1,737 research outputs found
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
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
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
Constant magnetic field and 2d non-commutative inverted oscillator
We consider a two-dimensional non-commutative inverted oscillator in the
presence of a constant magnetic field, coupled to the system in a
``symplectic'' and ``Poisson'' way. We show that it has a discrete energy
spectrum for some value of the magnetic field.Comment: 7 pages, LaTeX file, no figures, PACS number: 03.65.-
Coherent Bremsstrahlung in Imperfect Periodic Atomic Structures
Coherent bremsstrahlung of high energy electrons moving in a
three-dimensional imperfect periodic lattice consisting of a complicated system
of atoms is considered. On the basis of the normalized probability density
function of the distribution of atomic centers in the fundamental cell the
relations describing coherent and incoherent contributions into cross sections
are obtained. In particular, the cross section of coherent bremsstrahlung in
complex polyatomic single crystals is found.
The peculiarities of formation and possibilities of utilization of coherent
processes are discussed.Comment: 23 pages, 8 figures, to be published in Phys. Rev.
Multi-Component Sequential Synthesis of Dihydroorotic Acid-Based Amphiphilic Molecules
An efficient multicomponent sequential process, which occurs
in mild condition has been exploited for the synthesis of systematically
modified amphiphilic molecules where the cationic head is tethered
to a lipophilic tail through a dihydroorotic acid linker. The process
is operatively simple, high yielding, and flexible. Such a strategy could
impact combinatorial synthesis of wide libraries of amphiphilic molecules
to be tested as transfection agents and/or as antimicrobials
Doping- and size-dependent suppression of tunneling in carbon nanotubes
We study the effect of doping in the suppression of tunneling observed in
multi-walled nanotubes, incorporating as well the influence of the finite
dimensions of the system. A scaling approach allows us to encompass the
different values of the critical exponent measured for the tunneling
density of states in carbon nanotubes. We predict that further reduction of
should be observed in multi-walled nanotubes with a sizeable amount
of doping. In the case of nanotubes with a very large radius, we find a
pronounced crossover between a high-energy regime with persistent
quasiparticles and a low-energy regime with the properties of a one-dimensional
conductor.Comment: 4 pages, 2 figures, LaTeX file, pacs: 71.10.Pm, 71.20.Tx, 72.80.R
Quantum Oscillator on \DC P^n in a constant magnetic field
We construct the quantum oscillator interacting with a constant magnetic
field on complex projective spaces \DC P^N, as well as on their non-compact
counterparts, i. e. the dimensional Lobachewski spaces . We
find the spectrum of this system and the complete basis of wavefunctions.
Surprisingly, the inclusion of a magnetic field does not yield any qualitative
change in the energy spectrum. For the magnetic field does not break the
superintegrability of the system, whereas for N=1 it preserves the exact
solvability of the system.
We extend this results to the cones constructed over \DC P^N and , and perform the (Kustaanheimo-Stiefel) transformation of these systems
to the three-dimensional Coulomb-like systems.Comment: 9 pages, 1 figur
On Quantum Special Kaehler Geometry
We compute the effective black hole potential V of the most general N=2, d=4
(local) special Kaehler geometry with quantum perturbative corrections,
consistent with axion-shift Peccei-Quinn symmetry and with cubic leading order
behavior. We determine the charge configurations supporting axion-free
attractors, and explain the differences among various configurations in
relations to the presence of ``flat'' directions of V at its critical points.
Furthermore, we elucidate the role of the sectional curvature at the
non-supersymmetric critical points of V, and compute the Riemann tensor (and
related quantities), as well as the so-called E-tensor. The latter expresses
the non-symmetricity of the considered quantum perturbative special Kaehler
geometry.Comment: 1+43 pages; v2: typo corrected in the curvature of Jordan symmetric
sequence at page 2
Black Strings, Black Rings and State-space Manifold
State-space geometry is considered, for diverse three and four parameter
non-spherical horizon rotating black brane configurations, in string theory and
-theory. We have explicitly examined the case of unit Kaluza-Klein momentum
black strings, circular strings, small black rings and black
supertubes. An investigation of the state-space pair correlation functions
shows that there exist two classes of brane statistical configurations, {\it
viz.}, the first category divulges a degenerate intrinsic equilibrium basis,
while the second yields a non-degenerate, curved, intrinsic Riemannian
geometry. Specifically, the solutions with finitely many branes expose that the
two charged rotating black strings and three charged rotating small
black rings consort real degenerate state-space manifolds. Interestingly,
arbitrary valued -dipole charged rotating circular strings and Maldacena
Strominger Witten black rings exhibit non-degenerate, positively curved,
comprehensively regular state-space configurations. Furthermore, the
state-space geometry of single bubbled rings admits a well-defined, positive
definite, everywhere regular and curved intrinsic Riemannian manifold; except
for the two finite values of conserved electric charge. We also discuss the
implication and potential significance of this work for the physics of black
holes in string theory.Comment: 41 pages, Keywords: Rotating Black Branes; Microscopic
Configurations; State-space Geometry, PACS numbers: 04.70.-s Physics of black
holes; 04.70.Bw Classical black holes; 04.70.Dy Quantum aspects of black
holes, evaporation, thermodynamic
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