578 research outputs found
Bounds on the derivatives of the Isgur-Wise function from sum rules in the heavy quark limit of QCD
Using the OPE and the trace formalism, we have obtained a number of sum rules
in the heavy quark limit of QCD that include the sum over all excited states
for any value of the light cloud. We show that these sum rules imply that
the elastic Isgur-Wise function is an alternate series in powers of
. Moreover, we obtain sum rules involving the derivatives of the elastic
Isgur-Wise function at zero recoil, that imply that the -th
derivative can be bounded by the -th one. For the curvature , this proves the already proposed bound . Moreover, we obtain the absolute bound for the -th derivative
, that generalizes the
results and .Comment: 9 pages, Late
Resumming the color-octet contribution to e+ e- -> J/psi + X
Recent observations of the spectrum of J/psi produced in e+ e- collisions at
the Upsilon(4S) resonance are in conflict with fixed-order calculations using
the Non-Relativistic QCD (NRQCD) effective field theory. One problem is that
leading order color-octet mechanisms predict an enhancement of the cross
section for J/psi with maximal energy that is not observed in the data.
However, in this region of phase space large perturbative corrections (Sudakov
logarithms) as well as enhanced nonperturbative effects are important. In this
paper we use the newly developed Soft-Collinear Effective Theory (SCET) to
systematically include these effects. We find that these corrections
significantly broaden the color-octet contribution to the J/psi spectrum. Our
calculation employs a one-stage renormalization group evolution rather than the
two-stage evolution used in previous SCET calculations. We give a simple
argument for why the two methods yield identical results to lowest order in the
SCET power counting.Comment: 27 pages, 7 figure
The adjuvant treatment of kidney cancer: a multidisciplinary outlook
Approximately 70% of cases of kidney cancer are localized or locally advanced at diagnosis. Among patients who undergo surgery for these cancers, 30â35% will eventually develop potentially fatal metachronous distant metastases. Effective adjuvant treatments are urgently needed to reduce the risk of recurrence of kidney cancer and of dying of metastatic disease. To date, almost all of the tested adjuvant agents have failed to demonstrate any benefit. Only two trials of an autologous renal tumour cell vaccine and of the vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor sunitinib have shown positive results, but these have been criticized for methodological reasons and conflicting data, respectively. The results of two additional trials of targeted agents as adjuvant therapies have not yet been published. Novel immune checkpoint inhibitors are promising approaches to adjuvant therapy in kidney cancer, and a number of trials are now underway. An important component of the management of patients with kidney cancer, particularly those who undergo radical resection for localized renal cell carcinoma, is the preservation of kidney function to reduce morbidity and mortality. The optimal management of these patients therefore requires a multidisciplinary approach involving nephrologists, oncologists, urologists and pathologists
Increased Yield of ttbb at Hadron Colliders in Low-Energy Supersymmetry
Light bottom squarks and gluinos have been invoked to explain the b quark
pair production excess at the Tevatron. We investigate the associated
production of ttbb at hadron colliders in this scenario, and find that the
rates for this process are enhanced over the Standard Model prediction. If
light gluinos exist, it may be possible to detect them at the Tevatron, and
they could easily be observed at the LHC.Comment: 5p, references added, version accepted to PR
Semileptonic B Decays into Excited Charmed Mesons (, ) in HQEFT
Exclusive semileptonic B decays into excited charmed mesons (, )
are studied up to the order of in the framework of the heavy quark
effective field theory (HQEFT), which contains the contributions of both
particles and antiparticles. Two wave functions and ,
which characterize the contributions from the kinematic operator at the order
of , are calculated by using QCD sum rule approach in HQEFT. Zero recoil
values of other two wave functions and 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 are analyzed. It is shown that the experimental measurements for the
branching ratios of and can be understood
in the framework of HQEFT.Comment: 27 pages, RevTex, 4 figures, 3 tables, to be published in IJMP
Radiation reaction and gravitational waves in the effective field theory approach
We compute the contribution to the Lagrangian from the leading order (2.5
post-Newtonian) radiation reaction and the quadrupolar gravitational waves
emitted from a binary system using the effective field theory (EFT) approach of
Goldberger and Rothstein. We use an initial value formulation of the underlying
(quantum) framework to implement retarded boundary conditions and describe
these real-time dissipative processes. We also demonstrate why the usual
scattering formalism of quantum field theory inadequately accounts for these.
The methods discussed here should be useful for deriving real-time quantities
(including radiation reaction forces and gravitational wave emission) and
hereditary terms in the post-Newtonian approximation (including memory, tail
and other causal, history-dependent integrals) within the EFT approach. We also
provide a consistent formulation of the radiation sector in the equivalent
effective field theory approach of Kol and Smolkin.Comment: 23 pages, 8 figure
Constraints on Light Bottom Squarks from Radiative B-Meson Decays
The presence of a light b-squark (with mass about 4 GeV) and gluino (with
mass about 15 GeV) might explain the observed excess in b-quark production at
the Tevatron. Though provocative, this model is not excluded by present data.
The light supersymmetric particles can induce large flavor-changing effects in
radiative decays of B mesons. We analyse the decays B->X_s gamma and B->X_{sg}
in this scenario and derive restrictive bounds on the flavor-changing
quark-squark-gluino couplings.Comment: 14 pages, 3 figures. One reference added. Final version published in
Physics Letters
Object knowledge modulates colour appearance
We investigated the memory colour effect for colour diagnostic artificial objects. Since knowledge about these objects and their colours has been learned in everyday life, these stimuli allow the investigation of the influence of acquired object knowledge on colour appearance. These investigations are relevant for questions about how object and colour information in high-level vision interact as well as for research about the influence of learning and experience on perception in general. In order to identify suitable artificial objects, we developed a reaction time paradigm that measures (subjective) colour diagnosticity. In the main experiment, participants adjusted sixteen such objects to their typical colour as well as to grey. If the achromatic object appears in its typical colour, then participants should adjust it to the opponent colour in order to subjectively perceive it as grey. We found that knowledge about the typical colour influences the colour appearance of artificial objects. This effect was particularly strong along the daylight axis
Heavy bottom squark mass in the light gluino and light bottom squark scenario
Restrictive upper bounds on the heavy bottom squark mass when the gluino and
one bottom squark are both light are based on the predicted reduction of
(the fraction of hadronic decays to pairs) in such a scenario.
These bounds are found to be relaxed by the process , which may partially compensate for
the reduction of . The relaxation of bounds on the top squark and the
scale-dependence of the strong coupling constant are also discussed.Comment: 9 pages, LaTeX, 2 figures, to be submitted to Phys. Lett. B, more
discussions adde
Radiative decays of light vector mesons in a quark level linear sigma model
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma
decays in the framework of a U(3)xU(3) linear sigma model which includes
constituent quarks. For the first two decays this approach improves results
based on the anomalous Wess-Zumino term, with contributions due to SU(3)
symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays
are dominated by resonant eta' exchange . Our calculation for the later decays
improves and update similar calculations in the -closely related- framework of
vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x10^{-5} and
BR(phi to omega gamma gamma)=2.8x10^{-6} within the scope of the
high-luminosity phi factories.Comment: 8 pages, submitted to Phys. Rev.
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