310 research outputs found

### Arithmetic and the standard electroweak theory

We propose the relations 1/e - e =3 and tan(2theta_W)=3/2, where e is the
positron charge and theta_W is the weak angle. Present experimental data
support these relations to a very high accuracy. We suggest that some duality
relates the weak isospin and hypercharge gauge groups of the standard
electroweak theory.Comment: Latex, 6 page

### Masses and widths of the rho(770)

Isospin violation in the $\rho(770)$ mass and width is considered within the
$S$ matrix approach using combined fits to the $e^+e^- \to\pi^+\pi^-$ and
$\tau^- \to \nu_{\tau}\pi^-\pi^0$ data performed by the ALEPH collaboration. We
show that the pole position following from the parameters obtained from the
ALEPH fits are not sensitive to the details of the parametrization. In this
context, we have found that the pole mass difference and the pole width
difference between the charged and neutral $\rho$ are consistent with zero. We
show that a one loop calculation including vector, axial vector and
pseudo-scalar mesons can satisfactorily describe the observed isospin breaking.
We also give an estimate for the mass difference between the neutral and
charged states of the $a_1(1260)$.Comment: 8 pages, 1 figur

### Mixing of two-level unstable systems

Unstable particles can be consistently described in the framework of quantum
field theory. Starting from the full S-matrix amplitudes of B^+ --> (2 pi, 3
pi) l nu decays as examples in the energy region where the rho-omega resonances
are dominating, we propose a prescription for the mixing of two quasi
`physical' unstable states that differs from the one obtained from the
diagonalization of the M -i*Gamma/2 non-hermitian hamiltonian. We discuss some
important consequences for CP violation in the K_L - K_S system.Comment: 7 pages, Latex. A factor 1/2 removed from r.h.s. of Eqs. (12)-(15).
Conclusions unchange

### Binding energy corrections in positronium decays

Positronium annihilation amplitudes that are computed by assuming a
factorization approximation with on-shell intermediate leptons, do not exhibit
good analytical behavior. We propose an ansatz which allows to include binding
energy corrections and obtain the correct analytical and gauge invariance
behavior of these QED amplitudes. As a consequence of these non-perturbative
corrections, the parapositronium and orthopositronium decay rates receive
corrections of order alpha^4 and alpha^2, respectively. These new corrections
for orthopositronium are relevant in view of a precise comparison between
recent theoretical and experimental developments. Implications are pointed out
for analogous decays of quarkonia .Comment: 11 pages, 1 .ps figure, submitted for publicatio

### Tests of flavor symmetry in J/psi decays

We use SU(3) flavor symmetry to analyze the $PP', VP$ and baryon-antibaryon
decays of $J/\psi$. Both, the SU(3)-invariant and -violating contributions are
considered. Particular attention is paid to the interference of the
electromagnetic and strong amplitudes.Comment: 8 pages, latex. Talk given at CAM-94 Physics Meetin

### Hadronic Phases and Isospin Amplitudes in $D(B) \to \pi \pi$ and $D(B) \to K \bar K$ Decays

Hadronic phase in $\pi \pi$ and $K \bar K$ channels are calculated a la
Regge. At the D mass one finds $\delta_{\pi \pi} \approx \pi/3$ and $\delta_{K
\bar K} \approx -\pi/6$ in good agreement with the CLEO data while at the B
mass these angles are predicted to be, respectively, $11^\circ$ and $-7^\circ$.
With the hadronic phase $e^{i \delta_{K \bar K}}$ taken into account, a quark
diagram decomposition of the isospin invariant amplitudes in $D \to K \bar K$
decays fits the data provided the exchange diagram contribution is about 1/3 of
the tree level one.Comment: 10pages,late

### Parapositronium Decay and Dispersion Relations

Positronium decay rates are computed at the one-loop level, using
convolution-type factorized amplitudes. The dynamics of this factorization is
probed with dispersion relations, showing that unallowed approximations are
usually made, and some ordre alpha^2 corrections missed. Further, we discuss
the relevance of the Schrodinger wavefunction as the basis for perturbative
calculations. Finally, we apply our formalism to the parapositronium two-photon
decay.Comment: LaTeX, 13 pages, 1 eps figur

### Analytical Behaviour of Positronium Decay Amplitudes

Positronium annihilation amplitudes that are computed by assuming a
factorization approximation with on-shell intermediate leptons do not exhibit
good analytical behaviour. Using dispersion techniques, we find new
contributions that interfere with the known results to restore analytical
properties. Those new amplitudes which cannot be obtained using standard
factorized amplitude formalism, contribute at order alpha^2. Therefore they
have to be evaluated before any theoretical conclusion can be drawn upon the
orthopositronium lifetime puzzle.Comment: LaTeX, 22 pages, 3 eps figure

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