5 research outputs found
Nuclear Excitation by a Zeptosecond Multi--MeV Laser Pulse
A zeptosecond multi--MeV laser pulse may either excite a "plasma" of strongly
interacting nucleons or a collective mode. We derive the conditions on laser
energy and photon number such that either of these scenarios is realized. We
use the nuclear Giant Dipole Resonance as a representative example, and a
random--matrix description of the fine--structure states and perturbation
theory as tools.Comment: 4 page
Non-Universal Behavior of the k-Body Embedded Gaussian Unitary Ensemble of Random Matrices
Using a novel approach, we investigate the shape of the average spectrum and
the spectral fluctuations of the -body embedded unitary ensemble in the
limit of large matrix dimension. We identify the transition point between
semicircle and Gaussian shape. The transition also affects the spectral
fluctuations which deviate from Wigner-Dyson form and become Poissonian in the
limit . Here is the number of Fermions and the number of
degenerate single-particle states.Comment: 4 pages, no figures, revised version including a new proof of one of
our main claim
Random-Matrix Ensembles for Semi-Separable Systems
Many models for chaotic systems consist of joining two integrable systems
with incompatible constants of motion. The quantum counterparts of such models
have a propagator which factorizes into two integrable parts. Each part can be
diagonalized. The two eigenvector bases are related by an orthogonal (or
unitary) transformation. We construct a random matrix ensemble that mimics this
situation and consists of a product of a diagonal, an orthogonal, another
diagonal and the transposed orthogonal matrix. The diagonal phases are chosen
at random and the orthogonal matrix from Haar's measure. We derive asymptotic
results (dimension N -> \infty) using Wick contractions. A new approximation
for the group integration yields the next order in 1/N. We obtain a finite
correction to the circular orthogonal ensemble, important in the long-range
part of spectral correlations.Comment: 7 pages with 2 eps-figures, revised version, in press at Europhysics
Letter
Correlations of conductance peaks and transmission phases in deformed quantum dots
We investigate the Coulomb blockade resonances and the phase of the
transmission amplitude of a deformed ballistic quantum dot weakly coupled to
leads. We show that preferred single--particle levels exist which stay close to
the Fermi energy for a wide range of values of the gate voltage. These states
give rise to sequences of Coulomb blockade resonances with correlated peak
heights and transmission phases. The correlation of the peak heights becomes
stronger with increasing temperature. The phase of the transmission amplitude
shows lapses by between the resonances. Implications for recent
experiments on ballistic quantum dots are discussed.Comment: 29 pages, 9 eps-figure