266 research outputs found
Lattice study of semileptonic form factors with twisted boundary conditions
We apply twisted boundary conditions to lattice QCD simulations of
three-point correlation functions in order to access spatial components of
hadronic momenta different from the integer multiples of 2 pi / L. We calculate
the vector and scalar form factors relevant to the K -> pi semileptonic decay
and consider all the possible ways of twisting one of the quark lines in the
three-point functions. We show that the momentum shift produced by the twisted
boundary conditions does not introduce any additional noise and easily allows
to determine within a few percent statistical accuracy the form factors at
quite small values of the four-momentum transfer, which are not accessible when
periodic boundary conditions are considered. The use of twisted boundary
conditions turns out to be crucial for a precise determination of the form
factor at zero-momentum transfer, when a precise lattice point sufficiently
close to zero-momentum transfer is not accessible with periodic boundary
conditions.Comment: latex 15 pages, 4 figures and 3 tables; modified intro and
discussions of the results; version to appear in PR
Responsive Urban Models by Processing Sets of Heterogeneous Data
This paper presents some steps in experimentation aimed at describing urban spaces made following the series of earthquakes that affected a vast area of central Italy starting on 24 August 2016. More specifically, these spaces pertain to historical centres of limited size and case studies that can be called "problematic" (due to complex morphological and settlement conditions, because they are difficult to access, or because they have been affected by calamitous events, etc.). The main objectives were to verify the use of sets of heterogeneous data that are already largely available to define a workflow and develop procedures that would allow some of the steps to be automated as much as possible. The most general goal was to use the experimentation to define a methodology to approach the problem aimed at developing descriptive responsive models of the urban space, that is, morphological and computer-based models capable of being modified in relation to the constantly updated flow of input data
Neutron Electric Dipole Moment with Domain Wall Quarks
We present preliminary results for nucleon dipole moments computed with
domain wall fermions. Our main target is the electric dipole moment of the
neutron arising from the theta term in the gauge part of the QCD lagrangian.
The calculated magnetic dipole moments of the proton and neutron are in rough
accord with experimental values.Comment: 3 pages. Contribution to the proceedings of Lattice 2004 (Fermilab
SU(3)-breaking effects in kaon and hyperon semileptonic decays from lattice QCD
We discuss the result of a recent quenched lattice calculation of the K -> pi
vector form factor at zero-momentum transfer, relevant for the determination of
|V_us| from K-> pi l nu decays. Using suitable double ratios of three-point
correlation functions, we show that it is possible to calculate this quantity
at the percent-level precision. The leading quenched effects are corrected for
by means of quenched chiral perturbation theory. The final result, f+(0) =
0.960 +- 0.005_stat +- 0.007_syst, turns out to be in good agreement with the
old quark model estimate made by Leutwyler and Roos. In this paper, we discuss
the phenomenological impact of the lattice result for the extraction of |V_us|,
by updating the analysis of K -> pi l nu decays with the most recent
experimental data. We also present a preliminary lattice study of hyperon Sigma
-> n l nu decays, based on a similar strategy.Comment: 17 pages, 8 figures. Based on talks given at: DAFNE 2004: Physics at
meson factories, Laboratori Nazionali di Frascati (Italy), June 7-11, 2004;
VIII International Conference on "Electron-Nucleus Scattering", Marciana
Marina (Italy), June 21-25, 2004; Lattice 2004, Fermi National Accelerator
Laboratory, Batavia, Illinois (USA), June 21-26, 2004; ICHEP 2004, Beijing
(China), August 16-22, 200
Universality of Mixed Action Extrapolation Formulae
Mixed action theories with chirally symmetric valence fermions exhibit very
desirable features both at the level of the lattice calculations as well as in
the construction and implementation of the low energy mixed action effective
field theory. In this work we show that when such a mixed action effective
field theory is projected onto the valence sector, both the Lagrangian and the
extrapolation formulae become universal in form through next to leading order,
for all variants of discretization methods used for the sea fermions. Our
conclusion relies on the chiral nature of the valence quarks. The result
implies that for all sea quark methods which are in the same universality class
as QCD, the numerical values of the physical coefficients in the various mixed
action chiral Lagrangians will be the same up to lattice spacing dependent
corrections. This allows us to construct a prescription to determine the mixed
action extrapolation formulae for a large class of hadronic correlation
functions computed in partially quenched chiral perturbation theory at the
one-loop level. For specific examples, we apply this prescription to the
nucleon twist--2 matrix elements and the nucleon--nucleon system. In addition,
we determine the mixed action extrapolation formula for the neutron EDM as this
provides a nice example of a theta-dependent observable; these observables are
exceptions to our prescription.Comment: 36 pages, appendix on twisted mass sea fermions added, expanded
discussion of NLO operators, version published in JHEP; typographical errors
corrected in Eqs. (68) and (69
Flavor Twisted Boundary Conditions, Pion Momentum, and the Pion Electromagnetic Form Factor
We investigate the utility of partially twisted boundary conditions in
lattice calculations of meson observables. For dynamical simulations, we show
that the pion dispersion relation is modified by volume effects. In the isospin
limit, we demonstrate that the pion electromagnetic form factor can be computed
on the lattice at continuous values of the momentum transfer. Furthermore, the
finite volume effects are under theoretical control for extraction of the pion
charge radius.Comment: 15 pages, 8 figures, revisions to text, refs adde
The inhibition of the highly expressed miR-221 and miR-222 impairs the growth of prostate carcinoma xenografts in mice
MiR-221 and miR-222 are two highly homologous microRNAs whose upregulation has been recently described in several types of human tumors, for some of which their oncogenic role was explained by the discovery of their target p27, a key cell cycle regulator. We previously showed this regulatory relationship in prostate carcinoma cell lines in vitro, underlying the role of miR-221/222 as inducers of proliferation and tumorigenicity
Novel sources of Flavor Changed Neutral Currents in the model
Sources of Flavor Changed Neutral Currents (FCNC) naturally emerge from a
well motivated framework called 3-3-1 with right-handed neutrinos model,
for short, mediated by an extra neutral gauge boson .
Following previous works we calculate these sources and in addition we derive
new ones coming from CP-even and -odd neutral scalars which appear due to their
non-diagonal interactions with the physical standard quarks. Furthermore we
show that bounds related to the neutral mesons systems and may be significantly strengthened in the presence of these new
interactions allowing us to infer stronger constraints on the parameter space
of the model.Comment: Published version. 10 pages, 6 figure
The Impact of Flavour Changing Neutral Gauge Bosons on B->X_s gamma
The branching ratio of the rare decay B->X_s gamma provides potentially
strong constraints on models beyond the Standard Model. Considering a general
scenario with new heavy neutral gauge bosons, present in particular in Z' and
gauge flavour models, we point out two new contributions to the B->X_s gamma
decay. The first one originates from one-loop diagrams mediated by gauge bosons
and heavy exotic quarks with electric charge -1/3. The second contribution
stems from the QCD mixing of neutral current-current operators generated by
heavy neutral gauge bosons and the dipole operators responsible for the B->X_s
gamma decay. The latter mixing is calculated here for the first time. We
discuss general sum rules which have to be satisfied in any model of this type.
We emphasise that the neutral gauge bosons in question could also significantly
affect other fermion radiative decays as well as non-leptonic two-body B
decays, epsilon'/epsilon, anomalous (g-2)_mu and electric dipole moments.Comment: 31 pages, 5 figures; version published on JHEP; added magic QCD
numbers for flavour-violating Z gauge boson contribution to B -> X_s gamm
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