[Show abstract][Hide abstract] ABSTRACT: We extract the strong coupling constants of three mesons, each of which is
composed of either two charm quarks or one charm quark and one light (i.e.,
$u$, $d$, or $s$) quark, from the matrix elements for the transitions of two of
these mesons induced by appropriate quark currents within the framework of a
relativistic dispersion approach to the constituent-quark picture of mesons.
Among others, we also analyse the impact of the violation of the SU(3) flavour
symmetry by the quark masses. In the case of mesons containing one light quark,
we observe, in two respects, discrepancies between our findings and the
predictions of QCD sum rules: our strong couplings exceed considerably the ones
emerging from QCD sum rules, and, in our approach, the replacement of a light
quark by a strange quark entails, in contrast to QCD sum rules, a reduction of
the magnitudes of the strong couplings.
[Show abstract][Hide abstract] ABSTRACT: The relative magnitude of the decay constants of the pseudoscalar and vector
beauty mesons poses (in contrast to the case of charmed mesons) a long-standing
puzzle. We revisit this problem within the framework of our recent improvements
of the QCD sum-rule formalism for relating observable properties of mesons to
quantum chromodynamics and are led to conclude that the decay constants of the
beauty vector mesons are undoubtedly smaller than those of their pseudoscalar
counterparts.
[Show abstract][Hide abstract] ABSTRACT: We discuss the strong couplings $g_{PPV}$ and $g_{VVP}$ for vector ($V$) and
pseudoscalar ($P$) mesons, at least one of which is a charmonium state $J/\psi$
or $\eta_c$. The strong couplings are obtained as residues at the poles of
suitable form factors, calculated in a broad range of momentum transfers by a
relativistic dispersion approach relying on the constituent quark picture. The
spectral representations for the couplings under discussion satisfy all
constraints known for these quantities in the heavy-quark limit. Our results
suggest sizeably higher values than those reported in the literature from QCD
sum rules.
[Show abstract][Hide abstract] ABSTRACT: We present unquenched lattice QCD results for the matrix elements of
four-fermion operators relevant to the description of the neutral K and D
mixing in the Standard Model and its extensions. We have employed simulations
with Nf = 2 + 1 + 1 dynamical sea quarks at three values of the lattice
spacings in the interval 0.06 - 0.09 fm and pseudoscalar meson masses in the
range 210 - 450 MeV. Our results are extrapolated to the continuum limit and to
the physical pion mass. Renormalization constants have been determined
non-perturbatively in the RI-MOM scheme. In particular, for the Kaon
bag-parameter, which is relevant for the \overline{K}^0-K^0 mixing in the
Standard Model, we obtain B_K^{RGI} = 0.717(24).
Physical Review D 05/2015; 92(3). DOI:10.1103/PhysRevD.92.034516 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present our analysis of the decay constants of the beauty vector mesons
$B^*$ and $B^*_s$ within the framework of dispersive sum rules for the
two-point correlator of vector currents in QCD. While the decay constants of
the vector mesons $f_{B^*}$ and $f_{B_s^*}$ $-$ similar to the decay constants
of the pseudoscalar mesons $f_B$ and $f_{B_s}$ $-$ individually have large
uncertainties induced by theory parameters not known with a satisfactory
precision, these uncertainties almost entirely cancel out in the ratios of
vector over pseudoscalar decay constants. These ratios may be thus predicted
with very high accuracy due to the good control over the systematic
uncertainties of the decay constants gained upon application of our
hadron-parameter extraction algorithm. Our final results read
$f_{B^*}/f_B=0.944\pm0.011_{\rm OPE}\pm0.018_{\rm syst}$ and
$f_{B_s^*}/f_{B_s}=0.947\pm0.023_{\rm OPE}\pm0.020_{\rm syst}$. Thus, both
$f_{B^*}/f_B$ and $f_{B_s^*}/f_{B_s}$ are less than unity at 2.5$\sigma$ and
2$\sigma$ level, respectively.
