Related papers: Additional Isospin-Breaking Effects in epsilon'/ep…
In a recent paper we used chiral perturbation theory to determine the phase diagram and pion spectrum for Wilson and twisted-mass fermions at non-zero lattice spacing with non-degenerate up and down quarks. Here we extend this work to…
A quantitative understanding of isospin violation is an increasingly important ingredient for the extraction of the nucleon's strange vector form factors from experimental data. We calculate the isospin violating electric and magnetic form…
A new lattice estimate of K -> 2 pi transitions claims, contrary to all other computations, that the hadronic matrix element for the gluon penguin operator Q_6 has opposite sign and, in addition, is much larger than the vacuum saturation…
The $\tau^- \to \pi^-\eta\nu_{\tau}$ decay is forbidden in the Standard Model in the limit of exact $G$-parity, it becomes a rare decay due to isospin symmetry breaking and it is very sensitive to the effects of effective scalar…
In this paper we consider the effects of top quark compositeness on the electroweak parameters T-hat and S-hat and the Zbb coupling. We do so by using an effective field theory analysis to identify several promising patterns of mixing…
Isospin breaking in the Kl4 form factors induced by the difference between charged and neutral pion masses is studied. Starting from suitably subtracted dispersion representations, the form factors are constructed in an iterative way up to…
According to the quark model, the masses of eta and eta' mesons should be almost equal. However, the empirical values of these masses differ by more than the factor of two. Similarly, though the almost the same quark-antiquark content, the…
The anomalous magnetic moment of the muon $a_{\mu}$ and the running of the electromagnetic coupling $\alpha$ play a fundamental role in beyond Standard Model (SM) physics searches. Non-perturbative hadronic contributions to both quantities,…
Recently, the standard model prediction of $\epsilon'/\epsilon$ was improved, and a discrepancy from the experimental results was reported at the $2.9\sigma$ level. We study the chargino contributions to $Z$ penguin especially with the…
We show that in supersymmetric extensions of the Standard Model gluino box diagrams can yield a large CP-violating Delta(I)=3/2 contribution to s->d+q(bar)+q flavor-changing neutral current processes, which feeds into the I=2 isospin…
The long-distance contributions to $K\to 2\pi$ amplitudes can be pinned down, using well established Chiral Perturbation Theory techniques. The strong S--wave rescattering of the two final pions generates sizeable chiral loop corrections,…
The penguin loop-suppressed $B\to\phi K$ decays are highly sensitive to contributions of hypothetical heavy new particles. Particularly interesting probes for testing the Standard Model and revealing such phenomena are provided by CP…
We present an update on the ongoing computation of the isospin-breaking effects in the Pion Decay Constant from the BMW Collaboration. The calculation is carried out with N$_f$=2+1+1 staggered quarks with a near-physical pion mass and…
We point out that the standard chromomagnetic penguin dipole operator has a counterpart corresponding to off-shell momenta for external quarks. By employing the chiral quark model, we show that this new dipole penguin operator has the same…
This is the first of a series of papers devoted to a detailed analysis of isospin-breaking effects in the $\pi \pi$ scattering amplitude and the vector form factor of the pion. Isospin breaking originates from the mass difference between up…
The low energy dynamics of QCD is investigated with special attention paid to the matching between QCD and chiral perturbation theory(ChPT), and also to some useful algebraic chiral operator relations which survive even when we include…
We compute the isospin $I= 0$ and 2 amplitudes for the decay of a kaon into two pions by estimating the relevant hadronic matrix elements in the chiral quark model. The results are parametrized in terms of the quark and gluon condensates…
The 2.5 sigma discrepancy between theory and experiment observed in the difference A_CP(B^- --> pi^0 K^-)-A_CP(Bbar^0 --> pi^+ K^-) can be explained by a new electroweak penguin amplitude. Motivated by this result, we analyse the purely…
The space-like penguin contributions to branching ratios and CP asymmetries in charmless decays of $B$ to two pseudoscalar mesons are studied using the next-to-leading order low energy effective Hamiltonian. Both the gluonic penguin and the…
We present results on the pseudoscalar meson masses from a fully dynamical simulation of QCD+QED. We concentrate particularly on violations of isospin symmetry. We calculate the $\pi^+$-$\pi^0$ splitting and also look at other isospin…