5,553 research outputs found

### Comment on "On the $T_S$-Anomaly in Betaine Calcium Chloride Dihydrate"

Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed
the $T_S$-anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type
approach. We comment on the shortcomings of this approach and discuss the
$T_S$-anomaly in the framework of a microscopical pseudo spin model based on a
realistic description of BCCD in terms of symmetry-adapted local modes.Comment: 2 pages, RevTex, submitted to J. Phys. Soc. Jp

### Renormalization of Velocity-Changing Dimension-Five Operators in the Heavy-Quark Effective Theory

We study the renormalization of operators of the type ${\bar h_{v'}} \Gamma
G^{\mu\nu} h_v$ in the heavy-quark effective theory (HQET). We construct the
combinations of such operators that are renormalized multiplicatively, and
calculate their velocity-dependent anomalous dimensions at the one-loop order.
We then show that the virial theorem of the HQET is not renormalized, and that
in the limit of equal velocities the anomalous dimension of the chromo-electric
operator vanishes to all orders in perturbation theory. This implies an exact
relation between renormalization constants, which may help in a future
calculation of the two-loop anomalous dimension of the chromo-magnetic
operator.Comment: 9 pages, 1 figur

### Impact of Four-Quark Shape Functions on Inclusive B Decay Spectra

It has recently been pointed out that a new class of subleading shape
functions involving B-meson matrix elements of non-local four-quark operators
contributes at order Lambda_{QCD}/m_b to B->X_u+l+nu decay distributions in the
endpoint region. The corresponding functions f_u(omega) and f_v(omega) are
estimated using the vacuum-insertion approximation. A numerical analysis of
various B->X_u+l+nu decay spectra suggests that these power corrections are
very small, below present theoretical uncertainties due to other subleading
shape-function contributions.Comment: 8 pages, 2 figures; minor revisions and figure added; version to
appear in Eur. Phys. J.

### Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants

We discuss various tests of the factorization hypothesis making use of the
close relationship between semi-leptonic and factorized nonleptonic decay
amplitudes. It is pointed out that factorization leads to truely
model-independent predictions for the ratio of nonleptonic to semi-leptonic
decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or
a pion take the place of the lepton pair. Where the decay constants of those
mesons are known, these predictions represent ideal tests of the factorization
hypothesis. In other cases they may be used to extract the decay constants.
Currently available data on the decays $\bar B^0 \to D^+\pi^-,\, D^{*+}\pi^-,\,
D^+\varrho^-,\, D^{*+}\varrho^-$ are shown to be in excellent agreement with
the factorization results. A weighted average of the four independent values
for the QCD coefficient $a_1$ extracted from the data gives $a_1=1.15\pm 0.06$
suggesting that it may be equal to the Wilson coefficient $c_1(\mu)$ evaluated
at the scale $\mu = m_b$.Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3

### Infrared effects and the asymptotics of perturbation theory in weak decays of heavy particles

I discuss the interplay of infrared sensitivity in large order perturbative
expansions with the presence of explicit nonperturbative corrections in the
context of heavy quark expansions. The main focus is on inclusive decays and
the status of the kinetic energy of the heavy quark. This talk summarizes work
done with Braun and Zakharov.Comment: LATEX, world_sci.sty (appended to the file), UM-TH-94-30 (Invited
talk presented at the conference ``QCD'94'', Montpellier, France, July 7 -
13, 1994) [Typo in ref. 6 corrected, pardon.

