87,719 research outputs found
K ->pi l nu semileptonic form factors from two-flavor lattice QCD
No full textWe present new lattice results of the K ->pi l nu semileptonic form factors obtained from simulations with two flavors of dynamicaltwisted-mass fermions, using pion masses as light as 260 MeV. Our main result is f(+)(0)=0.9560(84), which, combined with the latest experimental data for Kl3 decays, leads to |Vus|=0.2267(5)(exp)(20)(f+(0)). Using the PDG(2008) determinations of|Vud| and |Vub| our result implies for the unitarity relation |Vud|^2+|Vus|^2+|Vub|^2=1.0004(15). For the O(p^6) term of the chiral expansion of f+(0) we get Delta f = f+(0)-1-f2=-0.0214(84)
Leptonic decay constants f(K), f(D), and f(Ds) with N-f=2+1+1 twisted-mass lattice QCD
No full textWe present a lattice QCD calculation of the pseudoscalar decay constants f(K), f(D) and f(Ds) performed using the gauge configurations produced by the European Twisted Mass Collaboration with N-f = 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 f(K+)/f(pi+) = 1.184(16), f(K+) = 154.4(2.0) MeV, which incorporate the leading strong isospin breaking correction due to the up and down quark mass difference, and f(K) = 155.0(1.9) MeV, f(D) = 207.4(3.8) MeV, f(Ds) = 247.2(4.1) MeV, f(Ds)/f(D) = 1.192(22) and (f(Ds)/f(D))/(f(K)/f(pi)) = 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 D-s mesons our results lead to the following determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements: vertical bar V-us vertical bar = 0.2269(29), vertical bar V-cd vertical bar = 0.2221(67) and vertical bar V-cs vertical bar = 1.014(24). Using the latest value of vertical bar V-ud vertical bar from superallowed nuclear beta decays the unitarity of the first row of the CKM matrix is fulfilled at the per mill level
The mitochondrial dynamics in cancer and immune-surveillance
No full textMitochondria-shaping proteins control the dynamic equilibrium between fusion and fission of the mitochondrial network. Their balance is strictly required to regulate various processes, including the quality of mitochondria, cell metabolism, cell death, proliferation and cell migration. Alterations in these processes are frequently encountered in cancer, during both its onset and later progression, as evidence emerge connecting alterations in mitochondrial dynamics with cancer development. In recent years, novel therapeutic approaches to fight against different human tumors aim at exploiting the immune system's ability to specifically recognize tumor antigens, thus killing malignant cells in a process named immune-surveillance. Interestingly, data are accumulating on the role that mitochondrial dynamics play also for the correct function of both the innate and the adaptive immune system. By this review, we overview how mitochondrial dynamics can affect various processes during cancer development, acting directly on tumor cells or indirectly on cells responsible for tumor aggression and defence
The nucleon Drell-Hearn-Gerasimov sum rule within a relativistic constituent quark model
No full textWe investigate the Drell-Hearn-Gerasimov sum rule within a relativistic constituent quark model based on the light-front formalism.The contribution of the nucleon to Delta transition is explicitly evaluated using different forms of the baryon wave functions and adopting a one-body relativistic current which includes Dirac and Pauli form factors for the constituent quark
Light-quark contribution to the leading hadronic vacuum polarization term of the muon g-2 from twisted-mass fermions
No full textWe present a lattice calculation of the leading hadronic vacuum polarization (HVP) contribution of the light u- and d-quarks to the anomalous magnetic moment of the muon, aμHVP(ud), adopting the gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with Nf=2+1+1 dynamical quarks at three values of the lattice spacing (a≃0.062,0.082,0.089 fm) with pion masses in the range Mπ≃210-450 MeV. Thanks to several lattices at fixed values of the light-quark mass and scale but with different sizes we perform a careful investigation of finite-volume effects (FVEs), which represent one of main source of uncertainty in modern lattice calculations of aμHVP(ud). In order to remove FVEs we develop an analytic representation of the vector correlator, which describes the lattice data for time distances larger than ≃0.2 fm. The representation is based on quark-hadron duality at small and intermediate time distances and on the two-pion contributions in a finite box at larger time distances. After removing FVEs we extrapolate the corrected lattice data to the physical pion point and to the continuum limit taking into account the chiral logs predicted by Chiral Perturbation Theory (ChPT). We obtain aμHVP(ud)=619.0(17.8)×10-10. Adding the contribution of strange and charm quarks, obtained by ETMC, and an estimate of the isospin-breaking corrections and quark-disconnected diagrams from the literature we get aμHVP(udsc)=683(19)×10-10, which is consistent with recent results based on dispersive analyses of the experimental cross section data for e+e- annihilation into hadrons. Using our analytic representation of the vector correlator, taken at the physical pion mass in the continuum and infinite volume limits, we provide the first eleven moments of the polarization function and we compare them with recent results of the dispersive analysis of the π+π- channels. We estimate also the light-quark contribution to the missing part of aμHVP not covered in the MUonE experiment
