2,533 research outputs found
Light-cone sum rules: A SCET-based formulation
We describe the construction of light-cone sum rules (LCSRs) for exclusive
-meson decays into light energetic hadrons from correlation functions within
soft-collinear effective theory (SCET). As an example, we consider the SCET sum
rule for the transition form factor at large recoil, including
radiative corrections from hard-collinear loop diagrams at first order in the
strong coupling constant.Comment: LaTex, 4 pages, 2 eps figures. Talk given at QCD05, 12th
International QCD Conference, 4-9th July 2005, Montpellier, Franc
decays in the standard model and in scenarios with universal extra dimensions
We study the radiative decays, which are
important to investigate CP violation, and are also relevant to assess the role
of the exclusive modes induced by the transition to saturate
the inclusive decay rate. Moreover, these channels do not
display the same hierarchy as modes, for which the
decay into is enhanced with respect to one into . The
three-body radiative decays reverse the role: we find that this experimentally
observed behavior (although affected by a large uncertainty in the case of the
) is reproduced in the theoretical analysis. We compute a form factor, needed for this study, using light cone QCD sum rules, and
discuss a relation expected to hold in the large energy limit for the light
meson. Finally, we examine in two extensions of the
standard model with universal extra dimensions, to investigate the sensitivity
of this rare mode to such a kind of new physics effects.Comment: RevTeX, 17 pages, 7 figures. High resolution figures available upon
request. Matches the published versio
SCET sum rules for B->P and B->V transition form factors
We investigate sum rules for heavy-to-light transition form factors at large
recoil derived from correlation functions with interpolating currents for light
pseudoscalar or vector fields in soft-collinear effective theory (SCET). We
consider both, factorizable and non-factorizable contributions at leading power
in the Lambda/m_b expansion and to first order in the strong coupling constant
alpha_s, neglecting contributions from 3-particle distribution amplitudes in
the B-meson. We pay particular attention to various sources of parametric and
systematic uncertainties. We also discuss certain form factor ratios where part
of the hadronic uncertainties related to the B-meson distribution amplitude and
to logarithmically enhanced alpha_s corrections cancel.Comment: 27 pages, 19 figures, minor corrections, matches journal versio
From perfect to fractal transmission in spin chains
Perfect state transfer is possible in modulated spin chains, imperfections
however are likely to corrupt the state transfer. We study the robustness of
this quantum communication protocol in the presence of disorder both in the
exchange couplings between the spins and in the local magnetic field. The
degradation of the fidelity can be suitably expressed, as a function of the
level of imperfection and the length of the chain, in a scaling form. In
addition the time signal of fidelity becomes fractal. We further characterize
the state transfer by analyzing the spectral properties of the Hamiltonian of
the spin chain.Comment: 8 pages, 10 figures, published versio
Two-photon decay of heavy quarkonium from heavy-quark spin symmetry
With the recent measurements on and at CLEO,
Babar and Belle, and with the prospect of finding the at the
Tevatron, it seems appropriate to have another look at the two-photon decay of
heavy quarkonium from the standpoint of an effective Lagrangian based on local
operator expansion and heavy-quark spin symmetry. In this talk, I would like to
discuss a recent work on the two-photon decay rates of ground states and
excited states of and using the local operator expansion
approach and heavy-quark spin symmetry and taking into account the
binding-energy. We find that the predicted two-photon width for agrees
well with experiment, but the predicted value for is twice larger
than the CLEO estimation. We point out that the essentially model-independent
ratio of two-photon width to the leptonic width and the
two-photon width could be used to extract the strong coupling
constant .Comment: 9 pages, Talk given at the QCD@Work 2007 International Workshop on
QCD: Theory and Experiment}, Martina Franca, Italy, 16--20 June 200