### Simply Modeling Meson HQET

A simple relativistic model of heavy-quark-light-quark mesons is proposed. In
an expansion in inverse powers of the heavy quark mass we find that all zeroth
and first order heavy quark symmetry relations are satisfied. The main results
are: - the difference between the meson mass and the heavy quark mass plays a
significant role even at zeroth order; - the slope of the Isgur-Wise function
at the zero recoil point is typically less than $-1$; - the first order
correction to the pseudoscalar decay constant is large and negative; - the four
universal functions describing the first order corrections to the semileptonic
decay form factors are small; - these latter corrections are quite insensitive
to the choice of model parameters, and in particular to the effects of
hyperfine mass splitting.Comment: 17 pages, LaTeX, 3 LaTeX figures in separate file, UTPT-92-16. This
is the version published long ago but not previously archive

### Higher-order estimates of the chromomagnetic moment of a heavy quark

The leading beta_0^(n-1) alpha_s^n terms in the Wilson coefficient and
anomalous dimension of the chromomagnetic operator in the heavy-quark effective
Lagrangian are summed to all orders of perturbation theory. The perturbation
series for the anomalous dimension is well behaved, while that for the Wilson
coefficient exhibits a divergent behaviour already in low orders, caused by a
nearby infrared renormalon singularity. The resulting ambiguity is commensurate
with terms of order 1/m^2 in the effective Lagrangian, whose corresponding
ultraviolet renormalons are identified. An excellent approximation for the
scheme-invariant Wilson coefficient at next-to-next-to-leading order in
renormalization-group improved perturbation theory is obtained.Comment: 16 pages, 3 figures embedde

### B -> X_u l nu decay distributions to order alpha_s

An analytic result for the O(alpha_s corrections to the triple differential B
-> X_u l nu decay rate is presented, to leading order in the heavy-quark
expansion. This is relevant for computing partially integrated decay
distributions with arbitrary cuts on kinematic variables. Several double and
single differential distributions are derived, most of which generalize known
results. In particular, an analytic result for the O(alpha_s) corrections to
the hadronic invariant mass spectrum is presented. The effects of Fermi motion,
which are important for the description of decay spectra close to infrared
sensitive regions, are included. The behaviour of perturbation theory in the
region of time-like momenta is also investigatedComment: 24 pages, 11 figures, 1 typo in eq.(5.4) corrected; version published
in JHEP06(1999)01

### Nonleptonic Weak Decays of B to D_s and D mesons

Branching ratios and polarization amplitudes for B decaying to all allowed
pseudoscalar, vector, axial-vector, scalar and tensor combinations of D_s and D
mesons are calculated in the Isgur Scora Grinstein Wise (ISGW) quark model
after assuming factorization. We find good agreement with other models in the
literature and the limited experimental data and make predictions for as yet
unseen decay modes. Lattice QCD results in this area are very limited. We make
phenomenological observations on decays in to D_s(2317) and D_s(2460) and
propose tests for determining the status and mixings of the axial mesons. We
use the same approach to calculate branching ratios and polarization fraction
for decays in to two D type mesons.Comment: 21 pages, 9 figures. v3: updated to reflect changes in published
paper, conclusions unchanged (see source file for details). Added comments on
factorization. v2: experimental data updated, references added, tables of
results added, more on axial D_s mixing, added section on D D decay modes and
typos correcte

### Decay constants and radiative decays of heavy mesons in light-front quark model

We investigate the magnetic dipole decays $V\to P\gamma$ of various
heavy-flavored mesons such as $(D,D^*,D_s,D^{*}_s,\eta_c, J/\psi)$ and
$(B,B^*,B_s,B^*_s,\eta_b,\Upsilon)$ using the light-front quark model
constrained by the variational principle for the QCD-motivated effective
Hamiltonian. The momentum dependent form factors $F_{VP}(q^2)$ for $V\to
P\gamma^*$ decays are obtained in the $q^+=0$ frame and then analytically
continued to the timelike region by changing ${\bf q}_\perp$ to $i{\bf
q}_\perp$ in the form factors. The coupling constant $g_{VP\gamma}$ for real
photon case is then obtained in the limit as $q^2\to 0$, i.e.
$g_{VP\gamma}=F_{VP}(q^2=0)$. The weak decay constants of heavy pseudoscalar
and vector mesons are also calculated. Our numerical results for the decay
constants and radiative decay widths for the heavy-flavored mesons are overall
in good agreement with the available experimental data as well as other
theoretical model calculations.Comment: 9 pages, 3figures, added few more references, typos correcte

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