[Show abstract][Hide abstract] ABSTRACT: The Chromomagnetic operator (CMO) mixes with a large number of operators
under renormalization. We identify which operators can mix with the CMO, at the
quantum level. Even in dimensional regularization (DR), which has the simplest
mixing pattern, the CMO mixes with a total of 9 other operators, forming a
basis of dimension-five, Lorentz scalar operators with the same flavor content
as the CMO. Among them, there are also gauge noninvariant operators; these are
BRST invariant and vanish by the equations of motion, as required by
renormalization theory. On the other hand using a lattice regularization
further operators with $d \leq 5$ will mix; choosing the lattice action in a
manner as to preserve certain discrete symmetries, a minimul set of 3
additional operators (all with $d<5$) will appear. In order to compute all
relevant mixing coefficients, we calculate the quark-antiquark (2-pt) and the
quark-antiquark-gluon (3-pt) Green's functions of the CMO at nonzero quark
masses. These calculations were performed in the continuum (dimensional
regularization) and on the lattice using the maximally twisted mass fermion
action and the Symanzik improved gluon action. In parallel, non-perturbative
measurements of the $K-\pi$ matrix element are being performed in simulations
with 4 dynamical ($N_f = 2+1+1$) twisted mass fermions and the Iwasaki improved
gluon action.
[Show abstract][Hide abstract] ABSTRACT: We present preliminary results of the first lattice QCD calculation of the K
-> pi matrix elements of the chromomagnetic operator O_{CM}=g sbar sigma_{munu}
G_{munu} d, which appears in the effective Hamiltonian describing Delta S=1
transitions in and beyond the Standard Model. Having dimension 5, the
chromomagnetic operator is characterized by a rich pattern of mixing with
operators of equal and lower dimensionality. The multiplicative renormalization
factor as well as the mixing coefficients with the operators of equal dimension
have been computed at one-loop in perturbation theory. The power divergent
coefficients controlling the mixing with operators of lower dimension have been
computed non-perturbatively, by imposing suitable subtraction conditions. The
numerical simulations have been carried out using the gauge field
configurations produced by the European Twisted Mass Collaboration with
N_f=2+1+1 dynamical quarks at three values of the lattice spacing. Our
preliminary result for the B-parameter of the chromomagnetic operator is
B_{CMO}=0.29(11), which can be compared with the estimate B_{CMO}~1-4 currently
used in phenomenological analyses.
[Show abstract][Hide abstract] ABSTRACT: We present a lattice QCD calculation of the pseudoscalar decay constants fK,
fD and fDs performed using the gauge configurations produced by the European
Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks, which include
in the sea, besides two light mass degenerate quarks, also the strange and
charm quarks with masses close to their values in the real world. The
simulations are based on a unitary setup for the two light mass-degenerate
quarks and on a mixed action approach for the strange and charm quarks. We use
data simulated at three different values of the lattice spacing in the range
0.06 - 0.09 fm and at pion masses in the range 210 - 450 MeV. Our main results
are: fK+ / fpi+ = 1.183 (16), fK+ = 154.3 (2.0) MeV, which incorporate the
leading strong isospin breaking correction due to the up- and down-quark mass
difference, and fK = 155.0 (1.9) MeV, fD = 207.4 (3.8) MeV, fDs = 247.2 (4.1)
MeV, fDs / fD = 1.192 (22) and (fD_s / fD) / (fK / fpi) = 1.003 (14) obtained
in the isospin symmetric limit of QCD. Combined with the experimental
measurements of the leptonic decay rates of kaon, pion, D- and Ds-mesons our
results lead to the following determination of the CKM matrix elements: |Vus| =
0.2271 (29), |Vcd| = 0.2221 (67) and |Vcs| = 1.014 (24). Using the latest value
of |Vud| from superallowed nuclear beta decays the unitarity of the first row
of the CKM matrix is fulfilled at the permille level.
Physical Review D 11/2014; 91(5). DOI:10.1103/PhysRevD.91.054507 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the outcomes of a very recent investigation of the decay constants
of nonstrange and strange heavy-light beauty vector mesons, with special
emphasis on the ratio of any such decay constant to the decay constant of the
corresponding pseudoscalar meson, by means of Borel-transformed QCD sum rules.
Our results suggest that both these ratios are below unity.
[Show abstract][Hide abstract] ABSTRACT: We discuss a lattice QCD computation of the $B$-meson decay constants by the
ETM collaboration where suitable ratios allow to reach the bottom quark sector
by combining simulations around the charm-quark mass with an exactly known
static limit. The different steps involved in this ratio method are discussed
together with an account of the assessment of various systematic effects. A
comparison of results from simulations with two and four flavour dynamical
quarks is presented.