D-meson decay constants and a check of factorization in non-leptonic B-decays
No full textWe compute the vector meson decay constants fD*((s)) from the simulation of twisted mass QeD on the lattice with N-f - 2 dynamical quarks. When combining these values with the pseudoscalar D-(s)-meson decay constants, we were able (1) to show that the heavy quark spin symmetry breaking effects with the charm quark are large. fD*(s)/fD(s) = 1.26(3), and (ii) to check the factorization approximation in a few specific B-meson non-leptonic decay modes. Besides our main results, fD* = 278 +/- 13 +/- 10 MeV, and fD*(s) = 311 +/- 9 MeV, other phenomenologically interesting results of this paper are: fD*(s)/fD* = 1.16 +/- 0.02 +/- 0.06, fD*(s)/fD - 1.46 +/- 0.05 +/- 0.06, and fD(s)/fD* - 0.89 +/- 0.02 +/- 0.03. Finally, we correct the value for B(B-0 -> D+pi(-)) quoted by PUG, and find B(B-0 -> D+pi(-)) = (7.8 +/- 1.1) x 10(-7). Alternatively, by using the ratios discussed in this paper, we obtain B(B-0 -> D+pi(-)) - (8.3 +/- 1.0 +/- 0.8) X 10(-7)
Rotated twisted-mass: a convenient regularization scheme for isospin breaking QCD and QED lattice calculations
No full textWe propose a scheme of lattice twisted-mass fermion regularization which is particularly convenient for application to isospin breaking (IB) QCD and QED calculations, based in particular on the so called RM123 approach, in which the IB terms of the action are treated as a perturbation. The main, practical advantage of this scheme is that it allows the calculation of IB effects on some mesonic observables, like e.g. the pi+ - pi0 mass splitting, using lattice correlation functions in which the quark and antiquark fields in the meson are regularized with opposite values of the Wilson parameter r. These correlation functions are found to be affected by much smaller statistical fluctuations, with respect to the analogous functions in which quark and antiquark fields are regularized with the same value of r. Two numerical application of this scheme, that we call "rotated twisted-mass", within pure QCD and QCD+QED respectively, are also provided for illustration
Lattice calculation of the pion mass difference at order
No full textWe present a lattice calculation of the charged/neutral pion mass difference
at order using the gauge
configurations produced by the Extended Twisted Mass Collaboration with
dynamical quark flavours at three values of the lattice spacing
() and pion masses in the range . We employ the RM123 method and expand the
path-integral around the isospin symmetric point at leading order in the
electromagnetic coupling . Making use of the recently proposed RTM
scheme, we evaluate the full contribution, with the
inclusion of the disconnected diagram. At the physical point, after performing
the continuum and infinite volume extrapolation, we obtain the value
which is in good agreement with
the experimental result .Comment: 13 pages, 5 figures, 1 tabl
The K ->pi vector form factor at zero momentum transfer on the lattice
No full textWe present a quenched lattice study of the form factors f(+)(q(2)) and f(0)(q2) of the matrix elements . We focus on the second-order SU(3)-breaking quantity [1-f(+)(0)], which is necessary to extract \V-us\ from K-l3 decays. For this quantity we show that it is possible to reach the percent precision which is the required one for a significant determination of \V-us\. The leading quenched chiral logarithms are corrected for by using analytic calculations in quenched chiral perturbation theory. Our final result, f(+)(K0pi-) (0) = 0.960 +/- 0.005(stat) +/- 0.007(syst), where the systematic error does not include the residual quenched effects, is in good agreement with the estimate made by Leutwyler and Roos. A comparison with other non-lattice computations and the impact of our result on the extraction of \V-us\ are also presented
Semileptonic D-decays with twisted mass QCD on the lattice
No full textWe study matrix elements of the "chromomagnetic" operator on the lattice. This operator is contained in the strangeness-changing effective Hamiltonian which describes electroweak effects in the Standard Model and beyond. Having dimension 5, the chromomagnetic operator is characterized by a rich pattern of mixing with other operators of equal and lower dimensionality, including also non gauge invariant quantities; it is thus quite a challenge to extract from lattice simulations a clear signal for the hadronic matrix elements of this operator. We compute all relevant mixing coefficients to one loop in lattice perturbation theory; this necessitates calculating both 2-point (quark-antiquark) and 3-point (gluon-quark-antiquark) Green's functions at nonzero quark masses. We use the twisted mass lattice formulation, with Symanzik improved gluon action. For a comprehensive presentation of our results, along with detailed explanations and a more complete list of references, we refer to our forthcoming publication [1]
- …
