12,984 research outputs found
Generalized Density Matrix Revisited: Microscopic Approach to Collective Dynamics in Soft Spherical Nuclei
The generalized density matrix (GDM) method is used to calculate
microscopically the parameters of the collective Hamiltonian. Higher order
anharmonicities are obtained consistently with the lowest order results, the
mean field [Hartree-Fock-Bogoliubov (HFB) equation] and the harmonic potential
[quasiparticle random phase approximation (QRPA)]. The method is applied to
soft spherical nuclei, where the anharmonicities are essential for restoring
the stability of the system, as the harmonic potential becomes small or
negative. The approach is tested in three models of increasing complexity: the
Lipkin model, model with factorizable forces, and the quadrupole plus pairing
model.Comment: submitted to Physical Review C on 08 May, 201
Hexadecapole Interaction and the Delta I=4 Staggering Effect in Rotational Bands
A role of the multipole interaction in the description of the =4
staggering phenomenon is investigated in a model consisting of a single-
shell filled by identical nucleons. Exact diagonalization of the
quadrupole-plus-hexadecapole Hamiltonian shows that the
hexadecapole-hexadecapole interaction can produce a =4 periodicity
in the yrast sequence.Comment: revised version with technical changes only, to be published in
Physica Scripta, latex, 4 pages, 3 PostScript figures available on request
from [email protected], preprint No. IFT/18/9
Multiple Scattering Theory for Slow Neutrons (from thermal to ultracold)
The general theory of neutron scattering is presented, valid for the whole
domain of slow neutrons from thermal to ultracold. Particular attention is
given to multiple scattering which is the dominant process for ultracold
neutrons (UCN). For thermal and cold neutrons, when the multiple scattering in
the target can be neglected, the cross section is reduced to the known value. A
new expression for inelastic scattering cross section for UCN is proposed.
Dynamical processes in the target are taken into account and their influence on
inelastic scattering of UCN is analyzed.Comment: 28 pages, latex, 2 Postscript figures, submitted to the European
Physical Journal
Continuum Coupling and Pair Correlation in Weakly Bound Deformed Nuclei
We formulate a new Hartree-Fock-Bogoliubov method applicable to weakly bound
deformed nuclei using the coordinate-space Green's function technique. An
emphasis is put on treatment of quasiparticle states in the continuum, on which
we impose the correct boundary condition of the asymptotic out-going wave. We
illustrate this method with numerical examples.Comment: 5 pages, 4 figures, Proceedings of the Japanese French Symposium -
New paradigms in Nuclear Physics, Paris, 29th September - 2nd October, to be
published in Int. J. of Modern Physics
The Technicolor Higgs in the Light of LHC Data
We consider scenarios in which the 125 GeV resonance observed at the Large
Hadron Collider is a Technicolor (TC) isosinglet scalar, the TC Higgs. By
comparison with quantum chromodynamics, we argue that the couplings of the TC
Higgs to the massive weak bosons are very close to the Standard Model (SM)
values. The couplings to photons and gluons are model-dependent, but close to
the SM values in several TC theories. The couplings of the TC Higgs to SM
fermions are due to interactions beyond TC, such as Extended Technicolor: if
such interactions successfully generate mass for the SM fermions, we argue that
the couplings of the latter to the TC Higgs are also SM-like.
We suggest a generic parameterization of the TC Higgs interactions with SM
particles that accommodates a large class of TC models, and we perform a fit of
these parameters to the Higgs LHC data. The fit reveals regions of parameter
space where the form factors are of order unity and consistent with data at the
95% CL, in agreement with expectations in TC theories. This indicates that the
discovered Higgs boson is consistent with the TC Higgs hypothesis for several
TC theories.Comment: 26 pages, 8 figure
Nuclear Schiff moment in nuclei with soft octupole and quadrupole vibrations
Nuclear forces violating parity and time reversal invariance (-odd) produce -odd nuclear moments, for example, the
nuclear Schiff moment. In turn, this moment can induce the electric dipole
moment in the atom. The nuclear Schiff moment is predicted to be enhanced in
nuclei with static quadrupole and octupole deformation. The analogous
suggestion of the enhanced contribution to the Schiff moment from the soft
collective quadrupole and octupole vibrations in spherical nuclei is tested in
this article in the framework of the quasiparticle random phase approximation
with separable quadrupole and octupole forces applied to the odd Ra
and Rn isotopes. We confirm the existence of the enhancement effect
due to the soft modes. However, in the standard approximation the enhancement
is strongly reduced by a small weight of the corresponding "particle + phonon"
component in a complicated wave function of a soft nucleus. The perspectives of
a better description of the structure of heavy soft nuclei are discussed.Comment: 27 pages, 3 figures, minor corrections in references adde
-pair Production in the Littlest Higgs Model with T parity in next-to-leading order QCD at LHC
In the framework of the littlest Higgs model with parity, we study the
-pair production at the CERN Large Hadron Collider up to the QCD
next-to-leading order (NLO). The kinematic distributions of final decay
products and the theoretical dependence of the cross section on the
factorization/renormalization scale are analyzed. We adopt the PROSPINO scheme
in the QCD NLO calculations to avoid double counting and keep the convergence
of the perturbative QCD description. Our numerical results show that the QCD
NLO corrections significantly reduce the scale uncertainty, and enhance the
leading order integrated cross section with a -factor in the range of
() with the symmetry breaking scale varying from
() to () at the LHC.
We find that it is possible to select the signal events of the -pair
production from the
background with high ratio of signature over background by taking proper lower
limits on transverse momenta, invariant mass of the final charged leptons and
the missing transverse momentum.Comment: 34 pages, 14 figures, 4 table
Quasi-particle continuum and resonances in the Hartree-Fock-Bogoliubov theory
The quasi-particle energy spectrum of the Hartree-Fock-Bogoliubov (HFB)
equations contains discrete bound states, resonances, and non-resonant
continuum states. We study the structure of the unbound quasi-particle spectrum
of weakly bound nuclei within several methods that do not rely on imposing
scattering or outgoing boundary conditions. Various approximations are examined
to estimate resonance widths. It is shown that the stabilization method works
well for all HFB resonances except for very narrow ones.
The Thomas-Fermi approximation to the non-resonant continuum has been shown
to be very effective, especially for coordinate-space HFB calculations in large
boxes that involve huge amounts of discretized quasi-particle continuum states.Comment: 12 pages,11 figures,submitted to PR
Nuclear Schiff moment and soft vibrational modes
The atomic electric dipole moment (EDM) currently searched by a number of
experimental groups requires that both parity and time-reversal invariance be
violated. According to current theoretical understanding, the EDM is induced by
the nuclear Schiff moment. The enhancement of the Schiff moment by the
combination of static quadrupole and octupole deformation was predicted
earlier. Here we study a further idea of the possible enhancement in the
absence of static deformation but in a nuclear system with soft collective
vibrations of two types. Both analytical approximation and numerical solution
of the simplified problem confirm the presence of the enhancement. We discuss
related aspects of nuclear structure which should be studied beyond mean-field
and random phase approximations.Comment: 14 pages, 4 figure
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