56 research outputs found
Lattice QCD calculation of form factors describing the rare decays and
The rare decays and
are now being observed with enough precision to test Standard Model
predictions. A full understanding of these decays requires accurate
determinations of the corresponding hadronic form factors. Here we present
results of lattice QCD calculations of the and form
factors; we also determine the form factors relevant for the tree-level decays
. We use full-QCD configurations including 2+1 flavors of
sea quarks using an improved staggered action, and we employ lattice
non-relativistic QCD to describe the bottom quark.Comment: 23 pages. Version 3 (accepted to Phys. Rev. D) includes
interpolations to the physical strange quark mass. Central values shift by
less than 1 sigma. Tables and figures updated accordingl
Calculation of and observables using form factors from lattice QCD
We calculate the differential branching fractions and angular distributions
of the rare decays and , using for the first time form factors from unquenched lattice QCD. We
focus on the kinematic region where the or recoils softly; there
the newly available form factors are most precise and the nonlocal matrix
elements can be included via an operator product expansion. Our results for the
differential branching fractions calculated in the Standard Model are higher
than the experimental data. We consider the possibility that the deviations are
caused by new physics, and perform a fit of the Wilson coefficients and
to the experimental data for multiple
and observables. In agreement with recent results
from complementary studies, we obtain and
, whose deviations from zero would indicate the
presence of non-standard fundamental interactions.Comment: 6 pages. Updated form factors according to arXiv:1310.3722v3. New
discussion of charmonium resonances. Accepted by PR
Wrapping Transition and Wrapping-Mediated Interactions for Discrete Binding along an Elastic Filament: An Exact Solution
The wrapping equilibria of one and two adsorbing cylinders are studied along
a semi-flexible filament (polymer) due to the interplay between elastic
rigidity and short-range adhesive energy between the cylinder and the filament.
We show that statistical mechanics of the system can be solved exactly using a
path integral formalism which gives access to the full effect of thermal
fluctuations, going thus beyond the usual Gaussian approximations which take
into account only the contributions from the minimal energy configuration and
small fluctuations about this minimal energy solution. We obtain the free
energy of the wrapping-unwrapping transition of the filament around the
cylinders as well as the effective interaction between two wrapped cylinders
due to thermal fluctuations of the elastic filament. A change of entropy due to
wrapping of the filament around the adsorbing cylinders as they move closer
together is identified as an additional source of interactions between them.
Such entropic wrapping effects should be distinguished from the usual entropic
configuration effects in semi-flexible polymers. Our results may be applicable
to the problem of adsorption of proteins as well as synthetic nano-particles on
semi-flexible polymers such as DNA.Comment: 24 pages, 12 figure
The one dimensional Coulomb lattice fluid capacitor
22 pages, 18 figures, RevTexInternational audienceThe one dimensional Coulomb lattice fluid in a capacitor configuration is studied. The model is formally exactly soluble via a transfer operator method within a field theoretic representation of the model. The only interactions present in the model are the one dimensional Coulomb interaction between cations and anions and the steric interaction imposed by restricting the maximal occupancy at any lattice site to one particle. Despite the simplicity of the model, a wide range of intriguing physical phenomena arise, some of which are strongly reminiscent of those seen in experiments and numerical simulations of three dimensional ionic liquid based capacitors. Notably we find regimes where over-screening and density oscillations are seen near the capacitor plates. The capacitance is also shown to exhibit strong oscillations as a function of applied voltage. It is also shown that the corresponding mean field theory misses most of these effects. The analytical results are confirmed by extensive numerical simulations
Parsing the passive: comparing children with Specific Language Impairment to sequential bilingual children
