240 research outputs found
Multiloop Superstring Amplitudes from Non-Minimal Pure Spinor Formalism
Using the non-minimal version of the pure spinor formalism, manifestly
super-Poincare covariant superstring scattering amplitudes can be computed as
in topological string theory without the need of picture-changing operators.
The only subtlety comes from regularizing the functional integral over the pure
spinor ghosts. In this paper, it is shown how to regularize this functional
integral in a BRST-invariant manner, allowing the computation of arbitrary
multiloop amplitudes. The regularization method simplifies for scattering
amplitudes which contribute to ten-dimensional F-terms, i.e. terms in the
ten-dimensional superspace action which do not involve integration over the
maximum number of 's.Comment: 23 pages harvmac, added acknowledgemen
Superstrings and Topological Strings at Large N
We embed the large N Chern-Simons/topological string duality in ordinary
superstrings. This corresponds to a large duality between generalized gauge
systems with N=1 supersymmetry in 4 dimensions and superstrings propagating on
non-compact Calabi-Yau manifolds with certain fluxes turned on. We also show
that in a particular limit of the N=1 gauge theory system, certain
superpotential terms in the N=1 system (including deformations if spacetime is
non-commutative) are captured to all orders in 1/N by the amplitudes of
non-critical bosonic strings propagating on a circle with self-dual radius. We
also consider D-brane/anti-D-brane system wrapped over vanishing cycles of
compact Calabi-Yau manifolds and argue that at large they induce a shift in
the background to a topologically distinct Calabi-Yau, which we identify as the
ground state system of the Brane/anti-Brane system.Comment: 30 pages, some minor clarifications adde
Delocalization of tightly bound excitons in disordered systems
The localization length of a low energy tightly bound electron-hole pair
(excitons) is calculated by exact diagonalization for small interacting
disordered systems. The exciton localization length (which corresponds to the
thermal electronic conductance) is strongly enhanced by electron-electron
interactions, while the localization length (pertaining to the charge
conductance) is only slightly enhanced. This shows that the two particle
delocalization mechanism widely discussed for the electron pair case is more
efficient close to the Fermi energy for an electron-hole pair. The relevance to
experiment is also discussed.Comment: 10 pages, 2 figures - old version was posted by mistak
On zero modes of the eleven dimensional superstring
It is shown that recently pointed out by Berkovits on-shell degrees of
freedom of the D=11 superstring do not make contributions into the quantum
states spectrum of the theory. As a consequence, the spectrum coincides with
that of the D=10 type IIA superstring.Comment: 7 pages, LaTex fil
Pure spinor computation towards open string three-loop
Using the recent results in the pure spinor formulation, we lay out a
ground-work towards the full momentum space amplitudes of open superstrings at
three-loop. After briefly reviewing the one-loop amplitude, we directly work
out the two-loop and reproduce the result that was obtained by a symmetry
argument. For the three-loop, first we use the two-loop regulator as a warm-up
exercise. The result vanishes. We then employ the regulator that has been
recently proposed by Aisaka and Berkovits (AB). It is noted that the terms in
higher power in that render the two-loop
regulator disqualified for the three-loop do not contribute. This with a few
other indications suggests a possibility that the AB regulator might also lead
to a vanishing result. Nevertheless, we argue that it is possible to acquire
the three-loop amplitude, and present a result that we anticipate to be the
three-loop amplitude.Comment: 41 pages, latex, cosmetic change
On pure spinor formalism for quantum superstring and spinor moving frame
The D=10 pure spinor constraint can be solved in terms of spinor moving frame
variables and 8-component complex null vector which can be related to the
kappa-symmetry ghost. Using this and similar solutions for the conjugate pure
spinor and other elements of the non-minimal pure spinor formalism we present a
(hopefully useful) reformulation of the measure of the pure spinor path
integral for superstring in terms of products of Cartan form corresponding to
the coset of 10D Lorentz group and to the coset of complex orthogonal group
SO(8,C). Our study suggests a possible complete reformulation of the pure
spinor superstring in terms of new irreducible set of variable.Comment: 23 pages, no figures. V2: references adde
Canonical description of D=10 superstring formulated in supertwistor space
Canonical description of the D=10 superstring action involving supertwistor
variables generalizing Penrose-Ferber supertwistors is developed. Primary and
secondary constraints are identified and arranged into the first- and
second-class sets. Dirac brackets are introduced and the deformation of the
Poisson bracket algebra of the first-class constraints is studied. The role of
the deformation parameter is played by alpha'.Comment: 20 pages, LateX. V2: comments and references added. Version accepted
to J.Phys.
Electron Spin Dynamics and Hyperfine Interactions in Fe/Al_0.1Ga_0.9As/GaAs Spin Injection Heterostructures
We have studied hyperfine interactions between spin-polarized electrons and
lattice nuclei in Al_0.1Ga_0.9As/GaAs quantum well (QW) heterostructures. The
spin-polarized electrons are electrically injected into the semiconductor
heterostructure from a metallic ferromagnet across a Schottky tunnel barrier.
The spin-polarized electron current dynamically polarizes the nuclei in the QW,
and the polarized nuclei in turn alter the electron spin dynamics. The
steady-state electron spin is detected via the circular polarization of the
emitted electroluminescence. The nuclear polarization and electron spin
dynamics are accurately modeled using the formalism of optical orientation in
GaAs. The nuclear spin polarization in the QW is found to depend strongly on
the electron spin polarization in the QW, but only weakly on the electron
density in the QW. We are able to observe nuclear magnetic resonance (NMR) at
low applied magnetic fields on the order of a few hundred Oe by electrically
modulating the spin injected into the QW. The electrically driven NMR
demonstrates explicitly the existence of a Knight field felt by the nuclei due
to the electron spin.Comment: 19 Figures - submitted to PR
Ectoplasm & Superspace Integration Measure for 2D Supergravity with Four Spinorial Supercurrents
Building on a previous derivation of the local chiral projector for a two
dimensional superspace with eight real supercharges, we provide the complete
density projection formula required for locally supersymmetrical theories in
this context. The derivation of this result is shown to be very efficient using
techniques based on the Ectoplasmic construction of local measures in
superspace.Comment: 18 pages, LaTeX; V2: minor changes, typos corrected, references
added; V3: version to appear in J. Phys. A: Math. Theor., some comments and
references added to address a referee reques
Critical Spectral Statistics at the Metal-Insulator Transition in Interacting Fermionic Systems
The spectral properties of a disordered system with few interacting
three-dimensional spinless fermions are investigated. We show the existence of
a critical spacings distribution which is invariant upon increase of the system
size, but strongly depends on the number of particles. At the critical point,
we report a substantial decrease of the degree of level repulsion as the number
of particles increases indicating a decrease of nearest level correlations
associated with the sparsity of the Hamiltonian matrix.Comment: Revtex, 4 pages, 3 encapsulated postscript figures appended Final
version as accepted for publication in PR
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