9 research outputs found
The convolution formula for a decay rate
The convolution formula is derived within the framework of the decay-chain
method for decay channels with three and four particles in a final state. To
get this formula exactly for unstable particle of any type one must modify the
propagators of vector and spinor fields. In this work we suggest proper
modifications and get the convolution formula by direct calculation. It was
noted that this approach naturally arises in the model of unstable particles
with random mass.Comment: 8 pages, typos adde
Diagonalization of the neutralino mass matrix and boson-neutralino interaction
We analyze a connection between neutralino mass sign, parity and structure of
the neutralino-boson interaction. Correct calculation of spin-dependent and
spin-independent contributions to neutralino-nuclear scattering should consider
this connection. A convenient diagonalization procedure, based on the
exponetial parametrization of unitary matrix, is suggested.Comment: 21 pages, RevTex
Penguin and Box Diagrams in Unitary Gauge
We evaluate one-loop diagrams in the unitary gauge that contribute to
flavor-changing neutral current (FCNC) transitions involving two and four
fermions. Specifically, we deal with penguin and box diagrams arising within
the standard model (SM) and in nonrenormalizable extensions thereof with
anomalous couplings of the W boson to quarks. We show explicitly in the SM the
subtle cancelation among divergences from individual unitary-gauge
contributions to some of the physical FCNC amplitudes and derive expressions
consistent with those obtained using R_xi gauges in the literature. Some of our
results can be used more generally in certain models involving fermions and
gauge bosons which have interactions similar in form to those we consider.Comment: 11 pages, 2 figures, to appear in EPJ