175 research outputs found
Kaon physics from lattice QCD
I review lattice calculations and results for hadronic parameters relevant
for kaon physics, in particular the vector form factor f+(0) of semileptonic
kaon decays, the ratio fK/fpi of leptonic decay constants and the kaon bag
parameter BK. For each lattice calculation a colour code rating is assigned, by
following a procedure which is being proposed by the Flavianet Lattice
Averaging Group (FLAG), and the following final averages are obtained:
f+(0)=0.962(3)(4), fK/fpi = 1.196(1)(10) and \hat BK = 0.731(7)(35). In the
last part of the talk, the present status of lattice studies of non-leptonic
K--> pi pi decays is also briefly summarized.Comment: Plenary talk at 27th International Symposium on Lattice Field Theory
(Lattice 2009), Beijing, China, 25-31 Jul 2009. v2: two references and one
comment added, typos correcte
Determination of V_us: recent progresses from theory
Recent experimental and theoretical results on kaon semileptonic decays have
significantly improved the determination of the CKM matrix element V_us. After
briefly summarizing the impact of the new experimental determinations, I will
concentrate in this talk on the theoretical progresses, coming in particular
from lattice QCD calculations. These results lead to the estimate |V_us|=0.2250
+- 0.0021, in good agreement with the expectation based on the determination of
|V_ud| and the unitarity of the CKM matrix.Comment: Prepared for 17th Les Rencontres de Physique de la Vallee d'Aoste:
Results and Perspectives in Particle Physics, La Thuile, Italy, February
27-March 5, 200
Determination of Vus: Recent Input from the Lattice
The two most precise determinations of the CKM matrix element V_us are based
on the analyses of leptonic and semileptonic kaon decays. These studies also
rely on the lattice QCD calculations of two hadronic parameters, namely the
ratio of the kaon and pion decay constants, f_K+/f_pi+, and the kaon
semileptonic vector form factor at zero momentum transfer, f_+(0). In this
talk, I review the recent lattice results for these quantities, by showing that
the sub-percent accuracy required by the phenomenological analyses has been
reached by lattice QCD. As best estimates of the lattice calculations I quote
f_K+/f_pi+ = 1.193(4) and f_+(0)=0.965(3). I also discuss some recent
theoretical progress in the evaluation of the small, but phenomenologically
relevant, SU(2) isospin breaking corrections.Comment: Kaon 2013 conference proceeding
Light quark masses and CKM matrix elements from lattice QCD
I give a brief overview of recent results from lattice QCD calculations which
are relevant for the phenomenology of the Standard Model. I discuss, in
particular, the lattice determination of light quark masses and the calculation
of those hadronic quantities, such as semileptonic form factors, decay
constants and B-parameters, which are of particular interest for the analysis
of the CKM mixing matrix and the origin of CP violation.Comment: 5 pages, 4 figures, uses espcrc2.sty (included). Based on invited
talk given at the QCD 98 Euroconference, Montpellier, France, 2-8 July 199
Lattice QCD, Flavor Physics and the Unitarity Triangle Analysis
Lattice QCD has always played a relevant role in the studies of flavor
physics and, in particular, in the Unitarity Triangle (UT) analysis. Before the
starting of the B factories, this analysis relied on the results of lattice QCD
simulations to relate the experimental determinations of semileptonic B decays,
K-Kbar and B_{d,s}-B_{d,s}bar mixing to the CKM parameters. In the last years
much more information has been obtained from the direct determination of the UT
angles from non-leptonic B decays. In this talk, after a presentation of recent
averages of lattice QCD results, we compare the outcome of the "classical" UT
analysis (UTlattice) with the analysis based on the angles determinations
(UTangles). We discuss the role of the different determinations of Vub, and
show that current data do not favour the value measured in inclusive decays.
