672 research outputs found
Rho-Omega Mixing and the Pion Form Factor in the Time-like Region
We determine the magnitude, phase, and -dependence of -
``mixing'' in the pion form factor in the time-like region through fits to
e^+e^- \ra \pi^+ \pi^- data. The associated systematic errors in these
quantities, arising from the functional form used to fit the resonance,
are small. The systematic errors in the mass and width, however, are
larger than previously estimated.Comment: 20 pages, REVTeX, epsfig, 2 ps figures, minor change
Temperature and wavelength drift tolerant WDM transmission and routing in on-chip silicon photonic interconnects
We demonstrate a temperature and wavelength shift resilient silicon transmission and routing interconnect system suitable for multi-socket interconnects, utilizing a dual-strategy CLIPP feedback circuitry that safeguards the operating point of the constituent photonic building blocks along the entire on-chip transmission-multiplexing-routing chain. The control circuit leverages a novel control power-independent and calibration-free locking strategy that exploits the 2nd derivative of ring resonator modulators (RMs) transfer function to lock them close to the point of minimum transmission penalty. The system performance was evaluated on an integrated Silicon Photonics 2-socket demonstrator, enforcing control over a chain of RM-MUX-AWGR resonant structures and stressed against thermal and wavelength shift perturbations. The thermal and wavelength stress tests ranged from 27 degrees C to 36 degrees C and 1309.90 nm to 1310.85 nm and revealed average eye diagrams Q-factor values of 5.8 and 5.9 respectively, validating the system robustness to unstable environments and fabrication variations. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreemen
Rescattering and chiral dynamics in B\to \rho\pi decay
We examine the role of B^0(\bar B^0) \to \sigma \pi^0 \to \pi^+\pi^- \pi^0
decay in the Dalitz plot analysis of B^0 (\bar B^0) \to \rho\pi \to
\pi^+\pi^-\pi^0 decays, employed to extract the CKM parameter \alpha. The
\sigma \pi channel is significant because it can break the relationship between
the penguin contributions in B\to\rho^0\pi^0, B\to\rho^+\pi^-, and
B\to\rho^-\pi^+ decays consequent to an assumption of isospin symmetry. Its
presence thus mimics the effect of isospin violation. The \sigma\pi^0 state is
of definite CP, however; we demonstrate that the B\to\rho\pi analysis can be
generalized to include this channel without difficulty. The \sigma or
f_0(400-1200) ``meson'' is a broad I=J=0 enhancement driven by strong \pi\pi
rescattering; a suitable scalar form factor is constrained by the chiral
dynamics of low-energy hadron-hadron interactions - it is rather different from
the relativistic Breit-Wigner form adopted in earlier B\to\sigma\pi and
D\to\sigma\pi analyses. We show that the use of this scalar form factor leads
to an improved theoretical understanding of the measured ratio Br(\bar B^0 \to
\rho^\mp \pi^\pm) / Br(B^-\to \rho^0 \pi^-).Comment: 26 pages, 8 figs, published version. typos fixed, minor change
Extracting Br(omega->pi^+ pi^-) from the Time-like Pion Form-factor
We extract the G-parity-violating branching ratio Br(omega->pi^+ pi^-) from
the effective rho-omega mixing matrix element Pi_{rho omega}(s), determined
from e^+e^- -> pi^+ pi^- data. The omega->pi^+ pi^- partial width can be
determined either from the time-like pion form factor or through the constraint
that the mixed physical propagator D_{rho omega}^{mu nu}(s) possesses no poles.
The two procedures are inequivalent in practice, and we show why the first is
preferred, to find finally Br(omega->pi^+ pi^-) = 1.9 +/- 0.3%.Comment: 12 pages (published version
Vector meson dominance and the rho meson
We discuss the properties of vector mesons, in particular the rho^0, in the
context of the Hidden Local Symmetry (HLS) model. This provides a unified
framework to study several aspects of the low energy QCD sector. Firstly, we
show that in the HLS model the physical photon is massless, without requiring
off field diagonalization. We then demonstrate the equivalence of HLS and the
two existing representations of vector meson dominance, VMD1 and VMD2, at both
tree level and one loop order. Finally the S matrix pole position is shown to
provide a model and process independent means of specifying the rho mass and
width, in contrast to the real axis prescription currently used in the Particle
Data Group tables.Comment: 18 pages, REVTE
Defending the genome from the enemy within:mechanisms of retrotransposon suppression in the mouse germline
The viability of any species requires that the genome is kept stable as it is transmitted from generation to generation by the germ cells. One of the challenges to transgenerational genome stability is the potential mutagenic activity of transposable genetic elements, particularly retrotransposons. There are many different types of retrotransposon in mammalian genomes, and these target different points in germline development to amplify and integrate into new genomic locations. Germ cells, and their pluripotent developmental precursors, have evolved a variety of genome defence mechanisms that suppress retrotransposon activity and maintain genome stability across the generations. Here, we review recent advances in understanding how retrotransposon activity is suppressed in the mammalian germline, how genes involved in germline genome defence mechanisms are regulated, and the consequences of mutating these genome defence genes for the developing germline
Size-dependent influence of NO_x on the growth rates of organic aerosol particles
Atmospheric new-particle formation (NPF) affects climate by contributing to a large fraction of the cloud condensation nuclei (CCN). Highly oxygenated organic molecules (HOMs) drive the early particle growth and therefore substantially influence the survival of newly formed particles to CCN. Nitrogen oxide (NO_x) is known to suppress the NPF driven by HOMs, but the underlying mechanism remains largely unclear. Here, we examine the response of particle growth to the changes of HOM formation caused by NO_x. We show that NO_x suppresses particle growth in general, but the suppression is rather nonuniform and size dependent, which can be quantitatively explained by the shifted HOM volatility after adding NO_x. By illustrating how NO_x affects the early growth of new particles, a critical step of CCN formation, our results help provide a refined assessment of the potential climatic effects caused by the diverse changes of NO_x level in forest regions around the globe
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