272 research outputs found
Spectral fluctuations effects on conductance peak height statistics in quantum dots
Within random matrix theory for quantum dots, both the dot's one-particle
eigenlevels and the dot-lead couplings are statistically distributed. While the
effect of the latter on the conductance is obvious and has been taken into
account in the literature, the statistical distribution of the one-particle
eigenlevels is generally replaced by a picket-fence spectrum. Here we take the
random matrix theory eigenlevel distribution explicitly into account and
observe significant deviations in the conductance distribution and
magnetoconductance of closed quantum dots at experimentally relevant
temperatures.Comment: 3 pages, 2 figure
Higher Spins from Tensorial Charges and OSp(N|2n) Symmetry
It is shown that the quantization of a superparticle propagating in an N=1,
D=4 superspace extended with tensorial coordinates results in an infinite tower
of massless spin states satisfying the Vasiliev unfolded equations for free
higher spin fields in flat and AdS_4 N=1 superspace. The tensorial extension of
the AdS_4 superspace is proved to be a supergroup manifold OSp(1|4). The model
is manifestly invariant under an OSp(N|8) (N=1,2) superconformal symmetry. As a
byproduct, we find that the Cartan forms of arbitrary Sp(2n) and OSp(1|2n)
groups are GL(2n) flat, i.e. they are equivalent to flat Cartan forms up to a
GL(2n) rotation. This property is crucial for carrying out the quantization of
the particle model on OSp(1|4) and getting the higher spin field dynamics in
super AdS_4, which can be performed in a way analogous to the flat case.Comment: LaTeX, 21 page (JHEP style), misprints corrected, added comments on
the relation of results of hep-th/0106149 with hep-th/9904109 and
hep-th/9907113, references adde
Superparticle Models with Tensorial Central Charges
A generalization of the Ferber-Shirafuji formulation of superparticle
mechanics is considered. The generalized model describes the dynamics of a
superparticle in a superspace extended by tensorial central charge coordinates
and commuting twistor-like spinor variables. The D=4 model contains a
continuous real parameter and at a=0 reduces to the SU(2,2|1)
supertwistor Ferber-Shirafuji model, while at a=1 one gets an OSp(1|8)
supertwistor model of ref. [1] (hep-th/9811022) which describes BPS states with
all but one unbroken target space supersymmetries. When 0<a<1 the model admits
an OSp(2|8) supertwistor description, and when a>1 the supertwistor group
becomes OSp(1,1|8). We quantize the model and find that its quantum spectrum
consists of massless states of an arbitrary (half)integer helicity. The
independent discrete central charge coordinate describes the helicity spectrum.
We also outline the generalization of the a=1 model to higher space-time
dimensions and demonstrate that in D=3,4,6 and 10, where the quantum states are
massless, the extra degrees of freedom (with respect to those of the standard
superparticle) parametrize compact manifolds. These compact manifolds can be
associated with higher-dimensional helicity states. In particular, in D=10 the
additional ``helicity'' manifold is isomorphic to the seven-sphere.Comment: 32 pages, LATEX, no figure
Nucleonic resonance excitations with linearly polarized photon in
In this work, an improved quark model approach to the meson
photo-production with an effective Lagrangian is presented. The {\it t}-channel
{\it natural}-parity exchange is taken into account through the Pomeron
exchange, while the {\it unnatural}-parity exchange is described by the
exchange. With a very limited number of parameters, the available experimental
data in the low energy regime can be consistently accounted for. We find that
the beam polarization observables show sensitivities to some {\it s}-channel
individual resonances in the quark model symmetry limit.
