24,290 research outputs found
Indirect Dissociative Recombination of LiH Molecules Fueled by Complex Resonance Manifolds
The LiH molecule is prototypical of the indirect dissociative
recombination (DR) process, in which a colliding electron destroys the molecule
through Rydberg capture pathways. This Letter develops the first quantitative
test of the Siegert state multichannel quantum defect theory description of
indirect DR for a diatomic molecular ion. The R-matrix approach is adopted to
calculate ab-initio quantum defects, functions of the internuclear distance
that characterize both Rydberg states and the zero-energy collisions of
electrons with LiH ions. The calculated DR rate coefficient agrees
accurately with recent experimental data (S. Krohn et al, Phys. Rev. Lett. 86,
4005). We identify the doorways to fast indirect DR as complex resonance
manifolds, which couple closed channels having both high and low principal
quantum numbers. This sheds new light on the competition between direct and
indirect DR pathways, and suggests the reason why previous theory
underestimated the DR rate by an order of magnitude.Comment: Submitted to PR
Inflation as a Probe of Short Distance Physics
We show that a string-inspired Planck scale modification of general
relativity can have observable cosmological effects. Specifically, we present a
complete analysis of the inflationary perturbation spectrum produced by a
phenomenological Lagrangian that has a standard form on large scales but
incorporates a string-inspired short distance cutoff, and find a deviation from
the standard result. We use the de Sitter calculation as the basis of a
qualitative analysis of other inflationary backgrounds, arguing that in these
cases the cutoff could have a more pronounced effect, changing the shape of the
spectrum. Moreover, the computational approach developed here can be used to
provide unambiguous calculations of the perturbation spectrum in other
heuristic models that modify trans-Planckian physics and thereby determine
their impact on the inflationary perturbation spectrum. Finally, we argue that
this model may provide an exception to constraints, recently proposed by Tanaka
and Starobinsky, on the ability of Planck-scale physics to modify the
cosmological spectrum.Comment: revtex, 8 pages, eps figures included, references adde
"So what will you do if string theory is wrong?"
I briefly discuss the accomplishments of string theory that would survive a
complete falsification of the theory as a model of nature and argue the
possibility that such a survival may necessarily mean that string theory would
become its own discipline, independently of both physics and mathematics
Low energy electron scattering from DNA and RNA bases: shape resonances and radiation damage
Calculations are carried out to determine elastic scattering cross sections
and resonance energies for low energy electron impact on uracil and on each of
the DNA bases (thymine, cytosine, adenine, guanine), for isolated molecules in
their equilibrium geometry. Our calculations are compared with available theory
and experiment. We also attempt to correlate this information with experimental
dissociation patterns through an analysis of the temporary anion structures
that are formed by electron capture in shape resonances.Comment: 20 pages, 12 figures, submitted to J. Chem. Phy
Evidence for Antiferromagnetic Order in LaCeCuO from Angular Magnetoresistance Measurements
We investigated the in-plane angular magnetoresistivity (AMR) of -phase LaCeCuO (LCCO) thin films () fabricated by a pulsed laser deposition technique. The in-plane
AMR with shows a twofold symmetry instead of the
fourfold behavior found in other electron-doped cuprates such as PrCeCuO and NdCeCuO. The twofold AMR
disappears above a certain temperature, . The is well above
for ( K), and decreases with increasing doping,
until it is no longer observed above at . This twofold AMR
below is suggested to originate from an antiferromagnetic or spin
density wave order.Comment: to be published in Phys. Rev. B, Vol. 80 (2009
- …