the ${S}_{4}$ flavor symmetry that leads to the new neutrino mass sum rule and discuss how to generate a nonzero value for the reactor angle ${\ensuremath{\theta}}_{13}$ indicated by recent experiments, and the resulting correlation with the solar angle ${\ensuremath{\theta}}_{12}$.
Fermion masses and unitarity without a Higgs boson
2004
We discuss the consistency of fermion mass generation by boundary conditions and brane localized terms in higher dimensional models of gauge symmetry breaking without a Higgs boson. The sum rules imposed by tree-level unitarity and Ward identities are applied to check the consistency of mass generation by orbifold projections and more general boundary conditions consistent with the variational principle. We find that the sum rules are satisfied for boundary conditions corresponding to brane localized mass and kinetic terms consistent with the reduced gauge symmetry on the brane.
Low-energy Compton scattering and the polarizabilities of the proton
2001
Differential cross-sections for Compton scattering from the proton have been measured at the MAMI tagged photon facility using the TAPS setup. The data cover an angular range of θlab γ = 59°-155° and photon energies ranging from 55 MeV to 165 MeV. Our results are in good agreement with those from previous experiments, but yield higher precision. Using dispersion relations the proton polarizabilities have been determined to be = [11.9±0.5stat.±1.3syst.±0.3mod.] . 10-4 fm 3 and = [1.2±0.7stat.±0.3syst.±0.4mod.)] . 10-4 fm 3. These results confirm the Baldin sum rule which was re-evaluated to be + = [13.8±0.4] . 10-4 fm 3. We can also conclude that there is no significant additional asymptotic…
Study of polarization observables in double pion photoproduction on the proton
2001
Using a model for two pion photoproduction on the proton previously tested in total cross sections and invariant mass distributions, we evaluate here polarization observables on which recent experiments are providing new information. We evaluate cross sections for spin 1/2 and 3/2, which are measured at Mainz and play an important role in tests of the GHD sum rule. We also evaluate the proton polarization asymmetry $\Sigma$ which is currently under investigation at GRAAL in Grenoble.
On the Gerasimov-Drell-Hearn sum rule for the deuteron
1997
The Gerasimov-Drell-Hearn sum rule is evaluated for the deuteron by explicit integration up to a photon energy of 550 MeV including contributions from the photodisintegration channel and from coherent and incoherent single pion production as well. The photodisintegration channel converges fast enough in this energy range and gives a large negative contribution, essentially from the $^1S_0$ resonant state near threshold. Its absolute value is about the same size than the sum of proton and neutron GDH values. It is only partially cancelled by the single pion production contribution. But the incoherent channel has not reached convergence at 550 MeV.
Determination of the total photo-absorption cross section of 197Au from () reaction cross sections
1984
Abstract Cross sections for the reactions 197Au ( γ, ℩ n ) (x ⩽ 12) have been measured for bremsstrahlung end-point energies in the range 60–340 MeV. From these dominant cross sections, the total photon absorption cross section is determined using a cascade-evaporation calculation to account for the missing reaction channels. The enhancement factor for the classical E1 sum rule is found to be 0.93 ± 0.10.
A sum-rule approach to nuclear ground state correlations
1985
By combining the sum-rule approximation to nuclear giant resonances with a generator-coordinate description of the collective ground-state we obtain a simple estimate of the collective ground-state correlations. We investigate the approach for a variety of nuclei and forces. The correlation effects are small but not negligible in view of the precision achieved in modern Skyrme-Hartree-Fock calculations.
Light-by-light scattering sum rules constraining meson transition form factors
2012
Relating the forward light-by-light scattering to energy weighted integrals of the \gamma* \gamma -fusion cross sections, with one real photon (\gamma) and one virtual photon (\gamma*), we find two new exact super-convergence relations. They complement the known super-convergence relation based on the extension of the GDH sum rule to the light-light system. We also find a set of sum rules for the low-energy photon-photon interaction. All of the new relations are verified here exactly at leading order in scalar and spinor QED. The super-convergence relations, applied to the \gamma* \gamma -production of mesons, lead to intricate relations between the \gamma \gamma -decay widths or the \gamma…
Oscillations of Dirac and Majorana neutrinos in matter and a magnetic field
2008
We study the evolution of massive mixed Dirac and Majorana neutrinos in matter under the influence of a transversal magnetic field. The analysis is based on relativistic quantum mechanics. We solve exactly the evolution equation for relativistic neutrinos, find the neutrino wave functions, and calculate the transition probability for spin-flavor oscillations. We analyze the dependence of the transition probability on the external fields and compare the cases of Dirac and Majorana neutrinos. The evolution of Majorana particles in vacuum is also studied and correction terms to the standard oscillation formula are derived and discussed. As a possible application of our results we discuss the s…
A Compact Solid State Detector for Small Angle Particle Tracking
1999
MIDAS (MIcrostrip Detector Array System) is a compact silicon tracking telescope for charged particles emitted at small angles in intermediate energy photonuclear reactions. It was realized to increase the angular acceptance of the DAPHNE detector and used in an experimental program to check the Gerasimov-Drell-Hearn sum rule at the Mainz electron microtron, MAMI. MIDAS provides a trigger for charged hadrons, p/pi identification and particle tracking in the region 7 deg < theta < 16 deg. In this paper we present the main characteristics of MIDAS and its measured performances.