152,880 research outputs found

### Lifetime Difference and Endpoint effect in the Inclusive Bottom Hadron Decays

The lifetime differences of bottom hadrons are known to be properly explained
within the framework of heavy quark effective field theory(HQEFT) of QCD via
the inverse expansion of the dressed heavy quark mass. In general, the spectrum
around the endpoint region is not well behaved due to the invalidity of $1/m_Q$
expansion near the endpoint. The curve fitting method is adopted to treat the
endpoint behavior. It turns out that the endpoint effects are truly small and
the explanation on the lifetime differences in the HQEFT of QCD is then well
justified. The inclusion of the endpoint effects makes the prediction on the
lifetime differences and the extraction on the CKM matrix element $|V_{cb}|$
more reliable.Comment: 11 pages, Revtex, 10 figures, 6 tables, published versio

### Lepton flavor-changing Scalar Interactions and Muon $g-2$

A systematic investigation on muon anomalous magnetic moment and related
lepton flavor-violating process such as \m\to e\g, \t\to e\g and \t\to
\m\g is made at two loop level in the models with flavor-changing scalar
interactions. The two loop diagrams with double scalar exchanges are studied
and their contributions are found to be compatible with the ones from Barr-Zee
diagram. By comparing with the latest data, the allowed ranges for the relevant
Yukawa couplings $Y_{ij}$ in lepton sector are obtained. The results show a
hierarchical structure of Y_{\m e, \t e} \ll Y_{\m \t} \simeq Y_{\m\m} in the
physical basis if $\Delta a_{\mu}$ is found to be $>50\times 10^{-11}$. It
deviates from the widely used ansatz in which the off diagonal elements are
proportional to the square root of the products of related fermion masses. An
alternative Yukawa coupling matrix in the lepton sector is suggested to
understand the current data. With such a reasonable Yukawa coupling ansatz, the
decay rate of \t\to \m\g is found to be near the current experiment upper
bound.Comment: 15 pages, Revtex, 9 figures, published version in EPJ

### Symmetry-preserving Loop Regularization and Renormalization of QFTs

A new symmetry-preserving loop regularization method proposed in \cite{ylw}
is further investigated. It is found that its prescription can be understood by
introducing a regulating distribution function to the proper-time formalism of
irreducible loop integrals. The method simulates in many interesting features
to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop
regularization method is also simple and general for the practical calculations
to higher loop graphs and can be applied to both underlying and effective
quantum field theories including gauge, chiral, supersymmetric and
gravitational ones as the new method does not modify either the lagrangian
formalism or the space-time dimension of original theory. The appearance of
characteristic energy scale $M_c$ and sliding energy scale $\mu_s$ offers a
systematic way for studying the renormalization-group evolution of gauge
theories in the spirit of Wilson-Kadanoff and for exploring important effects
of higher dimensional interaction terms in the infrared regime.Comment: 13 pages, Revtex, extended modified version, more references adde

### A More Precise Extraction of |V_{cb}| in HQEFT of QCD

The more precise extraction for the CKM matrix element |V_{cb}| in the heavy
quark effective field theory (HQEFT) of QCD is studied from both exclusive and
inclusive semileptonic B decays. The values of relevant nonperturbative
parameters up to order 1/m^2_Q are estimated consistently in HQEFT of QCD.
Using the most recent experimental data for B decay rates, |V_{cb}| is updated
to be |V_{cb}| = 0.0395 \pm 0.0011_{exp} \pm 0.0019_{th} from B\to D^{\ast} l
\nu decay and |V_{cb}| = 0.0434 \pm 0.0041_{exp} \pm 0.0020_{th} from B\to D l
\nu decay as well as |V_{cb}| = 0.0394 \pm 0.0010_{exp} \pm 0.0014_{th} from
inclusive B\to X_c l \nu decay.Comment: 7 pages, revtex, 4 figure

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