29,699 research outputs found
Muon g-2 through a flavor structure on soft SUSY terms
In this work we analyze the possibility to explain the muon anomalous
magnetic moment discrepancy within theory and experiment through lepton flavor
violation processes. We propose a flavor extended MSSM by considering a
hierarchical family structure for the trilinear scalar Soft-Supersymmetric
terms of the Lagranagian, present at the SUSY breaking scale. We obtain
analytical results for the rotation mass matrix, with the consequence of having
non-universal slepton masses and the possibility of leptonic flavour mixing.
The one-loop supersymmetric contributions to the leptonic flavour violating
process are calculated in the physical basis, with slepton
flavour mixed states, instead of using the well known Mass Insertion Method. We
present the regions in parameter space where the muon g-2 problem is either
entirely solved or partially reduced through the contribution of these flavor
violating processes.Comment: 21 pages, 7 figures. Changes on version 3: In order to obtain the
complete result for muon g-2 in the limit of non-flavor violation we added
the terms given in the appendix. We redid the graphics and numerical analysis
including these changes. We also corrected some typos and changed the order
of figure
Perturbative evolution of far off-resonance driven two-level systems: Coherent population trapping, localization, and harmonic generation
The time evolution of driven two-level systems in the far off-resonance
regime is studied analytically. We obtain a general first-order perturbative
expression for the time-dependent density operator which is applicable
regardless of the coupling strength value. In the strong field regime, our
perturbative expansion remains valid even when the far off-resonance condition
is not fulfilled. We find that, in the absence of dissipation, driven two-level
systems exhibit coherent population trapping in a certain region of parameter
space, a property which, in the particular case of a symmetric double-well
potential, implies the well-known localization of the system in one of the two
wells. Finally, we show how the high-order harmonic generation that this kind
of systems display can be obtained as a straightforward application of our
formulation.Comment: 14 pages, LaTeX, 2 figures, acknowledgments adde
Large Shell Model Calculations for Calcium Isotopes: Spectral Statistics and Chaos
We perform large shell model calculations for Calcium isotopes in the full fp
shell by using the realistic Kuo-Brown interaction. The Calcium isotopes are
especially interesting because the nearest-neighbour spacing distribution P(s)
of low-lying energy levels shows significant deviations from the predictions of
the Gaussian Orthogonal Ensemble of random--matrix theory. This contrasts with
other neighbouring nuclei which show fully chaotic spectral distributions. We
study the chaotic behaviour as a function of the excitation energy. In
addition, a clear signature of chaos suppression is obtained when the
single-particle spacings are increased. In our opinion the relatively weak
strength of the neutron-neutron interaction is unable to destroy the regular
single-particle mean-field motion completely. In the neighbouring nuclei with
both protons and neutrons in valence orbits, on the other hand, the stronger
proton-neutron interaction would appear to be sufficient to destroy the regular
mean-field motion.Comment: Latex, 7 pages, 2 postscript figures, to be published in the
Proceedings 'Highlights of Modern Nuclear Structure', S. Agata sui due Golfi
(italy), Ed. A. Covello (World Scientific
Spectral Statistics in Large Shell Model Calculations
The spectral statistics of low--lying states of shell nuclei are studied
by performing large shell--model calculations with a realistic nuclear
interaction. For isotopes, we find deviations from the predictions of the
random--matrix theory which suggest that some spherical nuclei are not as
chaotic in nature as the conventional view assumes.Comment: 9 pages, LaTex, 3 figures available upon request, to appear in
Proceedings of the V International Spring Seminar on Nuclear Physics, Ed. by
A. Covello (World Scientific
Different Facets of Chaos in Quantum Mechanics
Nowadays there is no universally accepted definition of quantum chaos. In
this paper we review and critically discuss different approaches to the
subject, such as Quantum Chaology and the Random Matrix Theory. Then we analyze
the problem of dynamical chaos and the time scales associated with chaos
suppression in quantum mechanics. Summary: 1. Introduction 2. Quantum Chaology
and Spectral Statistics 3. From Poisson to GOE Transition: Comparison with
Experimental Data 3.1 Atomic Nuclei 3.2 The Hydrogen Atom in the Strong
Magnetic Field 4. Quantum Chaos and Field Theory 5. Alternative Approaches to
Quantum Chaos 6. Dynamical Quantum Chaos and Time Scales 6.1 Mean-Field
Approximation and Dynamical Chaos 7. ConclusionsComment: RevTex, 25 pages, 7 postscript figures, to be published in Int. J.
Mod. Phys.
Charged-Lepton-Flavour Violation in the Light of the Super-Kamiokande Data
Motivated by the data from Super-Kamiokande and elsewhere indicating
oscillations of atmospheric and solar neutrinos, we study
charged-lepton-flavour violation, in particular the radiative decays mu -> e
gamma and tau -> mu gamma, but also commenting on mu -> 3e and tau -> 3 mu/e
decays, as well as mu - e conversion on nuclei. We first show how the
renormalization group may be used to calculate flavour-violating soft
supersymmetry-breaking masses for charged sleptons and sneutrinos in models
with universal input parameters. Subsequently, we classify possible patterns of
lepton-flavour violation in the context of phenomenological neutrino mass
textures that accommodate the Super-Kamiokande data, giving examples based on
Abelian flavour symmetries. Then we calculate in these examples rates for mu ->
e gamma and tau ->mu gamma, which may be close to the present experimental
upper limits, and show how they may distinguish between the different generic
mixing patterns. The rates are promisingly large when the soft
supersymmetry-breaking mass parameters are chosen to be consistent with the
cosmological relic-density constraints. In addition, we discuss mu -> e
conversion on Titanium, which may also be accessible to future experiments.Comment: 29 pages, 12 figures. References added, typos correcte
Heavy elements Ba, La, Ce, Nd, and Eu in 56 Galactic bulge red giants
Aims. The aim of this work is the study of abundances of the heavy elements
Ba, La, Ce, Nd, and Eu in 56 bulge giants (red giant branch and red clump) with
metallicities ranging from -1.3 dex to 0.5 dex. Methods. We obtained
high-resolution spectra of our giant stars using the FLAMES-UVES spectrograph
on the Very Large Telescope. We inspected four bulge fields along the minor
axis. Results. We measure the chemical evolution of heavy elements, as a
function of metallicity, in the Galactic bulge. Conclusions. The [Ba, La, Ce,
Nd/Fe] vs. [Fe/H] ratios decrease with increasing metallicity, in which aspect
they differ from disc stars. In our metal-poor bulge stars, La and Ba are
enhanced relative to their thick disc counterpart, while in our metal-rich
bulge stars La and Ba are underabundant relative to their disc counterpart.
Therefore, this contrast between bulge and discs trends indicates that bulge
and (solar neighbourhood) thick disc stars could behave differently. An
increase in [La, Nd/Eu] with increasing metallicity, for metal-rich stars with
[Fe/H] > 0 dex, may indicate that the s-process from AGB stars starts to
operate at a metallicity around solar. Finally, [Eu/Fe] follows the
[{\alpha}/Fe] behaviour, as expected, since these elements are produced by SNe
type II.Comment: 12 pages, 10 figures, accepted for publication in A&
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