[Show abstract][Hide abstract] ABSTRACT: Updated predictions for the decay constants of the D, Ds, B and Bs mesons
obtained from Borel QCD sum rules for heavy-light currents are presented and
compared with the recent lattice averages performed by the Flavor Lattice
Averaging Group. An excellent agreement is obtained in the charm sector, while
some tension is observed in the bottom sector. Moreover, available lattice and
QCD sum-rule calculations of the decay constants of the vector D*, Ds*, B* and
Bs* mesons are compared. Again some tension in the bottom sector is observed.
[Show abstract][Hide abstract] ABSTRACT: We present a lattice QCD determination of the vector form factor of the kaon
semileptonic decay K -> pi l nu which is relevant for the extraction of the CKM
matrix element |V_{us}| from experimental data. Our result is based on the
gauge configurations produced by the European Twisted Mass Collaboration with
N_f=2+1+1 dynamical fermions. We simulated at three different values of the
lattice spacing and with pion masses as small as 210 MeV. Our preliminary
estimate for the vector form factor at zero momentum transfer is
f_+(0)=0.9683(65), where the uncertainty is both statistical and systematic. By
combining our result with the experimental value of f_+(0)|V_{us}| we obtain
|V_{us}|=0.2234(16), which satisfies the unitarity constraint of the Standard
Model at the permille level.
[Show abstract][Hide abstract] ABSTRACT: Within the realm of QCD sum rules, one of the most important areas of
application of this nonperturbative approach is the prediction of the decay
constants of heavy mesons. However, in spite of the fact that, indisputably,
the adopted techniques are, of course, very similar, we encounter rather
dissimilar challenges, or obstacles, when extracting from two-point correlators
of appropriate heavy-light currents interpolating the mesons, the
characteristics of charmed mesons with different spin. In view of this, it
seems worthwhile to us to revisit this issue for the case of charmed
pseudoscalar mesons $D_{(s)}$ and vector mesons $D^*_{(s)}.$
[Show abstract][Hide abstract] ABSTRACT: We present precision lattice calculations of the pseudoscalar decay constants
of the charmed sector as well as determinations of the bottom quark mass and
its ratio to the charm quark mass. We employ Nf=2+1+1 dynamical quark gauge
configurations generated by the European Twisted Mass Collaboration, using data
at three values of the lattice spacing and pion masses as low as 210 MeV.
Strange and charm sea quark masses are close to their physical values.
[Show abstract][Hide abstract] ABSTRACT: We investigate the vector form factor relevant for the $K_{\ell 3}$
semileptonic decay using maximally twisted-mass fermions with 4 dynamical
flavours ($N_f=2+1+1$). Our simulations feature pion masses ranging from $210$
MeV to approximately $450$ MeV and lattice spacing values as small as $0.06$fm.
Our main result for the vector form factor at zero 4-momentum transfer is
$f_+(0)=0.9683(65)$ where the uncertainty is both statistical and systematic.
By combining our result with the experimental value of $f_+(0)|V_{us}|$ we
obtain $|V_{us}|=0.2234(16)$, which satisfies the unitarity constraint of the
Standard Model at the permille level.
[Show abstract][Hide abstract] ABSTRACT: Our recently completed analysis of the decay constants of both pseudoscalar
and vector beauty mesons reveals that in the bottom-quark sector two specific
features of the sum-rule predictions show up: (i) For the input value of the
bottom-quark mass in the $\overline{\rm MS}$ scheme
$\overline{m}_b(\overline{m}_b)\approx4.18\;\mbox{GeV},$ the sum-rule result
$f_B\approx210$-$220\;\mbox{MeV}$ for the $B$ meson decay constant is
substantially larger than the recent lattice-QCD finding
$f_B\approx190\;\mbox{MeV}.$ Requiring QCD sum rules to reproduce the
lattice-QCD value of $f_B$ yields a significantly larger $b$-quark mass:
$\overline{m}_b(\overline{m}_b)=4.247\;\mbox{GeV}.$ (ii) Whereas QCD sum-rule
predictions for the charmed-meson decay constants $f_D,$ $f_{D_s},$ $f_{D^*}$
and $f_{D_s^*}$ are practically independent of the choice of renormalization
scale, in the beauty sector the results for the decay constants - and
especially for the ratio $f_{B^*}/f_B$ - prove to be very sensitive to the
specific scale setting.
