12,382 research outputs found
On the Ricci tensor in type II B string theory
Let be a metric connection with totally skew-symmetric torsion \T
on a Riemannian manifold. Given a spinor field and a dilaton function
, the basic equations in type II B string theory are \bdm \nabla \Psi =
0, \quad \delta(\T) = a \cdot \big(d \Phi \haken \T \big), \quad \T \cdot \Psi
= b \cdot d \Phi \cdot \Psi + \mu \cdot \Psi . \edm We derive some relations
between the length ||\T||^2 of the torsion form, the scalar curvature of
, the dilaton function and the parameters . The main
results deal with the divergence of the Ricci tensor \Ric^{\nabla} of the
connection. In particular, if the supersymmetry is non-trivial and if
the conditions \bdm (d \Phi \haken \T) \haken \T = 0, \quad \delta^{\nabla}(d
\T) \cdot \Psi = 0 \edm hold, then the energy-momentum tensor is
divergence-free. We show that the latter condition is satisfied in many
examples constructed out of special geometries. A special case is . Then
the divergence of the energy-momentum tensor vanishes if and only if one
condition \delta^{\nabla}(d \T) \cdot \Psi = 0 holds. Strong models (d \T =
0) have this property, but there are examples with \delta^{\nabla}(d \T) \neq
0 and \delta^{\nabla}(d \T) \cdot \Psi = 0.Comment: 9 pages, Latex2
Tomographic readout of an opto-mechanical interferometer
The quantum state of light changes its nature when being reflected off a
mechanical oscillator due to the latter's susceptibility to radiation pressure.
As a result, a coherent state can transform into a squeezed state and can get
entangled with the motion of the oscillator. The complete tomographic
reconstruction of the state of light requires the ability to readout arbitrary
quadratures. Here we demonstrate such a readout by applying a balanced homodyne
detector to an interferometric position measurement of a thermally excited
high-Q silicon nitride membrane in a Michelson-Sagnac interferometer. A readout
noise of \unit{1.9 \cdot 10^{-16}}{\metre/\sqrt{\hertz}} around the
membrane's fundamental oscillation mode at \unit{133}{\kilo\hertz} has been
achieved, going below the peak value of the standard quantum limit by a factor
of 8.2 (9 dB). The readout noise was entirely dominated by shot noise in a
rather broad frequency range around the mechanical resonance.Comment: 7 pages, 5 figure
Killing spinors in supergravity with 4-fluxes
We study the spinorial Killing equation of supergravity involving a torsion
3-form \T as well as a flux 4-form \F. In dimension seven, we construct
explicit families of compact solutions out of 3-Sasakian geometries, nearly
parallel \G_2-geometries and on the homogeneous Aloff-Wallach space. The
constraint \F \cdot \Psi = 0 defines a non empty subfamily of solutions. We
investigate the constraint \T \cdot \Psi = 0, too, and show that it singles
out a very special choice of numerical parameters in the Killing equation,
which can also be justified geometrically
GW quasiparticle calculations with spin-orbit coupling for the light actinides
We report on the importance of GW self-energy corrections for the electronic
structure of light actinides in the weak-to-intermediate coupling regime. Our
study is based on calculations of the band structure and total density of
states of Np, U, and Pu using a one-shot GW approximation that includes
spin-orbit coupling within a full potential LAPW framework. We also present RPA
screened effective Coulomb interactions for the f-electron orbitals for
different lattice constants, and show that there is an increased contribution
from electron-electron correlation in these systems for expanded lattices. We
find a significant amount of electronic correlation in these highly localized
electronic systems.Comment: Accepted and to appear in Phys. Rev.
General Relativistic Scalar Field Models in the Large
For a class of scalar fields including the massless Klein-Gordon field the
general relativistic hyperboloidal initial value problems are equivalent in a
certain sense. By using this equivalence and conformal techniques it is proven
that the hyperboloidal initial value problem for those scalar fields has an
unique solution which is weakly asymptotically flat. For data sufficiently
close to data for flat spacetime there exist a smooth future null infinity and
a regular future timelike infinity.Comment: 22 pages, latex, AGG 1
First-order symmetrizable hyperbolic formulations of Einstein's equations including lapse and shift as dynamical fields
First-order hyperbolic systems are promising as a basis for numerical
integration of Einstein's equations. In previous work, the lapse and shift have
typically not been considered part of the hyperbolic system and have been
prescribed independently. This can be expensive computationally, especially if
the prescription involves solving elliptic equations. Therefore, including the
lapse and shift in the hyperbolic system could be advantageous for numerical
work. In this paper, two first-order symmetrizable hyperbolic systems are
presented that include the lapse and shift as dynamical fields and have only
physical characteristic speeds.Comment: 11 page
Otto Stern (1888-1969): The founding father of experimental atomic physics
We review the work and life of Otto Stern who developed the molecular beam
technique and with its aid laid the foundations of experimental atomic physics.
Among the key results of his research are: the experimental determination of
the Maxwell-Boltzmann distribution of molecular velocities (1920), experimental
demonstration of space quantization of angular momentum (1922), diffraction of
matter waves comprised of atoms and molecules by crystals (1931) and the
determination of the magnetic dipole moments of the proton and deuteron (1933).Comment: 39 pages, 8 figure
Initial states and infrared physics in locally de Sitter spacetime
The long wavelength physics in a de Sitter region depends on the initial
quantum state. While such long wavelength physics is under control for massive
fields near the Hartle-Hawking vacuum state, such initial states make unnatural
assumptions about initial data outside the region of causal contact of a local
observer. We argue that a reasonable approximation to a maximum entropy state,
one that makes minimal assumptions outside an observer's horizon volume, is one
where a cutoff is placed on a surface bounded by timelike geodesics, just
outside the horizon. For sufficiently early times, such a cutoff induces
secular logarithmic divergences with the expansion of the region. For massive
fields, these effects sum to finite corrections at sufficiently late times. The
difference between the cutoff correlators and Hartle-Hawking correlators
provides a measure of the theoretical uncertainty due to lack of knowledge of
the initial state in causally disconnected regions. These differences are
negligible for primordial inflation, but can become significant during epochs
with very long-lived de Sitter regions, such as we may be entering now.Comment: 19 pages, 4 figures, references adde
Efficient and spectrally bright source of polarization-entangled photons
We demonstrate an efficient fiber-coupled source of nondegenerate
polarization entangled photons at 795 and 1609 nm using bidirectionally pumped
parametric down-conversion in bulk periodically poled lithium niobate. The
single-mode source has an inferred bandwidth of 50 GHz and a spectral
brightness of 300 pairs/s/GHz/mW of pump power that is suitable for narrowband
applications such as entanglement transfer from photonic to atomic qubits.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
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