Especially, the two resonances and , which belong
to the representation , have dominant contributions
over other excited states. Concerning the essential motivation of searching for
"missing resonances" in meson photo-production, this approach provides a
feasible framework, on which systematic investigations can be done.Comment: 16 pages, Revtex, 9 eps figures, to appear in PR
Elastic Scattering of Pions From the Three-nucleon System
We examine the scattering of charged pions from the trinucleon system at a
pion energy of 180 MeV. The motivation for this study is the structure seen in
the experimental angular distribution of back-angle scattering for pi+ 3He and
pi- 3H but for neither pi- 3He nor pi+ 3H. We consider the addition of a double
spin flip term to an optical model treatment and find that, though the
contribution of this term is non-negligible at large angles for pi+ 3He and pi-
3H, it does not reproduce the structure seen in the experiment.Comment: 15 pages + 5 figure
Conformal Higher Spin Symmetries of 4d Massless Supermultiplets and Invariant Equations in Generalized (Super)Space
Realization of the conformal higher spin symmetry on the 4d massless field
supermultiplets is given. The self-conjugated supermultiplets, including the
linearized SYM theory, are considered in some detail. Duality
between non-unitary field-theoretical representations and the unitary
doubleton--type representations of the 4d conformal algebra is
formulated in terms of a Bogolyubov transform. The set of 4d massless fields of
all spins is shown to form a representation of .
The obtained results are extended to the generalized superspace invariant
under supersymmetries. World line particle interpretation of the
free higher spin theories in the invariant (super)space is
given. Compatible with unitarity free equations of motion in the
invariant (super)space are formulated. A conjecture on the chain of
dualities in the higher spin
gauge theories is proposed.Comment: Latex, 63 pages; no figures.V2 Typos corrected, References updated.
V3.Typos correced, references and an explanation on the relationship with
previous work in section 4 are added. The version to appear in Phys.Rev.
Analytic descriptions for transitional nuclei near the critical point
Exact solutions of the Bohr Hamiltonian with a five-dimensional square well
potential, in isolation or coupled to a fermion by the five-dimensional
spin-orbit interaction, are considered as examples of a new class of dynamical
symmetry or Bose-Fermi dynamical symmetry. The solutions provide baselines for
experimental studies of even-even [E(5)] and odd-mass [E(5|4)] nuclei near the
critical point of the spherical to deformed gamma-unstable phase transition.Comment: LaTeX (elsart), 53 pages; typographical correction to (3.15
Construction of SO(5)>SO(3) spherical harmonics and Clebsch-Gordan coefficients
The SO(5)>SO(3) spherical harmonics form a natural basis for expansion of
nuclear collective model angular wave functions. They underlie the
recently-proposed algebraic method for diagonalization of the nuclear
collective model Hamiltonian in an SU(1,1)xSO(5) basis. We present a computer
code for explicit construction of the SO(5)>SO(3) spherical harmonics and use
them to compute the Clebsch-Gordan coefficients needed for collective model
calculations in an SO(3)-coupled basis. With these Clebsch-Gordan coefficients
it becomes possible to compute the matrix elements of collective model
observables by purely algebraic methods.Comment: LaTeX (RevTeX), 15 pages; to be published in Computer Phys. Comm
On Conformal, SL(4,R) and Sp(8,R) Symmetries of 4d Massless Fields
The invariant formulation of free field equations of massless
fields of all spins in available previously in terms of gauge invariant
field strengths is extended to gauge potentials. As a by-product, free field
equations for a massless gauge field are shown to possess both and symmetry. The proposed formulation is
well-defined in the background but experiences certain degeneracy in
the flat limit that does not allow conformal invariant field equations for spin
gauge fields in Minkowski space. The basis model involves the doubled set
of fields of all spins. It is manifestly invariant under U(1) electric-magnetic
duality extended to higher spins. Reduction to a single massless field contains
the equations that relate its electric and magnetic potentials which are mixed
by the conformal transformations for s>1. We use the unfolded formulation
approach recalled in the paper with some emphasis on the role of
Chevalley-Eilenberg cohomology of a Lie algebra in -invariant field
equations. This method makes it easy to guess a form of the 4d
invariant massless field equations and then to extend them to the ten
dimensional invariant space-time. Dynamical content of the field
equations is analyzed in terms of cohomology.Comment: 66 pages, V2: minor corrections, references and acknowledgments
added, coefficients and typos corrected, V3: typos corrected, version to
appear in Nucl. Phys.
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