4,865 research outputs found
What is the Physics behind the 3He-4He Anomaly ?
We show that coalescence of nucleons emitted prior to thermalization in
highly excited nuclei can explain the anomaly of kinetic energies of helium
clusters. A new coalescence algorithm has been included into the statistical
approach to nuclear reactions formerly used to describe intermediate mass
fragment production.Comment: 5 pages, 4 figures, accepted at Eur. Phys.
A note on spectator effects and quark-hadron duality in inclusive beauty decays
In this paper, we evaluate the expectation values of four-quark operators for
the inclusive beauty decays from the differences in the inclusive total decay
rates, assuming that the heavy quark expansion converges at . The
obtained expectation values yeilds the ratio close to
the experimental onee. We further point out that the quark-hadron duality
violation would be rather small allowing predictions of inclusive quantities.Comment: 5 pages, typos corrected, version to be published in PL
Phenomenology of B -> pi pi, pi K Decays at O(alpha^2 beta_0) in QCD Factorization
We study O(alpha^2 beta_0) perturbative corrections to matrix elements
entering two-body exclusive decays of the form B -> pi pi, pi K in the QCD
factorization formalism, including chirally enhanced power corrections, and
discuss the effect of these corrections on direct CP asymmetries, which receive
their first contribution at O(alpha). We find that the O(alpha^2 beta_0)
corrections are often as large as the O(alpha) corrections. We find large
uncertainties due to renormalization scale dependence as well as poor knowledge
of the non-perturbative parameters. We assess the effect of the perturbative
corrections on the direct CP violation parameters of B -> pi^+ pi^-.Comment: 27 pages, 5 figures. Updated input parameters and added citations;
expanded discussio
Infrared singularities of scattering amplitudes in perturbative QCD
An exact formula is derived for the infrared singularities of dimensionally
regularized scattering amplitudes in massless QCD with an arbitrary number of
legs, valid at any number of loops. It is based on the conjecture that the
anomalous-dimension matrix of n-jet operators in soft-collinear effective
theory contains only a single non-trivial color structure, whose coefficient is
the cusp anomalous dimension of Wilson loops with light-like segments. Its
color-diagonal part is characterized by two anomalous dimensions, which are
extracted to three-loop order from known perturbative results for the quark and
gluon form factors. This allows us to predict the three-loop coefficients of
all 1/epsilon^k poles for an arbitrary n-parton scattering amplitudes,
generalizing existing two-loop results.Comment: 4 pages; v2: typo in eq. (12) fixed, references updated; v3:
additional term in (12
Improved Currents for Heavy Quarks
We discuss lattice artifacts for matrix elements of hadrons containing one or
more heavy quark. In particular, we analyze interrelations between lattice
artifacts and the expansion. The implications for calculations of
heavy-light decay constants and of semi-leptonic form factors are discussed.Comment: 3 pages, no figures, uuencoded PostScript, proceedings of Lattice
'94. LaTeX at ftp://fnth06.fnal.gov/pub/Fermilab-Pub/95.00
Flavor Physics in the Randall-Sundrum Model: I. Theoretical Setup and Electroweak Precision Tests
A complete discussion of tree-level flavor-changing effects in the
Randall-Sundrum (RS) model with brane-localized Higgs sector and bulk gauge and
matter fields is presented. The bulk equations of motion for the gauge and
fermion fields, supplemented by boundary conditions taking into account the
couplings to the Higgs sector, are solved exactly. For gauge fields the
Kaluza-Klein (KK) decomposition is performed in a covariant R_xi gauge. For
fermions the mixing between different generations is included in a completely
general way. The hierarchies observed in the fermion spectrum and the quark
mixing matrix are explained naturally in terms of anarchic five-dimensional
