189 research outputs found
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 ; - 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
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 . For the ground state pseudoscalar and vector mesons, this
expansion is constructed at order . 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 and 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 .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
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- 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 .Comment: 24 pages (REVTEX), 2 figures available upon request, SLAC-PUB-599
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
The Subleading Isgur-Wise Form Factor to Order in QCD Sum Rules
We calculate the contributions arising at order in the QCD sum
rule for the spin-symmetry violating universal function ,
which appears at order in the heavy quark expansion of meson form
factors. In particular, we derive the two-loop perturbative contribution to the
sum rule. Over the kinematic range accessible in
decays, we find that does not exceed the level of , indicating that power corrections induced by the chromo-magnetic operator
in the heavy quark expansion are small.Comment: 12 pages ReVTeX, 3 figures available upon request, SLAC-PUB-6017,
WIS-92/99/Dec-P
General relations of heavy quark-antiquark potentials induced by reparameterization invariance
A set of general relations between the spin-independent and spin-dependent
potentials of heavy quark and anti-quark interactions are derived from
reparameterization invariance in the Heavy Quark Effective Theory. It covers
the Gromes relation and includes some new interesting relations which are
useful in understanding the spin-independent and spin-dependent relativistic
corrections to the leading order nonrelativistic potential.Comment: 11 pages, TUIMP-TH-93/54, CCAST-93-3
The Subleading Isgur-Wise Form Factor and its Implications for the Decays
We calculate, in the framework of QCD sum rules and to next-to-leading order
in perturbation theory, the universal function which appears
at order in the heavy quark expansion of meson weak decay form factors.
We find that radiative corrections of order are very important. Over
the kinematic range accessible in semileptonic decays, is
proportional to the leading-order Isgur-Wise function to very
good accuracy. Taking into account all sources of uncertainty, we estimate
. This reduces the theoretical uncertainty in the
extraction of from transitions. A
measurement of the form factor ratio in
decays can be used to test our prediction.Comment: 14 pages (ReVTeX, 2 figures available), SLAC-PUB-6146,
WIS-93/33/May-P
Observation of the Smectic C -- Smectic I Critical Point
We report the first observation of the smectic C--smectic I (C--I) critical
point by Xray diffraction studies on a binary system. This is in confirmity
with the theoretical idea of Nelson and Halperin that coupling to the molecular
tilt should induce hexatic order even in the C phase and as such both C and I
(a tilted hexatic phase) should have the same symmetry. The results provide
evidence in support of the recent theory of Defontaines and Prost proposing a
new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from
[email protected] on request, Phys.Rev.Lett. (in press
Leptonic constant of pseudoscalar B_c meson
We calculate the leptonic constant for the ground pseudoscalar state of B_c
meson in the framework of QCD-motivated potential model taking into account the
two-loop anomalous dimension for the heavy quark current in the nonrelativistic
QCD as matched with the full QCD.Comment: 6 pages, RevTeX4 file, 3 eps-figures, several references and remarks
adde
High-resolution x-ray study of the nematic - smectic-A and smectic-A - smectic-C transitions in 8barS5-aerosil gels
The effects of dispersed aerosil nanoparticles on two of the phase
transitions of the thermotropic liquid crystal material
4-n-pentylphenylthiol-4'-n-octyloxybenzoate 8barS5 have been studied using
high-resolution x-ray diffraction techniques. The aerosils hydrogen bond
together to form a gel which imposes a weak quenched disorder on the liquid
crystal. The smectic-A fluctuations are well characterized by a two-component
line shape representing thermal and random-field contributions. An elaboration
on this line shape is required to describe the fluctuations in the smectic-C
phase; specifically the effect of the tilt on the wave-vector dependence of the
thermal fluctuations must be explicitly taken into account. Both the magnitude
and the temperature dependence of the smectic-C tilt order parameter are
observed to be unaffected by the disorder. This may be a consequence of the
large bare smectic correlation length in the direction of modulation for this
transition. These results show that the understanding developed for the nematic
to smectic-A transition for octylcyanobiphenyl (8CB) and octyloxycyanobiphenyl
(8OCB) liquid crystals with quenched disorder can be extended to quite
different materials and transitions.Comment: 7 pages, 8 figure
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