4,377 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

### Analyticity and the Isgur-Wise Function

We reconsider the recent derivation by de Rafael and Taron of bounds on the
slope of the Isgur-Wise function. We argue that one must be careful to include
cuts starting below the heavy meson pair production threshold, arising from
heavy quark-antiquark bound states, and that if such cuts are properly
accounted for then no constraints may be derived.Comment: 8 pages, uses harvmac, SLAC-PUB-5956, UCSD/PTH 92-35, CALT-68-183

### 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

### Low temperature phase diagram and critical behaviour of the four-state chiral clock model

The low temperature behaviour of the four-state chiral clock ($CC_4$) model
is reexamined using a systematic low temperature series expansion of the free
energy. Previously obtained results for the low temperature phases are
corrected and the low temperature phase diagram is derived. In addition, the
phase transition from the modulated region to the high temperature paraphase is
shown to belong to the universality class of the 3d-XY model.Comment: 17 pages in ioplppt style, 3 figure

### Second Order Power Corrections in the Heavy Quark Effective Theory I. Formalism and Meson Form Factors

In the heavy quark effective theory, hadronic matrix elements of currents
between two hadrons containing a heavy quark are expanded in inverse powers of
the heavy quark masses, with coefficients that are functions of the kinematic
variable $v\cdot v'$. For the ground state pseudoscalar and vector mesons, this
expansion is constructed at order $1/m_Q^2$. A minimal set of universal form
factors is defined in terms of matrix elements of higher dimension operators in
the effective theory. The zero recoil normalization conditions following from
vector current conservation are derived. Several phenomenological applications
of the general results are discussed in detail. It is argued that at zero
recoil the semileptonic decay rates for $B\to D\,\ell\,\nu$ and $B\to
D^*\ell\,\nu$ receive only small second order corrections, which are unlikely
to exceed the level of a few percent. This supports the usefulness of the heavy
quark expansion for a reliable determination of $V_{cb}$.Comment: (34 pages, REVTEX, two postscript figures available upon request),
SLAC-PUB-589

### Two-loop corrections to the Isgur-Wise function in QCD sum rules

We complete the QCD sum rule analysis of the Isgur Wise form factor
$\xi(v\cdot v')$ at next-to-leading order in renormalization-group improved
perturbation theory. To this end, the exact result for the two-loop corrections
to the perturbative contribution is derived using the heavy quark effective
theory. Several techniques for the evaluation of two-loop integrals involving
two different types of heavy quark propagators are discussed in detail, among
them the methods of integration by parts and differential equations. The
order-$\alpha_s$ corrections to the Isgur-Wise function turn out to be small
and well under control. At large recoil, they tend to decrease the form factor
by $5-10\%$.Comment: 24 pages (REVTEX), 2 figures available upon request, SLAC-PUB-599

### Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut

We compute the first two moments of the final hadronic invariant mass in
inclusive semileptonic B decay, in the presence of a cut on the charged lepton
energy. These moments may be measured directly by experiments at the
Upsilon(4S) using the neutrino reconstruction technique, which requires such a
cut. Measurement of these moments will place constraints on the nonperturbative
parameters \bar\Lambda and \lambda_1, which are relevant for extracting the
quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of
order \alpha_s^2\beta_0 and 1/m_b^3 in the operator product expansion, and use
the latter to estimate the theoretical uncertainty in the extraction of
\bar\Lambda and \lambda_1.Comment: 13 pages, 5 figures, REVTe

### Semileptonic B Decays into Excited Charmed Mesons ($D_1$, $D^*_2$) in HQEFT

Exclusive semileptonic B decays into excited charmed mesons ($D_1$, $D^*_2$)
are studied up to the order of $1/m_Q$ in the framework of the heavy quark
effective field theory (HQEFT), which contains the contributions of both
particles and antiparticles. Two wave functions $\eta^b_0$ and $\eta^c_0$,
which characterize the contributions from the kinematic operator at the order
of $1/m_Q$, are calculated by using QCD sum rule approach in HQEFT. Zero recoil
values of other two wave functions $\kappa'_1$ and $\kappa'_2$ are extracted
from the excited charmed-meson masses. Possible effects from the spin-dependent
transition wave functions which arise from the magnetic operators at the order
of $1/m_Q$ are analyzed. It is shown that the experimental measurements for the
branching ratios of $B \to D_1 l\nu$ and $B \to D^*_2 l\nu$ can be understood
in the framework of HQEFT.Comment: 27 pages, RevTex, 4 figures, 3 tables, to be published in IJMP

### Semileptonic B decays into excited charmed mesons from QCD sum rules

Exclusive semileptonic $B$ decays into excited charmed mesons are studied
with QCD sum rules in the leading order of heavy quark effective theory. Two
universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into
four lowest lying excited $D$ mesons ($D_1$, $D_2^*$, $D'_0$, and $D'_1$) are
determined. The decay rates and branching ratios for these processes are
calculated.Comment: RevTeX, 17 pages including 2 figure

### Anomalous Thresholds and the Isgur-Wise Function

The original de Rafael-Taron bound on the slope of the Isgur-Wise function at
zero recoil is known to be violated in QCD by singularities appearing in an
unphysical region. To be consistent, quark models must have corresponding
singularity structures. In an existing relativistic quark-loop model, the
meson-quark-antiquark vertex is such that the required singularity is an
anomalous threshold. We also discuss the implications of another anomalous
threshold, whose location is determined by quark masses alone.Comment: 8 pages, LaTeX, 4 LaTeX figures in separate uufile, UTPT-94-0

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