The European Physical Journal Conferences 10/2014; 80. DOI:10.1051/epjconf/20148000046
[Show abstract][Hide abstract] ABSTRACT: We present a sum-rule calculation of the decay constants of the charmed vector mesons D⁎D⁎ and Ds⁎ from the two-point correlator of vector currents. First, we show that the perturbative expansion in terms of the pole mass exhibits no sign of convergence whereas the reorganization of this expansion in terms of the MS¯ mass leads to a distinct hierarchy. Second, making use of the operator product expansion in terms of the MS¯ mass, we determine the decay constants of the D⁎D⁎ and Ds⁎ mesons with an emphasis on the uncertainties in these theoretically predicted quantities related both to the input QCD parameters and to the limited accuracy of the method of sum rules. Our results are fD⁎=(252.2±22.3OPE±4syst) MeVfD⁎=(252.2±22.3OPE±4syst) MeV and fDs⁎=(305.5±26.8OPE±5syst) MeV. For the ratios of the vector-to-pseudoscalar decay constants we report fD⁎/fD=1.221±0.080OPE±0.008systfD⁎/fD=1.221±0.080OPE±0.008syst and fDs⁎/fDs=1.241±0.057OPE±0.007syst.
Physics Letters B 07/2014; 735:12–18. DOI:10.1016/j.physletb.2014.06.007 · 6.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In spite of undeniable similarities of the applied techniques, somewhat
different challenges are encountered when extracting, from QCD sum rules
derived from two-point correlators of appropriate interpolating heavy-light
quark currents, the decay constants of charmed mesons of pseudoscalar nature,
on the one hand, or of vector nature, on the other hand. This observation
justifies a rather careful reassessment of the corresponding results.
The European Physical Journal Conferences 07/2014; 80. DOI:10.1051/epjconf/20148000043
[Show abstract][Hide abstract] ABSTRACT: We present the first unquenched lattice QCD results for the bag parameters
controlling the short distance contribution to D meson oscillations in the
Standard Model and beyond. We have used the gauge configurations produced by
the European Twisted Mass Collaboration with Nf = 2 dynamical quarks, at four
lattice spacings and light meson masses in the range 280-500 MeV.
Renormalization is carried out non-perturbatively with the RI-MOM method. The
bag-parameter results have been used to constrain New Physics effects in D-Dbar
mixing, to put a lower bound to the generic New Physics scale and to constrain
off-diagonal squark mass terms for TeV-scale Supersymmetry.
Physical Review D 03/2014; 90(1). DOI:10.1103/PhysRevD.90.014502 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a lattice QCD calculation of the up, down, strange and charm quark
masses performed using the gauge configurations produced by the European
Twisted Mass Collaboration with Nf = 2 + 1 + 1 dynamical quarks, which include
in the sea, besides two light mass degenerate quarks, also the strange and
charm quarks with masses close to their physical values. The simulations are
based on a unitary setup for the two light quarks and on a mixed action
approach for the strange and charm quarks. The analysis uses data at three
values of the lattice spacing and pion masses in the range 210 - 450 MeV,
allowing for accurate continuum limit and controlled chiral extrapolation. The
quark mass renormalization is carried out non-perturbatively using the RI-MOM
method. The results for the quark masses converted to the bar{MS} scheme are:
mud(2 GeV) = 3.70(17) MeV, ms(2 GeV) = 99.6(4.1) MeV and mc(mc) = 1.348(42)
GeV. We obtain also the quark mass ratios ms/mud = 26.66(32) and mc/ms =
11.62(16). By studying the mass splitting between the neutral and charged kaons
and using available lattice results for the electromagnetic contributions, we
evaluate mu/md = 0.470(56), leading to mu = 2.36(24) MeV and md = 5.03(26) MeV.
Nuclear Physics B 03/2014; 887. DOI:10.1016/j.nuclphysb.2014.07.025 · 3.93 Impact Factor