Two-photon width of eta_c and eta'_c from Heavy-Quark Spin Symmetry
We evaluate the two-photon width of the pseudoscalar charmonia, Gamma(eta_c
-> gamma gamma) and Gamma(eta'_c -> gamma gamma), within a Heavy-Quark
Spin-Symmetry setting and show that whereas the former agrees with experiment,
the latter is more than twice larger than the recent measurement by CLEO. When
binding-energy effects are included in the eta'_c case, the discrepancy is
worse, pointing out at a possible anomaly in the eta'_c decay.Comment: 4 pages, 2 figures, Revtex4; v2: discussions enlarged and some
references added. The conclusions are unchange
A two-loop relation between inclusive radiative and semileptonic B-decay spectra
A shape-function independent relation is derived between the partial
B->X_u+l+nu decay rate with a cut on P_+=E_X-P_X<Delta and a weighted integral
over the normalized B->X_s+gamma photon-energy spectrum. The leading-power
contribution to the weight function is calculated at next-to-next-to-leading
order in renormalization-group improved perturbation theory, including exact
two-loop matching corrections at the scale mu_i^2 ~ m_b*Lambda_{QCD}. The
overall normalization of the weight function is obtained up to yet unknown
corrections of order [alpha_s(m_b)]^2. Power corrections from phase-space
factors are included exactly, while the remaining subleading contributions are
included at first order in 1/m_b. At this level unavoidable hadronic
uncertainties enter, which are estimated in a conservative way. The combined
theoretical accuracy in the extraction of |V_{ub}| is at the level of 5% if a
value of Delta near the charm threshold can be achieved experimentally.Comment: 22 pages, 4 figures; few comments and one reference added; version to
appear in JHE
FCNC and transitions: Standard Model versus a single Universal Extra Dimension scenario
We study the FCNC and transitions in the Standard Model and in
a scenario with a single Universal Extra Dimension. In particular, we focus on
the present knowledge of the hadronic uncertainties and on possible
improvements. We discuss how the measurements of these modes can be used to
constrain the new parameter involved in the extra dimensional scenario, the
radius of the extra dimension, completing the information available from
B-factories. The rates of these induced decays are within the reach
of new experiments, such as LHCb.Comment: LaTex, 8 pages, 7 eps figures. Version to be published in Physical
Review
Metallo-organic ensembles of tritopic subphthalocyanine ligands
"This is the peer reviewed version of the following article: M. Ángel Revuelta-Maza, Ettore Fazio, Gema de la Torre and Tomás Torres, Metallo-organic ensembles of tritopic subphthalocyanine ligands, Journal of Porphyrins and PhthalocyaninesVol. 21, No. 12, pp. 782-789 (2017), which has been published in final form at https://doi.org/10.1142/S1088424617500882I. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use Self-Archived Versions"Organic building blocks containing amines and aldehydes can be used for the preparation of complex metallo-organic structures, such as M2L3 triple helicates or face-capped M4L4 tetrahedral cages, through the formation of both dynamic covalent and coordinative linkages during the self-Assembly process. Herein we describe how the subcomponent self-Assembly method can be succesfully applied over a triamine-functionalized subphthalocyanine (SubPc) ligand to build metallo-supramolecular helicates. Two isomeric SubPcs (C1-SubPc1 and C3-SubPc1) have been prepared from the corresponding C1-SubPcI3 and C3-SubPcI3 precursors under optimized Suzuki conditions. We selected the tritopic C3-SubPc1 derivative as ligand for the subcomponent self-Assembly experiments, which involved the reaction with 2-formylpyridine and different Fe(II) salts. The self-Assembly process was mainly studied by mass spectrometry (ESI direct injection techniques), and in all the conditions applied, we could observe the formation of helicate-Type Fe2SubPc3 structures and/or Fe2SubPc4 species, which can be considered as open precursors of Fe4SubPc4 tetrahedral cages. © 2017 World Scientific Publishing Company.Financial support from Comunidad de Madrid, Spain (S2013/MIT- 2841, FOTOCARBON), and Spanish MICINN (CTQ2014-52869-P) is acknowledged
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