392 research outputs found
Inclusive Measure of |V_ub| with the Analytic Coupling Model
By analyzing B -> X_u l nu_l spectra with a model based on soft-gluon
resummation and an analytic time-like QCD coupling, we obtain |V_ub| = (3.76
+-0.13 +- 0.22)*10^(-3), where the first and the second error refers to
experimental and theoretical errors, respectively. The V_ub value is obtained
from the available measured semileptonic branching fractions in limited regions
of the phase-space. The distributions in the lepton energy E_l, the hadron
invariant mass m_X, the light-cone momentum P_+ = E_X - p_X, together with the
double distributions in (m_X,q^2) and (E_l,s_h^max), are used to select the
phase-space regions. The q^2 is the dilepton squared momentum and s_h^max is
the maximal m_X^2 at fixed q^2 and E_l. The V_ub value obtained is in complete
agreement with the value coming from exclusive B decays and from an over-all
fit to the Standard Model parameters. We show that the slight disagreement (up
to +2 sigma) with respect to previous inclusive measurements is not related to
different choices for the b (and c) masses but to a different modelling of the
threshold (Sudakov) region.Comment: 19 pages, 2 figures, revised version accepted in Eur.Phys.J.
Radiatively corrected shape function for inclusive heavy hadron decays
We discuss the non-perturbative and the radiative corrections to inclusive B
decays from the point of view known from QED corrections to high energy e^+ e^-
processes. Here the leading contributions can be implemented through the so
called ``radiator function'' which corresponds to the shape function known in
heavy hadron decays. In this way some new insight into the origin of the shape
function is obtained. As a byproduct, a parameterization of the radiatively
corrected shape function is suggested which can be implemented in Monte Carlo
studies of inclusive heavy hadron decays.Comment: LaTeX, uses a4, graphicx and psfrag, 10 pages. The complete paper is
also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints
Extended HQEFT Lagrangian and currents
From the tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors we derive the vector current coupling to a
hard gluonic field allowing for heavy quark-antiquark pair annihilation and
creation.Comment: Talk given at 4th International Conference on Hyperons, Charm and
Beauty Hadrons, Valencia, Spain, 27-30 Jun 2000. LaTeX, 4 pages, 1 EPS figur
The PMS project: Poor Man's Supercomputer
We briefly describe the Poor Man's Supercomputer (PMS) project carried out at
Eotvos University, Budapest. The goal was to develop a cost effective,
scalable, fast parallel computer to perform numerical calculations of physical
problems that can be implemented on a lattice with nearest neighbour
interactions. To this end we developed the PMS architecture using PC components
and designed a special, low cost communication hardware and the driver software
for Linux OS. Our first implementation of PMS includes 32 nodes (PMS1). The
performance of PMS1 was tested by Lattice Gauge Theory simulations. Using SU(3)
pure gauge theory or bosonic MSSM on PMS1 we obtained 3Mflop
price-to-sustained performance for double and single precision operations,
respectively. The design of the special hardware and the communication driver
are freely available upon request for non-profit organizations.Comment: Latex, 13 pages, 6 figures included, minor additions, typos correcte
Chiral Solitons in Generalized Korteweg-de Vries Equations
Generalizations of the Korteweg-de Vries equation are considered, and some
explicit solutions are presented. There are situations where solutions engender
the interesting property of being chiral, that is, of having velocity
determined in terms of the parameters that define the generalized equation,
with a definite sign.Comment: 9 pages, latex, no figures. References added, typos correcte
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 EPS figure
Precise predictions for Higgs production in models with color-octet scalars
We describe an effective-theory computation of the next-to-next-to-leading
order (NNLO) QCD corrections to the gluon-fusion production of a Higgs boson in
models with massive color-octet scalars in the (8,1)_0 representation.
Numerical results are presented for both the Tevatron and the LHC. The
estimated theoretical uncertainty is greatly reduced by the inclusion of the
NNLO corrections. Color-octet scalars can increase the Standard Model rate by
more than a factor of two in allowed regions of parameter space.Comment: 6 pages, 5 figures, to appear in the proceedings of the "10th DESY
Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field
Theory", Woerlitz, Germany, April 25-30, 201
Multiscale expansions of difference equations in the small lattice spacing regime, and a vicinity and integrability test. I
We propose an algorithmic procedure i) to study the ``distance'' between an
integrable PDE and any discretization of it, in the small lattice spacing
epsilon regime, and, at the same time, ii) to test the (asymptotic)
integrability properties of such discretization. This method should provide, in
particular, useful and concrete informations on how good is any numerical
scheme used to integrate a given integrable PDE. The procedure, illustrated on
a fairly general 10-parameter family of discretizations of the nonlinear
Schroedinger equation, consists of the following three steps: i) the
construction of the continuous multiscale expansion of a generic solution of
the discrete system at all orders in epsilon, following the Degasperis -
Manakov - Santini procedure; ii) the application, to such expansion, of the
Degasperis - Procesi (DP) integrability test, to test the asymptotic
integrability properties of the discrete system and its ``distance'' from its
continuous limit; iii) the use of the main output of the DP test to construct
infinitely many approximate symmetries and constants of motion of the discrete
system, through novel and simple formulas.Comment: 34 pages, no figur
Exact solution of Calogero model with competing long-range interactions
An integrable extension of the Calogero model is proposed to study the
competing effect of momentum dependent long-range interaction over the original
{1 \ov r^2} interaction. The eigenvalue problem is exactly solved and the
consequences on the generalized exclusion statistics, which appears to differ
from the exchange statistics, are analyzed. Family of dual models with
different coupling constants is shown to exist with same exclusion statistics.Comment: Revtex, 6 pages, 1 figure, hermitian variant of the model included,
final version to appear in Phys. Rev.
Higgs Signal for h to aa at Hadron Colliders
We assess the prospect of observing a neutral Higgs boson at hadron colliders
in its decay to two spin-zero states, a, for a Higgs mass of 90-130 GeV, when
produced in association with a W or Z boson. Such a decay is allowed in
extensions of the MSSM with CP-violating interactions and in the NMSSM, and can
dominate Higgs boson final states, thereby evading the LEP constraints on
standard Higgs boson production. The light spin-zero state decays primarily via
a to bb and tau+tau-, so this signal channel retains features distinct from the
main backgrounds. Our study shows that at the Tevatron, there may be potential
to observe a few events in the bb tau+tau- or bbbb channels with relatively
small background, although this observation would be statistically limited. At
the LHC, the background problem is more severe, but with cross sections and
integrated luminosities orders of magnitude larger than at the Tevatron, the
observation of a Higgs boson in this decay mode would be possible. The channel
h to aa to bbbb would provide a large statistical significance, with a
signal-to-background ratio on the order of 1:2. In these searches, the main
challenge would be to retain the adequate tagging efficiency of b's and tau's
in the low p_T region.Comment: Version to be published in JHEP. 20 pages, 5 figure
- …