31,373 research outputs found
Quenched Spectroscopy for the N=1 Super-Yang-Mills Theory
We present results for the Quenched SU(2) N=1 Super-Yang-Mills spectrum at
, on a lattice, in the OZI approximation. This is
a first step towards the understanding of the chiral limit of lattice N=1 SUSY.Comment: 3 pages, Latex, 2 ps figures, contribution to Lattice 97, Edinburgh
22-26 July 1997; to appear on Nucl. Phys. B. (Proc. Suppl.
True high-order VCO-based ADC
A novel approach to use a voltage-controlled oscillator (VCO) as the first integrator of a high-order continuous-time delta-sigma modulator (CT-DSM) is presented. In the proposed architecture, the VCO is combined with a digital up-down counter to implement the first integrator of the CT-DSM. Thus, the first integrator is digital-friendly and hence can maximally benefit from technological scaling
The seesaw path to leptonic CP violation
Future experiments such as SHiP and high-intensity colliders will
have a superb sensitivity to heavy Majorana neutrinos with masses below .
We show that the measurement of the mixing to electrons and muons of one such
state could imply the discovery of leptonic CP violation in the context of
seesaw models. We quantify in the minimal model the CP discovery potential of
these future experiments, and demonstrate that a 5 CL discovery of
leptonic CP violation would be possible in a very significant fraction of
parameter space.Comment: An error has been fixed, main conclusions unchange
The projection of a nonlocal mechanical system onto the irreversible generalized Langevin equation, II: Numerical simulations
The irreversible generalized Langevin equation (iGLE) contains a
nonstationary friction kernel that in certain limits reduces to the GLE with
space-dependent friction. For more general forms of the friction kernel, the
iGLE was previously shown to be the projection of a mechanical system with a
time-dependent Hamiltonian. [R. Hernandez, J. Chem. Phys. 110, 7701 (1999)] In
the present work, the corresponding open Hamiltonian system is further
explored. Numerical simulations of this mechanical system illustrate that the
time dependence of the observed total energy and the correlations of the
solvent force are in precise agreement with the projected iGLE.Comment: 8 pages, 9 figures, submitted to J. Chem. Phy
Probing O-enrichment in C-rich dust planetary nebulae
The abundance of O in planetary nebulae (PNe) has been historically used as a
metallicity indicator of the interstellar medium (ISM) where they originated;
e.g., it has been widely used to study metallicity gradients in our Galaxy and
beyond. However, clear observational evidence for O self enrichment in
low-metallicity Galactic PNe with C-rich dust has been recently reported. Here
we report asymptotic giant branch (AGB) nucleosynthesis predictions for the
abundances of the CNO elements and helium in the metallicity range Zsun/4 < Z <
2Zsun. Our AGB models, with diffusive overshooting from all the convective
borders, predict that O is overproduced in low-Z low-mass (~1-3 Msun) AGB stars
and nicely reproduce the recent O overabundances observed in C-rich dust PNe.
This confirms that O is not always a good proxy of the original ISM metallicity
and another chemical elements such as Cl or Ar should be used instead. The
production of oxygen by low-mass stars should be thus considered in
galactic-evolution models.Comment: Accepted for publication in MNRAS Letters (5 pages, 1 figure, and 1
table
Galactic planetary nebulae with precise nebular abundances as a tool to understand the evolution of asymptotic giant branch stars
We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch
(AGB) models, with diffusive overshooting from all the convective borders, in
the metallicity range Z/4 < Z < 2Zsun. They are compared to recent precise
nebular abundances in a sample of Galactic planetary nebulae (PNe) that is
divided among double-dust chemistry (DC) and oxygen-dust chemistry (OC)
according to the infrared dust features. Unlike the similar subsample of
Galactic carbon-dust chemistry PNe recently analysed by us, here the individual
abundance errors, the higher metallicity spread, and the uncertain dust
types/subtypes in some PNe do not allow a clear determination of the AGB
progenitor masses (and formation epochs) for both PNe samples; the comparison
is thus more focussed on a object-by-object basis. The lowest metallicity OC
PNe evolve from low-mass (~1 Msun) O-rich AGBs, while the higher metallicity
ones (all with uncertain dust classifications) display a chemical pattern
similar to the DC PNe. In agreement with recent literature, the DC PNe mostly
descend from high-mass (M > 3.5 Msun) solar/supersolar metallicity AGBs that
experience hot bottom burning (HBB), but other formation channels in low-mass
AGBs like extra mixing, stellar rotation, binary interaction, or He
pre-enrichment cannot be disregarded until more accurate C/O ratios would be
obtained. Two objects among the DC PNe show the imprint of advanced CNO
processing and deep second dredge-up, suggesting progenitors masses close to
the limit to evolve as core collapse supernovae (above 6 Msun). Their actual
C/O ratio, if confirmed, indicate contamination from the third dredge-up,
rejecting the hypothesis that the chemical composition of such high-metallicity
massive AGBs is modified exclusively by HBB.Comment: Accepted for publication in MNRAS (11 pages, 3 figures, and 2 tables
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