33,261 research outputs found
B->gamma e nu Transitions from QCD Sum Rules
B->gamma e nu transitions have recently been studied in the framework of QCD
factorization. The attractiveness of this channel for such an analysis lies in
the fact that, at least in the heavy quark limit, the only hadron involved is
the B meson itself, so one expects a very simple description of the form factor
in terms of a convolution of the B meson distribution amplitude with a
perturbative kernel. This description, however, does not include contributions
suppressed by powers of the b quark mass. In this letter, we calculate
corrections to the factorized expression which are induced by the ``soft''
hadronic component of the photon. We demonstrate that the power-suppression of
these terms is numerically not effective for physical values of the quark
mass and that they increase the form factor by about 30% at zero momentum
transfer. We also derive a sum rule for lambda_B, the first negative moment of
the B meson distribution amplitude, and find lambda_B = 0.6 GeV (to leading
order in QCD).Comment: 13 pages, 5 figure
Incompatible sets of gradients and metastability
We give a mathematical analysis of a concept of metastability induced by
incompatibility. The physical setting is a single parent phase, just about to
undergo transformation to a product phase of lower energy density. Under
certain conditions of incompatibility of the energy wells of this energy
density, we show that the parent phase is metastable in a strong sense, namely
it is a local minimizer of the free energy in an neighbourhood of its
deformation. The reason behind this result is that, due to the incompatibility
of the energy wells, a small nucleus of the product phase is necessarily
accompanied by a stressed transition layer whose energetic cost exceeds the
energy lowering capacity of the nucleus. We define and characterize
incompatible sets of matrices, in terms of which the transition layer estimate
at the heart of the proof of metastability is expressed. Finally we discuss
connections with experiment and place this concept of metastability in the
wider context of recent theoretical and experimental research on metastability
and hysteresis.Comment: Archive for Rational Mechanics and Analysis, to appea
Preliminary Test of Prescribed Burning for Control of Maple Leaf Cutter (Lepidoptera: Incurvariidae)
Leaf litter burning in the spring resulted in 87.5% mortality of maple leaf cutter pupae, Paraclemensia acerifoliella (Fitch). No apparent damage was observed on sugar maple or beech trees within the burn area
Heavy to Light Meson Exclusive Semileptonic Decays in Effective Field Theory of Heavy Quark
We present a general study on exclusive semileptonic decays of heavy (B, D,
B_s) to light (pi, rho, K, K^*) mesons in the framework of effective field
theory of heavy quark. Transition matrix elements of these decays can be
systematically characterized by a set of wave functions which are independent
of the heavy quark mass except for the implicit scale dependence. Form factors
for all these decays are calculated consistently within the effective theory
framework using the light cone sum rule method at the leading order of 1/m_Q
expansion. The branching ratios of these decays are evaluated, and the heavy
and light flavor symmetry breaking effects are investigated. We also give
comparison of our results and the predictions from other approaches, among
which are the relations proposed recently in the framework of large energy
effective theory.Comment: 18 pages, ReVtex, 5 figures, added references and comparison of
results, and corrected signs in some formula
Exploiting entanglement in communication channels with correlated noise
We develop a model for a noisy communication channel in which the noise
affecting consecutive transmissions is correlated. This model is motivated by
fluctuating birefringence of fiber optic links. We analyze the role of
entanglement of the input states in optimizing the classical capacity of such a
channel. Assuming a general form of an ensemble for two consecutive
transmissions, we derive tight bounds on the classical channel capacity
depending on whether the input states used for communication are separable or
entangled across different temporal slots. This result demonstrates that by an
appropriate choice, the channel capacity may be notably enhanced by exploiting
entanglement.Comment: 9 pages, 5 figure
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