2,185 research outputs found
On the dynamics of BMN operators of finite size and the model of string bits
We consider the discretization effects of a string-bit model simulating the
near-BMN operators in the super--Yang--Mills model. The fermionic sector of
this model is altered by the so called species doubling. We analyze the
possibilities to cure this disease and propose an alternative formulation of
the fermionic sector free from the above drawbacks. Also we propose a
formulation of string bits with exact supersymmetry, which produces however an
even number of continuous strings in the limit .Comment: 10 pages, Contribution to BW2003 Workshop, 29 August - 02 September,
2003 Vrnjacka Banja, Serbi
The geometry of N=4 twisted string
We compare N=2 string and N=4 topological string within the framework of the
sigma model approach. Being classically equivalent on a flat background, the
theories are shown to lead to different geometries when put in a curved space.
In contrast to the well studied Kaehler geometry characterising the former
case, in the latter case a manifold has to admit a covariantly constant
holomorphic two-form in order to support an N=4 twisted supersymmetry. This
restricts the holonomy group to be a subgroup of SU(1,1) and leads to a
Ricci--flat manifold. We speculate that, the N=4 topological formalism is an
appropriate framework to smooth down ultraviolet divergences intrinsic to the
N=2 theory.Comment: 20 pages, LaTe
Crossover from Luttinger liquid to Coulomb blockade regime in carbon nanotubes
We develop a theoretical approach to the low-energy properties of 1D electron
systems aimed to encompass the mixed features of Luttinger liquid and Coulomb
blockade behavior observed in the crossover between the two regimes. For this
aim we extend the Luttinger liquid description by incorporating the effects of
a discrete single-particle spectrum. The intermediate regime is characterized
by a power-law behavior of the conductance, but with an exponent oscillating
with the gate voltage, in agreement with recent experimental observations. Our
construction also accounts naturally for the existence of a crossover in the
zero-bias conductance, mediating between two temperature ranges where the
power-law behavior is preserved but with different exponent.Comment: 5 pages, 3 figure
Making the hyper--K\"ahler structure of N=2 quantum string manifest
We show that the Lorentz covariant formulation of N=2 string in a curved
space reveals an explicit hyper--K\"ahler structure. Apart from the metric, the
superconformal currents couple to a background two--form. By superconformal
symmetry the latter is constrained to be holomorphic and covariantly constant
and allows one to construct three complex structures obeying a
(pseudo)quaternion algebra.Comment: 8 pages, no figures, PACS: 04.60.Ds; 11.30.Pb, Keywords: N=2 string,
hyper-K\"ahler geometry. Presentation improved, references added. The version
to appear in PR
Spin bits at two loops
We consider the Super Yang--Mills/spin system map to construct the SU(2) spin
bit model at the level of two loops in Yang--Mills perturbation theory. The
model describes a spin system with chaining interaction. In the large limit
the model is shown to be reduced to the two loop planar integrable spin chain.Comment: 10 pages, 3 figures, References and Acknowledgements adde
Non-Commutative Corrections to the MIC-Kepler Hamiltonian
Non-commutative corrections to the MIC-Kepler System (i.e. hydrogen atom in
the presence of a magnetic monopole) are computed in Cartesian and parabolic
coordinates. Despite the fact that there is no simple analytic expression for
non-commutative perturbative corrections to the MIC-Kepler spectrum, there is a
term that gives rise to the linear Stark effect which didn't exist in the
standard hydrogen model.Comment: 5 page
Suppression of electron-electron repulsion and superconductivity in Ultra Small Carbon Nanotubes
Recently, ultra-small-diameter Single Wall Nano Tubes with diameter of have been produced and many unusual properties were observed, such as
superconductivity, leading to a transition temperature , much
larger than that observed in the bundles of larger diameter tubes.
By a comparison between two different approaches, we discuss the issue
whether a superconducting behavior in these carbon nanotubes can arise by a
purely electronic mechanism. The first approach is based on the Luttinger Model
while the second one, which emphasizes the role of the lattice and short range
interaction, is developed starting from the Hubbard Hamiltonian. By using the
latter model we predict a transition temperature of the same order of magnitude
as the measured one.Comment: 7 pages, 3 figures, to appear in J. Phys.-Cond. Ma
Sexual Harassment:A Long-Dormant Demon
Because of its service nature, the hospitality industry is especially prone to cases of sexual harassment in the workplace, particularly from female employees. The author discusses Title VII of the Civil Rights Act of 1964 and the legal and moral implications of its guidelines for the industry
Symmetries of N=4 supersymmetric CP(n) mechanics
We explicitly constructed the generators of group which commute
with the supercharges of N=4 supersymmetric mechanics in the
background U(n) gauge fields. The corresponding Hamiltonian can be represented
as a direct sum of two Casimir operators: one Casimir operator on
group contains our bosonic and fermionic coordinates and momenta, while the
second one, on the SU(1,n) group, is constructed from isospin degrees of
freedom only.Comment: 10 pages, PACS numbers: 11.30.Pb, 03.65.-w; minor changes in
Introduction, references adde
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