25 monolingual (L1) children with Specific Language Impairment (SLI), 32 sequential bilingual (L2) children, and 29 L1 controls completed the Test of Active & Passive Sentences-Revised (van der Lely, 1996) and the self-paced listening task with picture verification for actives and passives (Marinis, 2007). These revealed important between-group differences in both tasks. The children with SLI showed difficulties in both actives and passives when they had to reanalyse thematic roles on-line. Their error pattern provided evidence for working memory limitations. The L2 children showed difficulties only in passives both on-line and off-line. We suggest that these relate to the complex syntactic algorithm in passives and reflect an earlier developmental stage due to reduced exposure to the L2. The results are discussed in relation to theories of SLI and can be best accommodated within accounts proposing that difficulties in the comprehension of passives stem from processing limitations
Rab11-FIP1C and Rab14 Direct Plasma Membrane Sorting and Particle Incorporation of the HIV-1 Envelope Glycoprotein Complex
The incorporation of the envelope glycoprotein complex (Env) onto the developing particle is a crucial step in the HIV-1 lifecycle. The long cytoplasmic tail (CT) of Env is required for the incorporation of Env onto HIV particles in T cells and macrophages. Here we identify the Rab11a-FIP1C/RCP protein as an essential cofactor for HIV-1 Env incorporation onto particles in relevant human cells. Depletion of FIP1C reduced Env incorporation in a cytoplasmic tail-dependent manner, and was rescued by replenishment of FIP1C. FIP1C was redistributed out of the endosomal recycling complex to the plasma membrane by wild type Env protein but not by CT-truncated Env. Rab14 was required for HIV-1 Env incorporation, and FIP1C mutants incapable of binding Rab14 failed to rescue Env incorporation. Expression of FIP1C and Rab14 led to an enhancement of Env incorporation, indicating that these trafficking factors are normally limiting for CT-dependent Env incorporation onto particles. These findings support a model for HIV-1 Env incorporation in which specific targeting to the particle assembly microdomain on the plasma membrane is mediated by FIP1C and Rab14. © 2013 Qi et al.Link_to_subscribed_fulltex
Recommended from our members
Improving the kinetic couplings in lattice nonrelativistic QCD
We improve the non-relativistic QCD (NRQCD) action by comparing the dispersion relation to that of the continuum through in perturbation theory. The one-loop matching coefficients of the kinetic operators are determined, as well as the scale at which to evaluate in the -scheme for each quantity. We utilise automated lattice perturbation theory using twisted boundary conditions as an infrared regulator. The one-loop radiative corrections to the mass renormalisation, zero-point energy and overall energy-shift of an NRQCD -quark are also found. We also explore how a Fat-smeared NRQCD action and changes of the stability parameter affect the coefficients. Finally, we use gluon field ensembles at multiple lattice spacing values, all of which include , , and quark vacuum polarisation, to test how the improvements affect the non-perturbatively determined and kinetic masses, and the tuning of the quark mass
Recommended from our members
Neutral B-meson mixing from full lattice QCD at the physical point
We calculate the bag parameters for neutral -meson mixing in and beyond the Standard Model, in full four-flavour lattice QCD for the first time. We work on gluon field configurations that include the effect of , , and sea quarks with the Highly Improved Staggered Quark (HISQ) action at three values of the lattice spacing and with three quark masses going down to the physical value. The valence quarks use the improved NRQCD action and the valence light quarks, the HISQ action. Our analysis was blinded. Our results for the bag parameters for all five operators are the most accurate to
date. For the Standard Model operator between and mesons we find:
, . Combining our results with lattice QCD calculations of the decay constants using HISQ quarks from the Fermilab/MILC collaboration and with experimental values for and oscillation frequencies allows determination of the CKM elements and . We find , and . Our results agree well (within ) with values determined from CKM unitarity constraints based on tree-level processes (only). Using a ratio to in which CKM elements cancel in the Standard Model, we determine the branching fractions
and
. We also give results for matrix elements of the operators , and
that contribute to neutral -meson width differences.This work was funded by STFC, the Royal Society, the Wolfson Foundation and the US DOE and National Science Foundation
- …