Yukawa matrices and wave-function overlap integrals. Detailed studies of the
flavor-changing couplings of the Higgs boson and of gauge bosons and their KK
excitations are performed, including in particular the couplings of the
standard W and Z bosons. A careful analysis of electroweak precision
observables including the S and T parameters and the Zbb couplings shows that
the simplest RS model containing only Standard Model particles and their KK
excitations is consistent with all experimental bounds for a KK scale as low as
a few TeV, if one allows for a heavy Higgs boson and/or for an ultra-violet
cutoff below the Planck scale. The study of flavor-changing effects includes
analyses of the non-unitarity of the quark mixing matrix, anomalous
right-handed couplings of the W bosons, tree-level flavor-changing neutral
current couplings of the Z and Higgs bosons, the rare decays t-->c(u)+Z and
t-->c(u)+h, and the flavor mixing among KK fermions. The results obtained in
this work form the basis for general calculations of flavor-changing processes
in the RS model and its extensions.Comment: 70 pages, 12 figures. v2: Incorrect treatment of phases in zero-mode
approximation corrected, and discussion of electroweak precision tests
modified. v3: Additional minor modifications and typos corrected; version
published in JHE
Decays of bottom mesons emitting tensor meson in final state using ISGW II model
In this paper, we investigate phenomenologically two-body weak decays of the
bottom mesons emitting pseudoscalar/vector meson and a tensor meson. Form
factors are obtained using the improved ISGW II model. Consequently, branching
ratios for the CKM-favored and CKM-suppressed decays are calculated.Comment: 32 pages, to be published in Phys. Rev.
How reliable are the HQET-sum rule predictions?
We test the internal consistencies and the reliability of the existing
estimates of the decay constant in the static limit, the meson-quark mass
gap and the kinetic energy of a heavy quark obtained from
the heavy quark effective theory (HQET)-sum rules. Finite energy local duality
sum rules (FESR) have also been used to fix the value of the
continuum energy and to study the correlations among these different
parameters. Then, we deduce to two-loop accuracy: \bl=(0.65\pm 0.05) GeV,
GeV^2M_b=
(4.61 \pm 0.05)f_B^\infty=(1.98 \pm 0.31)f_\pif_P\sqrt{M_P}=(0.33 \pm 0.06)^{3/2}\als^{1/\beta_1}2}\als^{1/\beta_1
1-2\als/3\pi-1.1/M_Q +0.7/M_Q^2 .$Comment: PS file, figures available by reques
A Consistent Calculation of Heavy Meson Decay Constants and Transition Wave Functions in the Complete HQEFT
Within the complete heavy quark effective field theory (HQEFT), the QCD sum
rule approach is used to evaluate the decay constants including 1/m_Q
corrections and the Isgur-Wise function and other additional important wave
functions concerned at 1/m_Q for the heavy-light mesons. The 1/m_Q corrections
to the scaling law f_M \sim F/\sqrt{m_M} are found to be small in HQEFT, which
demonstrates again the validity of 1/m_Q expansion in HQEFT. It is also shown
that the residual momentum v.k of heavy quark within hadrons does be around the
binding energy \bar{\Lambda} of the heavy hadrons. The calculations presented
in this paper provide a consistent check on the HQEFT and shows that the HQEFT
is more reliable than the usual HQET for describing a slightly off-mass shell
heavy quark within hadron as the usual HQET seems to lead to the breakdown of
1/m_Q expansion in evaluating the meson decay constants. It is emphasized that
the introduction of the `dressed heavy quark' mass is useful for the
heavy-light mesons (Qq) with m_Q >> \bar{\Lambda} >> m_q, while for heavy-heavy
bound states (\psi_1\psi_2) with masses m_1, m_2 >> \bar{\Lambda}, like
bottom-charm hadrons or similarly for muonium in QED, one needs to treat both
particles as heavy effective particles via 1/m_1 and 1/m_2 expansions and
redefine the effective bound states and modified `dressed heavy quark' masses
within the HQEFT.Comment: 20 pages, revtex, 22 figures, axodraw.sty, two irrelevant figures are
moved awa
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