12,970 research outputs found
Decoupling of heavy quarks in HQET
Decoupling of c-quark loops in b-quark HQET is considered. The decoupling
coefficients for the HQET heavy-quark field and the heavy-light quark current
are calculated with the three-loop accuracy. The last result can be used to
improve the accuracy of extracting f_B from HQET lattice simulations (without
c-quark loops). The decoupling coefficient for the flavour-nonsinglet QCD
current with n antisymmetrized gamma-matrices is also obtained at three loops;
the result for the tensor current (n=2) is new.Comment: JHEP3 documentclass; the results in a computer-readable form can be
found at http://www-ttp.physik.uni-karlsruhe.de/Progdata/ttp06/ttp06-25/ V2:
a few typos corrected, a few minor text improvements, a few references added;
V3: several typos in formulas fixe
Spin interfaces in the Ashkin-Teller model and SLE
We investigate the scaling properties of the spin interfaces in the
Ashkin-Teller model. These interfaces are a very simple instance of lattice
curves coexisting with a fluctuating degree of freedom, which renders the
analytical determination of their exponents very difficult. One of our main
findings is the construction of boundary conditions which ensure that the
interface still satisfies the Markov property in this case. Then, using a novel
technique based on the transfer matrix, we compute numerically the left-passage
probability, and our results confirm that the spin interface is described by an
SLE in the scaling limit. Moreover, at a particular point of the critical line,
we describe a mapping of Ashkin-Teller model onto an integrable 19-vertex
model, which, in turn, relates to an integrable dilute Brauer model.Comment: 12 pages, 6 figure
Form factors of descendant operators: Free field construction and reflection relations
The free field representation for form factors in the sinh-Gordon model and
the sine-Gordon model in the breather sector is modified to describe the form
factors of descendant operators, which are obtained from the exponential ones,
\e^{\i\alpha\phi}, by means of the action of the Heisenberg algebra
associated to the field . As a check of the validity of the
construction we count the numbers of operators defined by the form factors at
each level in each chiral sector. Another check is related to the so called
reflection relations, which identify in the breather sector the descendants of
the exponential fields \e^{\i\alpha\phi} and \e^{\i(2\alpha_0-\alpha)\phi}
for generic values of . We prove the operators defined by the obtained
families of form factors to satisfy such reflection relations. A generalization
of the construction for form factors to the kink sector is also proposed.Comment: 29 pages; v2: minor corrections, some references added; v3: minor
corrections; v4,v5: misprints corrected; v6: minor mistake correcte
Bimaximal Neutrino Mixing with Discrete Flavour Symmetries
In view of the fact that the data on neutrino mixing are still compatible
with a situation where Bimaximal mixing is valid in first approximation and it
is then corrected by terms of order of the Cabibbo angle, we present examples
where these properties are naturally realized. The models are supersymmetric in
4-dimensions and based on the discrete non-Abelian flavour symmetry S4.Comment: 8 pages, 1 figure; contribution prepared for DISCRETE'10 - Symposium
on Prospects in the Physics of Discrete Symmetrie
Secondary electron emission yield in the limit of low electron energy
Secondary electron emission (SEE) from solids plays an important role in many
areas of science and technology.1 In recent years, there has been renewed
interest in the experimental and theoretical studies of SEE. A recent study
proposed that the reflectivity of very low energy electrons from solid surface
approaches unity in the limit of zero electron energy2,3,4, If this was indeed
the case, this effect would have profound implications on the formation of
electron clouds in particle accelerators,2-4 plasma measurements with
electrostatic Langmuir probes, and operation of Hall plasma thrusters for
spacecraft propulsion5,6. It appears that, the proposed high electron
reflectivity at low electron energies contradicts to numerous previous
experimental studies of the secondary electron emission7. The goal of this note
is to discuss possible causes of these contradictions.Comment: 3 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Ital
Raising and lowering operators, factorization and differential/difference operators of hypergeometric type
Starting from Rodrigues formula we present a general construction of raising
and lowering operators for orthogonal polynomials of continuous and discrete
variable on uniform lattice. In order to have these operators mutually adjoint
we introduce orthonormal functions with respect to the scalar product of unit
weight. Using the Infeld-Hull factorization method, we generate from the
raising and lowering operators the second order self-adjoint
differential/difference operator of hypergeometric type.Comment: LaTeX, 24 pages, iopart style (late submission
Raising and lowering operators and their factorization for generalized orthogonal polynomials of hypergeometric type on homogeneous and non-homogeneous lattice
We complete the construction of raising and lowering operators, given in a
previous work, for the orthogonal polynomials of hypergeometric type on
non-homogeneous lattice, and extend these operators to the generalized
orthogonal polynomials, namely, those difference of orthogonal polynomials that
satisfy a similar difference equation of hypergeometric type.Comment: LaTeX, 19 pages, (late submission to arXiv.org
Neutrino oscillations: Entanglement, energy-momentum conservation and QFT
We consider several subtle aspects of the theory of neutrino oscillations
which have been under discussion recently. We show that the -matrix
formalism of quantum field theory can adequately describe neutrino oscillations
if correct physics conditions are imposed. This includes space-time
localization of the neutrino production and detection processes. Space-time
diagrams are introduced, which characterize this localization and illustrate
the coherence issues of neutrino oscillations. We discuss two approaches to
calculations of the transition amplitudes, which allow different physics
interpretations: (i) using configuration-space wave packets for the involved
particles, which leads to approximate conservation laws for their mean energies
and momenta; (ii) calculating first a plane-wave amplitude of the process,
which exhibits exact energy-momentum conservation, and then convoluting it with
the momentum-space wave packets of the involved particles. We show that these
two approaches are equivalent. Kinematic entanglement (which is invoked to
ensure exact energy-momentum conservation in neutrino oscillations) and
subsequent disentanglement of the neutrinos and recoiling states are in fact
irrelevant when the wave packets are considered. We demonstrate that the
contribution of the recoil particle to the oscillation phase is negligible
provided that the coherence conditions for neutrino production and detection
are satisfied. Unlike in the previous situation, the phases of both neutrinos
from decay are important, leading to a realization of the
Einstein-Podolsky-Rosen paradox.Comment: 30 pages, 3 eps figures; presentation improved, clarifications added.
To the memory of G.T. Zatsepi
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