Finally we show that the recent measurement of Delta ms, combined with Delta md
and epsilonK, allows a quite accurate extraction of the values of the hadronic
parameters, BK, fBs*sqrt(B_Bs) and xi. These values, obtained "experimentally"
by assuming the validity of the Standard Model, are compared with the
theoretical predictions from lattice QCD.Comment: Contribution to the proceedings of HQL06, Munich, October 16th-20th
2006. 11 page
Flavour physics and Lattice QCD: averages of lattice inputs for the Unitarity Triangle Analysis
We review recent results of Lattice QCD calculations relevant for flavour
physics. We discuss in particular the hadronic parameters entering the
amplitudes of K0-K0bar, D0-D0bar and B0-B0bar mixing, the B- and D-meson decay
constants and the form factors controlling B-meson semileptonic decays. On the
basis of these lattice results, which are extensively collected in the paper,
we also derive our averages of the relevant hadronic parameters.Comment: Plenary talk at IFAE 2008, Bologna, Italy, 26-28 March 200
Light quark masses and pseudoscalar decay constants from Nf=2 twisted mass QCD
We present the results of the lattice QCD calculation of the average up-down
and strange quark masses and of the light meson pseudoscalar decay constants,
recently performed with Nf=2 dynamical fermions by the ETM Collaboration. The
simulation is carried out at a single value of the lattice spacing with the
twisted mass fermionic action at maximal twist, which guarantees automatic
O(a)-improvement of the physical quantities. Quark masses are renormalized by
implementing the non perturbative RI-MOM renormalization procedure. Our results
for the light quark masses are m_{ud}^{MSbar}(2 Gev)=3.85 +- 0.12 +- 0.40 MeV,
m_s^{MSbar}(2 Gev)=105 +- 3 +- 9 MeV and m_s/m_{ud}=27.3 +- 0.3 +- 1.2. We also
obtain f_K=161.7 +- 1.2 +- 3.1 MeV and the ratio f_K/f_pi=1.227 +- 0.009 +-
0.024. From this ratio, by using the experimental determination of Gamma(K ->
mu {bar nu}_mu (gamma))/Gamma(pi -> mu {bar nu}_mu (gamma)) and the average
value of |V_{ud}| from nuclear beta decays, we obtain |V_{us}|=0.2192(5)(45),
in agreement with the determination from K_{l3} decays and the unitarity
constraint.Comment: 7 pages, 3 figures, Proceedings of Lattice 2007 (July 30 - 4 August
2007, Regensburg, Germany
Thermodynamics and microscopic theory: an educational proposal for the high school
We present an educational proposal which aims to illustrate the elegant,
refined and coherent physics contained in Thermodynamics, through a path which
assigns to the microscopic description of the physical systems a constantly
privileged role. This approach allows to reach a simple and, at the same time,
deep understanding of the laws of Thermodynamics, while still emphasizing their
great generality, which permits their application to all macroscopic systems,
from simple gases to black holes, arriving to characterize the evolution of the
entire Universe.Comment: Communications: SIF Congress 2022. 6 page
O(a^2) corrections to 1-loop matrix elements of 4-fermion operators with improved fermion/gluon actions
We calculate the corrections to the amputated Green's functions of 4-fermion
operators, in 1-loop Lattice Perturbation theory. The novel aspect of our
calculations is that they are carried out to second order in the lattice
spacing, O(a^2). We employ the Wilson/clover action for massless fermions (also
applicable for the twisted mass action in the chiral limit) and the Symanzik
improved action for gluons. Our calculations have been carried out in a general
covariant gauge. Results have been obtained for several popular choices of
values for the Symanzik coefficients (Plaquette, Tree-level Symanzik, Iwasaki,
TILW and DBW2 action). We pay particular attention to operators,
both Parity Conserving and Parity Violating ( stands for flavour: S, C, B).
We study the mixing pattern of these operators, to O(a^2), using the
appropriate projectors. Our results for the corresponding renormalization
matrices are given as a function of a large number of parameters: coupling
constant, clover parameter, number of colors, lattice spacing, external
momentum and gauge parameter. The O(a^2) correction terms (along with our
previous O(a^2) calculation of ) are essential ingredients for
minimizing the lattice artifacts which are present in non-perturbative
evaluations of renormalization constants with the RI'-MOM method. A longer
write-up of this work, including non-perturbative results, is in preparation
together with members of the ETM Collaboration.Comment: 8 pages, 1 figure. Presented at the "XXVII International Symposium on
Lattice Field Theory", July 26-31 2009, Peking University, Beijing, Chin
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